diff --git a/context/examples/catalog.md b/context/examples/catalog.md
index 327806b..b8d2b8f 100644
--- a/context/examples/catalog.md
+++ b/context/examples/catalog.md
@@ -2,7 +2,7 @@
 
 <!-- GENERATED by tools/examples-catalog/build.mjs — do not hand-edit. Run `bun run examples:catalog`. -->
 
-> Source of truth: `tools/examples-catalog/config.mjs`. Exemplar status: all 10 exemplar files pass oxlint.
+> Source of truth: `tools/examples-catalog/config.mjs`. Exemplar status: all 12 exemplar files pass oxlint.
 
 The reference shape for each kind of unit in this repo. Copy the linked exemplar
 instead of inventing a shape. Every entry points at real, in-repo code that
@@ -60,6 +60,16 @@ passes lint and (where paired) ships with its test — no throwaway samples.
   - Node built-ins imported explicitly; no hidden globals.
   - Ships WITH its test — no untested lib modules.
 
+### Read-only plan / filesystem apply boundary
+
+- **Exemplar:** `./src/lib/writer.ts`
+- **Paired with:** `./tests/writer-plan.test.ts`
+- **When to use:** Adding preview, dry-run, or conflict reporting to a filesystem workflow without letting read-only and mutating paths drift.
+- **Shape:**
+  - planBundle classifies every action without writing or prompting; applyBundle consumes that same plan.
+  - The shared result vocabulary covers created, unchanged, updated, and conflict outcomes.
+  - Parity tests prove planner classifications match apply results across the important state transitions.
+
 ### API client seam (allowlisted hosts)
 
 - **Exemplar:** `./src/lib/api-client.ts`
diff --git a/tools/examples-catalog/config.mjs b/tools/examples-catalog/config.mjs
index e221d46..89b5e50 100644
--- a/tools/examples-catalog/config.mjs
+++ b/tools/examples-catalog/config.mjs
@@ -84,6 +84,20 @@ export const examples = [
       'Ships WITH its test — no untested lib modules.',
     ],
   },
+  {
+    id: 'plan-apply-boundary',
+    category: 'lib',
+    title: 'Read-only plan / filesystem apply boundary',
+    file: 'src/lib/writer.ts',
+    subject: 'tests/writer-plan.test.ts',
+    whenToUse:
+      'Adding preview, dry-run, or conflict reporting to a filesystem workflow without letting read-only and mutating paths drift.',
+    shape: [
+      'planBundle classifies every action without writing or prompting; applyBundle consumes that same plan.',
+      'The shared result vocabulary covers created, unchanged, updated, and conflict outcomes.',
+      'Parity tests prove planner classifications match apply results across the important state transitions.',
+    ],
+  },
   {
     id: 'api-seam',
     category: 'lib',