22541 harden breadcrumb mapped route resolver against invalid entries

memory-bank/change-log.md

@@ -638,6 +638,36 @@ Follow-ups:
 - Next larger slice candidate: evaluate extraction viability for `/case` branch only if callback/`router.back()` behavior can remain explicit and parity-safe.
 - Next smaller slice candidate: add helper-level test coverage for unexpected non-function map values and explicit skip behavior (defensive precedence guard).
 
+### CL-22541-U: breadcrumbs smaller slice — defensive mapped-route resolver hardening
+
+date: 2026-04-09  
+author: Cline  
+scope: `lib/routing/breadcrumbRouteMaps.js`, `tests/phase22/breadcrumb-route-maps-helper.test.cjs`  
+type: change  
+rationale: Execute the queued smaller slice by hardening mapped-route lookup against malformed map entries and non-function values while keeping precedence behavior unchanged.
+impact: Refactor-hardening only; no intended breadcrumb route behavior change for valid mapped renderers.
+status: completed
+
+Summary:
+
+- Updated `getMappedRendererByPath(...)` to safely handle invalid route-map entries:
+    - returns `null` when map is missing/non-object
+    - returns `null` when mapped value is not a function
+- Preserved existing resolver precedence semantics for valid function renderers.
+- Added focused helper test asserting resolver skips:
+    - invalid map entries (`null`/`undefined`)
+    - non-function mapped values
+      and still resolves the first later valid renderer.
+
+Validation:
+
+- `npx eslint lib/routing/breadcrumbRouteMaps.js tests/phase22/breadcrumb-route-maps-helper.test.cjs tests/phase22/index.test.cjs` -> pass.
+- `node tests/phase22/index.test.cjs` -> pass (combined suite; breadcrumb-route-maps-helper 5/5).
+
+Follow-ups:
+
+- Next larger slice: extract remaining callback-bearing deterministic branches into mapped route groups with callback injection, then update structure guards accordingly.
+
 ### CL-00X: 22500 `components/elements/index.js` Phase 1 helper extraction
 
 date: 2026-04-07