From 0cd78e6f4639d16ee704574d26101208eb06654e Mon Sep 17 00:00:00 2001
From: robbond <rob@rdbsolutions.co.uk>
Date: Thu, 9 Apr 2026 14:45:12 +0100
Subject: [PATCH] 22541 harden breadcrumb mapped route resolver against invalid
 entries

---
 lib/routing/breadcrumbRouteMaps.js            | 10 +++++--
 memory-bank/change-log.md                     | 30 +++++++++++++++++++
 .../breadcrumb-route-maps-helper.test.cjs     | 28 +++++++++++++++++
 3 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/lib/routing/breadcrumbRouteMaps.js b/lib/routing/breadcrumbRouteMaps.js
index c3cbde18..ef46b5f5 100644
--- a/lib/routing/breadcrumbRouteMaps.js
+++ b/lib/routing/breadcrumbRouteMaps.js
@@ -1,5 +1,11 @@
-const getMappedRendererByPath = (path, routeRendererMap) =>
-    routeRendererMap[path] || null;
+const getMappedRendererByPath = (path, routeRendererMap) => {
+    if (!routeRendererMap || typeof routeRendererMap !== "object") {
+        return null;
+    }
+
+    const routeRenderer = routeRendererMap[path];
+    return typeof routeRenderer === "function" ? routeRenderer : null;
+};
 
 const resolveMappedRouteRenderer = (path, routeRendererMaps = []) => {
     for (const routeRendererMap of routeRendererMaps) {
diff --git a/memory-bank/change-log.md b/memory-bank/change-log.md
index 1a07eb6c..89b9bfc6 100644
--- a/memory-bank/change-log.md
+++ b/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  
diff --git a/tests/phase22/breadcrumb-route-maps-helper.test.cjs b/tests/phase22/breadcrumb-route-maps-helper.test.cjs
index 23c40e38..8f04ee21 100644
--- a/tests/phase22/breadcrumb-route-maps-helper.test.cjs
+++ b/tests/phase22/breadcrumb-route-maps-helper.test.cjs
@@ -191,6 +191,34 @@ test("resolveMappedRouteRenderer returns null for unmapped path", () => {
     );
 });
 
+test("resolveMappedRouteRenderer skips invalid map entries and non-function renderer values", () => {
+    const { buildBreadcrumbRendererMaps, resolveMappedRouteRenderer } =
+        loadHelpers();
+
+    const validRenderer = () => "valid";
+
+    const maps = buildBreadcrumbRendererMaps({
+        simpleRouteRenderersByPath: {
+            "/known": "not-a-function"
+        },
+        simpleLinkTextPairRenderersByPath: null,
+        simpleMyPortalRouteRenderersByPath: {
+            "/known": validRenderer
+        },
+        newAppealRouteRenderersByPath: undefined,
+        caseDetailRouteRenderersByPath: {},
+        detailAndAccountRouteRenderersByPath: {}
+    });
+
+    const result = resolveMappedRouteRenderer("/known", maps);
+
+    assert.strictEqual(
+        result,
+        validRenderer,
+        "Expected resolver to skip invalid/non-function entries and return first valid renderer"
+    );
+});
+
 const run = async () => {
     let passed = 0;