diff --git a/.env.example b/.env.example
index 2a51030e9..9544ea1f6 100644
--- a/.env.example
+++ b/.env.example
@@ -40,3 +40,14 @@ AUTH_OIDC_CLIENT_SECRET=""
 # When E2E_DEBUG_AUTH=1 (e.g. Playwright), set both — no defaults in non-dev NODE_ENV:
 # DEV_DEBUG_PASSWORD="..."
 # DEV_ADMIN_PASSWORD="..."
+
+# Static loader only. Missing Sections are never retired unless this is set to
+# true after the production backup/restore prerequisite has been verified.
+# The first committed import after adding the global watermark must be a manual
+# bootstrap with this flag plus the exact SHA-256 from a preceding dry run.
+# Destructive runs also require the exact SHA-256 and candidate count observed
+# in a preceding dry run.
+# STATIC_LOADER_BOOTSTRAP_IMPORT_STATE="false"
+# STATIC_LOADER_RETIRE_MISSING_SECTIONS="false"
+# STATIC_LOADER_EXPECTED_SNAPSHOT_SHA256=""
+# STATIC_LOADER_EXPECTED_SECTION_RETIREMENT_CANDIDATES=""
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 709f81f67..c22c0db49 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -109,6 +109,7 @@ jobs:
             -v "${report_dir}:/tmp/static-loader-report" \
             -e DATABASE_URL="postgresql://postgres:postgres@${postgres}:5432/life_ustc_static_loader" \
             -e STATIC_LOADER_DRY_RUN=true \
+            -e STATIC_LOADER_BOOTSTRAP_IMPORT_STATE=true \
             -e STATIC_LOADER_MIN_SEMESTER=401 \
             -e STATIC_LOADER_STATS_FILE=/tmp/static-loader-report/report.json \
             life-ustc-static-loader:check
@@ -119,6 +120,11 @@ jobs:
               report.mode !== "dry-run" ||
               report.outcome !== "rolled-back" ||
               report.databaseRecordCounts !== null ||
+              report.reconciliation?.sectionLifecycle?.enabled !== false ||
+              !Number.isInteger(
+                report.reconciliation?.sectionLifecycle
+                  ?.retirementCandidateCount,
+              ) ||
               !/^[a-f0-9]{64}$/.test(report.snapshot?.sha256 ?? "")
             ) {
               throw new Error("Static loader report has invalid dry-run semantics");
diff --git a/.github/workflows/static-sync.yml b/.github/workflows/static-sync.yml
index c5f744a89..984bd2b4b 100644
--- a/.github/workflows/static-sync.yml
+++ b/.github/workflows/static-sync.yml
@@ -10,6 +10,24 @@ on:
         required: false
         default: false
         type: boolean
+      bootstrap_import_state:
+        description: "Initialize the global import watermark (manual only; committed runs require the exact snapshot SHA below)"
+        required: false
+        default: false
+        type: boolean
+      retire_missing_sections:
+        description: "Retire missing Sections (manual runs only; requires both approval fields below)"
+        required: false
+        default: false
+        type: boolean
+      expected_snapshot_sha256:
+        description: "Exact snapshot SHA-256 approved from a preceding bootstrap/retirement dry run"
+        required: false
+        type: string
+      expected_section_retirement_candidates:
+        description: "Exact missing-Section candidate count approved from a preceding dry run"
+        required: false
+        type: string
 
 concurrency:
   group: production-database-writes
@@ -55,6 +73,10 @@ jobs:
           STATIC_SNAPSHOT_URL: ${{ vars.STATIC_SNAPSHOT_URL || 'https://static.life-ustc.tiankaima.dev/life-ustc-static.sqlite' }}
           STATIC_LOADER_MIN_SEMESTER: ${{ vars.STATIC_LOADER_MIN_SEMESTER || '401' }}
           STATIC_LOADER_DRY_RUN: ${{ inputs.dry-run }}
+          STATIC_LOADER_BOOTSTRAP_IMPORT_STATE: ${{ github.event_name == 'workflow_dispatch' && inputs.bootstrap_import_state || false }}
+          STATIC_LOADER_RETIRE_MISSING_SECTIONS: ${{ github.event_name == 'workflow_dispatch' && inputs.retire_missing_sections || false }}
+          STATIC_LOADER_EXPECTED_SNAPSHOT_SHA256: ${{ github.event_name == 'workflow_dispatch' && inputs.expected_snapshot_sha256 || '' }}
+          STATIC_LOADER_EXPECTED_SECTION_RETIREMENT_CANDIDATES: ${{ github.event_name == 'workflow_dispatch' && inputs.expected_section_retirement_candidates || '' }}
           STATIC_LOADER_STATS_FILE: /tmp/static-load-stats.json
         run: scripts/load-static-sqlite.sh
 
diff --git a/Dockerfile b/Dockerfile
index f782715f2..1e1a76854 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -13,6 +13,7 @@ COPY package.json prisma.config.ts ./
 COPY prisma ./prisma
 RUN DATABASE_URL="postgresql://localhost:5432/life_ustc" bun run db:generate
 COPY src/static-loader ./src/static-loader
+COPY src/lib/db/section-lifecycle-lock.ts ./src/lib/db/section-lifecycle-lock.ts
 COPY scripts/load-static-sqlite.sh ./scripts/load-static-sqlite.sh
 COPY docker-entrypoint.load.sh /usr/local/bin/docker-entrypoint.load.sh
 
diff --git a/docker-compose.load.yml b/docker-compose.load.yml
index b0580b7ae..d38ab0037 100644
--- a/docker-compose.load.yml
+++ b/docker-compose.load.yml
@@ -8,6 +8,10 @@ services:
       STATIC_SNAPSHOT_PATH: ${STATIC_SNAPSHOT_PATH:-}
       STATIC_LOADER_MIN_SEMESTER: ${STATIC_LOADER_MIN_SEMESTER:-401}
       STATIC_LOADER_DRY_RUN: ${STATIC_LOADER_DRY_RUN:-false}
+      STATIC_LOADER_BOOTSTRAP_IMPORT_STATE: ${STATIC_LOADER_BOOTSTRAP_IMPORT_STATE:-false}
+      STATIC_LOADER_RETIRE_MISSING_SECTIONS: ${STATIC_LOADER_RETIRE_MISSING_SECTIONS:-false}
+      STATIC_LOADER_EXPECTED_SNAPSHOT_SHA256: ${STATIC_LOADER_EXPECTED_SNAPSHOT_SHA256:-}
+      STATIC_LOADER_EXPECTED_SECTION_RETIREMENT_CANDIDATES: ${STATIC_LOADER_EXPECTED_SECTION_RETIREMENT_CANDIDATES:-}
     # To use a local snapshot file instead of downloading, set STATIC_SNAPSHOT_PATH
     # and mount the host file to the same path inside the container, for example:
     # volumes:
diff --git a/docs/contracts/_audit.json b/docs/contracts/_audit.json
index c1d23b3d8..ade5c5f57 100644
--- a/docs/contracts/_audit.json
+++ b/docs/contracts/_audit.json
@@ -24,6 +24,14 @@
       "trigger": "DELETE /api/uploads/[id] or MCP delete_my_upload",
       "description": "User deletes an upload they own. MCP-originated writes include metadata.source=mcp. After storage deletion succeeds, metadata deletion and the audit row are committed together."
     },
+    "section_retire": {
+      "trigger": "Reserved",
+      "description": "The importer marks one missing in-scope Section retired without deleting the row or children. The same transaction records the Section target, source snapshot SHA-256, observation time, jwId, and previous sourceLastSeenAt."
+    },
+    "section_reactivate": {
+      "trigger": "Reserved",
+      "description": "The importer clears retiredAt and refreshes sourceLastSeenAt. The same transaction records the Section target, source snapshot SHA-256, observation time, jwId, and previous retiredAt."
+    },
     "admin_user_suspend": {
       "trigger": "POST /api/admin/suspensions",
       "description": "Admin suspends a user account. The suspension change and audit row are committed together."
@@ -41,5 +49,5 @@
       "description": "Admin updates description content from the moderation workflow. The description row, edit history, and audit row are committed together."
     }
   },
-  "writer": "writeAuditLog records audit rows and Cloudflare Analytics Engine datapoints. Required domain/security trails await writeAuditLog and use the same Prisma transaction as DB-only mutations where practical. fireAuditLog is reserved for non-critical telemetry and logs failures without blocking the request."
+  "writer": "writeAuditLog records app audit rows and Cloudflare Analytics Engine datapoints. The Node-only static loader writes Section lifecycle rows directly with its import transaction. Required trails are awaited in the same transaction where practical; fireAuditLog remains non-critical telemetry."
 }
diff --git a/docs/contracts/calendar.json b/docs/contracts/calendar.json
index 1d4c07403..cdfab6760 100644
--- a/docs/contracts/calendar.json
+++ b/docs/contracts/calendar.json
@@ -8,6 +8,7 @@
   },
   "rules": {
     "views": "Provides selectable semester, month, and week views.",
+    "retired-sections": "Current/public collection calendars, personal calendar views, feeds, and calendar event tools exclude retired Sections. A direct single-Section detail/calendar URL remains available as a historical reference, and retirement does not delete underlying schedules, exams, homeworks, or subscription relationships.",
     "mobile-agenda-first": "At mobile widths, the personal calendar presents the selected week as a vertically readable agenda with time, title, type, and available location context. Previous week, today, next week, and iCal actions remain directly accessible without page-level horizontal scrolling; desktop retains the selectable grid views.",
     "week-starts-sunday": "The week view starts on Sunday.",
     "event-card-types": "Calendar event cards uniformly carry course, exam, homework, and todo events."
diff --git a/docs/contracts/course.json b/docs/contracts/course.json
index 63dfe3aff..0afb0f855 100644
--- a/docs/contracts/course.json
+++ b/docs/contracts/course.json
@@ -12,6 +12,7 @@
     "static-section-course-link": "Each imported Section resolves the exact Course semantic identity attached to its lesson parent. Static sync assigns that link when inserting a Section but never silently rebinds courseId on an existing Section; missing identity mappings abort the transaction.",
     "static-legacy-course-merge": "After resolving current snapshot identities, static sync merges only stale Course rows absent from the snapshot that have exactly one compatible canonical match with the same code, Chinese name, and complete classification metadata. The merge preserves Sections, Comments, compatible Description history and latest edit metadata, and the stale jwId as a CourseAlias; ambiguous matches, conflicting descriptions, and alias collisions abort the transaction.",
     "course-jwid-alias": "Legacy course jwIds remain valid for REST, MCP, comment and description targets. Course and CourseAlias jwId namespaces are globally disjoint, and collisions abort instead of resolving ambiguously. Web detail routes permanently redirect aliases to the canonical jwId, while serialized course data always reports the canonical jwId.",
+    "retired-section-history": "Direct Course detail retains retired Section offerings as historical references; public Section discovery excludes them.",
     "jwid-url-only": "jwId is used only for URLs, APIs, MCP, and backend logic; it should not be directly displayed in ordinary course UI.",
     "education-level-display-casing": "English education-level filter labels uppercase only their initial character for consistent display while preserving all remaining source casing; non-English labels remain unchanged.",
     "public-list-cache": "Anonymous course list REST responses and server-side list data may use short public runtime/CDN caching because course fact data is read-only; localized HTML pages must not use shared edge caching unless the cache key varies by locale.",
diff --git a/docs/contracts/section.json b/docs/contracts/section.json
index 587bd6618..14e9eb59f 100644
--- a/docs/contracts/section.json
+++ b/docs/contracts/section.json
@@ -8,6 +8,11 @@
   },
   "rules": {
     "semester-offering": "A section is a specific teaching class for a course in a given semester.",
+    "source-lifecycle": "Before any model write, static sync rejects generated_at values more than 15 minutes in the future and compares each import with one transactionally persisted global generated_at/SHA-256 watermark. Older snapshots and same-time/different-SHA snapshots fail. It records sourceLastSeenAt from the validated time. A missing in-scope Section may set retiredAt only after completeness and mapped-jwId validation; reappearing rows clear retiredAt only when seen after retirement.",
+    "import-state-bootstrap": "When no global import watermark exists, scheduled and ordinary manual writes fail closed. A manual bootstrap must keep Section retirement disabled; a committed bootstrap also requires the exact snapshot SHA-256 observed in a preceding dry run. The watermark update commits in the same advisory-locked transaction as all imported models.",
+    "retirement-approval": "Scheduled production sync can never enable retirement. A manual run must explicitly set STATIC_LOADER_RETIRE_MISSING_SECTIONS=true and provide the exact snapshot SHA-256 plus exact candidate count observed in a preceding dry run; any mismatch aborts before lifecycle writes. Semesters with zero source lessons are excluded from destructive scope.",
+    "retirement-preserves-data": "Retirement never deletes the Section or its comments, description, homeworks, subscription relationships, schedules, exams, or audit history. Each retirement/reactivation writes a Section-targeted audit row and the import report includes candidate, before/after, retired, and reactivated counts.",
+    "retired-read-semantics": "Public Section/search/match and public/current calendar collection queries exclude retired rows. Direct Section detail and single-Section calendar access remain available for historical references; the detail page labels the record historical and does not offer a new subscription. Course/Teacher detail histories and the owner's subscribed Sections list also retain retired rows. New subscription discovery/add operations reject retired rows, while an existing owner can still remove one.",
     "subscription-not-enrollment": "Pages involving subscription actions must clearly state this is not official academic course enrollment.",
     "jwid-url-only": "jwId is used only for routing and API endpoints; it should not be directly displayed in ordinary section UI.",
     "public-list-cache": "Anonymous section list REST responses and server-side list data may use short public runtime/CDN caching because section fact data is read-only; localized HTML pages must not use shared edge caching unless the cache key varies by locale.",
@@ -30,7 +35,8 @@
             "path": "/api/sections",
             "returns": "PaginatedResponse<SectionSummary>",
             "notes": [
-              "REST pageSize accepts 1-100; the deprecated limit alias remains accepted and pageSize wins when both are supplied. Out-of-range values are rejected instead of clamped."
+              "REST pageSize accepts 1-100; the deprecated limit alias remains accepted and pageSize wins when both are supplied. Out-of-range values are rejected instead of clamped.",
+              "Retired Sections are excluded."
             ]
           }
         ]
@@ -43,7 +49,8 @@
             "rest_equivalent": "GET /api/sections",
             "mcp_equivalent": "search_sections",
             "notes": [
-              "PageInput defaults to page=1 and pageSize=20; pageSize must remain within 1-100."
+              "PageInput defaults to page=1 and pageSize=20; pageSize must remain within 1-100.",
+              "Retired Sections are excluded."
             ]
           }
         ]
@@ -55,7 +62,8 @@
             "returns": "PaginatedResponse<SectionSummary>",
             "rest_equivalent": "GET /api/sections",
             "notes": [
-              "MCP limit accepts 1-100 and rejects out-of-range values instead of clamping."
+              "MCP limit accepts 1-100 and rejects out-of-range values instead of clamping.",
+              "Retired Sections are excluded."
             ]
           }
         ]
@@ -91,7 +99,10 @@
         "routes": [
           {
             "path": "/api/sections/[jwId]",
-            "returns": "SectionDetail (schedules without room/teacher expansion)"
+            "returns": "SectionDetail (schedules without room/teacher expansion)",
+            "notes": [
+              "Direct historical lookup remains available for retired Sections; retiredAt identifies retirement and sourceLastSeenAt records the last successful source observation."
+            ]
           }
         ]
       },
diff --git a/docs/contracts/subscribed-sections.json b/docs/contracts/subscribed-sections.json
index 1de361b23..d34ffbbce 100644
--- a/docs/contracts/subscribed-sections.json
+++ b/docs/contracts/subscribed-sections.json
@@ -8,6 +8,7 @@
   },
   "rules": {
     "grouped-by-semester": "The list is grouped by semester rather than presented as a single flat list.",
+    "retired-history": "Existing subscription relationships to retired Sections remain visible in the owner's subscribed Sections list and can be removed. Retired Sections cannot be newly discovered or added and are omitted from current personal calendar events/feeds.",
     "section-codes-promoted": "In the 'subscribed context', users manage specific section relationships, so section codes are intentionally promoted.",
     "legacy-sections-route": "/dashboard/subscriptions/sections is a legacy redirect-only route to /dashboard/subscriptions and must not expose page actions."
   },
diff --git a/docs/contracts/subscription.json b/docs/contracts/subscription.json
index c08fc4a4f..97d2d16e4 100644
--- a/docs/contracts/subscription.json
+++ b/docs/contracts/subscription.json
@@ -98,8 +98,8 @@
             "notes": [
               "Preferred mutation endpoint for batch subscribe, unsubscribe, and replace/update flows.",
               "Accepts action plus sectionIds and/or mixed section/course codes.",
-              "action=set requires semesterId and replaces only the requested semester, preserving subscriptions from every other semester.",
-              "A semester-scoped action=set may omit sectionIds/codes to clear only that semester."
+              "action=set requires semesterId, replaces only that semester (an empty target clears it), and preserves every other semester.",
+              "action=set preserves a retired Section only when it is already subscribed and its ID is explicitly included; omitted or newly requested retired Sections remain unsubscribed."
             ]
           },
           {
@@ -114,7 +114,8 @@
             "returns": "{ subscription: CalendarSubscription }",
             "notes": [
               "Compatibility replace endpoint for ID-only callers.",
-              "subscription.sections[] is the user's new set of subscribed sections."
+              "subscription.sections[] is the user's new set of subscribed sections.",
+              "A retired Section is preserved only when it is already subscribed and its ID is explicitly included; retired Sections cannot be newly subscribed."
             ]
           },
           {
diff --git a/messages/en-us.json b/messages/en-us.json
index 48e52eee3..5c9971482 100644
--- a/messages/en-us.json
+++ b/messages/en-us.json
@@ -1052,6 +1052,8 @@
     "courseCode": "Course Code",
     "sectionCode": "Section Code",
     "teachingSection": "Teaching section",
+    "historicalSectionLabel": "Historical section",
+    "historicalSectionDescription": "This section is absent from the latest academic snapshot. Its history remains available, but it cannot be newly followed.",
     "semester": "Semester",
     "campus": "Campus",
     "credits": "Credits",
diff --git a/messages/zh-cn.json b/messages/zh-cn.json
index 15f085b31..26ecbbd3c 100644
--- a/messages/zh-cn.json
+++ b/messages/zh-cn.json
@@ -1018,6 +1018,8 @@
     "courseCode": "课程代码",
     "sectionCode": "班级代码",
     "teachingSection": "授课班级",
+    "historicalSectionLabel": "历史班级",
+    "historicalSectionDescription": "该班级已不在最新教务快照中，保留此页面用于查看历史信息；不能新增关注。",
     "semester": "学期",
     "campus": "校区",
     "credits": "学分",
diff --git a/prisma/migrations/20260718110000_add_static_import_state/migration.sql b/prisma/migrations/20260718110000_add_static_import_state/migration.sql
new file mode 100644
index 000000000..4b91faeee
--- /dev/null
+++ b/prisma/migrations/20260718110000_add_static_import_state/migration.sql
@@ -0,0 +1,11 @@
+CREATE TABLE "StaticImportState" (
+  "id" TEXT NOT NULL,
+  "snapshotGeneratedAt" TIMESTAMP(3) NOT NULL,
+  "snapshotSha256" TEXT NOT NULL,
+  "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  "updatedAt" TIMESTAMP(3) NOT NULL,
+
+  CONSTRAINT "StaticImportState_pkey" PRIMARY KEY ("id"),
+  CONSTRAINT "StaticImportState_snapshotSha256_check"
+    CHECK ("snapshotSha256" ~ '^[0-9a-f]{64}$')
+);
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index 8b6d87b24..6ac40dd14 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -452,6 +452,16 @@ model Section {
   @@index([teachLanguageId])
 }
 
+model StaticImportState {
+  id String @id
+
+  snapshotGeneratedAt DateTime
+  snapshotSha256      String
+
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+}
+
 model Exam {
   id   Int @id @default(autoincrement())
   jwId Int @unique
diff --git a/public/openapi.generated.json b/public/openapi.generated.json
index 0ddfe1475..a11ccd35b 100644
--- a/public/openapi.generated.json
+++ b/public/openapi.generated.json
@@ -8840,6 +8840,18 @@
                       "minimum": -9007199254740991,
                       "maximum": 9007199254740991
                     },
+                    "sourceLastSeenAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
+                    "retiredAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
                     "code": {
                       "type": "string"
                     },
@@ -9545,6 +9557,18 @@
                       "minimum": -9007199254740991,
                       "maximum": 9007199254740991
                     },
+                    "sourceLastSeenAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
+                    "retiredAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
                     "code": {
                       "type": "string"
                     },
@@ -10262,6 +10286,18 @@
                       "minimum": -9007199254740991,
                       "maximum": 9007199254740991
                     },
+                    "sourceLastSeenAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
+                    "retiredAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
                     "code": {
                       "type": "string"
                     },
@@ -12046,6 +12082,18 @@
                       "minimum": -9007199254740991,
                       "maximum": 9007199254740991
                     },
+                    "sourceLastSeenAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
+                    "retiredAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
                     "code": {
                       "type": "string"
                     },
@@ -12881,6 +12929,18 @@
                     "minimum": -9007199254740991,
                     "maximum": 9007199254740991
                   },
+                  "sourceLastSeenAt": {
+                    "nullable": true,
+                    "type": "string",
+                    "format": "date-time",
+                    "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                  },
+                  "retiredAt": {
+                    "nullable": true,
+                    "type": "string",
+                    "format": "date-time",
+                    "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                  },
                   "code": {
                     "type": "string"
                   },
@@ -14283,6 +14343,18 @@
                       "minimum": -9007199254740991,
                       "maximum": 9007199254740991
                     },
+                    "sourceLastSeenAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
+                    "retiredAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
                     "code": {
                       "type": "string"
                     },
@@ -17662,6 +17734,18 @@
                   "minimum": -9007199254740991,
                   "maximum": 9007199254740991
                 },
+                "sourceLastSeenAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
+                "retiredAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
                 "code": {
                   "type": "string"
                 },
@@ -18349,6 +18433,18 @@
                       "minimum": -9007199254740991,
                       "maximum": 9007199254740991
                     },
+                    "sourceLastSeenAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
+                    "retiredAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
                     "code": {
                       "type": "string"
                     },
@@ -19048,6 +19144,18 @@
                       "minimum": -9007199254740991,
                       "maximum": 9007199254740991
                     },
+                    "sourceLastSeenAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
+                    "retiredAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
                     "code": {
                       "type": "string"
                     },
@@ -19803,6 +19911,18 @@
                   "minimum": -9007199254740991,
                   "maximum": 9007199254740991
                 },
+                "sourceLastSeenAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
+                "retiredAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
                 "code": {
                   "type": "string"
                 },
@@ -20460,6 +20580,18 @@
                   "minimum": -9007199254740991,
                   "maximum": 9007199254740991
                 },
+                "sourceLastSeenAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
+                "retiredAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
                 "code": {
                   "type": "string"
                 },
@@ -21117,6 +21249,18 @@
                   "minimum": -9007199254740991,
                   "maximum": 9007199254740991
                 },
+                "sourceLastSeenAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
+                "retiredAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
                 "code": {
                   "type": "string"
                 },
@@ -21776,6 +21920,18 @@
                       "minimum": -9007199254740991,
                       "maximum": 9007199254740991
                     },
+                    "sourceLastSeenAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
+                    "retiredAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
                     "code": {
                       "type": "string"
                     },
@@ -22562,6 +22718,18 @@
                   "minimum": -9007199254740991,
                   "maximum": 9007199254740991
                 },
+                "sourceLastSeenAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
+                "retiredAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
                 "code": {
                   "type": "string"
                 },
@@ -23780,6 +23948,18 @@
                   "minimum": -9007199254740991,
                   "maximum": 9007199254740991
                 },
+                "sourceLastSeenAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
+                "retiredAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
                 "code": {
                   "type": "string"
                 },
@@ -24355,6 +24535,18 @@
                     "minimum": -9007199254740991,
                     "maximum": 9007199254740991
                   },
+                  "sourceLastSeenAt": {
+                    "nullable": true,
+                    "type": "string",
+                    "format": "date-time",
+                    "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                  },
+                  "retiredAt": {
+                    "nullable": true,
+                    "type": "string",
+                    "format": "date-time",
+                    "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                  },
                   "code": {
                     "type": "string"
                   },
@@ -25579,6 +25771,18 @@
                           "minimum": -9007199254740991,
                           "maximum": 9007199254740991
                         },
+                        "sourceLastSeenAt": {
+                          "nullable": true,
+                          "type": "string",
+                          "format": "date-time",
+                          "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                        },
+                        "retiredAt": {
+                          "nullable": true,
+                          "type": "string",
+                          "format": "date-time",
+                          "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                        },
                         "code": {
                           "type": "string"
                         },
@@ -26188,6 +26392,18 @@
                           "minimum": -9007199254740991,
                           "maximum": 9007199254740991
                         },
+                        "sourceLastSeenAt": {
+                          "nullable": true,
+                          "type": "string",
+                          "format": "date-time",
+                          "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                        },
+                        "retiredAt": {
+                          "nullable": true,
+                          "type": "string",
+                          "format": "date-time",
+                          "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                        },
                         "code": {
                           "type": "string"
                         },
@@ -26817,6 +27033,18 @@
                           "minimum": -9007199254740991,
                           "maximum": 9007199254740991
                         },
+                        "sourceLastSeenAt": {
+                          "nullable": true,
+                          "type": "string",
+                          "format": "date-time",
+                          "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                        },
+                        "retiredAt": {
+                          "nullable": true,
+                          "type": "string",
+                          "format": "date-time",
+                          "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                        },
                         "code": {
                           "type": "string"
                         },
@@ -27155,6 +27383,18 @@
             "minimum": -9007199254740991,
             "maximum": 9007199254740991
           },
+          "sourceLastSeenAt": {
+            "nullable": true,
+            "type": "string",
+            "format": "date-time",
+            "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+          },
+          "retiredAt": {
+            "nullable": true,
+            "type": "string",
+            "format": "date-time",
+            "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+          },
           "code": {
             "type": "string"
           },
@@ -28554,6 +28794,18 @@
                   "minimum": -9007199254740991,
                   "maximum": 9007199254740991
                 },
+                "sourceLastSeenAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
+                "retiredAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
                 "code": {
                   "type": "string"
                 },
@@ -29371,6 +29623,18 @@
                   "minimum": -9007199254740991,
                   "maximum": 9007199254740991
                 },
+                "sourceLastSeenAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
+                "retiredAt": {
+                  "nullable": true,
+                  "type": "string",
+                  "format": "date-time",
+                  "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                },
                 "code": {
                   "type": "string"
                 },
@@ -31380,6 +31644,18 @@
                       "minimum": -9007199254740991,
                       "maximum": 9007199254740991
                     },
+                    "sourceLastSeenAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
+                    "retiredAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
                     "code": {
                       "type": "string"
                     },
@@ -32433,6 +32709,18 @@
                       "minimum": -9007199254740991,
                       "maximum": 9007199254740991
                     },
+                    "sourceLastSeenAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
+                    "retiredAt": {
+                      "nullable": true,
+                      "type": "string",
+                      "format": "date-time",
+                      "pattern": "^(?:(?:\\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]|[02468][048]00|[13579][26]00)-02-29|\\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\\d|30)|(?:02)-(?:0[1-9]|1\\d|2[0-8])))T(?:(?:[01]\\d|2[0-3]):[0-5]\\d(?::[0-5]\\d(?:\\.\\d+)?)?(?:Z|([+-](?:[01]\\d|2[0-3]):[0-5]\\d)))$"
+                    },
                     "code": {
                       "type": "string"
                     },
diff --git a/src/features/calendar/server/calendar-event-sources.ts b/src/features/calendar/server/calendar-event-sources.ts
index 40661c4d0..23e4c08b2 100644
--- a/src/features/calendar/server/calendar-event-sources.ts
+++ b/src/features/calendar/server/calendar-event-sources.ts
@@ -1,6 +1,6 @@
 import { withHomeworkItemState } from "@/features/homeworks/server/homework-item-state";
 import {
-  getSubscribedSectionIds,
+  getActiveSubscribedSectionIds,
   listSubscribedExams,
   listSubscribedHomeworks,
   listSubscribedSchedules,
@@ -26,9 +26,10 @@ export async function loadCalendarEventSources({
   windowEnd: Date;
   windowStart: Date;
 }) {
-  const scopedSectionIds = sectionIds
-    ? Array.from(sectionIds)
-    : await getSubscribedSectionIds(userId);
+  const scopedSectionIds = await getActiveSubscribedSectionIds(
+    userId,
+    sectionIds,
+  );
 
   const [schedules, homeworks, exams, todos] = await Promise.all([
     listSubscribedSchedules(userId, {
diff --git a/src/features/calendar/server/calendar-export-data.ts b/src/features/calendar/server/calendar-export-data.ts
index 93722c5e0..02f2079b8 100644
--- a/src/features/calendar/server/calendar-export-data.ts
+++ b/src/features/calendar/server/calendar-export-data.ts
@@ -69,6 +69,7 @@ export async function getSectionsForCalendar(sectionIds: number[]) {
       id: {
         in: sectionIds,
       },
+      retiredAt: null,
     },
     include: sectionCalendarInclude,
   });
@@ -79,6 +80,7 @@ export async function getUserCalendarRecord(userId: string) {
     where: { id: userId },
     include: {
       subscribedSections: {
+        where: { retiredAt: null },
         include: sectionCalendarInclude,
       },
       todos: {
diff --git a/src/features/catalog/lib/schedule-filters.ts b/src/features/catalog/lib/schedule-filters.ts
index 0f1fd934c..b54b37b03 100644
--- a/src/features/catalog/lib/schedule-filters.ts
+++ b/src/features/catalog/lib/schedule-filters.ts
@@ -32,7 +32,10 @@ export function buildScheduleDateWhere(
     : {};
 }
 
-export function buildScheduleListWhere(filters: ScheduleListFilters) {
+export function buildScheduleListWhere(
+  filters: ScheduleListFilters,
+  options: { excludeRetiredSections?: boolean } = {},
+) {
   const {
     sectionId,
     sectionJwId,
@@ -49,8 +52,11 @@ export function buildScheduleListWhere(filters: ScheduleListFilters) {
   applyIntegerFilter(where, "sectionId", sectionId);
 
   const sectionFilter = buildRelatedFilter("jwId", sectionJwId, sectionCode);
-  if (sectionFilter) {
-    where.section = sectionFilter;
+  if (sectionFilter || options.excludeRetiredSections) {
+    where.section = {
+      ...(sectionFilter ?? {}),
+      ...(options.excludeRetiredSections ? { retiredAt: null } : {}),
+    };
   }
 
   const teacherFilter = buildRelatedFilter("id", teacherId, teacherCode);
diff --git a/src/features/catalog/server/academic-query-includes.ts b/src/features/catalog/server/academic-query-includes.ts
index 1fdebd522..a5e57c1c8 100644
--- a/src/features/catalog/server/academic-query-includes.ts
+++ b/src/features/catalog/server/academic-query-includes.ts
@@ -128,7 +128,7 @@ export const teacherListInclude = {
   teacherTitle: true,
   _count: {
     select: {
-      sections: true,
+      sections: { where: { retiredAt: null } },
     },
   },
 } satisfies Prisma.TeacherInclude;
diff --git a/src/features/catalog/server/public-catalog-data.ts b/src/features/catalog/server/public-catalog-data.ts
index f7cecb988..1e3aad541 100644
--- a/src/features/catalog/server/public-catalog-data.ts
+++ b/src/features/catalog/server/public-catalog-data.ts
@@ -13,10 +13,13 @@ export async function getPublicCatalog(locale = "zh-cn") {
         code: true,
         nameCn: true,
         nameEn: true,
-        _count: { select: { sections: true } },
+        _count: {
+          select: { sections: { where: { retiredAt: null } } },
+        },
       },
     }),
     prisma.section.findMany({
+      where: { retiredAt: null },
       take: CATALOG_HOME_LIST_LIMIT,
       orderBy: [{ id: "desc" }],
       select: {
@@ -35,7 +38,9 @@ export async function getPublicCatalog(locale = "zh-cn") {
         nameCn: true,
         nameEn: true,
         department: { select: { nameCn: true, nameEn: true } },
-        _count: { select: { sections: true } },
+        _count: {
+          select: { sections: { where: { retiredAt: null } } },
+        },
       },
     }),
   ]);
diff --git a/src/features/catalog/server/schedule-read-model.ts b/src/features/catalog/server/schedule-read-model.ts
index a8e16f2f1..19f0273a8 100644
--- a/src/features/catalog/server/schedule-read-model.ts
+++ b/src/features/catalog/server/schedule-read-model.ts
@@ -118,7 +118,9 @@ export async function listPublicSchedules(input: {
   pageSize?: number;
 }) {
   const prisma = getPrisma(input.locale ?? DEFAULT_LOCALE);
-  const where = buildScheduleListWhere(input.filters);
+  const where = buildScheduleListWhere(input.filters, {
+    excludeRetiredSections: true,
+  });
   const result = await paginatedQuery(
     (skip, take) =>
       prisma.schedule.findMany({
diff --git a/src/features/catalog/server/section-code-match-query.ts b/src/features/catalog/server/section-code-match-query.ts
index e56b3fc9e..c612fbeb6 100644
--- a/src/features/catalog/server/section-code-match-query.ts
+++ b/src/features/catalog/server/section-code-match-query.ts
@@ -18,6 +18,7 @@ export async function findSectionCodeMatches(
   const sections = await getPrisma(locale).section.findMany({
     where: {
       code: { in: codes },
+      retiredAt: null,
       semesterId: semester.id,
     },
     include: sectionCompactInclude,
diff --git a/src/features/catalog/server/section-code-match-suggestions.ts b/src/features/catalog/server/section-code-match-suggestions.ts
index 57f7a18db..e522f7fd6 100644
--- a/src/features/catalog/server/section-code-match-suggestions.ts
+++ b/src/features/catalog/server/section-code-match-suggestions.ts
@@ -32,6 +32,7 @@ export async function buildSectionCodeSuggestions({
           await prisma.section.findMany({
             where: {
               semesterId,
+              retiredAt: null,
               OR: batchedPrefixes.map((prefix) => ({
                 code: ilike(prefix),
               })),
diff --git a/src/features/catalog/server/section-query-filters.ts b/src/features/catalog/server/section-query-filters.ts
index 5644f86a0..7ff946101 100644
--- a/src/features/catalog/server/section-query-filters.ts
+++ b/src/features/catalog/server/section-query-filters.ts
@@ -24,7 +24,7 @@ export function buildSectionListQuery(filters: SectionListFilters): {
     jwIds,
     search,
   } = filters;
-  const where: Prisma.SectionWhereInput = {};
+  const where: Prisma.SectionWhereInput = { retiredAt: null };
 
   applyIntegerFilter(where, "courseId", courseId);
 
diff --git a/src/features/dashboard/server/assistant-dashboard-snapshot-helpers.ts b/src/features/dashboard/server/assistant-dashboard-snapshot-helpers.ts
index 09686da17..046df287e 100644
--- a/src/features/dashboard/server/assistant-dashboard-snapshot-helpers.ts
+++ b/src/features/dashboard/server/assistant-dashboard-snapshot-helpers.ts
@@ -50,6 +50,7 @@ export async function listAssistantCurrentSemesterSections({
     ? localizedPrisma.section.findMany({
         where: {
           id: { in: sectionIds },
+          retiredAt: null,
           semesterId: currentSemesterId,
         },
         orderBy: [{ code: "asc" }],
diff --git a/src/features/dashboard/server/compact-overview-read-model.ts b/src/features/dashboard/server/compact-overview-read-model.ts
index 9a6b7b007..4b846581c 100644
--- a/src/features/dashboard/server/compact-overview-read-model.ts
+++ b/src/features/dashboard/server/compact-overview-read-model.ts
@@ -1,7 +1,7 @@
 import { withHomeworkItemState } from "@/features/homeworks/server/homework-item-state";
 import {
   countUpcomingSubscribedExams,
-  getSubscribedSectionIds,
+  getActiveSubscribedSectionIds,
   listSubscribedHomeworks,
   listSubscribedSchedules,
   listUpcomingSubscribedExams,
@@ -56,7 +56,7 @@ export async function getCompactOverview(
       where: { id: userId },
       select: { id: true, image: true, isAdmin: true, name: true },
     }),
-    getSubscribedSectionIds(userId),
+    getActiveSubscribedSectionIds(userId),
     listTodoSummary({
       filters: { completed: false },
       now,
diff --git a/src/features/dashboard/server/dashboard-nav-stats.ts b/src/features/dashboard/server/dashboard-nav-stats.ts
index c7c75e299..351935f01 100644
--- a/src/features/dashboard/server/dashboard-nav-stats.ts
+++ b/src/features/dashboard/server/dashboard-nav-stats.ts
@@ -40,12 +40,17 @@ export async function getDashboardNavStats(
 
   const pendingTodosCountPromise = countIncompleteTodos(user.id);
 
-  if (subscribedSections.length === 0) {
+  const activeSubscribedSections = subscribedSections.filter(
+    (section) => section.retiredAt === null || section.retiredAt === undefined,
+  );
+  if (activeSubscribedSections.length === 0) {
     const pendingTodosCount = await pendingTodosCountPromise;
     return emptyDashboardNavStats({ pendingTodosCount, user });
   }
 
-  const scopedSectionIds = subscribedSections.map((section) => section.id);
+  const scopedSectionIds = activeSubscribedSections.map(
+    (section) => section.id,
+  );
   const [
     pendingTodosCount,
     pendingHomeworksCount,
@@ -78,7 +83,11 @@ export async function getDashboardNavStats(
       atTime: referenceNow.toDate(),
       sectionIds: scopedSectionIds,
     }),
-    getDashboardCalendarItemsCount(user.id, subscribedSections, referenceNow),
+    getDashboardCalendarItemsCount(
+      user.id,
+      activeSubscribedSections,
+      referenceNow,
+    ),
   ]);
 
   return {
diff --git a/src/features/dashboard/server/dashboard-page-public-summary.ts b/src/features/dashboard/server/dashboard-page-public-summary.ts
index 91640710a..09b62e3e0 100644
--- a/src/features/dashboard/server/dashboard-page-public-summary.ts
+++ b/src/features/dashboard/server/dashboard-page-public-summary.ts
@@ -27,7 +27,7 @@ export async function loadDashboardPublicSummary(
     await Promise.all([
       prisma.semester.count(),
       prisma.course.count(),
-      prisma.section.count(),
+      prisma.section.count({ where: { retiredAt: null } }),
       prisma.semester.findMany({
         select: {
           id: true,
diff --git a/src/features/dashboard/server/dashboard-user-context.ts b/src/features/dashboard/server/dashboard-user-context.ts
index 265449967..36422e259 100644
--- a/src/features/dashboard/server/dashboard-user-context.ts
+++ b/src/features/dashboard/server/dashboard-user-context.ts
@@ -8,6 +8,7 @@ export type DashboardUserSummary = {
 
 export type DashboardSubscribedSection = {
   id: number;
+  retiredAt?: Date | null;
   semesterId: number | null;
 };
 
@@ -28,7 +29,7 @@ export async function getDashboardUserContext(
       username: true,
       calendarFeedToken: true,
       subscribedSections: {
-        select: { id: true, semesterId: true },
+        select: { id: true, retiredAt: true, semesterId: true },
       },
     },
   });
diff --git a/src/features/section-detail/components/SectionDetailDialogs.svelte b/src/features/section-detail/components/SectionDetailDialogs.svelte
index 8fe28a5ca..7cd929dc9 100644
--- a/src/features/section-detail/components/SectionDetailDialogs.svelte
+++ b/src/features/section-detail/components/SectionDetailDialogs.svelte
@@ -144,7 +144,7 @@ export let applyEditStartNow: SectionDetailDialogsProps["applyEditStartNow"];
   {subscriptionCalendarUrl}
 />
 
-{#if showSubscribeDialog}
+{#if showSubscribeDialog && data.section.retiredAt == null}
   <SectionSubscribeDialog
     close={closeSubscribeDialog}
     {commonCopy}
diff --git a/src/features/section-detail/components/SectionDetailHeader.svelte b/src/features/section-detail/components/SectionDetailHeader.svelte
index 1fb34d9e8..61135be27 100644
--- a/src/features/section-detail/components/SectionDetailHeader.svelte
+++ b/src/features/section-detail/components/SectionDetailHeader.svelte
@@ -11,6 +11,8 @@ import type {
 
 type SectionHeaderCopy = {
   addToCalendar: string;
+  historicalSectionDescription: string;
+  historicalSectionLabel: string;
   subscribeLabel: string;
   teachingSection: string;
   unsubscribeLabel: string;
@@ -21,6 +23,7 @@ type SectionHeaderSection = {
   campus?: SectionLocalizedName | null;
   code: string;
   limitCount?: number | null;
+  retiredAt?: string | Date | null;
   semester?: {
     nameCn?: string | null;
   } | null;
@@ -65,6 +68,7 @@ export let viewer: SectionHeaderViewer;
     <SectionDetailPrimaryActions
       {onOpenCalendar}
       {onOpenSubscribe}
+      retired={section.retiredAt != null}
       {sectionCopy}
       {subscriptionAction}
       {subscriptionPendingAction}
@@ -81,6 +85,13 @@ export let viewer: SectionHeaderViewer;
         {/if}
       </div>
 
+      {#if section.retiredAt != null}
+        <Alert.Root>
+          <Alert.Title>{sectionCopy.historicalSectionLabel}</Alert.Title>
+          <Alert.Description>{sectionCopy.historicalSectionDescription}</Alert.Description>
+        </Alert.Root>
+      {/if}
+
       {#if formError}
         <Alert.Root variant="destructive">
           <Alert.Description>{formError}</Alert.Description>
diff --git a/src/features/section-detail/components/SectionDetailMainContent.svelte b/src/features/section-detail/components/SectionDetailMainContent.svelte
index a7b794d9c..43520658f 100644
--- a/src/features/section-detail/components/SectionDetailMainContent.svelte
+++ b/src/features/section-detail/components/SectionDetailMainContent.svelte
@@ -265,6 +265,7 @@ $: activeNavItem =
       <SectionDetailPrimaryActions
         onOpenCalendar={openCalendarDialog}
         onOpenSubscribe={openSubscribeDialog}
+        retired={data.section.retiredAt != null}
         {sectionCopy}
         stretched
         {subscriptionAction}
diff --git a/src/features/section-detail/components/SectionDetailPrimaryActions.svelte b/src/features/section-detail/components/SectionDetailPrimaryActions.svelte
index 78a64b264..35bf997d4 100644
--- a/src/features/section-detail/components/SectionDetailPrimaryActions.svelte
+++ b/src/features/section-detail/components/SectionDetailPrimaryActions.svelte
@@ -17,6 +17,7 @@ type SectionActionsCopy = {
 
 export let onOpenCalendar: () => void;
 export let onOpenSubscribe: () => void;
+export let retired = false;
 export let sectionCopy: SectionActionsCopy;
 export let stretched = false;
 export let subscriptionAction: (
@@ -28,7 +29,9 @@ export let viewer: { isSubscribed?: boolean };
 
 <div
   class={stretched
-    ? "grid w-full grid-cols-2 gap-2"
+    ? retired && !viewer.isSubscribed
+      ? "grid w-full grid-cols-1 gap-2"
+      : "grid w-full grid-cols-2 gap-2"
     : "flex flex-wrap gap-2"}
 >
   <Button
@@ -59,7 +62,7 @@ export let viewer: { isSubscribed?: boolean };
           : sectionCopy.unsubscribeLabel}
       </Button>
     </form>
-  {:else}
+  {:else if !retired}
     <form class={stretched ? "w-full" : undefined} method="GET">
       <input name="subscribe" type="hidden" value="1" />
       <Button
diff --git a/src/features/section-detail/components/section-detail-dialog-types.ts b/src/features/section-detail/components/section-detail-dialog-types.ts
index d53be8c4f..a0eba3308 100644
--- a/src/features/section-detail/components/section-detail-dialog-types.ts
+++ b/src/features/section-detail/components/section-detail-dialog-types.ts
@@ -59,6 +59,8 @@ export type SectionDetailSectionCopy = SectionCreateHomeworkSectionCopy & {
   copied: string;
   copyToClipboard: string;
   due: string;
+  historicalSectionDescription: string;
+  historicalSectionLabel: string;
   homeworkDescription: string;
   loginRequired: string;
   subscribeLabel: string;
@@ -172,6 +174,8 @@ export type SectionDetailMainSectionCopy = SectionCalendarCopy &
     examLegend: string;
     exams: string;
     homeworkDescription: string;
+    historicalSectionDescription: string;
+    historicalSectionLabel: string;
     tabs: {
       calendar: string;
       comments: string;
diff --git a/src/features/section-detail/lib/section-detail-controller-types.ts b/src/features/section-detail/lib/section-detail-controller-types.ts
index 822d8c41d..75d07810d 100644
--- a/src/features/section-detail/lib/section-detail-controller-types.ts
+++ b/src/features/section-detail/lib/section-detail-controller-types.ts
@@ -82,6 +82,7 @@ export type SectionDetailSection = {
   periodsPerWeek?: number | null;
   practicePeriods?: number | null;
   remark?: string | null;
+  retiredAt?: string | Date | null;
   roomType?: SectionDetailNamed | null;
   schedules: SectionDetailSchedule[];
   sameSemesterOtherTeachers: SectionDetailRelatedSection[];
@@ -272,6 +273,8 @@ export type SectionDetailCopy = {
     flags: string;
     homeworkDescription: string;
     homeworkView: string;
+    historicalSectionDescription: string;
+    historicalSectionLabel: string;
     previousMonth: string;
     nextMonth: string;
     moreEvents: string;
diff --git a/src/features/section-detail/server/section-detail-page-server.ts b/src/features/section-detail/server/section-detail-page-server.ts
index fabc66b81..6efe20479 100644
--- a/src/features/section-detail/server/section-detail-page-server.ts
+++ b/src/features/section-detail/server/section-detail-page-server.ts
@@ -89,7 +89,8 @@ export async function loadSectionDetailPage({
     focusedHomeworkId: url.searchParams.get("homeworkId"),
     homeworkView:
       url.searchParams.get("homeworkView") === "list" ? "list" : "cards",
-    showSubscribeDialog: url.searchParams.get("subscribe") === "1",
+    showSubscribeDialog:
+      section.retiredAt === null && url.searchParams.get("subscribe") === "1",
     socialMetadata: buildSocialMetadata({
       canonicalPath: `/sections/${jwId}`,
       description: formatSocialMetadataMessage(
diff --git a/src/features/section-detail/server/section-page-related-data.ts b/src/features/section-detail/server/section-page-related-data.ts
index 16f2b05fa..237dd6407 100644
--- a/src/features/section-detail/server/section-page-related-data.ts
+++ b/src/features/section-detail/server/section-page-related-data.ts
@@ -46,7 +46,11 @@ export async function getSectionPageRelatedData({
     }),
     getLatestComments({ sectionId: section.id }, 5, locale),
     prisma.section.findMany({
-      where: { courseId: section.courseId, id: { not: section.id } },
+      where: {
+        courseId: section.courseId,
+        id: { not: section.id },
+        retiredAt: null,
+      },
       orderBy: [{ semester: { jwId: "desc" } }, { code: "asc" }],
       select: {
         id: true,
diff --git a/src/features/section-detail/server/section-page-select.ts b/src/features/section-detail/server/section-page-select.ts
index 48b24f21e..8a5d10f5e 100644
--- a/src/features/section-detail/server/section-page-select.ts
+++ b/src/features/section-detail/server/section-page-select.ts
@@ -9,6 +9,7 @@ import type { Prisma } from "@/generated/prisma/client";
 export const sectionPageSelect = {
   id: true,
   jwId: true,
+  retiredAt: true,
   code: true,
   credits: true,
   period: true,
diff --git a/src/features/subscriptions/server/subscription-dashboard-section-read-model.ts b/src/features/subscriptions/server/subscription-dashboard-section-read-model.ts
index 91ab3a192..7a0ddc1c5 100644
--- a/src/features/subscriptions/server/subscription-dashboard-section-read-model.ts
+++ b/src/features/subscriptions/server/subscription-dashboard-section-read-model.ts
@@ -45,7 +45,7 @@ export async function listSubscribedDashboardSections(
 
       const [sectionRows, scheduleRows, examRows] = await Promise.all([
         localizedPrisma.section.findMany({
-          where: { id: { in: ids } },
+          where: { id: { in: ids }, retiredAt: null },
           select: {
             id: true,
             jwId: true,
@@ -58,6 +58,7 @@ export async function listSubscribedDashboardSections(
           ? localizedPrisma.schedule.findMany({
               where: {
                 sectionId: { in: ids },
+                section: { retiredAt: null },
                 ...detailSemesterWhere,
                 ...(dateFilter ? { date: dateFilter } : {}),
               },
@@ -86,7 +87,11 @@ export async function listSubscribedDashboardSections(
           : Promise.resolve([]),
         shouldLoadDetails
           ? localizedPrisma.exam.findMany({
-              where: { sectionId: { in: ids }, ...detailSemesterWhere },
+              where: {
+                sectionId: { in: ids },
+                section: { retiredAt: null },
+                ...detailSemesterWhere,
+              },
               select: {
                 id: true,
                 sectionId: true,
diff --git a/src/features/subscriptions/server/subscription-read-model-shared.ts b/src/features/subscriptions/server/subscription-read-model-shared.ts
index 3cddbf5cf..84bb84ff8 100644
--- a/src/features/subscriptions/server/subscription-read-model-shared.ts
+++ b/src/features/subscriptions/server/subscription-read-model-shared.ts
@@ -41,6 +41,25 @@ export async function getSubscribedSectionIds(
   return user?.subscribedSections.map((s) => s.id) ?? [];
 }
 
+export async function getActiveSubscribedSectionIds(
+  userId: string,
+  sectionIds?: readonly number[],
+): Promise<number[]> {
+  const user = await prisma.user.findUnique({
+    where: { id: userId },
+    select: {
+      subscribedSections: {
+        where: {
+          retiredAt: null,
+          ...(sectionIds ? { id: { in: Array.from(sectionIds) } } : {}),
+        },
+        select: { id: true },
+      },
+    },
+  });
+  return user?.subscribedSections.map((section) => section.id) ?? [];
+}
+
 export async function getSubscribedSectionIdsForSemester(
   userId: string,
   semesterId: number,
diff --git a/src/features/subscriptions/server/subscription-read-model.ts b/src/features/subscriptions/server/subscription-read-model.ts
index ce12304fd..66cee625e 100644
--- a/src/features/subscriptions/server/subscription-read-model.ts
+++ b/src/features/subscriptions/server/subscription-read-model.ts
@@ -12,6 +12,7 @@ export {
   listSubscribedHomeworks,
 } from "./subscription-homework-read-model";
 export {
+  getActiveSubscribedSectionIds,
   getSubscribedSectionIds,
   SECTION_SUBSCRIPTION_NOTE,
   type SectionOption,
diff --git a/src/features/subscriptions/server/subscription-schedule-exam-read-model.ts b/src/features/subscriptions/server/subscription-schedule-exam-read-model.ts
index c144de4f5..2ff283c84 100644
--- a/src/features/subscriptions/server/subscription-schedule-exam-read-model.ts
+++ b/src/features/subscriptions/server/subscription-schedule-exam-read-model.ts
@@ -84,6 +84,7 @@ function upcomingKnownExamWhere(input: {
 
   return {
     sectionId: { in: sectionIds },
+    section: { retiredAt: null },
     OR: [
       { examDate: { gte: tomorrowStart } },
       {
@@ -136,6 +137,7 @@ export async function listSubscribedSchedules(
       return localizedPrisma.schedule.findMany({
         where: {
           sectionId: { in: ids },
+          section: { retiredAt: null },
           ...(dateFilter ? { date: dateFilter } : {}),
           ...(weekday ? { weekday } : {}),
         },
@@ -174,6 +176,7 @@ export function listSubscribedSchedulePage(
   const where = {
     section: {
       subscribedUsers: { some: { id: userId } },
+      retiredAt: null,
       ...(semesterId !== undefined ? { semesterId } : {}),
     },
     ...(dateFilter ? { date: dateFilter } : {}),
@@ -240,6 +243,7 @@ export async function listSubscribedExams(
       return localizedPrisma.exam.findMany({
         where: {
           sectionId: { in: ids },
+          section: { retiredAt: null },
           ...examDateWhere({ dateFrom, dateTo, includeDateUnknown }),
         },
         include: subscribedExamInclude,
@@ -276,6 +280,7 @@ export function listSubscribedExamPage(
   const where = {
     section: {
       subscribedUsers: { some: { id: userId } },
+      retiredAt: null,
       ...(semesterId !== undefined ? { semesterId } : {}),
     },
     ...examDateWhere({ dateFrom, dateTo, includeDateUnknown }),
diff --git a/src/features/subscriptions/server/subscription-section-resolver.ts b/src/features/subscriptions/server/subscription-section-resolver.ts
index 62ca50629..6b1804760 100644
--- a/src/features/subscriptions/server/subscription-section-resolver.ts
+++ b/src/features/subscriptions/server/subscription-section-resolver.ts
@@ -27,11 +27,13 @@ function normalizeCode(code: string) {
 
 export async function resolveCalendarSubscriptionSections({
   codes = [],
+  includeRetired = false,
   locale = DEFAULT_LOCALE,
   sectionIds = [],
   semesterId,
 }: {
   codes?: readonly string[];
+  includeRetired?: boolean;
   locale?: AppLocale;
   sectionIds?: readonly number[];
   semesterId?: number;
@@ -51,12 +53,14 @@ export async function resolveCalendarSubscriptionSections({
   if (requestedSectionIds.length > 0) {
     where.push({
       id: { in: requestedSectionIds },
+      ...(!includeRetired ? { retiredAt: null } : {}),
       ...(semester ? { semesterId: semester.id } : {}),
     });
   }
   if (semester && requestedCodes.length > 0) {
     where.push({
       semesterId: semester.id,
+      ...(!includeRetired ? { retiredAt: null } : {}),
       OR: requestedCodes.flatMap((code) => [
         { code: { equals: code, mode: "insensitive" } },
         { course: { code: { equals: code, mode: "insensitive" } } },
diff --git a/src/features/subscriptions/server/subscription-write-model.ts b/src/features/subscriptions/server/subscription-write-model.ts
index fd739a7ea..42fd9b01d 100644
--- a/src/features/subscriptions/server/subscription-write-model.ts
+++ b/src/features/subscriptions/server/subscription-write-model.ts
@@ -1,19 +1,21 @@
+import type { Prisma } from "@/generated/prisma/client";
 import type { AppLocale } from "@/i18n/config";
 import { DEFAULT_LOCALE } from "@/i18n/config";
 import { prisma } from "@/lib/db/prisma";
+import { acquireSectionLifecycleAdvisoryLocks } from "@/lib/db/section-lifecycle-lock";
 import {
   getUserCalendarSubscription,
   getUserSectionSubscriptionState,
 } from "./subscription-calendar-read-model";
-import { getSubscribedSectionIds } from "./subscription-read-model-shared";
 import { uniqueSectionIds } from "./subscription-section-id-helpers";
 import { resolveCalendarSubscriptionSections } from "./subscription-section-resolver";
 
 async function replaceUserSectionIds(
+  tx: Prisma.TransactionClient,
   userId: string,
   nextIds: readonly number[],
 ) {
-  await prisma.user.update({
+  await tx.user.update({
     where: { id: userId },
     data: {
       subscribedSections: {
@@ -24,13 +26,14 @@ async function replaceUserSectionIds(
 }
 
 async function replaceUserSectionIdsInSemester(
+  tx: Prisma.TransactionClient,
   userId: string,
   currentIds: readonly number[],
   nextIds: readonly number[],
 ) {
   const currentIdSet = new Set(currentIds);
   const nextIdSet = new Set(nextIds);
-  await prisma.user.update({
+  await tx.user.update({
     where: { id: userId },
     data: {
       subscribedSections: {
@@ -45,33 +48,48 @@ async function replaceUserSectionIdsInSemester(
   });
 }
 
-async function getExistingSectionIds(sectionIds: readonly number[]) {
+async function getExistingSectionIds(
+  sectionIds: readonly number[],
+  options: { includeRetired?: boolean } = {},
+) {
   if (sectionIds.length === 0) {
     return [];
   }
 
   const sections = await prisma.section.findMany({
-    where: { id: { in: uniqueSectionIds(sectionIds) } },
+    where: {
+      id: { in: uniqueSectionIds(sectionIds) },
+      ...(!options.includeRetired ? { retiredAt: null } : {}),
+    },
     select: { id: true },
   });
   return sections.map((section) => section.id);
 }
 
-async function getSectionIdByJwId(jwId: number) {
-  const section = await prisma.section.findUnique({
-    where: { jwId },
+async function getSectionIdByJwId(
+  jwId: number,
+  options: { includeRetired?: boolean } = {},
+) {
+  const section = await prisma.section.findFirst({
+    where: {
+      jwId,
+      ...(!options.includeRetired ? { retiredAt: null } : {}),
+    },
     select: { id: true },
   });
   return section?.id ?? null;
 }
 
-async function getMutableUserSubscriptions(userId: string) {
-  return prisma.user.findUnique({
+async function getMutableUserSubscriptions(
+  userId: string,
+  client: Prisma.TransactionClient = prisma,
+) {
+  return client.user.findUnique({
     where: { id: userId },
     select: {
       id: true,
       subscribedSections: {
-        select: { id: true, jwId: true, semesterId: true },
+        select: { id: true, jwId: true, semesterId: true, retiredAt: true },
       },
     },
   });
@@ -94,6 +112,7 @@ export async function hasUserSubscribedSectionByJwId(
 }
 
 async function connectUserSectionIds(
+  tx: Prisma.TransactionClient,
   userId: string,
   sectionIds: readonly number[],
 ) {
@@ -101,7 +120,7 @@ async function connectUserSectionIds(
     return;
   }
 
-  await prisma.user.update({
+  await tx.user.update({
     where: { id: userId },
     data: {
       subscribedSections: {
@@ -111,11 +130,207 @@ async function connectUserSectionIds(
   });
 }
 
+type LockedSectionSubscriptionMutationInput = {
+  candidateSectionIds: readonly number[];
+  mode: "connect" | "replace";
+  preserveRetiredSectionIds?: readonly number[];
+  semesterId?: number;
+  userId: string;
+};
+
+export type LockedSectionSubscriptionMutationResult = {
+  activeCandidateSectionIds: number[];
+  addedSectionIds: number[];
+  effectiveSectionIds: number[];
+  preservedRetiredSectionIds: number[];
+  removedSectionIds: number[];
+  unchangedSectionIds: number[];
+};
+
+async function lockSubscriptionUser(
+  tx: Prisma.TransactionClient,
+  userId: string,
+) {
+  const rows = await tx.$queryRaw<Array<{ id: string }>>`
+    SELECT "id" FROM "User" WHERE "id" = ${userId} FOR UPDATE
+  `;
+  return rows.length > 0;
+}
+
+async function lockSubscriptionSections(
+  tx: Prisma.TransactionClient,
+  sectionIds: readonly number[],
+) {
+  await acquireSectionLifecycleAdvisoryLocks(tx, sectionIds, "shared");
+}
+
+export async function mutateUserSectionSubscriptionsInTransaction(
+  tx: Prisma.TransactionClient,
+  input: LockedSectionSubscriptionMutationInput,
+): Promise<LockedSectionSubscriptionMutationResult | null> {
+  if (!(await lockSubscriptionUser(tx, input.userId))) {
+    return null;
+  }
+
+  const user = await getMutableUserSubscriptions(input.userId, tx);
+  if (!user) {
+    return null;
+  }
+
+  const candidateSectionIds = uniqueSectionIds(input.candidateSectionIds);
+  const currentSectionIds = uniqueSectionIds(
+    user.subscribedSections.map((section) => section.id),
+  );
+  const preserveRetiredSectionIds = uniqueSectionIds(
+    input.preserveRetiredSectionIds ?? [],
+  );
+  const sectionIdsToLock =
+    input.mode === "replace"
+      ? uniqueSectionIds([
+          ...candidateSectionIds,
+          ...currentSectionIds,
+          ...preserveRetiredSectionIds,
+        ])
+      : candidateSectionIds;
+
+  await lockSubscriptionSections(tx, sectionIdsToLock);
+  const lockedSections =
+    sectionIdsToLock.length === 0
+      ? []
+      : await tx.section.findMany({
+          where: { id: { in: sectionIdsToLock } },
+          select: { id: true, retiredAt: true, semesterId: true },
+        });
+  const lockedSectionById = new Map(
+    lockedSections.map((section) => [section.id, section] as const),
+  );
+  const inScope = (sectionId: number) => {
+    const section = lockedSectionById.get(sectionId);
+    return (
+      section != null &&
+      (input.semesterId === undefined ||
+        section.semesterId === input.semesterId)
+    );
+  };
+  const activeCandidateSectionIds = candidateSectionIds.filter((sectionId) => {
+    const section = lockedSectionById.get(sectionId);
+    return section?.retiredAt == null && inScope(sectionId);
+  });
+  const currentSectionIdSet = new Set(currentSectionIds);
+  const preservedRetiredSectionIds =
+    input.mode === "replace"
+      ? preserveRetiredSectionIds.filter((sectionId) => {
+          const section = lockedSectionById.get(sectionId);
+          return (
+            currentSectionIdSet.has(sectionId) &&
+            section?.retiredAt != null &&
+            inScope(sectionId)
+          );
+        })
+      : [];
+  const effectiveSectionIds = uniqueSectionIds([
+    ...activeCandidateSectionIds,
+    ...preservedRetiredSectionIds,
+  ]);
+  const effectiveSectionIdSet = new Set(effectiveSectionIds);
+  const currentSectionIdsInScope =
+    input.mode === "replace"
+      ? currentSectionIds.filter(inScope)
+      : currentSectionIds;
+  const addedSectionIds = effectiveSectionIds.filter(
+    (sectionId) => !currentSectionIdSet.has(sectionId),
+  );
+  const unchangedSectionIds = effectiveSectionIds.filter((sectionId) =>
+    currentSectionIdSet.has(sectionId),
+  );
+  const removedSectionIds =
+    input.mode === "replace"
+      ? currentSectionIdsInScope.filter(
+          (sectionId) => !effectiveSectionIdSet.has(sectionId),
+        )
+      : [];
+
+  if (input.mode === "connect") {
+    await connectUserSectionIds(tx, input.userId, addedSectionIds);
+  } else if (input.semesterId === undefined) {
+    await replaceUserSectionIds(tx, input.userId, effectiveSectionIds);
+  } else {
+    await replaceUserSectionIdsInSemester(
+      tx,
+      input.userId,
+      currentSectionIdsInScope,
+      effectiveSectionIds,
+    );
+  }
+
+  return {
+    activeCandidateSectionIds,
+    addedSectionIds,
+    effectiveSectionIds,
+    preservedRetiredSectionIds,
+    removedSectionIds,
+    unchangedSectionIds,
+  };
+}
+
+async function mutateUserSectionSubscriptions(
+  input: LockedSectionSubscriptionMutationInput,
+) {
+  return prisma.$transaction((tx) =>
+    mutateUserSectionSubscriptionsInTransaction(tx, input),
+  );
+}
+
+type ResolvedCalendarSubscriptionSections = NonNullable<
+  Awaited<ReturnType<typeof resolveCalendarSubscriptionSections>>
+>;
+
+function filterResolvedCalendarSubscriptionSections(
+  resolved: ResolvedCalendarSubscriptionSections,
+  acceptedSectionIds: readonly number[],
+  requestedCodes: readonly string[] = [],
+): ResolvedCalendarSubscriptionSections {
+  const acceptedSectionIdSet = new Set(acceptedSectionIds);
+  const sections = resolved.sections.filter((section) =>
+    acceptedSectionIdSet.has(section.id),
+  );
+  const acceptedCodeSet = new Set(
+    sections.flatMap((section) =>
+      [section.code, section.course.code].map((code) =>
+        code.trim().toUpperCase(),
+      ),
+    ),
+  );
+  const seenCodes = new Set<string>();
+  const uniqueRequestedCodes: string[] = [];
+  for (const requestedCode of requestedCodes) {
+    const code = requestedCode.trim();
+    const normalized = code.toUpperCase();
+    if (!code || seenCodes.has(normalized)) continue;
+    seenCodes.add(normalized);
+    uniqueRequestedCodes.push(code);
+  }
+
+  return {
+    ...resolved,
+    matchedCodes: uniqueRequestedCodes.filter((code) =>
+      acceptedCodeSet.has(code.toUpperCase()),
+    ),
+    unmatchedCodes: uniqueRequestedCodes.filter(
+      (code) => !acceptedCodeSet.has(code.toUpperCase()),
+    ),
+    sections,
+    total: sections.length,
+  };
+}
+
 async function disconnectUserSectionIds(
   userId: string,
   sectionIds: readonly number[],
 ) {
-  const validSectionIds = await getExistingSectionIds(sectionIds);
+  const validSectionIds = await getExistingSectionIds(sectionIds, {
+    includeRetired: true,
+  });
   if (validSectionIds.length === 0) {
     return;
   }
@@ -135,9 +350,15 @@ export async function replaceUserSectionSubscriptions(
   sectionIds: number[],
   locale = DEFAULT_LOCALE,
 ) {
-  const validSectionIds = await getExistingSectionIds(sectionIds);
-
-  await replaceUserSectionIds(userId, validSectionIds);
+  const mutation = await mutateUserSectionSubscriptions({
+    candidateSectionIds: sectionIds,
+    mode: "replace",
+    preserveRetiredSectionIds: sectionIds,
+    userId,
+  });
+  if (!mutation) {
+    return null;
+  }
 
   return getUserCalendarSubscription(userId, locale);
 }
@@ -151,23 +372,18 @@ export async function appendUserSectionSubscriptions({
   sectionIds: readonly number[];
   userId: string;
 }) {
-  const user = await getMutableUserSubscriptions(userId);
-  if (!user) {
+  const mutation = await mutateUserSectionSubscriptions({
+    candidateSectionIds: sectionIds,
+    mode: "connect",
+    userId,
+  });
+  if (!mutation) {
     return null;
   }
 
-  const currentIdSet = new Set(
-    user.subscribedSections.map((section) => section.id),
-  );
-  const validSectionIds = await getExistingSectionIds(sectionIds);
-  const addedSectionIds = validSectionIds.filter((id) => !currentIdSet.has(id));
-
-  await connectUserSectionIds(userId, addedSectionIds);
-
   return {
-    addedCount: addedSectionIds.length,
-    alreadySubscribedCount: validSectionIds.filter((id) => currentIdSet.has(id))
-      .length,
+    addedCount: mutation.addedSectionIds.length,
+    alreadySubscribedCount: mutation.unchangedSectionIds.length,
     subscription: await getUserCalendarSubscription(userId, locale),
   };
 }
@@ -176,19 +392,15 @@ export async function addUserSectionSubscriptions(
   userId: string,
   sectionIds: readonly number[],
 ) {
-  const user = await getMutableUserSubscriptions(userId);
-  if (!user) {
+  const mutation = await mutateUserSectionSubscriptions({
+    candidateSectionIds: sectionIds,
+    mode: "connect",
+    userId,
+  });
+  if (!mutation) {
     return null;
   }
 
-  const existingIds = new Set(
-    user.subscribedSections.map((section) => section.id),
-  );
-  await connectUserSectionIds(
-    userId,
-    sectionIds.filter((id) => !existingIds.has(id)),
-  );
-
   return getUserSectionSubscriptionState(userId);
 }
 
@@ -212,21 +424,30 @@ export async function importUserSectionSubscriptionsByCodes({
     return null;
   }
 
-  const existingIds = new Set(await getSubscribedSectionIds(userId));
-  const addedSections = matches.sections.filter(
-    (section) => !existingIds.has(section.id),
+  const mutation = await mutateUserSectionSubscriptions({
+    candidateSectionIds: matches.sections.map((section) => section.id),
+    mode: "connect",
+    userId,
+  });
+  if (!mutation) {
+    return null;
+  }
+  const acceptedMatches = filterResolvedCalendarSubscriptionSections(
+    matches,
+    mutation.activeCandidateSectionIds,
+    codes,
   );
-  const alreadySubscribedSections = matches.sections.filter((section) =>
-    existingIds.has(section.id),
+  const addedSectionIdSet = new Set(mutation.addedSectionIds);
+  const unchangedSectionIdSet = new Set(mutation.unchangedSectionIds);
+  const addedSections = acceptedMatches.sections.filter((section) =>
+    addedSectionIdSet.has(section.id),
   );
-
-  await addUserSectionSubscriptions(
-    userId,
-    matches.sections.map((section) => section.id),
+  const alreadySubscribedSections = acceptedMatches.sections.filter((section) =>
+    unchangedSectionIdSet.has(section.id),
   );
 
   return {
-    matches,
+    matches: acceptedMatches,
     addedSections,
     alreadySubscribedSections,
     subscription: await getUserCalendarSubscription(userId, locale),
@@ -250,6 +471,7 @@ export async function batchUpdateUserSectionSubscriptions({
 }) {
   const resolved = await resolveCalendarSubscriptionSections({
     codes,
+    includeRetired: action === "remove",
     locale,
     sectionIds,
     semesterId,
@@ -258,57 +480,92 @@ export async function batchUpdateUserSectionSubscriptions({
     return null;
   }
 
-  const user = await getMutableUserSubscriptions(userId);
-  if (!user) {
-    return null;
-  }
-
-  const currentIds = user.subscribedSections.map((section) => section.id);
-  const currentIdSet = new Set(currentIds);
   const targetIds = uniqueSectionIds(
     resolved.sections.map((section) => section.id),
   );
-  const targetIdSet = new Set(targetIds);
 
   let addedCount = 0;
   let removedCount = 0;
   let unchangedCount = 0;
+  let acceptedTargetIds = targetIds;
+  let preservedRetiredIds: number[] = [];
+  let responseResolved = resolved;
+  let responseSections = resolved.sections;
+  let responseTotal = resolved.total;
 
   if (action === "add") {
-    const addedIds = targetIds.filter((id) => !currentIdSet.has(id));
-    addedCount = addedIds.length;
-    unchangedCount = targetIds.length - addedCount;
-    await connectUserSectionIds(userId, addedIds);
+    const mutation = await mutateUserSectionSubscriptions({
+      candidateSectionIds: targetIds,
+      mode: "connect",
+      userId,
+    });
+    if (!mutation) return null;
+    acceptedTargetIds = mutation.activeCandidateSectionIds;
+    addedCount = mutation.addedSectionIds.length;
+    unchangedCount = mutation.unchangedSectionIds.length;
+    responseResolved = filterResolvedCalendarSubscriptionSections(
+      resolved,
+      acceptedTargetIds,
+      codes ?? [],
+    );
+    responseSections = responseResolved.sections;
+    responseTotal = responseSections.length;
   } else if (action === "remove") {
+    const user = await getMutableUserSubscriptions(userId);
+    if (!user) return null;
+    const currentIdSet = new Set(
+      user.subscribedSections.map((section) => section.id),
+    );
     const removedIds = targetIds.filter((id) => currentIdSet.has(id));
     removedCount = removedIds.length;
     unchangedCount = targetIds.length - removedCount;
     await disconnectUserSectionIds(userId, removedIds);
   } else {
-    const currentIdsInScope =
-      semesterId === undefined
-        ? currentIds
-        : user.subscribedSections
-            .filter((section) => section.semesterId === semesterId)
-            .map((section) => section.id);
-    addedCount = targetIds.filter((id) => !currentIdSet.has(id)).length;
-    removedCount = currentIdsInScope.filter(
-      (id) => !targetIdSet.has(id),
-    ).length;
-    unchangedCount = targetIds.length - addedCount;
-    if (semesterId === undefined) {
-      await replaceUserSectionIds(userId, targetIds);
-    } else {
-      await replaceUserSectionIdsInSemester(
-        userId,
-        currentIdsInScope,
-        targetIds,
-      );
-    }
+    const mutation = await mutateUserSectionSubscriptions({
+      candidateSectionIds: targetIds,
+      mode: "replace",
+      preserveRetiredSectionIds: sectionIds,
+      semesterId,
+      userId,
+    });
+    if (!mutation) return null;
+    acceptedTargetIds = mutation.activeCandidateSectionIds;
+    preservedRetiredIds = mutation.preservedRetiredSectionIds;
+    addedCount = mutation.addedSectionIds.length;
+    removedCount = mutation.removedSectionIds.length;
+    unchangedCount = mutation.unchangedSectionIds.length;
+    responseResolved = filterResolvedCalendarSubscriptionSections(
+      resolved,
+      acceptedTargetIds,
+      codes ?? [],
+    );
+    const effectiveResolved = await resolveCalendarSubscriptionSections({
+      includeRetired: true,
+      locale,
+      sectionIds: mutation.effectiveSectionIds,
+    });
+    responseSections = effectiveResolved?.sections ?? [];
+    responseTotal = responseSections.length;
   }
 
+  const acceptedTargetIdSet = new Set(acceptedTargetIds);
+  const acceptedRequestedIdSet = new Set([
+    ...resolved.matchedSectionIds.filter((sectionId) =>
+      acceptedTargetIdSet.has(sectionId),
+    ),
+    ...preservedRetiredIds,
+  ]);
+  const requestedSectionIds = uniqueSectionIds(sectionIds ?? []);
   return {
-    ...resolved,
+    ...responseResolved,
+    matchedSectionIds: requestedSectionIds.filter((id) =>
+      acceptedRequestedIdSet.has(id),
+    ),
+    unmatchedSectionIds: requestedSectionIds.filter(
+      (id) => !acceptedRequestedIdSet.has(id),
+    ),
+    sections: responseSections,
+    total: responseTotal,
     action,
     addedCount,
     removedCount,
@@ -341,8 +598,12 @@ export async function subscribeUserToSectionByJwId(
     return null;
   }
 
-  const state = await addUserSectionSubscriptions(userId, [sectionId]);
-  if (!state) {
+  const mutation = await mutateUserSectionSubscriptions({
+    candidateSectionIds: [sectionId],
+    mode: "connect",
+    userId,
+  });
+  if (!mutation?.activeCandidateSectionIds.includes(sectionId)) {
     return null;
   }
 
@@ -354,7 +615,9 @@ export async function unsubscribeUserFromSectionByJwId(
   sectionJwId: number,
   locale = DEFAULT_LOCALE,
 ) {
-  const sectionId = await getSectionIdByJwId(sectionJwId);
+  const sectionId = await getSectionIdByJwId(sectionJwId, {
+    includeRetired: true,
+  });
   if (sectionId === null) {
     return null;
   }
@@ -372,20 +635,35 @@ export async function setUserSectionSubscriptionByJwId(input: {
   subscribed: boolean;
   userId: string;
 }) {
-  const sectionId = await getSectionIdByJwId(input.sectionJwId);
+  const sectionId = await getSectionIdByJwId(input.sectionJwId, {
+    includeRetired: !input.subscribed,
+  });
   if (sectionId === null) return null;
 
+  if (input.subscribed) {
+    const mutation = await mutateUserSectionSubscriptions({
+      candidateSectionIds: [sectionId],
+      mode: "connect",
+      userId: input.userId,
+    });
+    if (!mutation?.activeCandidateSectionIds.includes(sectionId)) {
+      return null;
+    }
+    return {
+      sectionJwId: input.sectionJwId,
+      subscribed: true,
+    };
+  }
+
   await prisma.user.update({
     where: { id: input.userId },
     data: {
-      subscribedSections: input.subscribed
-        ? { connect: { id: sectionId } }
-        : { disconnect: { id: sectionId } },
+      subscribedSections: { disconnect: { id: sectionId } },
     },
   });
 
   return {
     sectionJwId: input.sectionJwId,
-    subscribed: input.subscribed,
+    subscribed: false,
   };
 }
diff --git a/src/lib/api/schemas/academic-section-base-response-schemas.ts b/src/lib/api/schemas/academic-section-base-response-schemas.ts
index bc8c3d870..67e8b1533 100644
--- a/src/lib/api/schemas/academic-section-base-response-schemas.ts
+++ b/src/lib/api/schemas/academic-section-base-response-schemas.ts
@@ -29,6 +29,8 @@ export const adminClassSchema = z.object({
 export const sectionBaseSchema = z.object({
   id: z.number().int(),
   jwId: z.number().int(),
+  sourceLastSeenAt: dateTimeSchema.nullable().optional(),
+  retiredAt: dateTimeSchema.nullable().optional(),
   code: z.string(),
   bizTypeId: z.number().int().nullable(),
   credits: z.number().nullable(),
diff --git a/src/lib/db/section-lifecycle-lock.ts b/src/lib/db/section-lifecycle-lock.ts
new file mode 100644
index 000000000..756b1d8cc
--- /dev/null
+++ b/src/lib/db/section-lifecycle-lock.ts
@@ -0,0 +1,33 @@
+// Both interactive subscription writes and the static loader use this namespace.
+const SECTION_LIFECYCLE_LOCK_NAMESPACE = "life-ustc-section-lifecycle";
+
+type AdvisoryLockTransaction = {
+  $queryRawUnsafe<T = unknown>(query: string, ...values: unknown[]): Promise<T>;
+};
+
+export async function acquireSectionLifecycleAdvisoryLocks(
+  tx: AdvisoryLockTransaction,
+  sectionIds: readonly number[],
+  mode: "exclusive" | "shared",
+) {
+  const ids = [...new Set(sectionIds)].sort((left, right) => left - right);
+  if (ids.length === 0) return;
+
+  const placeholders = ids.map((_, index) => `$${index + 2}`).join(",");
+  const lockFunction =
+    mode === "shared"
+      ? "pg_advisory_xact_lock_shared"
+      : "pg_advisory_xact_lock";
+  await tx.$queryRawUnsafe(
+    `WITH lock_ids AS MATERIALIZED (
+       SELECT "id"
+       FROM unnest(ARRAY[${placeholders}]::integer[]) AS ids("id")
+       ORDER BY "id"
+     )
+     SELECT ${lockFunction}(hashtext($1), "id")::text AS "acquired"
+     FROM lock_ids
+     ORDER BY "id"`,
+    SECTION_LIFECYCLE_LOCK_NAMESPACE,
+    ...ids,
+  );
+}
diff --git a/src/routes/sitemap.xml/+server.ts b/src/routes/sitemap.xml/+server.ts
index b0a9ecd76..8c9b176c9 100644
--- a/src/routes/sitemap.xml/+server.ts
+++ b/src/routes/sitemap.xml/+server.ts
@@ -16,7 +16,10 @@ const STATIC_ROUTES = [
 async function getEntityUrls(origin: string) {
   const [courses, sections, teachers] = await Promise.all([
     prisma.course.findMany({ select: { jwId: true } }),
-    prisma.section.findMany({ select: { jwId: true } }),
+    prisma.section.findMany({
+      where: { retiredAt: null },
+      select: { jwId: true },
+    }),
     prisma.teacher.findMany({ select: { id: true } }),
   ]);
 
diff --git a/src/static-loader/cli.ts b/src/static-loader/cli.ts
index 6ba4ce746..d981f4a04 100644
--- a/src/static-loader/cli.ts
+++ b/src/static-loader/cli.ts
@@ -5,7 +5,12 @@ import { writeFile } from "node:fs/promises";
 import { runImport } from "./import";
 import { createPrismaClient } from "./prisma";
 import { Snapshot } from "./snapshot";
-import { parseBooleanSetting, parsePositiveIntegerSetting } from "./validation";
+import {
+  parseBooleanSetting,
+  parseOptionalNonNegativeIntegerSetting,
+  parseOptionalSha256Setting,
+  parsePositiveIntegerSetting,
+} from "./validation";
 
 function getEnv(name: string, defaultValue?: string): string {
   const value = process.env[name] ?? defaultValue;
@@ -35,6 +40,25 @@ async function main() {
     process.env.STATIC_LOADER_DRY_RUN,
     false,
   );
+  const bootstrapImportState = parseBooleanSetting(
+    "STATIC_LOADER_BOOTSTRAP_IMPORT_STATE",
+    process.env.STATIC_LOADER_BOOTSTRAP_IMPORT_STATE,
+    false,
+  );
+  const retireMissingSections = parseBooleanSetting(
+    "STATIC_LOADER_RETIRE_MISSING_SECTIONS",
+    process.env.STATIC_LOADER_RETIRE_MISSING_SECTIONS,
+    false,
+  );
+  const expectedSnapshotSha256 = parseOptionalSha256Setting(
+    "STATIC_LOADER_EXPECTED_SNAPSHOT_SHA256",
+    process.env.STATIC_LOADER_EXPECTED_SNAPSHOT_SHA256,
+  );
+  const expectedSectionRetirementCandidates =
+    parseOptionalNonNegativeIntegerSetting(
+      "STATIC_LOADER_EXPECTED_SECTION_RETIREMENT_CANDIDATES",
+      process.env.STATIC_LOADER_EXPECTED_SECTION_RETIREMENT_CANDIDATES,
+    );
 
   if (!existsSync(snapshotPath)) {
     throw new Error(`Snapshot not found: ${snapshotPath}`);
@@ -43,6 +67,11 @@ async function main() {
   console.log(`snapshotPath: ${snapshotPath}`);
   console.log(`minSemester: ${minSemester}`);
   console.log(`dryRun: ${dryRun}`);
+  console.log(`bootstrapImportState: ${bootstrapImportState}`);
+  console.log(`retireMissingSections: ${retireMissingSections}`);
+  console.log(
+    `expectedSectionRetirementCandidates: ${expectedSectionRetirementCandidates ?? "not set"}`,
+  );
 
   const snapshot = new Snapshot(snapshotPath);
   const metadata = snapshot.metadata();
@@ -59,6 +88,10 @@ async function main() {
       snapshotSha256,
       minSemester,
       dryRun,
+      bootstrapImportState,
+      retireMissingSections,
+      expectedSnapshotSha256,
+      expectedSectionRetirementCandidates,
     });
     console.log("Import report:", report);
 
diff --git a/src/static-loader/import-state.ts b/src/static-loader/import-state.ts
new file mode 100644
index 000000000..6f530b422
--- /dev/null
+++ b/src/static-loader/import-state.ts
@@ -0,0 +1,99 @@
+import type { Prisma } from "../generated/prisma-node/client";
+
+const GLOBAL_IMPORT_STATE_ID = "global";
+const SHA256_PATTERN = /^[a-f0-9]{64}$/;
+
+type StaticImportStateTransaction = {
+  staticImportState: Pick<
+    Prisma.TransactionClient["staticImportState"],
+    "findUnique" | "upsert"
+  >;
+};
+
+type StaticImportStateInput = {
+  bootstrapEnabled: boolean;
+  dryRun: boolean;
+  expectedSnapshotSha256: string | null;
+  observedAt: Date;
+  retirementEnabled: boolean;
+  snapshotSha256: string;
+};
+
+function validateSnapshotSha256(snapshotSha256: string) {
+  if (!SHA256_PATTERN.test(snapshotSha256)) {
+    throw new Error("Static snapshot SHA-256 must be 64 lowercase hex digits");
+  }
+}
+
+export async function assertStaticImportStateAllowsSnapshot(
+  tx: StaticImportStateTransaction,
+  input: StaticImportStateInput,
+) {
+  validateSnapshotSha256(input.snapshotSha256);
+  const current = await tx.staticImportState.findUnique({
+    where: { id: GLOBAL_IMPORT_STATE_ID },
+    select: { snapshotGeneratedAt: true, snapshotSha256: true },
+  });
+
+  if (current == null) {
+    if (!input.bootstrapEnabled) {
+      throw new Error(
+        "Static import state is not initialized; run an approved manual bootstrap before importing",
+      );
+    }
+    if (input.retirementEnabled) {
+      throw new Error(
+        "Missing-Section retirement cannot run while bootstrapping static import state",
+      );
+    }
+    if (!input.dryRun && input.expectedSnapshotSha256 == null) {
+      throw new Error(
+        "STATIC_LOADER_EXPECTED_SNAPSHOT_SHA256 is required for a committed static import state bootstrap",
+      );
+    }
+    if (
+      input.expectedSnapshotSha256 != null &&
+      input.expectedSnapshotSha256 !== input.snapshotSha256
+    ) {
+      throw new Error(
+        `Approved static snapshot SHA-256 ${input.expectedSnapshotSha256} does not match downloaded snapshot ${input.snapshotSha256}`,
+      );
+    }
+    return;
+  }
+
+  const incomingTime = input.observedAt.getTime();
+  const currentTime = current.snapshotGeneratedAt.getTime();
+  if (incomingTime < currentTime) {
+    throw new Error(
+      `Refusing to import snapshot generated at ${input.observedAt.toISOString()} because the last committed snapshot was generated at ${current.snapshotGeneratedAt.toISOString()}`,
+    );
+  }
+  if (
+    incomingTime === currentTime &&
+    input.snapshotSha256 !== current.snapshotSha256
+  ) {
+    throw new Error(
+      `Refusing snapshot SHA-256 ${input.snapshotSha256} because generated_at ${input.observedAt.toISOString()} was already committed with SHA-256 ${current.snapshotSha256}`,
+    );
+  }
+}
+
+export async function recordStaticImportState(
+  tx: StaticImportStateTransaction,
+  input: Pick<StaticImportStateInput, "observedAt" | "snapshotSha256">,
+) {
+  validateSnapshotSha256(input.snapshotSha256);
+  await tx.staticImportState.upsert({
+    where: { id: GLOBAL_IMPORT_STATE_ID },
+    create: {
+      id: GLOBAL_IMPORT_STATE_ID,
+      snapshotGeneratedAt: input.observedAt,
+      snapshotSha256: input.snapshotSha256,
+    },
+    update: {
+      snapshotGeneratedAt: input.observedAt,
+      snapshotSha256: input.snapshotSha256,
+    },
+  });
+}
diff --git a/src/static-loader/import.ts b/src/static-loader/import.ts
index 07f9a304a..93230615d 100644
--- a/src/static-loader/import.ts
+++ b/src/static-loader/import.ts
@@ -14,6 +14,10 @@ import {
   mergeLegacyCourseDuplicates,
 } from "./course-merge";
 import { acquireStaticImportLock } from "./import-lock";
+import {
+  assertStaticImportStateAllowsSnapshot,
+  recordStaticImportState,
+} from "./import-state";
 import {
   type AdminClassSectionPair,
   type BuildingBuild,
@@ -57,6 +61,12 @@ import {
   type TeacherLessonTypeBuild,
   type TeacherTitleBuild,
 } from "./mappers";
+import {
+  assertSectionSnapshotNotOlderThanSource,
+  emptySectionLifecycleStats,
+  reconcileSectionSourceLifecycle,
+  type SectionLifecycleStats,
+} from "./section-lifecycle";
 import {
   asBoolean,
   asInt,
@@ -82,6 +92,9 @@ import {
 } from "./upsert-policy";
 import {
   missingSnapshotRowsWhere,
+  parseSnapshotGeneratedAt,
+  validateMappedSectionJwIds,
+  validateSectionRetirementSnapshotApproval,
   validateSnapshotCompleteness,
 } from "./validation";
 
@@ -90,6 +103,10 @@ export type ImportConfig = {
   snapshotSha256: string;
   minSemester: number;
   dryRun: boolean;
+  bootstrapImportState: boolean;
+  retireMissingSections: boolean;
+  expectedSnapshotSha256: string | null;
+  expectedSectionRetirementCandidates: number | null;
 };
 
 export type ImportRecordCounts = {
@@ -118,6 +135,7 @@ export type ImportReport = {
   plannedRecordCounts: ImportRecordCounts;
   databaseRecordCounts: ImportRecordCounts | null;
   reconciliation: {
+    sectionLifecycle: SectionLifecycleStats;
     teacherFallbacks: TeacherFallbackReconciliationStats;
     legacyCourses: CourseMergeStats;
   };
@@ -139,16 +157,24 @@ export async function runImport(
   prisma: PrismaClient,
   config: ImportConfig,
 ): Promise<ImportReport> {
+  validateSectionRetirementSnapshotApproval({
+    enabled: config.retireMissingSections,
+    expectedSnapshotSha256: config.expectedSnapshotSha256,
+    snapshotSha256: config.snapshotSha256,
+  });
   const snapshot = new Snapshot(config.snapshotPath);
   const metadata = snapshot.metadata();
   const schemaVersion = metadata.schema_version;
+  let snapshotGeneratedAt: Date;
+  let completeness: ReturnType<typeof validateSnapshotCompleteness>;
   try {
     if (schemaVersion !== "5") {
       throw new Error(
         `Unsupported snapshot schema version: ${schemaVersion ?? "unknown"}`,
       );
     }
-    validateSnapshotCompleteness(
+    snapshotGeneratedAt = parseSnapshotGeneratedAt(metadata.generated_at);
+    completeness = validateSnapshotCompleteness(
       {
         metadata,
         semesterRows: snapshot.queryAll("catalog_teach_semester_list"),
@@ -209,6 +235,10 @@ export async function runImport(
       (sectionJwId) => allSectionJwIds.add(sectionJwId),
       sectionTeacherPairs,
     );
+  validateMappedSectionJwIds(
+    completeness.sectionJwIds,
+    sections.map((section) => section.jwId),
+  );
 
   const placeholderDepartments = mergePlaceholderDepartments(
     sectionPlaceholderDepartments,
@@ -247,6 +277,10 @@ export async function runImport(
     ...EMPTY_TEACHER_RECONCILIATION_STATS,
   };
   let courseMergeStats = { ...EMPTY_COURSE_MERGE_STATS };
+  let sectionLifecycleStats = emptySectionLifecycleStats(
+    config.retireMissingSections,
+  );
+  const observedAt = snapshotGeneratedAt;
 
   async function logStep<T>(
     name: string,
@@ -266,9 +300,36 @@ export async function runImport(
     await logStep("acquireStaticImportLock", 1, () =>
       acquireStaticImportLock(tx),
     );
+    await logStep("validateStaticImportState", 1, () =>
+      assertStaticImportStateAllowsSnapshot(tx, {
+        bootstrapEnabled: config.bootstrapImportState,
+        dryRun: config.dryRun,
+        expectedSnapshotSha256: config.expectedSnapshotSha256,
+        observedAt,
+        retirementEnabled: config.retireMissingSections,
+        snapshotSha256: config.snapshotSha256,
+      }),
+    );
     const semesterMap = await logStep("upsertSemesters", semesters.length, () =>
       upsertSemesters(tx, semesters),
     );
+    const scopedSemesterIds = completeness.sectionSemesterJwIds.map(
+      (semesterJwId) => {
+        const semesterId = semesterMap.get(semesterJwId);
+        if (semesterId == null) {
+          throw new Error(
+            `Validated snapshot semester ${semesterJwId} did not resolve to a database row`,
+          );
+        }
+        return semesterId;
+      },
+    );
+    await logStep("validateSnapshotRecency", scopedSemesterIds.length, () =>
+      assertSectionSnapshotNotOlderThanSource(tx, {
+        observedAt,
+        scopedSemesterIds,
+      }),
+    );
     const departmentMap = await logStep(
       "upsertDepartments",
       departments.length + placeholderDepartments.length,
@@ -433,10 +494,33 @@ export async function runImport(
           courseImport.canonicalJwIds,
         ),
     );
+    const databaseRecordCounts = await logStep("countDatabaseRecords", 12, () =>
+      countStats(tx),
+    );
+    sectionLifecycleStats = await logStep(
+      "reconcileSectionSourceLifecycle",
+      sections.length,
+      () =>
+        reconcileSectionSourceLifecycle(tx, {
+          observedAt,
+          retirementEnabled: config.retireMissingSections,
+          expectedRetirementCandidateCount:
+            config.expectedSectionRetirementCandidates,
+          scopedSemesterIds,
+          seenSectionJwIds: [...allSectionJwIds],
+          snapshotSha256: config.snapshotSha256,
+        }),
+    );
+    await logStep("recordStaticImportState", 1, () =>
+      recordStaticImportState(tx, {
+        observedAt,
+        snapshotSha256: config.snapshotSha256,
+      }),
+    );
 
     if (config.dryRun) throw new Error("DRY_RUN: rolling back transaction");
 
-    return logStep("countDatabaseRecords", 12, () => countStats(tx));
+    return databaseRecordCounts;
   };
 
   let databaseRecordCounts: ImportRecordCounts | null = null;
@@ -470,6 +554,7 @@ export async function runImport(
     plannedRecordCounts,
     databaseRecordCounts,
     reconciliation: {
+      sectionLifecycle: sectionLifecycleStats,
       teacherFallbacks: teacherReconciliationStats,
       legacyCourses: courseMergeStats,
     },
diff --git a/src/static-loader/section-lifecycle.ts b/src/static-loader/section-lifecycle.ts
new file mode 100644
index 000000000..0d51b1099
--- /dev/null
+++ b/src/static-loader/section-lifecycle.ts
@@ -0,0 +1,305 @@
+import type { Prisma } from "../generated/prisma-node/client";
+import { acquireSectionLifecycleAdvisoryLocks } from "../lib/db/section-lifecycle-lock";
+
+type SectionLifecycleTransaction = Pick<
+  Prisma.TransactionClient,
+  "$queryRawUnsafe"
+> & {
+  auditLog: Pick<Prisma.TransactionClient["auditLog"], "createMany">;
+  section: Pick<
+    Prisma.TransactionClient["section"],
+    "count" | "findFirst" | "findMany" | "updateMany"
+  >;
+};
+
+export type SectionLifecycleStats = {
+  enabled: boolean;
+  scopeSemesterCount: number;
+  seenSectionCount: number;
+  retirementCandidateCount: number;
+  retiredCount: number;
+  reactivatedCount: number;
+  before: SectionLifecycleCounts;
+  after: SectionLifecycleCounts;
+};
+
+type SectionLifecycleCounts = {
+  active: number;
+  retired: number;
+  total: number;
+};
+
+type SectionLifecycleInput = {
+  observedAt: Date;
+  retirementEnabled: boolean;
+  expectedRetirementCandidateCount: number | null;
+  scopedSemesterIds: readonly number[];
+  seenSectionJwIds: readonly number[];
+  snapshotSha256: string;
+};
+
+function uniqueSorted(values: readonly number[]) {
+  return [...new Set(values)].sort((left, right) => left - right);
+}
+
+function lifecycleCounts(active: number, retired: number) {
+  return { active, retired, total: active + retired };
+}
+
+function validateRetirementCandidates(
+  input: SectionLifecycleInput,
+  retirementCandidates: Array<{
+    sourceLastSeenAt: Date | null;
+  }>,
+) {
+  if (!input.retirementEnabled) return;
+  if (input.expectedRetirementCandidateCount == null) {
+    throw new Error(
+      "STATIC_LOADER_EXPECTED_SECTION_RETIREMENT_CANDIDATES is required when missing-Section retirement is enabled",
+    );
+  }
+  if (retirementCandidates.length !== input.expectedRetirementCandidateCount) {
+    throw new Error(
+      `Approved Section retirement candidate count ${input.expectedRetirementCandidateCount} does not match actual count ${retirementCandidates.length}`,
+    );
+  }
+  if (
+    retirementCandidates.some(
+      (section) =>
+        section.sourceLastSeenAt != null &&
+        section.sourceLastSeenAt > input.observedAt,
+    )
+  ) {
+    throw new Error(
+      "Refusing to retire Sections from a snapshot older than their latest source observation",
+    );
+  }
+}
+
+export function emptySectionLifecycleStats(
+  enabled: boolean,
+): SectionLifecycleStats {
+  return {
+    enabled,
+    scopeSemesterCount: 0,
+    seenSectionCount: 0,
+    retirementCandidateCount: 0,
+    retiredCount: 0,
+    reactivatedCount: 0,
+    before: lifecycleCounts(0, 0),
+    after: lifecycleCounts(0, 0),
+  };
+}
+
+export async function assertSectionSnapshotNotOlderThanSource(
+  tx: Pick<SectionLifecycleTransaction, "section">,
+  input: {
+    observedAt: Date;
+    scopedSemesterIds: readonly number[];
+  },
+) {
+  const scopedSemesterIds = uniqueSorted(input.scopedSemesterIds);
+  if (scopedSemesterIds.length === 0) {
+    return;
+  }
+
+  const newerSection = await tx.section.findFirst({
+    where: {
+      semesterId: { in: scopedSemesterIds },
+      sourceLastSeenAt: { gt: input.observedAt },
+    },
+    orderBy: { sourceLastSeenAt: "desc" },
+    select: { jwId: true, sourceLastSeenAt: true },
+  });
+  if (newerSection != null) {
+    throw new Error(
+      `Refusing to import snapshot generated at ${input.observedAt.toISOString()} because Section ${newerSection.jwId} was observed in a newer snapshot at ${newerSection.sourceLastSeenAt?.toISOString()}`,
+    );
+  }
+}
+
+export async function reconcileSectionSourceLifecycle(
+  tx: SectionLifecycleTransaction,
+  input: SectionLifecycleInput,
+): Promise<SectionLifecycleStats> {
+  const scopedSemesterIds = uniqueSorted(input.scopedSemesterIds);
+  const seenSectionJwIds = uniqueSorted(input.seenSectionJwIds);
+  if (scopedSemesterIds.length === 0) {
+    return emptySectionLifecycleStats(input.retirementEnabled);
+  }
+  if (input.retirementEnabled && seenSectionJwIds.length === 0) {
+    throw new Error(
+      "Refusing to retire Sections because the validated source set is empty",
+    );
+  }
+
+  const scopedWhere = { semesterId: { in: scopedSemesterIds } };
+  const activeBefore = await tx.section.count({
+    where: { ...scopedWhere, retiredAt: null },
+  });
+  const retiredBefore = await tx.section.count({
+    where: { ...scopedWhere, retiredAt: { not: null } },
+  });
+
+  let reactivatedSections =
+    seenSectionJwIds.length > 0
+      ? await tx.section.findMany({
+          where: {
+            ...scopedWhere,
+            jwId: { in: seenSectionJwIds },
+            retiredAt: { lt: input.observedAt },
+          },
+          select: { id: true, jwId: true, retiredAt: true },
+        })
+      : [];
+
+  let retirementCandidates = await tx.section.findMany({
+    where: {
+      ...scopedWhere,
+      jwId: { notIn: seenSectionJwIds },
+      retiredAt: null,
+    },
+    select: { id: true, jwId: true, sourceLastSeenAt: true },
+  });
+
+  validateRetirementCandidates(input, retirementCandidates);
+
+  const lifecycleStateChangeIds = uniqueSorted([
+    ...reactivatedSections.map((section) => section.id),
+    ...(input.retirementEnabled
+      ? retirementCandidates.map((section) => section.id)
+      : []),
+  ]);
+  if (lifecycleStateChangeIds.length > 0) {
+    await acquireSectionLifecycleAdvisoryLocks(
+      tx,
+      lifecycleStateChangeIds,
+      "exclusive",
+    );
+    const lockedSections = await tx.section.findMany({
+      where: { id: { in: lifecycleStateChangeIds } },
+      select: {
+        id: true,
+        jwId: true,
+        retiredAt: true,
+        sourceLastSeenAt: true,
+      },
+    });
+    const lockedSectionById = new Map(
+      lockedSections.map((section) => [section.id, section] as const),
+    );
+    reactivatedSections = reactivatedSections.flatMap((section) => {
+      const locked = lockedSectionById.get(section.id);
+      if (locked?.retiredAt == null || locked.retiredAt >= input.observedAt) {
+        return [];
+      }
+      return [
+        {
+          id: locked.id,
+          jwId: locked.jwId,
+          retiredAt: locked.retiredAt,
+        },
+      ];
+    });
+    if (input.retirementEnabled) {
+      retirementCandidates = retirementCandidates.flatMap((section) => {
+        const locked = lockedSectionById.get(section.id);
+        if (!locked || locked.retiredAt != null) return [];
+        return [
+          {
+            id: locked.id,
+            jwId: locked.jwId,
+            sourceLastSeenAt: locked.sourceLastSeenAt,
+          },
+        ];
+      });
+      validateRetirementCandidates(input, retirementCandidates);
+    }
+  }
+
+  await tx.section.updateMany({
+    where: {
+      ...scopedWhere,
+      jwId: { in: seenSectionJwIds },
+      retiredAt: null,
+      OR: [
+        { sourceLastSeenAt: null },
+        { sourceLastSeenAt: { lt: input.observedAt } },
+      ],
+    },
+    data: {
+      sourceLastSeenAt: input.observedAt,
+    },
+  });
+  if (reactivatedSections.length > 0) {
+    await tx.section.updateMany({
+      where: {
+        id: { in: reactivatedSections.map((section) => section.id) },
+        retiredAt: { lt: input.observedAt },
+      },
+      data: {
+        sourceLastSeenAt: input.observedAt,
+        retiredAt: null,
+      },
+    });
+  }
+
+  const sectionsToRetire = input.retirementEnabled ? retirementCandidates : [];
+  if (sectionsToRetire.length > 0) {
+    await tx.section.updateMany({
+      where: {
+        id: { in: sectionsToRetire.map((section) => section.id) },
+        retiredAt: null,
+      },
+      data: { retiredAt: input.observedAt },
+    });
+  }
+
+  const observedAt = input.observedAt.toISOString();
+  const auditRows: Prisma.AuditLogCreateManyInput[] = [
+    ...reactivatedSections.map((section) => ({
+      action: "section_reactivate" as const,
+      targetId: String(section.id),
+      targetType: "section",
+      metadata: {
+        jwId: section.jwId,
+        observedAt,
+        previousRetiredAt: section.retiredAt?.toISOString() ?? null,
+        snapshotSha256: input.snapshotSha256,
+        source: "static-loader",
+      },
+    })),
+    ...sectionsToRetire.map((section) => ({
+      action: "section_retire" as const,
+      targetId: String(section.id),
+      targetType: "section",
+      metadata: {
+        jwId: section.jwId,
+        observedAt,
+        previousSourceLastSeenAt:
+          section.sourceLastSeenAt?.toISOString() ?? null,
+        snapshotSha256: input.snapshotSha256,
+        source: "static-loader",
+      },
+    })),
+  ];
+  if (auditRows.length > 0) {
+    await tx.auditLog.createMany({ data: auditRows });
+  }
+
+  const reactivatedCount = reactivatedSections.length;
+  const retiredCount = sectionsToRetire.length;
+  return {
+    enabled: input.retirementEnabled,
+    scopeSemesterCount: scopedSemesterIds.length,
+    seenSectionCount: seenSectionJwIds.length,
+    retirementCandidateCount: retirementCandidates.length,
+    retiredCount,
+    reactivatedCount,
+    before: lifecycleCounts(activeBefore, retiredBefore),
+    after: lifecycleCounts(
+      activeBefore + reactivatedCount - retiredCount,
+      retiredBefore - reactivatedCount + retiredCount,
+    ),
+  };
+}
diff --git a/src/static-loader/validation.ts b/src/static-loader/validation.ts
index 498ecf72e..e709cb17f 100644
--- a/src/static-loader/validation.ts
+++ b/src/static-loader/validation.ts
@@ -1,6 +1,13 @@
+import * as z from "zod";
+
 const CATALOG_LESSON_SOURCE = "catalog_teach_lesson_list_for_teach";
 const CATALOG_EXAM_SOURCE = "catalog_teach_exam_list";
 const JW_SCHEDULE_SOURCE = "jw_ws_schedule_table_datum";
+const SNAPSHOT_MAX_FUTURE_SKEW_MS = 15 * 60 * 1000;
+const SNAPSHOT_GENERATED_AT_SCHEMA = z
+  .string()
+  .regex(/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:\.\d+)?(?:Z|[+-]\d{2}:\d{2})$/)
+  .datetime({ offset: true });
 const SEMESTER_SOURCES = new Set([
   CATALOG_LESSON_SOURCE,
   CATALOG_EXAM_SOURCE,
@@ -62,6 +69,73 @@ export function parsePositiveIntegerSetting(
   return parsed;
 }
 
+export function parseOptionalNonNegativeIntegerSetting(
+  name: string,
+  value: string | undefined,
+): number | null {
+  if (value == null || value.trim() === "") return null;
+  const normalized = value.trim();
+  if (!/^\d+$/.test(normalized)) {
+    throw new Error(`${name} must be a non-negative integer`);
+  }
+  const parsed = Number(normalized);
+  if (!Number.isSafeInteger(parsed)) {
+    throw new Error(`${name} must be a safe non-negative integer`);
+  }
+  return parsed;
+}
+
+export function parseOptionalSha256Setting(
+  name: string,
+  value: string | undefined,
+): string | null {
+  if (value == null || value.trim() === "") return null;
+  const normalized = value.trim().toLowerCase();
+  if (!/^[a-f0-9]{64}$/.test(normalized)) {
+    throw new Error(`${name} must be a 64-character SHA-256 digest`);
+  }
+  return normalized;
+}
+
+export function parseSnapshotGeneratedAt(
+  value: string | undefined,
+  now = new Date(),
+): Date {
+  if (value == null || value.trim() === "") {
+    throw new Error("snapshot metadata generated_at is required");
+  }
+  if (!SNAPSHOT_GENERATED_AT_SCHEMA.safeParse(value).success) {
+    throw new Error(
+      "snapshot metadata generated_at must be a valid timestamp in RFC 3339 format",
+    );
+  }
+  const parsed = new Date(value);
+  if (parsed.getTime() > now.getTime() + SNAPSHOT_MAX_FUTURE_SKEW_MS) {
+    throw new Error(
+      "snapshot metadata generated_at must not be more than 15 minutes in the future",
+    );
+  }
+  return parsed;
+}
+
+export function validateSectionRetirementSnapshotApproval(input: {
+  enabled: boolean;
+  expectedSnapshotSha256: string | null;
+  snapshotSha256: string;
+}): void {
+  if (!input.enabled) return;
+  if (input.expectedSnapshotSha256 == null) {
+    throw new Error(
+      "STATIC_LOADER_EXPECTED_SNAPSHOT_SHA256 is required when missing-Section retirement is enabled",
+    );
+  }
+  if (input.expectedSnapshotSha256 !== input.snapshotSha256) {
+    throw new Error(
+      `Approved static snapshot SHA-256 ${input.expectedSnapshotSha256} does not match downloaded snapshot ${input.snapshotSha256}`,
+    );
+  }
+}
+
 function optionalNonNegativeIntegerMetadata(
   name: string,
   value: string | undefined,
@@ -84,6 +158,11 @@ type SnapshotCompletenessInput = {
   fetchRows: SnapshotRow[];
 };
 
+export type SnapshotCompleteness = {
+  sectionJwIds: number[];
+  sectionSemesterJwIds: number[];
+};
+
 type SemesterFetchState = {
   catalogLessonFetches: number;
   catalogExamFetches: number;
@@ -115,7 +194,7 @@ function contextInteger(
 export function validateSnapshotCompleteness(
   input: SnapshotCompletenessInput,
   minSemester: number,
-): void {
+): SnapshotCompleteness {
   const chunkSize = parsePositiveIntegerSetting(
     "snapshot metadata jw_schedule_chunk_size",
     input.metadata.jw_schedule_chunk_size,
@@ -136,6 +215,7 @@ export function validateSnapshotCompleteness(
       ),
   );
   const lessonCounts = new Map<number, number>();
+  const sectionJwIds = new Set<number>();
   const fetchState = new Map<number, SemesterFetchState>();
   for (const semesterId of targetSemesters) {
     lessonCounts.set(semesterId, 0);
@@ -149,6 +229,18 @@ export function validateSnapshotCompleteness(
   for (const row of input.catalogLessonRows) {
     const semesterId = rowInteger(row.semester_id);
     if (semesterId == null || !targetSemesters.has(semesterId)) continue;
+    const sectionJwId = rowInteger(row.id);
+    if (sectionJwId == null) {
+      throw new Error(
+        `Snapshot lesson for semester ${semesterId} has an invalid Section jwId`,
+      );
+    }
+    if (sectionJwIds.has(sectionJwId)) {
+      throw new Error(
+        `Snapshot contains duplicate Section jwId ${sectionJwId}`,
+      );
+    }
+    sectionJwIds.add(sectionJwId);
     lessonCounts.set(semesterId, (lessonCounts.get(semesterId) ?? 0) + 1);
   }
 
@@ -219,6 +311,47 @@ export function validateSnapshotCompleteness(
       );
     }
   }
+
+  return {
+    sectionJwIds: [...sectionJwIds].sort((left, right) => left - right),
+    sectionSemesterJwIds: [...targetSemesters]
+      .filter((semesterId) => (lessonCounts.get(semesterId) ?? 0) > 0)
+      .sort((left, right) => left - right),
+  };
+}
+
+export function validateMappedSectionJwIds(
+  expectedJwIds: readonly number[],
+  mappedJwIds: readonly number[],
+): void {
+  const expected = new Set(expectedJwIds);
+  const mapped = new Set(mappedJwIds);
+  const duplicates = mappedJwIds.filter(
+    (jwId, index) => mappedJwIds.indexOf(jwId) !== index,
+  );
+  const missing = [...expected].filter((jwId) => !mapped.has(jwId));
+  const unexpected = [...mapped].filter((jwId) => !expected.has(jwId));
+  if (
+    duplicates.length === 0 &&
+    missing.length === 0 &&
+    unexpected.length === 0
+  )
+    return;
+
+  const summarize = (values: readonly number[]) =>
+    [...new Set(values)].slice(0, 10).join(",");
+  throw new Error(
+    [
+      "Static Section mapping is incomplete",
+      missing.length > 0 ? `missing jwIds=${summarize(missing)}` : null,
+      unexpected.length > 0
+        ? `unexpected jwIds=${summarize(unexpected)}`
+        : null,
+      duplicates.length > 0 ? `duplicate jwIds=${summarize(duplicates)}` : null,
+    ]
+      .filter((part): part is string => part != null)
+      .join("; "),
+  );
 }
 
 export type MissingSnapshotRowsWhere = {
diff --git a/tests/e2e/src/app/api/calendar-subscriptions/test.ts b/tests/e2e/src/app/api/calendar-subscriptions/test.ts
index ad64cfb80..826f85e62 100644
--- a/tests/e2e/src/app/api/calendar-subscriptions/test.ts
+++ b/tests/e2e/src/app/api/calendar-subscriptions/test.ts
@@ -27,7 +27,11 @@
 import { expect, test } from "@playwright/test";
 import { signInAsDebugUser } from "../../../../utils/auth";
 import { DEV_SEED } from "../../../../utils/dev-seed";
-import { getSeedSectionSemesterFixture } from "../../../../utils/e2e-db";
+import {
+  getCurrentSessionUser,
+  getSeedSectionSemesterFixture,
+} from "../../../../utils/e2e-db";
+import { withE2ePrisma } from "../../../../utils/e2e-db/prisma";
 import { resolveSeedSectionMatches } from "../../../../utils/seed-lookups";
 import { assertApiContract } from "../../_shared/api-contract";
 
@@ -305,6 +309,164 @@ test.describe("日历订阅 API", () => {
     }
   });
 
+  test("replace 和 set 保留请求中已有的退役班级但不能重新添加", async ({
+    page,
+  }) => {
+    await signInAsDebugUser(page, "/");
+    const sessionUser = await getCurrentSessionUser(page);
+    const previous = await withE2ePrisma(async (prisma) => {
+      const [section, user] = await Promise.all([
+        prisma.section.findUniqueOrThrow({
+          where: { jwId: DEV_SEED.section.jwId },
+          select: { id: true, retiredAt: true, semesterId: true },
+        }),
+        prisma.user.findUniqueOrThrow({
+          where: { id: sessionUser.id },
+          select: {
+            subscribedSections: {
+              orderBy: { id: "asc" },
+              select: { id: true },
+            },
+          },
+        }),
+      ]);
+      return {
+        section,
+        subscribedSectionIds: user.subscribedSections.map(
+          (subscribedSection) => subscribedSection.id,
+        ),
+      };
+    });
+
+    await withE2ePrisma((prisma) =>
+      prisma.$transaction([
+        prisma.section.update({
+          where: { id: previous.section.id },
+          data: { retiredAt: new Date("2026-01-01T00:00:00.000Z") },
+        }),
+        prisma.user.update({
+          where: { id: sessionUser.id },
+          data: {
+            subscribedSections: { set: [{ id: previous.section.id }] },
+          },
+        }),
+      ]),
+    );
+
+    try {
+      if (previous.section.semesterId == null) {
+        throw new Error(
+          "Expected retired test Section to belong to a semester",
+        );
+      }
+      const replaceResponse = await page.request.post(BASE, {
+        data: { sectionIds: [previous.section.id] },
+      });
+      expect(replaceResponse.status()).toBe(200);
+      const replaceBody = (await replaceResponse.json()) as {
+        subscription?: { sections?: Array<{ id?: number }> };
+      };
+      expect(
+        replaceBody.subscription?.sections?.map((section) => section.id),
+      ).toContain(previous.section.id);
+
+      const setResponse = await page.request.post(BATCH_BASE, {
+        data: {
+          action: "set",
+          sectionIds: [previous.section.id],
+          semesterId: previous.section.semesterId,
+        },
+      });
+      expect(setResponse.status()).toBe(200);
+      const setBody = (await setResponse.json()) as {
+        matchedSectionIds?: number[];
+        removedCount?: number;
+        sections?: Array<{ id?: number }>;
+        total?: number;
+        unchangedCount?: number;
+        unmatchedSectionIds?: number[];
+        subscription?: { sections?: Array<{ id?: number }> };
+      };
+      expect(setBody.matchedSectionIds).toEqual([previous.section.id]);
+      expect(setBody.unmatchedSectionIds).toEqual([]);
+      expect(setBody.removedCount).toBe(0);
+      expect(setBody.unchangedCount).toBe(1);
+      expect(setBody.sections?.map((section) => section.id)).toEqual([
+        previous.section.id,
+      ]);
+      expect(setBody.total).toBe(1);
+      expect(
+        setBody.subscription?.sections?.map((section) => section.id),
+      ).toContain(previous.section.id);
+
+      const omitResponse = await page.request.post(BATCH_BASE, {
+        data: {
+          action: "set",
+          sectionIds: [],
+          semesterId: previous.section.semesterId,
+        },
+      });
+      expect(omitResponse.status()).toBe(200);
+      const omitBody = (await omitResponse.json()) as {
+        removedCount?: number;
+        subscription?: { sections?: Array<{ id?: number }> };
+      };
+      expect(omitBody.removedCount).toBe(1);
+      expect(
+        omitBody.subscription?.sections?.map((section) => section.id),
+      ).not.toContain(previous.section.id);
+
+      const setReAddResponse = await page.request.post(BATCH_BASE, {
+        data: {
+          action: "set",
+          sectionIds: [previous.section.id],
+          semesterId: previous.section.semesterId,
+        },
+      });
+      expect(setReAddResponse.status()).toBe(200);
+      const setReAddBody = (await setReAddResponse.json()) as {
+        matchedSectionIds?: number[];
+        unchangedCount?: number;
+        unmatchedSectionIds?: number[];
+        subscription?: { sections?: Array<{ id?: number }> };
+      };
+      expect(setReAddBody.matchedSectionIds).toEqual([]);
+      expect(setReAddBody.unmatchedSectionIds).toEqual([previous.section.id]);
+      expect(setReAddBody.unchangedCount).toBe(0);
+      expect(
+        setReAddBody.subscription?.sections?.map((section) => section.id),
+      ).not.toContain(previous.section.id);
+
+      const replaceReAddResponse = await page.request.post(BASE, {
+        data: { sectionIds: [previous.section.id] },
+      });
+      expect(replaceReAddResponse.status()).toBe(200);
+      const replaceReAddBody = (await replaceReAddResponse.json()) as {
+        subscription?: { sections?: Array<{ id?: number }> };
+      };
+      expect(
+        replaceReAddBody.subscription?.sections?.map((section) => section.id),
+      ).not.toContain(previous.section.id);
+    } finally {
+      await withE2ePrisma((prisma) =>
+        prisma.$transaction([
+          prisma.section.update({
+            where: { id: previous.section.id },
+            data: { retiredAt: previous.section.retiredAt },
+          }),
+          prisma.user.update({
+            where: { id: sessionUser.id },
+            data: {
+              subscribedSections: {
+                set: previous.subscribedSectionIds.map((id) => ({ id })),
+              },
+            },
+          }),
+        ]),
+      );
+    }
+  });
+
   test("remove sections 删除指定 id 且不替换并发添加", async ({ page }) => {
     await signInAsDebugUser(page, "/");
     const [firstSection, secondSection] = await resolveSeedSectionMatches(page);
diff --git a/tests/e2e/src/app/sections/[jwId]/test.ts b/tests/e2e/src/app/sections/[jwId]/test.ts
index 837912ab3..b65cfb468 100644
--- a/tests/e2e/src/app/sections/[jwId]/test.ts
+++ b/tests/e2e/src/app/sections/[jwId]/test.ts
@@ -37,6 +37,8 @@ import { expect, type Locator, type Page, test } from "@playwright/test";
 import { signInAsDebugUser, signInAsDevAdmin } from "../../../../utils/auth";
 import { cleanupCommentsForE2e } from "../../../../utils/comments";
 import { DEV_SEED } from "../../../../utils/dev-seed";
+import { getCurrentSessionUser } from "../../../../utils/e2e-db";
+import { withE2ePrisma } from "../../../../utils/e2e-db/prisma";
 import { cleanupHomeworksForE2e } from "../../../../utils/homeworks";
 import {
   gotoAndWaitForReady,
@@ -457,6 +459,159 @@ test.describe("/sections/[jwId] 班级详情页", () => {
     ).toBeHidden();
   });
 
+  test("已退役班级保留历史详情与日历但禁止新增关注", async ({ page }) => {
+    test.setTimeout(60_000);
+    const previous = await withE2ePrisma((prisma) =>
+      prisma.section.findUniqueOrThrow({
+        where: { jwId: DEV_SEED.section.jwId },
+        select: { retiredAt: true },
+      }),
+    );
+
+    await withE2ePrisma((prisma) =>
+      prisma.section.update({
+        where: { jwId: DEV_SEED.section.jwId },
+        data: { retiredAt: new Date("2026-01-01T00:00:00.000Z") },
+      }),
+    );
+
+    try {
+      await page.setViewportSize({ width: 1440, height: 900 });
+      await gotoAndWaitForReady(page, `${SECTION_URL}?subscribe=1`);
+
+      await expect(
+        page.getByText(/历史班级|Historical section/i).first(),
+      ).toBeVisible();
+      await expect(
+        page.getByRole("button", {
+          name: /关注班级|Subscribe to section/i,
+        }),
+      ).toHaveCount(0);
+      await expect(
+        page
+          .getByTestId("detail-pinned-summary")
+          .getByRole("button", { name: /添加到日历|Add to calendar/i }),
+      ).toBeVisible();
+      await expect(page.getByRole("dialog")).toHaveCount(0);
+    } finally {
+      await withE2ePrisma((prisma) =>
+        prisma.section.update({
+          where: { jwId: DEV_SEED.section.jwId },
+          data: { retiredAt: previous.retiredAt },
+        }),
+      );
+    }
+  });
+
+  test("已关注用户仍可取消关注已退役班级", async ({ page }) => {
+    test.setTimeout(60_000);
+    await signInAsDebugUser(page, SECTION_URL);
+    const sessionUser = await getCurrentSessionUser(page);
+    const previous = await withE2ePrisma(async (prisma) => {
+      const [section, user] = await Promise.all([
+        prisma.section.findUniqueOrThrow({
+          where: { jwId: DEV_SEED.section.jwId },
+          select: { id: true, retiredAt: true },
+        }),
+        prisma.user.findUniqueOrThrow({
+          where: { id: sessionUser.id },
+          select: {
+            subscribedSections: {
+              orderBy: { id: "asc" },
+              select: { id: true },
+            },
+          },
+        }),
+      ]);
+      return {
+        section,
+        subscribedSectionIds: user.subscribedSections.map(
+          (subscribedSection) => subscribedSection.id,
+        ),
+      };
+    });
+
+    await withE2ePrisma((prisma) =>
+      prisma.$transaction([
+        prisma.section.update({
+          where: { id: previous.section.id },
+          data: { retiredAt: new Date("2026-01-01T00:00:00.000Z") },
+        }),
+        prisma.user.update({
+          where: { id: sessionUser.id },
+          data: {
+            subscribedSections: {
+              set: [
+                ...new Set([
+                  ...previous.subscribedSectionIds,
+                  previous.section.id,
+                ]),
+              ].map((id) => ({ id })),
+            },
+          },
+        }),
+      ]),
+    );
+
+    try {
+      await gotoAndWaitForReady(page, SECTION_URL);
+
+      await expect(
+        page.getByText(/历史班级|Historical section/i).first(),
+      ).toBeVisible();
+      const unsubscribe = page.getByRole("button", {
+        name: /取消关注|Unsubscribe from section/i,
+      });
+      await expect(unsubscribe.first()).toBeVisible();
+      await expect(
+        page.getByRole("button", {
+          name: /关注班级|Subscribe to section/i,
+        }),
+      ).toHaveCount(0);
+
+      await unsubscribe.first().click();
+      await expect
+        .poll(() =>
+          withE2ePrisma(async (prisma) => {
+            const user = await prisma.user.findUniqueOrThrow({
+              where: { id: sessionUser.id },
+              select: {
+                subscribedSections: {
+                  where: { id: previous.section.id },
+                  select: { id: true },
+                },
+              },
+            });
+            return user.subscribedSections.length;
+          }),
+        )
+        .toBe(0);
+      await expect(unsubscribe).toHaveCount(0);
+      await expect(
+        page.getByRole("button", {
+          name: /关注班级|Subscribe to section/i,
+        }),
+      ).toHaveCount(0);
+    } finally {
+      await withE2ePrisma((prisma) =>
+        prisma.$transaction([
+          prisma.section.update({
+            where: { id: previous.section.id },
+            data: { retiredAt: previous.section.retiredAt },
+          }),
+          prisma.user.update({
+            where: { id: sessionUser.id },
+            data: {
+              subscribedSections: {
+                set: previous.subscribedSectionIds.map((id) => ({ id })),
+              },
+            },
+          }),
+        ]),
+      );
+    }
+  });
+
   test("详情导航后内容滚动回到顶部", async ({ page }) => {
     await page.setViewportSize({ width: 1440, height: 900 });
     await gotoAndWaitForReady(page, `${SECTION_URL}/comments`);
diff --git a/tests/integration/static-import-state.test.ts b/tests/integration/static-import-state.test.ts
new file mode 100644
index 000000000..e8019bbff
--- /dev/null
+++ b/tests/integration/static-import-state.test.ts
@@ -0,0 +1,88 @@
+import { afterAll, describe, expect, it } from "vitest";
+import {
+  assertStaticImportStateAllowsSnapshot,
+  recordStaticImportState,
+} from "@/static-loader/import-state";
+import { createTestPrisma, disconnectTestPrisma } from "../shared/prisma";
+
+const prisma = createTestPrisma();
+
+afterAll(() => disconnectTestPrisma(prisma));
+
+describe("global static import state persistence", () => {
+  it("bootstraps once and rejects stale or conflicting snapshots", async () => {
+    const rollback = new Error("ROLLBACK_STATIC_IMPORT_STATE_TEST");
+    const snapshotSha = "a".repeat(64);
+    const otherSnapshotSha = "b".repeat(64);
+    const observedAt = new Date("2026-07-18T03:00:00.000Z");
+
+    try {
+      await prisma.$transaction(async (tx) => {
+        await tx.staticImportState.deleteMany({ where: { id: "global" } });
+
+        await expect(
+          assertStaticImportStateAllowsSnapshot(tx, {
+            bootstrapEnabled: false,
+            dryRun: false,
+            expectedSnapshotSha256: null,
+            observedAt,
+            retirementEnabled: false,
+            snapshotSha256: snapshotSha,
+          }),
+        ).rejects.toThrow("manual bootstrap");
+
+        await expect(
+          assertStaticImportStateAllowsSnapshot(tx, {
+            bootstrapEnabled: true,
+            dryRun: false,
+            expectedSnapshotSha256: snapshotSha,
+            observedAt,
+            retirementEnabled: false,
+            snapshotSha256: snapshotSha,
+          }),
+        ).resolves.toBeUndefined();
+        await recordStaticImportState(tx, {
+          observedAt,
+          snapshotSha256: snapshotSha,
+        });
+
+        await expect(
+          tx.staticImportState.findUnique({
+            where: { id: "global" },
+            select: {
+              snapshotGeneratedAt: true,
+              snapshotSha256: true,
+            },
+          }),
+        ).resolves.toEqual({
+          snapshotGeneratedAt: observedAt,
+          snapshotSha256: snapshotSha,
+        });
+        await expect(
+          assertStaticImportStateAllowsSnapshot(tx, {
+            bootstrapEnabled: false,
+            dryRun: false,
+            expectedSnapshotSha256: null,
+            observedAt,
+            retirementEnabled: false,
+            snapshotSha256: otherSnapshotSha,
+          }),
+        ).rejects.toThrow("already committed with SHA-256");
+        await expect(
+          assertStaticImportStateAllowsSnapshot(tx, {
+            bootstrapEnabled: false,
+            dryRun: false,
+            expectedSnapshotSha256: null,
+            observedAt: new Date("2026-07-17T03:00:00.000Z"),
+            retirementEnabled: false,
+            snapshotSha256: snapshotSha,
+          }),
+        ).rejects.toThrow("last committed snapshot");
+
+        throw rollback;
+      });
+    } catch (error) {
+      if (error !== rollback) throw error;
+    }
+  });
+});
diff --git a/tests/integration/static-section-lifecycle.test.ts b/tests/integration/static-section-lifecycle.test.ts
new file mode 100644
index 000000000..87b886757
--- /dev/null
+++ b/tests/integration/static-section-lifecycle.test.ts
@@ -0,0 +1,235 @@
+import { afterAll, describe, expect, it } from "vitest";
+import { reconcileSectionSourceLifecycle } from "@/static-loader/section-lifecycle";
+import { createTestPrisma, disconnectTestPrisma } from "../shared/prisma";
+
+const prisma = createTestPrisma();
+
+afterAll(() => disconnectTestPrisma(prisma));
+
+describe("static Section source lifecycle persistence", () => {
+  it("retires and reactivates without deleting user data or history", async () => {
+    const rollback = new Error("ROLLBACK_STATIC_SECTION_LIFECYCLE_TEST");
+    const marker = `[integration-test] section-lifecycle-${Date.now()}`;
+    const numericMarker = 2_140_000_000 + (Date.now() % 1_000_000);
+    const firstObservedAt = new Date("2026-07-18T03:00:00.000Z");
+    const secondObservedAt = new Date("2026-07-19T03:00:00.000Z");
+
+    try {
+      await prisma.$transaction(async (tx) => {
+        const semester = await tx.semester.create({
+          data: {
+            jwId: numericMarker,
+            code: marker,
+            nameCn: marker,
+          },
+        });
+        const course = await tx.course.create({
+          data: {
+            jwId: numericMarker,
+            code: marker,
+            nameCn: marker,
+          },
+        });
+        const reappearingSection = await tx.section.create({
+          data: {
+            jwId: numericMarker,
+            code: `${marker}-reappearing`,
+            courseId: course.id,
+            semesterId: semester.id,
+            retiredAt: new Date("2026-07-17T03:00:00.000Z"),
+          },
+        });
+        const missingSection = await tx.section.create({
+          data: {
+            jwId: numericMarker + 1,
+            code: `${marker}-missing`,
+            courseId: course.id,
+            semesterId: semester.id,
+            sourceLastSeenAt: new Date("2026-07-16T03:00:00.000Z"),
+          },
+        });
+        const user = await tx.user.create({
+          data: {
+            email: `${numericMarker}@section-lifecycle.integration`,
+            name: marker,
+            subscribedSections: { connect: { id: missingSection.id } },
+          },
+        });
+        const comment = await tx.comment.create({
+          data: {
+            body: marker,
+            sectionId: missingSection.id,
+            userId: user.id,
+          },
+        });
+        const description = await tx.description.create({
+          data: {
+            content: marker,
+            lastEditedById: user.id,
+            sectionId: missingSection.id,
+          },
+        });
+        const homework = await tx.homework.create({
+          data: {
+            sectionId: missingSection.id,
+            title: marker,
+            createdById: user.id,
+          },
+        });
+        const homeworkAudit = await tx.homeworkAuditLog.create({
+          data: {
+            action: "created",
+            homeworkId: homework.id,
+            sectionId: missingSection.id,
+            titleSnapshot: marker,
+          },
+        });
+
+        await expect(
+          reconcileSectionSourceLifecycle(tx, {
+            observedAt: firstObservedAt,
+            retirementEnabled: true,
+            expectedRetirementCandidateCount: 1,
+            scopedSemesterIds: [semester.id],
+            seenSectionJwIds: [reappearingSection.jwId],
+            snapshotSha256: "first-snapshot",
+          }),
+        ).resolves.toEqual({
+          enabled: true,
+          scopeSemesterCount: 1,
+          seenSectionCount: 1,
+          retirementCandidateCount: 1,
+          retiredCount: 1,
+          reactivatedCount: 1,
+          before: { active: 1, retired: 1, total: 2 },
+          after: { active: 1, retired: 1, total: 2 },
+        });
+
+        await expect(
+          tx.section.findMany({
+            where: { id: { in: [reappearingSection.id, missingSection.id] } },
+            orderBy: { id: "asc" },
+            select: {
+              id: true,
+              retiredAt: true,
+              sourceLastSeenAt: true,
+            },
+          }),
+        ).resolves.toEqual([
+          {
+            id: reappearingSection.id,
+            retiredAt: null,
+            sourceLastSeenAt: firstObservedAt,
+          },
+          {
+            id: missingSection.id,
+            retiredAt: firstObservedAt,
+            sourceLastSeenAt: new Date("2026-07-16T03:00:00.000Z"),
+          },
+        ]);
+        await expect(
+          tx.user.findUnique({
+            where: { id: user.id },
+            select: {
+              subscribedSections: {
+                where: { id: missingSection.id },
+                select: { id: true },
+              },
+            },
+          }),
+        ).resolves.toEqual({
+          subscribedSections: [{ id: missingSection.id }],
+        });
+        const preservedUserData = [
+          await tx.comment.findUnique({ where: { id: comment.id } }),
+          await tx.description.findUnique({ where: { id: description.id } }),
+          await tx.homework.findUnique({ where: { id: homework.id } }),
+          await tx.homeworkAuditLog.findUnique({
+            where: { id: homeworkAudit.id },
+          }),
+        ];
+        expect(preservedUserData).toEqual([
+          expect.objectContaining({ sectionId: missingSection.id }),
+          expect.objectContaining({ sectionId: missingSection.id }),
+          expect.objectContaining({ sectionId: missingSection.id }),
+          expect.objectContaining({ sectionId: missingSection.id }),
+        ]);
+        await expect(
+          tx.auditLog.findMany({
+            where: {
+              targetId: {
+                in: [String(reappearingSection.id), String(missingSection.id)],
+              },
+              targetType: "section",
+            },
+            orderBy: { action: "asc" },
+            select: { action: true, metadata: true, targetId: true },
+          }),
+        ).resolves.toEqual([
+          {
+            action: "section_retire",
+            metadata: expect.objectContaining({
+              snapshotSha256: "first-snapshot",
+            }),
+            targetId: String(missingSection.id),
+          },
+          {
+            action: "section_reactivate",
+            metadata: expect.objectContaining({
+              snapshotSha256: "first-snapshot",
+            }),
+            targetId: String(reappearingSection.id),
+          },
+        ]);
+
+        await expect(
+          reconcileSectionSourceLifecycle(tx, {
+            observedAt: secondObservedAt,
+            retirementEnabled: true,
+            expectedRetirementCandidateCount: 0,
+            scopedSemesterIds: [semester.id],
+            seenSectionJwIds: [reappearingSection.jwId, missingSection.jwId],
+            snapshotSha256: "second-snapshot",
+          }),
+        ).resolves.toMatchObject({
+          retirementCandidateCount: 0,
+          retiredCount: 0,
+          reactivatedCount: 1,
+          after: { active: 2, retired: 0, total: 2 },
+        });
+        await expect(
+          tx.section.findUnique({
+            where: { id: missingSection.id },
+            select: {
+              retiredAt: true,
+              sourceLastSeenAt: true,
+              _count: {
+                select: {
+                  comments: true,
+                  homeworks: true,
+                  homeworkAuditLogs: true,
+                  subscribedUsers: true,
+                },
+              },
+              description: { select: { id: true } },
+            },
+          }),
+        ).resolves.toEqual({
+          retiredAt: null,
+          sourceLastSeenAt: secondObservedAt,
+          _count: {
+            comments: 1,
+            homeworks: 1,
+            homeworkAuditLogs: 1,
+            subscribedUsers: 1,
+          },
+          description: { id: description.id },
+        });
+
+        throw rollback;
+      });
+    } catch (error) {
+      if (error !== rollback) throw error;
+    }
+  });
+});
diff --git a/tests/integration/subscription-retirement-concurrency.test.ts b/tests/integration/subscription-retirement-concurrency.test.ts
new file mode 100644
index 000000000..3be71933d
--- /dev/null
+++ b/tests/integration/subscription-retirement-concurrency.test.ts
@@ -0,0 +1,329 @@
+import { afterAll, describe, expect, it } from "vitest";
+import { mutateUserSectionSubscriptionsInTransaction } from "@/features/subscriptions/server/subscription-write-model";
+import { reconcileSectionSourceLifecycle } from "@/static-loader/section-lifecycle";
+import {
+  createTestPrisma,
+  disconnectTestPrisma,
+  type TestPrismaClient,
+} from "../shared/prisma";
+
+const prisma = createTestPrisma();
+let fixtureSequence = 0;
+
+afterAll(() => disconnectTestPrisma(prisma));
+
+function deferred() {
+  let resolve: () => void = () => {};
+  const promise = new Promise<void>((done) => {
+    resolve = done;
+  });
+  return { promise, resolve };
+}
+
+async function waitForSignal(
+  signal: Promise<void>,
+  operation: Promise<unknown>,
+  earlyCompletionMessage: string,
+) {
+  await Promise.race([
+    signal,
+    operation.then(() => {
+      throw new Error(earlyCompletionMessage);
+    }),
+  ]);
+}
+
+async function settleOperations(
+  ...operations: Array<Promise<unknown> | undefined>
+) {
+  await Promise.allSettled(
+    operations.filter(
+      (operation): operation is Promise<unknown> => operation !== undefined,
+    ),
+  );
+}
+
+async function waitForBackendLock(
+  observer: TestPrismaClient,
+  pid: number,
+  failureMessage: string,
+) {
+  for (let attempt = 0; attempt < 100; attempt += 1) {
+    const [activity] = await observer.$queryRaw<
+      Array<{ waitEventType: string | null }>
+    >`
+      SELECT "wait_event_type" AS "waitEventType"
+      FROM pg_stat_activity
+      WHERE pid = ${pid}
+    `;
+    if (activity?.waitEventType === "Lock") return;
+    if (attempt === 99) throw new Error(failureMessage);
+    await new Promise((resolve) => setTimeout(resolve, 20));
+  }
+}
+
+async function createFixture(options: { subscribedToFirst: boolean }) {
+  fixtureSequence += 1;
+  const numericMarker =
+    2_120_000_000 + (Date.now() % 10_000_000) + fixtureSequence * 10;
+  const marker = `[integration-test] subscription-lock-${numericMarker}`;
+  return prisma.$transaction(async (tx) => {
+    const semester = await tx.semester.create({
+      data: {
+        jwId: numericMarker,
+        code: marker,
+        nameCn: marker,
+      },
+    });
+    const course = await tx.course.create({
+      data: {
+        jwId: numericMarker,
+        code: marker,
+        nameCn: marker,
+      },
+    });
+    const sections = await Promise.all(
+      [0, 1, 2].map((offset) =>
+        tx.section.create({
+          data: {
+            jwId: numericMarker + offset,
+            code: `${marker}-${offset}`,
+            courseId: course.id,
+            semesterId: semester.id,
+          },
+        }),
+      ),
+    );
+    const user = await tx.user.create({
+      data: {
+        email: `${numericMarker}@subscription-lock.integration`,
+        name: marker,
+        subscribedSections: options.subscribedToFirst
+          ? { connect: { id: sections[0].id } }
+          : undefined,
+      },
+    });
+    return { course, sections, semester, user };
+  });
+}
+
+async function deleteFixture(
+  fixture: Awaited<ReturnType<typeof createFixture>>,
+) {
+  await prisma.$transaction(async (tx) => {
+    await tx.user.delete({ where: { id: fixture.user.id } });
+    await tx.section.deleteMany({
+      where: { id: { in: fixture.sections.map((section) => section.id) } },
+    });
+    await tx.course.delete({ where: { id: fixture.course.id } });
+    await tx.semester.delete({ where: { id: fixture.semester.id } });
+  });
+}
+
+describe("Section subscription retirement linearization", () => {
+  it("rejects a newly retired candidate while preserving one explicit existing relation once", async () => {
+    const fixture = await createFixture({ subscribedToFirst: true });
+    const importerPrisma = createTestPrisma();
+    const subscriberPrisma = createTestPrisma();
+    const importerLocked = deferred();
+    const releaseImporter = deferred();
+    const subscriberPidReady = deferred();
+    const retiredAt = new Date("2026-07-18T04:00:00.000Z");
+    let subscriberPid = 0;
+    let importer: Promise<void> | undefined;
+    let subscriber:
+      | Promise<
+          Awaited<
+            ReturnType<typeof mutateUserSectionSubscriptionsInTransaction>
+          >
+        >
+      | undefined;
+
+    try {
+      importer = importerPrisma.$transaction(async (tx) => {
+        await reconcileSectionSourceLifecycle(tx, {
+          observedAt: retiredAt,
+          retirementEnabled: true,
+          expectedRetirementCandidateCount: 2,
+          scopedSemesterIds: [fixture.semester.id],
+          seenSectionJwIds: [fixture.sections[2].jwId],
+          snapshotSha256: "importer-first",
+        });
+        importerLocked.resolve();
+        await releaseImporter.promise;
+      });
+      await waitForSignal(
+        importerLocked.promise,
+        importer,
+        "Lifecycle transaction completed before acquiring its advisory locks",
+      );
+
+      subscriber = subscriberPrisma.$transaction(async (tx) => {
+        const [backend] = await tx.$queryRaw<Array<{ pid: number }>>`
+          SELECT pg_backend_pid()::integer AS pid
+        `;
+        subscriberPid = backend.pid;
+        subscriberPidReady.resolve();
+        return mutateUserSectionSubscriptionsInTransaction(tx as never, {
+          candidateSectionIds: [
+            fixture.sections[0].id,
+            fixture.sections[0].id,
+            fixture.sections[1].id,
+            fixture.sections[1].id,
+          ],
+          mode: "replace",
+          preserveRetiredSectionIds: [
+            fixture.sections[0].id,
+            fixture.sections[0].id,
+            fixture.sections[1].id,
+          ],
+          userId: fixture.user.id,
+        });
+      });
+      await waitForSignal(
+        subscriberPidReady.promise,
+        subscriber,
+        "Subscription transaction completed before exposing its backend PID",
+      );
+      await waitForBackendLock(
+        prisma,
+        subscriberPid,
+        "Subscription mutation did not wait for the lifecycle advisory lock",
+      );
+
+      releaseImporter.resolve();
+      await importer;
+      const result = await subscriber;
+
+      expect(result).toEqual({
+        activeCandidateSectionIds: [],
+        addedSectionIds: [],
+        effectiveSectionIds: [fixture.sections[0].id],
+        preservedRetiredSectionIds: [fixture.sections[0].id],
+        removedSectionIds: [],
+        unchangedSectionIds: [fixture.sections[0].id],
+      });
+      await expect(
+        prisma.user.findUnique({
+          where: { id: fixture.user.id },
+          select: {
+            subscribedSections: {
+              orderBy: { id: "asc" },
+              select: { id: true, retiredAt: true },
+            },
+          },
+        }),
+      ).resolves.toEqual({
+        subscribedSections: [{ id: fixture.sections[0].id, retiredAt }],
+      });
+    } finally {
+      releaseImporter.resolve();
+      await settleOperations(importer, subscriber);
+      await Promise.all([
+        disconnectTestPrisma(importerPrisma),
+        disconnectTestPrisma(subscriberPrisma),
+      ]);
+      await deleteFixture(fixture);
+    }
+  });
+
+  it("lets a subscriber that owns the advisory lock commit before retirement", async () => {
+    const fixture = await createFixture({ subscribedToFirst: false });
+    const importerPrisma = createTestPrisma();
+    const subscriberPrisma = createTestPrisma();
+    const subscriberMutated = deferred();
+    const releaseSubscriber = deferred();
+    const importerPidReady = deferred();
+    const retiredAt = new Date("2026-07-18T05:00:00.000Z");
+    let importerPid = 0;
+    let subscriber: Promise<void> | undefined;
+    let importer: Promise<void> | undefined;
+
+    try {
+      let mutationResult:
+        | Awaited<
+            ReturnType<typeof mutateUserSectionSubscriptionsInTransaction>
+          >
+        | undefined;
+      subscriber = subscriberPrisma.$transaction(async (tx) => {
+        mutationResult = await mutateUserSectionSubscriptionsInTransaction(
+          tx as never,
+          {
+            candidateSectionIds: [fixture.sections[0].id],
+            mode: "connect",
+            userId: fixture.user.id,
+          },
+        );
+        subscriberMutated.resolve();
+        await releaseSubscriber.promise;
+      });
+      await waitForSignal(
+        subscriberMutated.promise,
+        subscriber,
+        "Subscription transaction completed before acquiring its advisory lock",
+      );
+
+      importer = importerPrisma.$transaction(async (tx) => {
+        const [backend] = await tx.$queryRaw<Array<{ pid: number }>>`
+          SELECT pg_backend_pid()::integer AS pid
+        `;
+        importerPid = backend.pid;
+        importerPidReady.resolve();
+        await reconcileSectionSourceLifecycle(tx, {
+          observedAt: retiredAt,
+          retirementEnabled: true,
+          expectedRetirementCandidateCount: 1,
+          scopedSemesterIds: [fixture.semester.id],
+          seenSectionJwIds: [
+            fixture.sections[1].jwId,
+            fixture.sections[2].jwId,
+          ],
+          snapshotSha256: "subscriber-first",
+        });
+      });
+      await waitForSignal(
+        importerPidReady.promise,
+        importer,
+        "Lifecycle transaction completed before exposing its backend PID",
+      );
+      await waitForBackendLock(
+        prisma,
+        importerPid,
+        "Retirement did not wait for the subscription advisory lock",
+      );
+
+      releaseSubscriber.resolve();
+      await subscriber;
+      await importer;
+
+      expect(mutationResult).toEqual({
+        activeCandidateSectionIds: [fixture.sections[0].id],
+        addedSectionIds: [fixture.sections[0].id],
+        effectiveSectionIds: [fixture.sections[0].id],
+        preservedRetiredSectionIds: [],
+        removedSectionIds: [],
+        unchangedSectionIds: [],
+      });
+      await expect(
+        prisma.user.findUnique({
+          where: { id: fixture.user.id },
+          select: {
+            subscribedSections: {
+              select: { id: true, retiredAt: true },
+            },
+          },
+        }),
+      ).resolves.toEqual({
+        subscribedSections: [{ id: fixture.sections[0].id, retiredAt }],
+      });
+    } finally {
+      releaseSubscriber.resolve();
+      await settleOperations(subscriber, importer);
+      await Promise.all([
+        disconnectTestPrisma(importerPrisma),
+        disconnectTestPrisma(subscriberPrisma),
+      ]);
+      await deleteFixture(fixture);
+    }
+  });
+});
diff --git a/tests/unit/course-section-queries.test.ts b/tests/unit/course-section-queries.test.ts
index 6f14595a4..1345c464f 100644
--- a/tests/unit/course-section-queries.test.ts
+++ b/tests/unit/course-section-queries.test.ts
@@ -63,6 +63,7 @@ describe("课程与开课查询辅助函数", () => {
     });
 
     expect(result.where).toMatchObject({
+      retiredAt: null,
       courseId: 11,
       semesterId: 22,
       campusId: 33,
@@ -206,7 +207,7 @@ describe("课程与开课查询辅助函数", () => {
       search: "credits:3abc",
     });
 
-    expect(result.where).toEqual({});
+    expect(result.where).toEqual({ retiredAt: null });
   });
 
   it("接受数字 ID 数组作为开课筛选条件", () => {
@@ -215,6 +216,7 @@ describe("课程与开课查询辅助函数", () => {
         ids: [7, 8, 9],
       }).where,
     ).toEqual({
+      retiredAt: null,
       id: {
         in: [7, 8, 9],
       },
@@ -227,6 +229,7 @@ describe("课程与开课查询辅助函数", () => {
       semesterJwId: 202,
     });
     expect(result.where).toMatchObject({
+      retiredAt: null,
       semester: { jwId: 202 },
     });
     expect(result.where).not.toHaveProperty("course");
diff --git a/tests/unit/dashboard-page-public-summary.test.ts b/tests/unit/dashboard-page-public-summary.test.ts
new file mode 100644
index 000000000..c7d05ec37
--- /dev/null
+++ b/tests/unit/dashboard-page-public-summary.test.ts
@@ -0,0 +1,34 @@
+import { describe, expect, it, vi } from "vitest";
+import { loadDashboardPublicSummary } from "@/features/dashboard/server/dashboard-page-public-summary";
+
+vi.mock("@/features/dashboard-links/server/dashboard-link-data", () => ({
+  getPublicDashboardLinksData: () => ({
+    dashboardLinks: [],
+    overviewLinks: [],
+  }),
+}));
+
+describe("dashboard public summary", () => {
+  it("counts only active Sections", async () => {
+    const sectionCount = vi.fn().mockResolvedValue(11);
+    const prisma = {
+      course: { count: vi.fn().mockResolvedValue(7) },
+      section: { count: sectionCount },
+      semester: {
+        count: vi.fn().mockResolvedValue(3),
+        findMany: vi.fn().mockResolvedValue([]),
+      },
+    };
+
+    const summary = await loadDashboardPublicSummary(
+      prisma as never,
+      new Date("2026-07-18T00:00:00.000Z"),
+    );
+
+    expect(sectionCount).toHaveBeenCalledOnce();
+    expect(sectionCount).toHaveBeenCalledWith({
+      where: { retiredAt: null },
+    });
+    expect(summary.counts.sections).toBe(11);
+  });
+});
diff --git a/tests/unit/retired-section-discovery.test.ts b/tests/unit/retired-section-discovery.test.ts
new file mode 100644
index 000000000..c62c6b46b
--- /dev/null
+++ b/tests/unit/retired-section-discovery.test.ts
@@ -0,0 +1,176 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const {
+  buildSuggestionsMock,
+  getLatestCommentsMock,
+  sectionFindFirstMock,
+  sectionFindManyMock,
+  semesterMock,
+} = vi.hoisted(() => ({
+  buildSuggestionsMock: vi.fn().mockResolvedValue({}),
+  getLatestCommentsMock: vi.fn().mockResolvedValue([]),
+  sectionFindFirstMock: vi.fn(),
+  sectionFindManyMock: vi.fn().mockResolvedValue([]),
+  semesterMock: {
+    code: "2026-spring",
+    id: 44,
+    nameCn: "2026年春季学期",
+  },
+}));
+
+vi.mock("@/features/catalog/server/section-code-match-semester", () => ({
+  resolveSectionCodeMatchSemester: vi.fn().mockResolvedValue(semesterMock),
+}));
+
+vi.mock("@/features/catalog/server/section-code-match-suggestions", () => ({
+  buildSectionCodeSuggestions: buildSuggestionsMock,
+}));
+
+vi.mock("@/features/comments/server/latest-comments", () => ({
+  getLatestComments: getLatestCommentsMock,
+}));
+
+vi.mock("@/lib/db/prisma", () => ({
+  getPrisma: () => ({
+    section: { findMany: sectionFindManyMock },
+  }),
+  prisma: {
+    section: {
+      findFirst: sectionFindFirstMock,
+      findMany: sectionFindManyMock,
+    },
+  },
+}));
+
+describe("retired Section discovery boundaries", () => {
+  beforeEach(() => {
+    sectionFindFirstMock.mockReset().mockResolvedValue(null);
+    sectionFindManyMock.mockReset().mockResolvedValue([]);
+    buildSuggestionsMock.mockClear();
+    getLatestCommentsMock.mockReset().mockResolvedValue([]);
+  });
+
+  it("excludes retired rows from public code matching", async () => {
+    const { findSectionCodeMatches } = await import(
+      "@/features/catalog/server/section-code-match-query"
+    );
+
+    await findSectionCodeMatches(["CS100"]);
+
+    expect(sectionFindManyMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        where: {
+          code: { in: ["CS100"] },
+          retiredAt: null,
+          semesterId: semesterMock.id,
+        },
+      }),
+    );
+  });
+
+  it("loads retirement state for historical Section detail UI", async () => {
+    const { sectionPageSelect } = await import(
+      "@/features/section-detail/server/section-page-select"
+    );
+
+    expect(sectionPageSelect.retiredAt).toBe(true);
+  });
+
+  it("excludes retired rows from public related-Section discovery", async () => {
+    const commentCount = vi.fn().mockResolvedValue(0);
+    const { getSectionPageRelatedData } = await import(
+      "@/features/section-detail/server/section-page-related-data"
+    );
+
+    await getSectionPageRelatedData({
+      locale: "zh-cn",
+      prisma: {
+        comment: { count: commentCount },
+        section: { findMany: sectionFindManyMock },
+      } as never,
+      section: {
+        courseId: 77,
+        id: 11,
+        semesterId: 44,
+        teachers: [{ id: 5 }],
+      },
+    });
+
+    expect(sectionFindManyMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        where: {
+          courseId: 77,
+          id: { not: 11 },
+          retiredAt: null,
+        },
+      }),
+    );
+  });
+
+  it("counts only active Sections in public teacher results", async () => {
+    const { teacherListInclude } = await import(
+      "@/features/catalog/server/academic-query-includes"
+    );
+
+    expect(teacherListInclude._count.select.sections).toEqual({
+      where: { retiredAt: null },
+    });
+  });
+
+  it("rejects retired rows for add/set resolution but allows removal resolution", async () => {
+    const { resolveCalendarSubscriptionSections } = await import(
+      "@/features/subscriptions/server/subscription-section-resolver"
+    );
+
+    await resolveCalendarSubscriptionSections({ sectionIds: [11] });
+    expect(sectionFindManyMock).toHaveBeenLastCalledWith(
+      expect.objectContaining({
+        where: { id: { in: [11] }, retiredAt: null },
+      }),
+    );
+
+    await resolveCalendarSubscriptionSections({
+      includeRetired: true,
+      sectionIds: [11],
+    });
+    expect(sectionFindManyMock).toHaveBeenLastCalledWith(
+      expect.objectContaining({
+        where: { id: { in: [11] } },
+      }),
+    );
+  });
+
+  it("requires an active row to subscribe but accepts a retired row to unsubscribe", async () => {
+    const { subscribeUserToSectionByJwId, unsubscribeUserFromSectionByJwId } =
+      await import("@/features/subscriptions/server/subscription-write-model");
+
+    await subscribeUserToSectionByJwId("user-1", 101);
+    expect(sectionFindFirstMock).toHaveBeenLastCalledWith({
+      where: { jwId: 101, retiredAt: null },
+      select: { id: true },
+    });
+
+    await unsubscribeUserFromSectionByJwId("user-1", 102);
+    expect(sectionFindFirstMock).toHaveBeenLastCalledWith({
+      where: { jwId: 102 },
+      select: { id: true },
+    });
+  });
+
+  it("allows GraphQL removal to resolve a retired subscription", async () => {
+    const { setUserSectionSubscriptionByJwId } = await import(
+      "@/features/subscriptions/server/subscription-write-model"
+    );
+
+    await setUserSectionSubscriptionByJwId({
+      sectionJwId: 103,
+      subscribed: false,
+      userId: "user-1",
+    });
+
+    expect(sectionFindFirstMock).toHaveBeenLastCalledWith({
+      where: { jwId: 103 },
+      select: { id: true },
+    });
+  });
+});
diff --git a/tests/unit/schedule-queries.test.ts b/tests/unit/schedule-queries.test.ts
index 3d92c63a7..e4db7ccf6 100644
--- a/tests/unit/schedule-queries.test.ts
+++ b/tests/unit/schedule-queries.test.ts
@@ -2,6 +2,17 @@ import { describe, expect, it } from "vitest";
 import { buildScheduleListWhere } from "@/features/catalog/lib/schedule-filters";
 
 describe("buildScheduleListWhere", () => {
+  it("can exclude retired Sections for current public schedule lists", () => {
+    expect(
+      buildScheduleListWhere(
+        { sectionJwId: 9902001 },
+        { excludeRetiredSections: true },
+      ),
+    ).toEqual({
+      section: { jwId: 9902001, retiredAt: null },
+    });
+  });
+
   it("无过滤条件时返回空 where 子句", () => {
     expect(buildScheduleListWhere({})).toEqual({});
   });
diff --git a/tests/unit/section-lifecycle-lock.test.ts b/tests/unit/section-lifecycle-lock.test.ts
new file mode 100644
index 000000000..f2f35e9fd
--- /dev/null
+++ b/tests/unit/section-lifecycle-lock.test.ts
@@ -0,0 +1,36 @@
+import { describe, expect, it, vi } from "vitest";
+import { acquireSectionLifecycleAdvisoryLocks } from "@/lib/db/section-lifecycle-lock";
+
+describe("Section lifecycle advisory locks", () => {
+  it("deduplicates and sorts shared lock IDs in one materialized query", async () => {
+    const queryRawUnsafe = vi.fn().mockResolvedValue([]);
+
+    await acquireSectionLifecycleAdvisoryLocks(
+      { $queryRawUnsafe: queryRawUnsafe },
+      [12, 3, 12],
+      "shared",
+    );
+
+    expect(queryRawUnsafe).toHaveBeenCalledOnce();
+    const [sql, namespace, ...ids] = queryRawUnsafe.mock.calls[0];
+    expect(sql).toContain("WITH lock_ids AS MATERIALIZED");
+    expect(sql).toContain("pg_advisory_xact_lock_shared");
+    expect(sql).toContain('::text AS "acquired"');
+    expect(sql).toContain("ARRAY[$2,$3]::integer[]");
+    expect(sql).toContain('ORDER BY "id"');
+    expect(namespace).toBe("life-ustc-section-lifecycle");
+    expect(ids).toEqual([3, 12]);
+  });
+
+  it("uses blocking exclusive locks for lifecycle state changes", async () => {
+    const queryRawUnsafe = vi.fn().mockResolvedValue([]);
+
+    await acquireSectionLifecycleAdvisoryLocks(
+      { $queryRawUnsafe: queryRawUnsafe },
+      [9],
+      "exclusive",
+    );
+
+    expect(queryRawUnsafe.mock.calls[0][0]).toContain("pg_advisory_xact_lock(");
+  });
+});
diff --git a/tests/unit/section-lifecycle-queries.test.ts b/tests/unit/section-lifecycle-queries.test.ts
new file mode 100644
index 000000000..bb8cf2880
--- /dev/null
+++ b/tests/unit/section-lifecycle-queries.test.ts
@@ -0,0 +1,123 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const {
+  localizedUserFindUniqueMock,
+  sectionFindManyMock,
+  sectionFindUniqueMock,
+  userFindUniqueMock,
+} = vi.hoisted(() => ({
+  localizedUserFindUniqueMock: vi.fn(),
+  sectionFindManyMock: vi.fn(),
+  sectionFindUniqueMock: vi.fn(),
+  userFindUniqueMock: vi.fn(),
+}));
+
+vi.mock("@/lib/db/prisma", () => ({
+  getPrisma: () => ({
+    user: { findUnique: localizedUserFindUniqueMock },
+  }),
+  prisma: {
+    section: {
+      findMany: sectionFindManyMock,
+      findUnique: sectionFindUniqueMock,
+    },
+    user: { findUnique: userFindUniqueMock },
+  },
+}));
+
+describe("retired Section query contracts", () => {
+  beforeEach(() => {
+    sectionFindManyMock.mockReset().mockResolvedValue([]);
+    sectionFindUniqueMock.mockReset().mockResolvedValue(null);
+    localizedUserFindUniqueMock.mockReset().mockResolvedValue(null);
+    userFindUniqueMock.mockReset().mockResolvedValue(null);
+  });
+
+  it("excludes retired rows from a multi-section calendar export", async () => {
+    const { getSectionsForCalendar } = await import(
+      "@/features/calendar/server/calendar-export-data"
+    );
+
+    await getSectionsForCalendar([11, 12]);
+
+    expect(sectionFindManyMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        where: {
+          id: { in: [11, 12] },
+          retiredAt: null,
+        },
+      }),
+    );
+  });
+
+  it("keeps direct historical Section calendar access available", async () => {
+    const { getSectionForCalendar } = await import(
+      "@/features/calendar/server/calendar-export-data"
+    );
+
+    await getSectionForCalendar(101);
+
+    expect(sectionFindUniqueMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        where: { jwId: 101 },
+      }),
+    );
+  });
+
+  it("excludes retired rows from the generated personal calendar only", async () => {
+    const { getUserCalendarRecord } = await import(
+      "@/features/calendar/server/calendar-export-data"
+    );
+
+    await getUserCalendarRecord("user-1");
+
+    expect(userFindUniqueMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        include: expect.objectContaining({
+          subscribedSections: expect.objectContaining({
+            where: { retiredAt: null },
+          }),
+        }),
+      }),
+    );
+  });
+
+  it("keeps retired rows in the user's owned subscription history", async () => {
+    const { getUserCalendarSubscription } = await import(
+      "@/features/subscriptions/server/subscription-calendar-read-model"
+    );
+
+    await getUserCalendarSubscription("user-1");
+
+    expect(localizedUserFindUniqueMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        select: expect.objectContaining({
+          subscribedSections: expect.not.objectContaining({
+            where: expect.anything(),
+          }),
+        }),
+      }),
+    );
+  });
+
+  it("derives current calendar IDs from active owned subscriptions", async () => {
+    const { getActiveSubscribedSectionIds } = await import(
+      "@/features/subscriptions/server/subscription-read-model-shared"
+    );
+
+    await getActiveSubscribedSectionIds("user-1", [11, 12]);
+
+    expect(userFindUniqueMock).toHaveBeenCalledWith({
+      where: { id: "user-1" },
+      select: {
+        subscribedSections: {
+          where: {
+            id: { in: [11, 12] },
+            retiredAt: null,
+          },
+          select: { id: true },
+        },
+      },
+    });
+  });
+});
diff --git a/tests/unit/static-import-lifecycle-order.test.ts b/tests/unit/static-import-lifecycle-order.test.ts
new file mode 100644
index 000000000..e49848e25
--- /dev/null
+++ b/tests/unit/static-import-lifecycle-order.test.ts
@@ -0,0 +1,46 @@
+import { readFile } from "node:fs/promises";
+import { describe, expect, it } from "vitest";
+
+async function importSource() {
+  return readFile(
+    new URL("../../src/static-loader/import.ts", import.meta.url),
+    "utf8",
+  );
+}
+
+function stageIndex(source: string, stage: string) {
+  const index = source.indexOf(`"${stage}",`);
+  expect(index, `missing static import stage ${stage}`).toBeGreaterThan(-1);
+  return index;
+}
+
+describe("static Section lifecycle orchestration", () => {
+  it("acquires lifecycle locks only after the long import stages and counts", async () => {
+    const source = await importSource();
+    const lifecycleIndex = stageIndex(
+      source,
+      "reconcileSectionSourceLifecycle",
+    );
+
+    for (const stage of [
+      "upsertScheduleGroups",
+      "writeSectionTeachers",
+      "writeTeacherAssignments",
+      "writeAdminClassSections",
+      "writeSchedules",
+      "reconcileCatalogTeacherFallbacks",
+      "upsertExams",
+      "writeExamRooms",
+      "reconcileRemovedSnapshotRows",
+      "mergeLegacyCourseDuplicates",
+      "countDatabaseRecords",
+    ]) {
+      expect(lifecycleIndex).toBeGreaterThan(stageIndex(source, stage));
+    }
+    const importStateIndex = stageIndex(source, "recordStaticImportState");
+    expect(importStateIndex).toBeGreaterThan(lifecycleIndex);
+    expect(source.indexOf("logStep(", lifecycleIndex)).toBe(
+      source.lastIndexOf("logStep(", importStateIndex),
+    );
+  });
+});
diff --git a/tests/unit/static-import-state.test.ts b/tests/unit/static-import-state.test.ts
new file mode 100644
index 000000000..7bbb05f65
--- /dev/null
+++ b/tests/unit/static-import-state.test.ts
@@ -0,0 +1,163 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import {
+  assertStaticImportStateAllowsSnapshot,
+  recordStaticImportState,
+} from "@/static-loader/import-state";
+
+const SNAPSHOT_SHA = "a".repeat(64);
+const OTHER_SNAPSHOT_SHA = "b".repeat(64);
+const OBSERVED_AT = new Date("2026-07-18T03:00:00.000Z");
+
+function stateClient() {
+  return {
+    staticImportState: {
+      findUnique: vi.fn(),
+      upsert: vi.fn().mockResolvedValue({}),
+    },
+  };
+}
+
+function input(
+  overrides: Partial<
+    Parameters<typeof assertStaticImportStateAllowsSnapshot>[1]
+  > = {},
+) {
+  return {
+    bootstrapEnabled: false,
+    dryRun: false,
+    expectedSnapshotSha256: null,
+    observedAt: OBSERVED_AT,
+    retirementEnabled: false,
+    snapshotSha256: SNAPSHOT_SHA,
+    ...overrides,
+  };
+}
+
+describe("global static import state", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("fails closed when the first import is not an explicit bootstrap", async () => {
+    const tx = stateClient();
+    tx.staticImportState.findUnique.mockResolvedValue(null);
+
+    await expect(
+      assertStaticImportStateAllowsSnapshot(tx, input()),
+    ).rejects.toThrow("manual bootstrap");
+    expect(tx.staticImportState.upsert).not.toHaveBeenCalled();
+  });
+
+  it("allows an uncommitted bootstrap dry run without an approval hash", async () => {
+    const tx = stateClient();
+    tx.staticImportState.findUnique.mockResolvedValue(null);
+
+    await expect(
+      assertStaticImportStateAllowsSnapshot(
+        tx,
+        input({ bootstrapEnabled: true, dryRun: true }),
+      ),
+    ).resolves.toBeUndefined();
+  });
+
+  it("requires the exact hash and disables retirement for a committed bootstrap", async () => {
+    const tx = stateClient();
+    tx.staticImportState.findUnique.mockResolvedValue(null);
+
+    await expect(
+      assertStaticImportStateAllowsSnapshot(
+        tx,
+        input({ bootstrapEnabled: true }),
+      ),
+    ).rejects.toThrow("required for a committed");
+    await expect(
+      assertStaticImportStateAllowsSnapshot(
+        tx,
+        input({
+          bootstrapEnabled: true,
+          expectedSnapshotSha256: OTHER_SNAPSHOT_SHA,
+        }),
+      ),
+    ).rejects.toThrow("does not match downloaded snapshot");
+    await expect(
+      assertStaticImportStateAllowsSnapshot(
+        tx,
+        input({
+          bootstrapEnabled: true,
+          expectedSnapshotSha256: SNAPSHOT_SHA,
+          retirementEnabled: true,
+        }),
+      ),
+    ).rejects.toThrow("cannot run while bootstrapping");
+    await expect(
+      assertStaticImportStateAllowsSnapshot(
+        tx,
+        input({
+          bootstrapEnabled: true,
+          expectedSnapshotSha256: SNAPSHOT_SHA,
+        }),
+      ),
+    ).resolves.toBeUndefined();
+  });
+
+  it("rejects older snapshots and equal timestamps with different content", async () => {
+    const tx = stateClient();
+    tx.staticImportState.findUnique.mockResolvedValue({
+      snapshotGeneratedAt: new Date("2026-07-19T03:00:00.000Z"),
+      snapshotSha256: SNAPSHOT_SHA,
+    });
+
+    await expect(
+      assertStaticImportStateAllowsSnapshot(tx, input()),
+    ).rejects.toThrow("last committed snapshot");
+
+    tx.staticImportState.findUnique.mockResolvedValue({
+      snapshotGeneratedAt: OBSERVED_AT,
+      snapshotSha256: OTHER_SNAPSHOT_SHA,
+    });
+    await expect(
+      assertStaticImportStateAllowsSnapshot(tx, input()),
+    ).rejects.toThrow("already committed with SHA-256");
+  });
+
+  it("accepts an idempotent snapshot or a newer snapshot", async () => {
+    const tx = stateClient();
+    tx.staticImportState.findUnique.mockResolvedValue({
+      snapshotGeneratedAt: OBSERVED_AT,
+      snapshotSha256: SNAPSHOT_SHA,
+    });
+    await expect(
+      assertStaticImportStateAllowsSnapshot(tx, input()),
+    ).resolves.toBeUndefined();
+
+    tx.staticImportState.findUnique.mockResolvedValue({
+      snapshotGeneratedAt: new Date("2026-07-17T03:00:00.000Z"),
+      snapshotSha256: OTHER_SNAPSHOT_SHA,
+    });
+    await expect(
+      assertStaticImportStateAllowsSnapshot(tx, input()),
+    ).resolves.toBeUndefined();
+  });
+
+  it("records the watermark through the singleton upsert", async () => {
+    const tx = stateClient();
+
+    await recordStaticImportState(tx, {
+      observedAt: OBSERVED_AT,
+      snapshotSha256: SNAPSHOT_SHA,
+    });
+
+    expect(tx.staticImportState.upsert).toHaveBeenCalledWith({
+      where: { id: "global" },
+      create: {
+        id: "global",
+        snapshotGeneratedAt: OBSERVED_AT,
+        snapshotSha256: SNAPSHOT_SHA,
+      },
+      update: {
+        snapshotGeneratedAt: OBSERVED_AT,
+        snapshotSha256: SNAPSHOT_SHA,
+      },
+    });
+  });
+});
diff --git a/tests/unit/static-loader-future-snapshot.test.ts b/tests/unit/static-loader-future-snapshot.test.ts
new file mode 100644
index 000000000..1aa96bd84
--- /dev/null
+++ b/tests/unit/static-loader-future-snapshot.test.ts
@@ -0,0 +1,65 @@
+/// <reference path="../../src/static-loader/bun-sqlite.d.ts" />
+
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+const { closeMock, queryAllMock, transactionMock } = vi.hoisted(() => ({
+  closeMock: vi.fn(),
+  queryAllMock: vi.fn(),
+  transactionMock: vi.fn(),
+}));
+
+vi.mock("@/static-loader/snapshot", () => ({
+  Snapshot: class {
+    close() {
+      closeMock();
+    }
+
+    metadata() {
+      return {
+        generated_at: "2099-01-01T00:00:00.000Z",
+        schema_version: "5",
+      };
+    }
+
+    queryAll() {
+      return queryAllMock();
+    }
+  },
+}));
+
+afterEach(() => {
+  vi.useRealTimers();
+  vi.clearAllMocks();
+});
+
+describe("static loader snapshot time gate", () => {
+  it("rejects a far-future snapshot before writes when retirement is disabled", async () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-07-18T03:00:00.000Z"));
+    const { runImport } = await import("@/static-loader/import");
+
+    await expect(
+      runImport(
+        {
+          $transaction: transactionMock,
+        } as never,
+        {
+          bootstrapImportState: false,
+          dryRun: false,
+          expectedSectionRetirementCandidates: null,
+          expectedSnapshotSha256: null,
+          minSemester: 401,
+          retireMissingSections: false,
+          snapshotPath: "/not-read.sqlite",
+          snapshotSha256: "a".repeat(64),
+        },
+      ),
+    ).rejects.toThrow(
+      "snapshot metadata generated_at must not be more than 15 minutes in the future",
+    );
+
+    expect(queryAllMock).not.toHaveBeenCalled();
+    expect(transactionMock).not.toHaveBeenCalled();
+    expect(closeMock).toHaveBeenCalledOnce();
+  });
+});
diff --git a/tests/unit/static-loader-validation.test.ts b/tests/unit/static-loader-validation.test.ts
index cab578ce5..a80b44b48 100644
--- a/tests/unit/static-loader-validation.test.ts
+++ b/tests/unit/static-loader-validation.test.ts
@@ -2,7 +2,12 @@ import { describe, expect, it } from "vitest";
 import {
   missingSnapshotRowsWhere,
   parseBooleanSetting,
+  parseOptionalNonNegativeIntegerSetting,
+  parseOptionalSha256Setting,
   parsePositiveIntegerSetting,
+  parseSnapshotGeneratedAt,
+  validateMappedSectionJwIds,
+  validateSectionRetirementSnapshotApproval,
   validateSnapshotCompleteness,
 } from "@/static-loader/validation";
 
@@ -11,7 +16,10 @@ function semesterRows(...ids: number[]) {
 }
 
 function lessonRows(semesterId: number, count: number) {
-  return Array.from({ length: count }, () => ({ semester_id: semesterId }));
+  return Array.from({ length: count }, (_, index) => ({
+    id: semesterId * 10_000 + index,
+    semester_id: semesterId,
+  }));
 }
 
 function fetchRow(
@@ -61,6 +69,23 @@ describe("static loader configuration", () => {
     ).toThrow("STATIC_LOADER_DRY_RUN");
   });
 
+  it("keeps missing-Section retirement disabled unless explicitly enabled", () => {
+    expect(
+      parseBooleanSetting(
+        "STATIC_LOADER_RETIRE_MISSING_SECTIONS",
+        undefined,
+        false,
+      ),
+    ).toBe(false);
+    expect(
+      parseBooleanSetting(
+        "STATIC_LOADER_RETIRE_MISSING_SECTIONS",
+        "true",
+        false,
+      ),
+    ).toBe(true);
+  });
+
   it.each([
     [undefined, 401],
     ["401", 401],
@@ -82,6 +107,94 @@ describe("static loader configuration", () => {
       parsePositiveIntegerSetting("STATIC_LOADER_MIN_SEMESTER", value, 401),
     ).toThrow("STATIC_LOADER_MIN_SEMESTER");
   });
+
+  it("parses optional retirement approval settings", () => {
+    expect(
+      parseOptionalNonNegativeIntegerSetting(
+        "STATIC_LOADER_EXPECTED_SECTION_RETIREMENT_CANDIDATES",
+        "0",
+      ),
+    ).toBe(0);
+    expect(
+      parseOptionalNonNegativeIntegerSetting(
+        "STATIC_LOADER_EXPECTED_SECTION_RETIREMENT_CANDIDATES",
+        "",
+      ),
+    ).toBeNull();
+    expect(
+      parseOptionalSha256Setting(
+        "STATIC_LOADER_EXPECTED_SNAPSHOT_SHA256",
+        "A".repeat(64),
+      ),
+    ).toBe("a".repeat(64));
+  });
+
+  it("requires an exact snapshot approval before retirement", () => {
+    expect(() =>
+      validateSectionRetirementSnapshotApproval({
+        enabled: true,
+        expectedSnapshotSha256: null,
+        snapshotSha256: "a".repeat(64),
+      }),
+    ).toThrow("STATIC_LOADER_EXPECTED_SNAPSHOT_SHA256");
+    expect(() =>
+      validateSectionRetirementSnapshotApproval({
+        enabled: true,
+        expectedSnapshotSha256: "b".repeat(64),
+        snapshotSha256: "a".repeat(64),
+      }),
+    ).toThrow("does not match downloaded snapshot");
+  });
+
+  it("requires a valid snapshot generation timestamp", () => {
+    const now = new Date("2026-07-18T03:00:00.000Z");
+    expect(parseSnapshotGeneratedAt("2026-07-18T03:00:00.000Z", now)).toEqual(
+      new Date("2026-07-18T03:00:00.000Z"),
+    );
+    expect(
+      parseSnapshotGeneratedAt("2026-07-18T03:00:00.123456+00:00", now),
+    ).toEqual(new Date("2026-07-18T03:00:00.123Z"));
+    expect(() => parseSnapshotGeneratedAt(undefined, now)).toThrow("required");
+    expect(() => parseSnapshotGeneratedAt("not-a-date", now)).toThrow(
+      "valid timestamp",
+    );
+  });
+
+  it.each([
+    "2026-02-30T03:00:00.000Z",
+    "2026-07-18 03:00:00.000Z",
+    "2026-07-18T03:00Z",
+    "2026-07-18T03:00:00.000",
+  ])("rejects non-RFC 3339 snapshot timestamp %s", (value) => {
+    expect(() =>
+      parseSnapshotGeneratedAt(value, new Date("2026-07-18T03:00:00.000Z")),
+    ).toThrow("RFC 3339");
+  });
+
+  it("accepts the maximum future clock skew boundary", () => {
+    const now = new Date("2026-07-18T03:00:00.000Z");
+    expect(parseSnapshotGeneratedAt("2026-07-18T03:15:00.000Z", now)).toEqual(
+      new Date("2026-07-18T03:15:00.000Z"),
+    );
+  });
+
+  it("rejects far-future metadata", () => {
+    expect(() =>
+      parseSnapshotGeneratedAt(
+        "2099-01-01T00:00:00.000Z",
+        new Date("2026-07-18T03:00:00.000Z"),
+      ),
+    ).toThrow("must not be more than 15 minutes in the future");
+  });
+
+  it("rejects timestamps beyond the future clock skew boundary", () => {
+    expect(() =>
+      parseSnapshotGeneratedAt(
+        "2026-07-18T03:15:00.001Z",
+        new Date("2026-07-18T03:00:00.000Z"),
+      ),
+    ).toThrow("must not be more than 15 minutes in the future");
+  });
 });
 
 describe("snapshot completeness validation", () => {
@@ -91,17 +204,18 @@ describe("snapshot completeness validation", () => {
   };
 
   it("accepts all expected JW chunks and a zero-lesson semester", () => {
-    expect(() =>
-      validateSnapshotCompleteness(
-        {
-          metadata,
-          semesterRows: semesterRows(381, 401, 421),
-          catalogLessonRows: [...lessonRows(401, 101), ...lessonRows(421, 0)],
-          fetchRows: [...completeFetches(401, 2), ...completeFetches(421, 0)],
-        },
-        401,
-      ),
-    ).not.toThrow();
+    const result = validateSnapshotCompleteness(
+      {
+        metadata,
+        semesterRows: semesterRows(381, 401, 421),
+        catalogLessonRows: [...lessonRows(401, 101), ...lessonRows(421, 0)],
+        fetchRows: [...completeFetches(401, 2), ...completeFetches(421, 0)],
+      },
+      401,
+    );
+
+    expect(result.sectionJwIds).toHaveLength(101);
+    expect(result.sectionSemesterJwIds).toEqual([401]);
   });
 
   it("rejects a failed JW chunk", () => {
@@ -204,6 +318,29 @@ describe("snapshot completeness validation", () => {
       ),
     ).not.toThrow();
   });
+
+  it("rejects an in-scope lesson without a usable Section jwId", () => {
+    expect(() =>
+      validateSnapshotCompleteness(
+        {
+          metadata,
+          semesterRows: semesterRows(401),
+          catalogLessonRows: [{ semester_id: 401 }],
+          fetchRows: completeFetches(401, 1),
+        },
+        401,
+      ),
+    ).toThrow("invalid Section jwId");
+  });
+
+  it("rejects incomplete or duplicate mapped Section sets", () => {
+    expect(() => validateMappedSectionJwIds([101, 102], [101])).toThrow(
+      "missing jwIds=102",
+    );
+    expect(() =>
+      validateMappedSectionJwIds([101, 102], [101, 102, 102]),
+    ).toThrow("duplicate jwIds=102");
+  });
 });
 
 describe("snapshot reconciliation scope", () => {
diff --git a/tests/unit/static-section-lifecycle.test.ts b/tests/unit/static-section-lifecycle.test.ts
new file mode 100644
index 000000000..10e846606
--- /dev/null
+++ b/tests/unit/static-section-lifecycle.test.ts
@@ -0,0 +1,321 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import {
+  assertSectionSnapshotNotOlderThanSource,
+  reconcileSectionSourceLifecycle,
+} from "@/static-loader/section-lifecycle";
+
+const OBSERVED_AT = new Date("2026-07-18T03:00:00.000Z");
+const PREVIOUSLY_RETIRED_AT = new Date("2026-07-17T03:00:00.000Z");
+const PREVIOUSLY_SEEN_AT = new Date("2026-07-16T03:00:00.000Z");
+
+function lifecycleClient() {
+  return {
+    $queryRawUnsafe: vi.fn().mockResolvedValue([]),
+    auditLog: {
+      createMany: vi.fn().mockResolvedValue({ count: 0 }),
+    },
+    section: {
+      count: vi.fn(),
+      findFirst: vi.fn().mockResolvedValue(null),
+      findMany: vi.fn(),
+      updateMany: vi.fn().mockResolvedValue({ count: 0 }),
+    },
+  };
+}
+
+describe("static Section source lifecycle", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("reactivates seen rows, retires only missing in-scope rows, and audits both", async () => {
+    const tx = lifecycleClient();
+    tx.section.count.mockResolvedValueOnce(8).mockResolvedValueOnce(2);
+    tx.section.findMany
+      .mockResolvedValueOnce([
+        {
+          id: 11,
+          jwId: 101,
+          retiredAt: PREVIOUSLY_RETIRED_AT,
+        },
+      ])
+      .mockResolvedValueOnce([
+        {
+          id: 12,
+          jwId: 102,
+          sourceLastSeenAt: PREVIOUSLY_SEEN_AT,
+        },
+      ])
+      .mockResolvedValueOnce([
+        {
+          id: 11,
+          jwId: 101,
+          retiredAt: PREVIOUSLY_RETIRED_AT,
+          sourceLastSeenAt: PREVIOUSLY_SEEN_AT,
+        },
+        {
+          id: 12,
+          jwId: 102,
+          retiredAt: null,
+          sourceLastSeenAt: PREVIOUSLY_SEEN_AT,
+        },
+      ]);
+
+    const result = await reconcileSectionSourceLifecycle(tx, {
+      observedAt: OBSERVED_AT,
+      retirementEnabled: true,
+      expectedRetirementCandidateCount: 1,
+      scopedSemesterIds: [41, 42],
+      seenSectionJwIds: [101, 103],
+      snapshotSha256: "snapshot-sha",
+    });
+
+    expect(tx.section.updateMany).toHaveBeenNthCalledWith(1, {
+      where: {
+        semesterId: { in: [41, 42] },
+        jwId: { in: [101, 103] },
+        retiredAt: null,
+        OR: [
+          { sourceLastSeenAt: null },
+          { sourceLastSeenAt: { lt: OBSERVED_AT } },
+        ],
+      },
+      data: {
+        sourceLastSeenAt: OBSERVED_AT,
+      },
+    });
+    expect(tx.section.updateMany).toHaveBeenNthCalledWith(2, {
+      where: {
+        id: { in: [11] },
+        retiredAt: { lt: OBSERVED_AT },
+      },
+      data: {
+        sourceLastSeenAt: OBSERVED_AT,
+        retiredAt: null,
+      },
+    });
+    expect(tx.section.updateMany).toHaveBeenNthCalledWith(3, {
+      where: { id: { in: [12] }, retiredAt: null },
+      data: { retiredAt: OBSERVED_AT },
+    });
+    expect(tx.auditLog.createMany).toHaveBeenCalledWith({
+      data: [
+        expect.objectContaining({
+          action: "section_reactivate",
+          targetId: "11",
+          targetType: "section",
+          metadata: expect.objectContaining({
+            jwId: 101,
+            observedAt: OBSERVED_AT.toISOString(),
+            previousRetiredAt: PREVIOUSLY_RETIRED_AT.toISOString(),
+            snapshotSha256: "snapshot-sha",
+            source: "static-loader",
+          }),
+        }),
+        expect.objectContaining({
+          action: "section_retire",
+          targetId: "12",
+          targetType: "section",
+          metadata: expect.objectContaining({
+            jwId: 102,
+            observedAt: OBSERVED_AT.toISOString(),
+            previousSourceLastSeenAt: PREVIOUSLY_SEEN_AT.toISOString(),
+            snapshotSha256: "snapshot-sha",
+            source: "static-loader",
+          }),
+        }),
+      ],
+    });
+    expect(result).toEqual({
+      enabled: true,
+      scopeSemesterCount: 2,
+      seenSectionCount: 2,
+      retirementCandidateCount: 1,
+      retiredCount: 1,
+      reactivatedCount: 1,
+      before: { active: 8, retired: 2, total: 10 },
+      after: { active: 8, retired: 2, total: 10 },
+    });
+  });
+
+  it("reports candidates but cannot retire them without the explicit opt-in", async () => {
+    const tx = lifecycleClient();
+    tx.section.count.mockResolvedValueOnce(8).mockResolvedValueOnce(0);
+    tx.section.findMany.mockResolvedValueOnce([]).mockResolvedValueOnce([
+      {
+        id: 12,
+        jwId: 102,
+        sourceLastSeenAt: PREVIOUSLY_SEEN_AT,
+      },
+    ]);
+
+    const result = await reconcileSectionSourceLifecycle(tx, {
+      observedAt: OBSERVED_AT,
+      retirementEnabled: false,
+      expectedRetirementCandidateCount: null,
+      scopedSemesterIds: [41],
+      seenSectionJwIds: [101],
+      snapshotSha256: "snapshot-sha",
+    });
+
+    expect(tx.section.updateMany).toHaveBeenCalledTimes(1);
+    expect(tx.auditLog.createMany).not.toHaveBeenCalled();
+    expect(result).toMatchObject({
+      enabled: false,
+      retirementCandidateCount: 1,
+      retiredCount: 0,
+      reactivatedCount: 0,
+      before: { active: 8, retired: 0, total: 8 },
+      after: { active: 8, retired: 0, total: 8 },
+    });
+  });
+
+  it("does nothing when the completeness gate yields no semester scope", async () => {
+    const tx = lifecycleClient();
+
+    await expect(
+      reconcileSectionSourceLifecycle(tx, {
+        observedAt: OBSERVED_AT,
+        retirementEnabled: true,
+        expectedRetirementCandidateCount: null,
+        scopedSemesterIds: [],
+        seenSectionJwIds: [],
+        snapshotSha256: "snapshot-sha",
+      }),
+    ).resolves.toEqual({
+      enabled: true,
+      scopeSemesterCount: 0,
+      seenSectionCount: 0,
+      retirementCandidateCount: 0,
+      retiredCount: 0,
+      reactivatedCount: 0,
+      before: { active: 0, retired: 0, total: 0 },
+      after: { active: 0, retired: 0, total: 0 },
+    });
+    expect(tx.section.findMany).not.toHaveBeenCalled();
+    expect(tx.section.updateMany).not.toHaveBeenCalled();
+    expect(tx.auditLog.createMany).not.toHaveBeenCalled();
+  });
+
+  it("rejects an older snapshot before writes regardless of retirement opt-in", async () => {
+    const tx = lifecycleClient();
+    const newerObservedAt = new Date("2026-07-19T03:00:00.000Z");
+    tx.section.findFirst.mockResolvedValueOnce({
+      jwId: 102,
+      sourceLastSeenAt: newerObservedAt,
+    });
+
+    await expect(
+      assertSectionSnapshotNotOlderThanSource(tx, {
+        observedAt: OBSERVED_AT,
+        scopedSemesterIds: [42, 41, 42],
+      }),
+    ).rejects.toThrow(
+      `Section 102 was observed in a newer snapshot at ${newerObservedAt.toISOString()}`,
+    );
+    expect(tx.section.findFirst).toHaveBeenCalledWith({
+      where: {
+        semesterId: { in: [41, 42] },
+        sourceLastSeenAt: { gt: OBSERVED_AT },
+      },
+      orderBy: { sourceLastSeenAt: "desc" },
+      select: { jwId: true, sourceLastSeenAt: true },
+    });
+    expect(tx.section.updateMany).not.toHaveBeenCalled();
+    expect(tx.auditLog.createMany).not.toHaveBeenCalled();
+  });
+
+  it("does not reactivate or regress a row from an older snapshot", async () => {
+    const tx = lifecycleClient();
+    tx.section.count.mockResolvedValueOnce(7).mockResolvedValueOnce(1);
+    tx.section.findMany.mockResolvedValueOnce([]).mockResolvedValueOnce([]);
+
+    const result = await reconcileSectionSourceLifecycle(tx, {
+      observedAt: OBSERVED_AT,
+      retirementEnabled: false,
+      expectedRetirementCandidateCount: null,
+      scopedSemesterIds: [41],
+      seenSectionJwIds: [101],
+      snapshotSha256: "older-snapshot",
+    });
+
+    expect(tx.section.findMany).toHaveBeenNthCalledWith(1, {
+      where: {
+        semesterId: { in: [41] },
+        jwId: { in: [101] },
+        retiredAt: { lt: OBSERVED_AT },
+      },
+      select: { id: true, jwId: true, retiredAt: true },
+    });
+    expect(tx.section.updateMany).toHaveBeenCalledOnce();
+    expect(result.reactivatedCount).toBe(0);
+    expect(tx.auditLog.createMany).not.toHaveBeenCalled();
+  });
+
+  it("fails closed when a destructive scope has no seen Sections", async () => {
+    const tx = lifecycleClient();
+
+    await expect(
+      reconcileSectionSourceLifecycle(tx, {
+        observedAt: OBSERVED_AT,
+        retirementEnabled: true,
+        expectedRetirementCandidateCount: 0,
+        scopedSemesterIds: [41],
+        seenSectionJwIds: [],
+        snapshotSha256: "snapshot-sha",
+      }),
+    ).rejects.toThrow("validated source set is empty");
+    expect(tx.section.count).not.toHaveBeenCalled();
+    expect(tx.section.updateMany).not.toHaveBeenCalled();
+  });
+
+  it("aborts before writes when the approved candidate count changed", async () => {
+    const tx = lifecycleClient();
+    tx.section.count.mockResolvedValueOnce(8).mockResolvedValueOnce(0);
+    tx.section.findMany
+      .mockResolvedValueOnce([])
+      .mockResolvedValueOnce([
+        { id: 12, jwId: 102, sourceLastSeenAt: PREVIOUSLY_SEEN_AT },
+      ]);
+
+    await expect(
+      reconcileSectionSourceLifecycle(tx, {
+        observedAt: OBSERVED_AT,
+        retirementEnabled: true,
+        expectedRetirementCandidateCount: 2,
+        scopedSemesterIds: [41],
+        seenSectionJwIds: [101],
+        snapshotSha256: "snapshot-sha",
+      }),
+    ).rejects.toThrow(
+      "Approved Section retirement candidate count 2 does not match actual count 1",
+    );
+    expect(tx.section.updateMany).not.toHaveBeenCalled();
+    expect(tx.auditLog.createMany).not.toHaveBeenCalled();
+  });
+
+  it("refuses to retire a row last seen by a newer snapshot", async () => {
+    const tx = lifecycleClient();
+    tx.section.count.mockResolvedValueOnce(8).mockResolvedValueOnce(0);
+    tx.section.findMany.mockResolvedValueOnce([]).mockResolvedValueOnce([
+      {
+        id: 12,
+        jwId: 102,
+        sourceLastSeenAt: new Date("2026-07-19T03:00:00.000Z"),
+      },
+    ]);
+
+    await expect(
+      reconcileSectionSourceLifecycle(tx, {
+        observedAt: OBSERVED_AT,
+        retirementEnabled: true,
+        expectedRetirementCandidateCount: 1,
+        scopedSemesterIds: [41],
+        seenSectionJwIds: [101],
+        snapshotSha256: "older-snapshot",
+      }),
+    ).rejects.toThrow("snapshot older than their latest source observation");
+    expect(tx.section.updateMany).not.toHaveBeenCalled();
+    expect(tx.auditLog.createMany).not.toHaveBeenCalled();
+  });
+});
diff --git a/tests/unit/subscription-semester-filters.test.ts b/tests/unit/subscription-semester-filters.test.ts
index f96032841..a47455706 100644
--- a/tests/unit/subscription-semester-filters.test.ts
+++ b/tests/unit/subscription-semester-filters.test.ts
@@ -85,6 +85,7 @@ describe("subscription semester filters", () => {
       expect.objectContaining({
         where: expect.objectContaining({
           sectionId: { in: [201, 202] },
+          section: { retiredAt: null },
         }),
       }),
     );
@@ -114,6 +115,7 @@ describe("subscription semester filters", () => {
       expect.objectContaining({
         where: expect.objectContaining({
           sectionId: { in: [301, 302] },
+          section: { retiredAt: null },
         }),
       }),
     );
diff --git a/tests/unit/viewer-page-services.test.ts b/tests/unit/viewer-page-services.test.ts
index 28154825d..caf14e739 100644
--- a/tests/unit/viewer-page-services.test.ts
+++ b/tests/unit/viewer-page-services.test.ts
@@ -169,6 +169,7 @@ describe("viewer page services", () => {
     const where = {
       section: {
         subscribedUsers: { some: { id: "user-1" } },
+        retiredAt: null,
         semesterId: 8,
       },
       date: { gte: dateFrom },
@@ -182,7 +183,11 @@ describe("viewer page services", () => {
             include: expect.objectContaining({
               department: true,
               teacherTitle: true,
-              _count: { select: { sections: true } },
+              _count: {
+                select: {
+                  sections: { where: { retiredAt: null } },
+                },
+              },
             }),
           },
         }),
@@ -210,6 +215,7 @@ describe("viewer page services", () => {
     const where = {
       section: {
         subscribedUsers: { some: { id: "user-1" } },
+        retiredAt: null,
         semesterId: 9,
       },
       OR: [{ examDate: { lte: dateTo } }],