diff --git a/devloop b/devloop
index 904caad..843a100 100755
--- a/devloop
+++ b/devloop
@@ -72,6 +72,12 @@ CODER_SESSION_ID=""
 REVIEWER_SESSION_ID=""
 PULL_REQUEST=""
 PULL_REQUEST_ERROR=""
+REVIEWED_HEAD=""
+ACCEPTED_HEAD=""
+REMOTE_HEAD=""
+CHECKS_STATE=""
+READINESS=""
+READINESS_DETAIL=""
 RUN_START_PASS=1
 VERIFY_LOG=""
 VERIFY_DETAIL=""
@@ -3060,6 +3066,10 @@ run_devloop() {
   FINAL_COMMIT_MESSAGE=""
   PULL_REQUEST=""
   PULL_REQUEST_ERROR=""
+  REVIEWED_HEAD=""
+  ACCEPTED_HEAD=""
+  READINESS=""
+  READINESS_DETAIL=""
   COMMIT_PASSES=()
   COMMIT_HASHES=()
   COMMIT_MESSAGES=()
@@ -3281,8 +3291,9 @@ run_devloop() {
     local review=".devloop/reviews/$slug-r$pass.md"
     local reviewer_log=".devloop/logs/$slug-r$pass-reviewer.log"
     local reviewer_id="reviewer-$pass"
+    REVIEWED_HEAD="$(head_sha "$repo")"
     event_step "$reviewer_id" "pass $pass/$max: $(agent_label "$reviewer") reviewing"
-    if run_agent "$reviewer" "$repo" "$repo/$reviewer_session" "$repo/$reviewer_log" "$(review_prompt "$coder" "$run_spec" "$TRACK" "$base" "$pass" "$review" "$slug" "$max" "$obligations_file" "$strict")" "$reviewer_id"; then
+    if run_agent "$reviewer" "$repo" "$repo/$reviewer_session" "$repo/$reviewer_log" "$(review_prompt "$coder" "$run_spec" "$TRACK" "$base" "$pass" "$review" "$slug" "$max" "$obligations_file" "$strict" "$REVIEWED_HEAD")" "$reviewer_id"; then
       event_done "$reviewer_id" true "done"
     else
       if [ "$RUN_TIMED_OUT" = true ]; then STATUS="timeout"; else STATUS="reviewer-error"; fi
@@ -3311,11 +3322,15 @@ run_devloop() {
     verdict="$(parse_verdict "$repo/$review")"
     if [ "$verdict" = "ACCEPT" ]; then
       event_gate "pass $pass review verdict" 1 "$verdict"
-      if [ "$strict" = true ] && ! has_passing_matrix "$repo/$review" "$obligations_file"; then
+      if head_drifted "$repo" "$REVIEWED_HEAD"; then
+        event_gate "pass $pass checkpoint" 0 "head moved off reviewed $(short_sha "$REVIEWED_HEAD")"
+        STATUS="head-drift"
+      elif [ "$strict" = true ] && ! has_passing_matrix "$repo/$review" "$obligations_file"; then
         STATUS="unclear"
       elif [ "$strict" = true ] && ! has_passing_quality_matrix "$repo/$review"; then
         STATUS="unclear"
       else
+        ACCEPTED_HEAD="$REVIEWED_HEAD"
         STATUS="accepted"
       fi
       break
@@ -3355,6 +3370,23 @@ run_devloop() {
     fi
   fi
 
+  if [ "$create_pr" = true ] && [ -n "$PULL_REQUEST" ] && [ "$STATUS" = "accepted" ]; then
+    event_step "final-verification" "verifying accepted checkpoint"
+    if final_verification "$repo" "$PULL_REQUEST" "$ACCEPTED_HEAD" "$initial_dirty"; then
+      event_done "final-verification" true "$READINESS_DETAIL"
+      event_step "pr-ready" "marking pull request ready for review"
+      if mark_pull_request_ready "$repo" "$PULL_REQUEST"; then
+        event_done "pr-ready" true "ready for human review"
+      else
+        READINESS="blocked"
+        READINESS_DETAIL="$PULL_REQUEST_ERROR"
+        event_done "pr-ready" false "$PULL_REQUEST_ERROR"
+      fi
+    else
+      event_done "final-verification" false "$READINESS_DETAIL"
+    fi
+  fi
+
   print_result
   rm -f "$criteria_file" "$obligations_file" "$initial_dirty"
   return 0
@@ -4483,6 +4515,7 @@ review_prompt() {
   local max="$8"
   local obligations_file="$9"
   local strict="${10}"
+  local checkpoint="${11:-}"
   local obligations priors review_skill strict_rule
   obligations="$(cat "$obligations_file")"
   priors="$(list_reviews "$slug" "$pass" "$max")"
@@ -4499,6 +4532,8 @@ Spec: $spec
 Track: $track
 Base: $base
 Pass: $pass
+Checkpoint: ${checkpoint:-unknown}
+Review exactly this checkpoint. Do not commit, amend, or push. Any new commit invalidates the verdict.
 Prior reviews:
 $priors
 Spec obligations (acceptance criteria, invariants, and failure modes):
@@ -4712,6 +4747,118 @@ parse_verdict() {
   sed -nE 's/^Verdict:[[:space:]]+(ACCEPT|REJECT|UNCLEAR).*/\1/p' "$file" | head -n 1
 }
 
+head_sha() {
+  local repo="$1"
+  git -C "$repo" rev-parse HEAD 2>/dev/null
+}
+
+short_sha() {
+  local sha="$1"
+  printf '%s\n' "${sha:0:7}"
+}
+
+head_drifted() {
+  local repo="$1"
+  local reviewed="$2"
+  local current
+  [ -n "$reviewed" ] || return 1
+  current="$(head_sha "$repo")" || return 1
+  [ "$current" != "$reviewed" ]
+}
+
+worktree_clean() {
+  local repo="$1"
+  local initial_dirty="$2"
+  local pending
+  pending="$(committable_paths "$repo" "$initial_dirty")"
+  [ -z "$pending" ]
+}
+
+remote_pull_request_head() {
+  local repo="$1"
+  local pr="$2"
+  local out
+  REMOTE_HEAD=""
+  if ! out="$(cd "$repo" >/dev/null 2>&1 && gh pr view "$pr" --json headRefOid --jq '.headRefOid // ""' 2>&1)"; then
+    PULL_REQUEST_ERROR="PR head lookup failed: $(gh_error_detail "$out")"
+    return 1
+  fi
+  REMOTE_HEAD="$(printf '%s\n' "$out" | sed '/^[[:space:]]*$/d' | head -n 1)"
+}
+
+pull_request_checks_state() {
+  local repo="$1"
+  local pr="$2"
+  local query out
+  CHECKS_STATE=""
+  query='[.statusCheckRollup[]?]
+    | if length == 0 then "none"
+      elif ([.[] | select((.conclusion // .state // "") | ascii_downcase | test("^(success|neutral|skipped)$"))] | length) == length then "green"
+      elif ([.[] | select((.conclusion // .state // "") == "")] | length) > 0 then "pending"
+      else "failing" end'
+  if ! out="$(cd "$repo" >/dev/null 2>&1 && gh pr view "$pr" --json statusCheckRollup --jq "$query" 2>&1)"; then
+    PULL_REQUEST_ERROR="PR checks lookup failed: $(gh_error_detail "$out")"
+    return 1
+  fi
+  CHECKS_STATE="$(printf '%s\n' "$out" | sed '/^[[:space:]]*$/d' | head -n 1)"
+}
+
+mark_pull_request_ready() {
+  local repo="$1"
+  local pr="$2"
+  local out
+  if ! run_compact_command "$repo" "mark pull request ready" gh pr ready "$pr"; then
+    out="$RUN_OUTPUT"
+    PULL_REQUEST_ERROR="PR ready failed: $(gh_error_detail "$out")"
+    return 1
+  fi
+}
+
+final_verification() {
+  local repo="$1"
+  local pr="$2"
+  local accepted="$3"
+  local initial_dirty="$4"
+  local local_head
+  READINESS="blocked"
+  READINESS_DETAIL=""
+  if [ -z "$accepted" ]; then
+    READINESS_DETAIL="no accepted checkpoint recorded"
+    return 1
+  fi
+  local_head="$(head_sha "$repo")"
+  if [ "$local_head" != "$accepted" ]; then
+    READINESS_DETAIL="local head $(short_sha "$local_head") moved off accepted checkpoint $(short_sha "$accepted")"
+    return 1
+  fi
+  if ! worktree_clean "$repo" "$initial_dirty"; then
+    READINESS_DETAIL="worktree has uncommitted task changes"
+    return 1
+  fi
+  if ! remote_pull_request_head "$repo" "$pr"; then
+    READINESS_DETAIL="$PULL_REQUEST_ERROR"
+    return 1
+  fi
+  if [ "$REMOTE_HEAD" != "$accepted" ]; then
+    READINESS_DETAIL="remote PR head $(short_sha "$REMOTE_HEAD") differs from accepted checkpoint $(short_sha "$accepted")"
+    return 1
+  fi
+  if ! pull_request_checks_state "$repo" "$pr"; then
+    READINESS_DETAIL="$PULL_REQUEST_ERROR"
+    return 1
+  fi
+  case "$CHECKS_STATE" in
+    green|none)
+      READINESS="ready"
+      READINESS_DETAIL="accepted checkpoint $(short_sha "$accepted") verified"
+      ;;
+    *)
+      READINESS_DETAIL="required checks are $CHECKS_STATE for $(short_sha "$accepted")"
+      return 1
+      ;;
+  esac
+}
+
 has_passing_matrix() {
   local file="$1"
   local obligations_file="$2"
@@ -5295,6 +5442,8 @@ print_result() {
   result_line "Branch" "$FINAL_BRANCH"
   result_line "Commit" "${FINAL_COMMIT:-none}"
   if [ "$WORKTREE_REPO" != "$SOURCE_REPO" ]; then result_line "Worktree" "$WORKTREE_REPO"; fi
+  if [ -n "$ACCEPTED_HEAD" ]; then result_line "Accepted" "$(short_sha "$ACCEPTED_HEAD")"; fi
+  if [ -n "$READINESS" ]; then result_line "Readiness" "$READINESS${READINESS_DETAIL:+ ($READINESS_DETAIL)}"; fi
   printf '\nOpen Next\n'
   if [ -n "$PULL_REQUEST" ]; then result_line "PR" "$PULL_REQUEST"; fi
   result_line "Report" "$(display_path "$REPORT")"
diff --git a/scripts/devloop_test.sh b/scripts/devloop_test.sh
index 4410895..6113dd8 100755
--- a/scripts/devloop_test.sh
+++ b/scripts/devloop_test.sh
@@ -1080,6 +1080,111 @@ PULL_REQUEST_ERROR=""
 if create_pull_request "$branch_repo" "feat/chat-retry" "main" >/dev/null 2>&1; then fail "pull request creation unexpectedly passed without remote"; fi
 contains "$PULL_REQUEST_ERROR" "branch push failed" "pull request push failure"
 contains "$PULL_REQUEST_ERROR" "repository exists" "pull request push failure"
+
+checkpoint_repo="$work/checkpoint-repo"
+git init -q "$checkpoint_repo"
+git -C "$checkpoint_repo" config user.email devloop-test@example.com
+git -C "$checkpoint_repo" config user.name "devloop test"
+printf 'one\n' > "$checkpoint_repo/file.txt"
+git -C "$checkpoint_repo" add file.txt
+git -C "$checkpoint_repo" commit -q -m init
+checkpoint_head="$(head_sha "$checkpoint_repo")"
+equals "$checkpoint_head" "$(git -C "$checkpoint_repo" rev-parse HEAD)" "head_sha resolves full sha"
+equals "$(short_sha "$checkpoint_head")" "${checkpoint_head:0:7}" "short_sha truncates"
+
+if head_drifted "$checkpoint_repo" "$checkpoint_head"; then fail "head_drifted reported drift on an unchanged head"; fi
+if head_drifted "$checkpoint_repo" ""; then fail "head_drifted reported drift without a reviewed checkpoint"; fi
+printf 'two\n' >> "$checkpoint_repo/file.txt"
+git -C "$checkpoint_repo" commit -q -am "second"
+head_drifted "$checkpoint_repo" "$checkpoint_head" || fail "head_drifted missed a new commit"
+ok "checkpoint drift detection"
+
+checkpoint_dirty="$work/checkpoint-dirty.txt"
+: > "$checkpoint_dirty"
+worktree_clean "$checkpoint_repo" "$checkpoint_dirty" || fail "worktree_clean rejected a clean worktree"
+printf 'scratch\n' > "$checkpoint_repo/extra.txt"
+if worktree_clean "$checkpoint_repo" "$checkpoint_dirty"; then fail "worktree_clean accepted an uncommitted change"; fi
+printf 'extra.txt\n' > "$checkpoint_dirty"
+worktree_clean "$checkpoint_repo" "$checkpoint_dirty" || fail "worktree_clean did not preserve pre-existing changes"
+rm -f "$checkpoint_repo/extra.txt"
+: > "$checkpoint_dirty"
+ok "worktree_clean preserves pre-existing changes"
+
+checkpoint_accepted="$(head_sha "$checkpoint_repo")"
+gh() {
+  case "$*" in
+    *"--json headRefOid"*) printf '%s\n' "$GH_STUB_HEAD" ;;
+    *"--json statusCheckRollup"*) printf '%s\n' "$GH_STUB_CHECKS" ;;
+    *"pr ready"*) [ "$GH_STUB_READY" = "ok" ] || { printf 'gh: not a draft\n'; return 1; }; printf 'marked ready\n' ;;
+    *) return "$GH_STUB_CODE" ;;
+  esac
+  return "$GH_STUB_CODE"
+}
+GH_STUB_CODE=0
+GH_STUB_HEAD="$checkpoint_accepted"
+GH_STUB_CHECKS="green"
+GH_STUB_READY="ok"
+
+remote_pull_request_head "$checkpoint_repo" "https://pr/1" || fail "remote_pull_request_head failed"
+equals "$REMOTE_HEAD" "$checkpoint_accepted" "remote_pull_request_head"
+pull_request_checks_state "$checkpoint_repo" "https://pr/1" || fail "pull_request_checks_state failed"
+equals "$CHECKS_STATE" "green" "pull_request_checks_state"
+mark_pull_request_ready "$checkpoint_repo" "https://pr/1" || fail "mark_pull_request_ready failed on a draft PR"
+
+final_verification "$checkpoint_repo" "https://pr/1" "$checkpoint_accepted" "$checkpoint_dirty" || fail "final_verification blocked a verified checkpoint"
+equals "$READINESS" "ready" "final_verification ready"
+contains "$READINESS_DETAIL" "$(short_sha "$checkpoint_accepted")" "final_verification detail names the checkpoint"
+
+if final_verification "$checkpoint_repo" "https://pr/1" "" "$checkpoint_dirty"; then fail "final_verification accepted an empty checkpoint"; fi
+contains "$READINESS_DETAIL" "no accepted checkpoint" "final_verification empty checkpoint detail"
+equals "$READINESS" "blocked" "final_verification blocked state"
+
+if final_verification "$checkpoint_repo" "https://pr/1" "$checkpoint_head" "$checkpoint_dirty"; then fail "final_verification accepted a stale local head"; fi
+contains "$READINESS_DETAIL" "moved off accepted checkpoint" "final_verification stale local head detail"
+
+GH_STUB_HEAD="0000000000000000000000000000000000000000"
+if final_verification "$checkpoint_repo" "https://pr/1" "$checkpoint_accepted" "$checkpoint_dirty"; then fail "final_verification accepted a mismatched remote head"; fi
+contains "$READINESS_DETAIL" "remote PR head" "final_verification remote head detail"
+GH_STUB_HEAD="$checkpoint_accepted"
+
+GH_STUB_CHECKS="pending"
+if final_verification "$checkpoint_repo" "https://pr/1" "$checkpoint_accepted" "$checkpoint_dirty"; then fail "final_verification accepted pending checks"; fi
+contains "$READINESS_DETAIL" "required checks are pending" "final_verification pending checks detail"
+
+GH_STUB_CHECKS="none"
+final_verification "$checkpoint_repo" "https://pr/1" "$checkpoint_accepted" "$checkpoint_dirty" || fail "final_verification blocked a PR with no checks"
+equals "$READINESS" "ready" "final_verification treats absent checks as ready"
+GH_STUB_CHECKS="green"
+
+printf 'dirty\n' > "$checkpoint_repo/uncommitted.txt"
+if final_verification "$checkpoint_repo" "https://pr/1" "$checkpoint_accepted" "$checkpoint_dirty"; then fail "final_verification accepted a dirty worktree"; fi
+contains "$READINESS_DETAIL" "uncommitted task changes" "final_verification dirty worktree detail"
+rm -f "$checkpoint_repo/uncommitted.txt"
+
+GH_STUB_CODE=1
+if remote_pull_request_head "$checkpoint_repo" "https://pr/1"; then fail "remote_pull_request_head ignored a gh failure"; fi
+contains "$PULL_REQUEST_ERROR" "PR head lookup failed" "remote_pull_request_head error"
+equals "$REMOTE_HEAD" "" "remote_pull_request_head clears its result on failure"
+if pull_request_checks_state "$checkpoint_repo" "https://pr/1"; then fail "pull_request_checks_state ignored a gh failure"; fi
+contains "$PULL_REQUEST_ERROR" "PR checks lookup failed" "pull_request_checks_state error"
+if final_verification "$checkpoint_repo" "https://pr/1" "$checkpoint_accepted" "$checkpoint_dirty"; then fail "final_verification accepted a gh lookup failure"; fi
+contains "$READINESS_DETAIL" "PR head lookup failed" "final_verification propagates lookup failure"
+GH_STUB_CODE=0
+
+GH_STUB_READY="fail"
+if mark_pull_request_ready "$checkpoint_repo" "https://pr/1"; then fail "mark_pull_request_ready ignored a gh failure"; fi
+contains "$PULL_REQUEST_ERROR" "PR ready failed" "mark_pull_request_ready error"
+GH_STUB_READY="ok"
+unset -f gh
+READINESS=""
+READINESS_DETAIL=""
+PULL_REQUEST_ERROR=""
+ok "final verification gates"
+
+: > "$work/empty-obligations.txt"
+contains "$(review_prompt codex spec.md track.md main 2 out.md slug 5 "$work/empty-obligations.txt" false abc1234)" "Checkpoint: abc1234" "review prompt checkpoint"
+contains "$(review_prompt codex spec.md track.md main 2 out.md slug 5 "$work/empty-obligations.txt" false abc1234)" "Do not commit, amend, or push" "review prompt checkpoint rule"
+contains "$(review_prompt codex spec.md track.md main 2 out.md slug 5 "$work/empty-obligations.txt" false)" "Checkpoint: unknown" "review prompt missing checkpoint"
 mkdir -p "$branch_repo/.devloop/reports" "$branch_repo/.devloop/tracks" "$branch_repo/.devloop/reviews"
 printf '%s\n' "# Report" > "$branch_repo/.devloop/reports/chat-retry.md"
 branch_repo_real="$(cd "$branch_repo" && pwd -P)"
@@ -2702,12 +2807,34 @@ case "${1:-}" in
         fi
         printf '%s\n' "commented"
         ;;
+      ready)
+        if [ "${DEVLOOP_GH_READY_FAIL:-0}" = "1" ]; then
+          printf '%s\n' "gh pr ready exploded" >&2
+          exit 1
+        fi
+        printf '%s\n' "ready" > "$state/pr_ready"
+        printf '%s\n' "marked ready"
+        ;;
       view)
         if [ "${DEVLOOP_GH_VIEW_FAIL:-0}" = "1" ]; then
           printf '%s\n' "gh pr view exploded" >&2
           exit 1
         fi
-        if [ -f "$state/latest_round_comment" ]; then cat "$state/latest_round_comment"; fi
+        case "$*" in
+          *headRefOid*)
+            if [ "${DEVLOOP_GH_REMOTE_HEAD:-}" = "drift" ]; then
+              printf '%s\n' "0000000000000000000000000000000000000000"
+            else
+              git rev-parse HEAD 2>/dev/null
+            fi
+            ;;
+          *statusCheckRollup*)
+            printf '%s\n' "${DEVLOOP_GH_CHECKS:-none}"
+            ;;
+          *)
+            if [ -f "$state/latest_round_comment" ]; then cat "$state/latest_round_comment"; fi
+            ;;
+        esac
         ;;
       *)
         exit 1
@@ -3381,6 +3508,7 @@ contains "$final_body" "Commit References" "final PR comment"
 if printf '%s\n' "$final_body" | grep -q '/Users/'; then fail "final PR comment leaked absolute local path"; fi
 if printf '%s\n' "$round_body" | grep -q 'Local cache'; then fail "round PR comment leaked local cache path"; fi
 if printf '%s\n' "$final_body" | grep -Eq '<(html|script|style)'; then fail "final PR comment embedded standalone HTML"; fi
+equals "$(cat "$pr_state/pr_ready" 2>/dev/null || printf 'draft')" "ready" "accepted PR is marked ready"
 unset DEVLOOP_GH_STATE DEVLOOP_GH_LOG DEVLOOP_AGENT_LOG
 ok "PR-backed accept comments"
 
@@ -3403,6 +3531,7 @@ contains "$pr_terminal_output" "unclear" "PR terminal failure"
 equals "$(find "$pr_state/comments" -name 'round-*.md' | wc -l | tr -d ' ')" "1" "terminal round PR comment"
 equals "$(find "$pr_state/comments" -name 'final-*.md' | wc -l | tr -d ' ')" "1" "terminal final PR comment"
 contains "$(cat "$pr_state/comments/final-1.md")" "| Final status | unclear |" "terminal final PR comment"
+if [ -f "$pr_state/pr_ready" ]; then fail "unclear run marked the PR ready"; fi
 unset DEVLOOP_GH_STATE DEVLOOP_GH_LOG DEVLOOP_AGENT_LOG
 ok "PR-backed terminal final comment"