diff --git a/Cargo.lock b/Cargo.lock
index 7dad4e44..1fa793f3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2729,7 +2729,7 @@ dependencies = [
 
 [[package]]
 name = "rheo"
-version = "0.5.0"
+version = "0.5.1"
 dependencies = [
  "atty",
  "axum",
@@ -2766,7 +2766,7 @@ dependencies = [
 
 [[package]]
 name = "rheo-core"
-version = "0.5.0"
+version = "0.5.1"
 dependencies = [
  "atty",
  "chrono",
@@ -2806,7 +2806,7 @@ dependencies = [
 
 [[package]]
 name = "rheo-epub"
-version = "0.5.0"
+version = "0.5.1"
 dependencies = [
  "chrono",
  "iref",
@@ -2825,7 +2825,7 @@ dependencies = [
 
 [[package]]
 name = "rheo-html"
-version = "0.5.0"
+version = "0.5.1"
 dependencies = [
  "atom_syndication",
  "axum",
@@ -2848,7 +2848,7 @@ dependencies = [
 
 [[package]]
 name = "rheo-pdf"
-version = "0.5.0"
+version = "0.5.1"
 dependencies = [
  "rheo-core",
  "thiserror 2.0.18",
diff --git a/Cargo.toml b/Cargo.toml
index 7fe923cf..51c99e12 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,7 +3,7 @@ resolver = "2"
 members = ["crates/core", "crates/html", "crates/pdf", "crates/epub", "crates/cli"]
 
 [workspace.package]
-version = "0.5.0"
+version = "0.5.1"
 edition = "2024"
 authors = ["Lachlan Kermode <lachie@ohrg.org>"]
 description = "A typesetting and static site engine based on Typst"
@@ -13,10 +13,10 @@ readme = "README.md"
 
 [workspace.dependencies]
 # Internal crates (for convenience in workspace)
-rheo-core = { path = "crates/core", version = "0.5.0" }
-rheo-html = { path = "crates/html", version = "0.5.0" }
-rheo-pdf = { path = "crates/pdf", version = "0.5.0" }
-rheo-epub = { path = "crates/epub", version = "0.5.0" }
+rheo-core = { path = "crates/core", version = "0.5.1" }
+rheo-html = { path = "crates/html", version = "0.5.1" }
+rheo-pdf = { path = "crates/pdf", version = "0.5.1" }
+rheo-epub = { path = "crates/epub", version = "0.5.1" }
 
 # Typst dependencies
 typst = "0.15.0"
diff --git a/crates/cli/src/migrate.rs b/crates/cli/src/migrate.rs
index ec77f425..db8fd750 100644
--- a/crates/cli/src/migrate.rs
+++ b/crates/cli/src/migrate.rs
@@ -24,6 +24,14 @@
 //! an older version have their direct references rewritten (`migrate_target_references`).
 //! Authors using the polyfilled `target()` need no change — it already reports
 //! the output format.
+//!
+//! # Context binding: `rheo-context` dict → `rheo-context()` function
+//!
+//! The per-vertebra `rheo-context` binding, first injected as a bare data dict,
+//! was encapsulated behind a zero-arg function `rheo-context()`. Projects on the
+//! dict-era version have a one-line compatibility shim prepended to each file
+//! that reads the binding (`migrate_context_references`), so existing
+//! `rheo-context.field` / `ctx: rheo-context` code keeps working untouched.
 
 use regex::{Captures, Regex};
 use rheo_core::build::resolve_effective_content_dir;
@@ -42,6 +50,21 @@ use walkdir::WalkDir;
 /// `#link(<handle>)` label syntax. Projects older than this need a link rewrite.
 const LINK_SYNTAX_VERSION: &str = "0.4.0";
 
+/// Version at which `sys.inputs.rheo-target` and the `rheo-target()` helper were
+/// removed in favour of `sys.inputs.rheo-context.target` / the polyfilled
+/// `target()`. Projects older than this have their direct references rewritten.
+const TARGET_REMOVED_VERSION: &str = "0.5.0";
+
+/// Version at which the `[spine] vertebrae` inclusion-filter glob list was retired
+/// by the directory-scan default. Projects older than this have any `vertebrae`
+/// list converted to an equivalent `exclude`.
+const VERTEBRAE_RETIRED_VERSION: &str = "0.5.0";
+
+/// Version at which the per-vertebra `rheo-context` binding changed from a bare
+/// dict to a zero-arg function `rheo-context()`. Projects older than this have a
+/// compatibility shim prepended to each file that reads the binding.
+const CONTEXT_FN_VERSION: &str = "0.5.1";
+
 /// Run migration for the project at `path`.
 ///
 /// `apply == false` is a dry run: it reports the version gap, prints each link
@@ -67,21 +90,15 @@ pub fn migrate_project(path: &Path, apply: bool) -> Result<()> {
         return Ok(());
     }
 
-    let link_threshold = ManifestVersion::parse(LINK_SYNTAX_VERSION).expect("valid semver");
-    let needs_link_rewrite = from < link_threshold;
-
-    // `rheo-target` was removed as of the current release, so any project on an
-    // older version (i.e. every project reaching this point past the up-to-date
-    // check above) has its direct references rewritten.
-    let needs_target_rewrite = from < to;
-
-    // `vertebrae` was retired by the structured-spine directory-scan default,
-    // in the same release as the rheo-target removal above — same threshold.
-    let needs_vertebrae_migration = from < to;
-
-    // The per-vertebra `rheo-context` binding became a function `rheo-context()`;
-    // any older project's references are rewritten.
-    let needs_context_rewrite = from < to;
+    // Each migration is gated on the version at which its change actually landed,
+    // so a patch/minor bump only runs the migrations introduced since the
+    // project's recorded version — not every historical migration on every bump.
+    let threshold =
+        |v: &str| ManifestVersion::parse(v).expect("hardcoded threshold must be valid semver");
+    let needs_link_rewrite = from < threshold(LINK_SYNTAX_VERSION);
+    let needs_target_rewrite = from < threshold(TARGET_REMOVED_VERSION);
+    let needs_vertebrae_migration = from < threshold(VERTEBRAE_RETIRED_VERSION);
+    let needs_context_rewrite = from < threshold(CONTEXT_FN_VERSION);
 
     println!("\nMigrations:");
     if needs_link_rewrite {