diff --git a/frontend/src/lib/entryPaths.js b/frontend/src/lib/entryPaths.js
index b780f5a..a4ce000 100644
--- a/frontend/src/lib/entryPaths.js
+++ b/frontend/src/lib/entryPaths.js
@@ -4,7 +4,7 @@
 // project-scoped, so the builders emit the default collection segment; the
 // collection-aware link layer (named collections) lands in S2. Components build
 // links via these helpers so that flip happens in one place.
-import { useParams } from 'react-router-dom'
+import { useParams, useLocation } from 'react-router-dom'
 import { useProject } from '../components/ProjectLayout.jsx'
 import { useDeployment } from '../context/DeploymentProvider'
 
@@ -41,7 +41,17 @@ export function useProjectId() {
 
 // §22 S2 — the collection id a component should scope to: the `/c/:collectionId/`
 // route segment when present, else the project's default collection.
+//
+// The route param is only in scope for components rendered *under* the
+// `c/:collectionId` route (e.g. RFCView). The Catalog renders one level up at
+// `/p/:projectId/*` — a sibling of that route — so `useParams().collectionId`
+// is undefined there and it would wrongly fall back to the default collection
+// (the faceted/bulk catalog UI would then never scope to a named collection).
+// Fall back to parsing the `/c/<id>/` segment from the pathname so the Catalog
+// scopes correctly regardless of its position in the route tree.
 export function useCollectionId() {
   const { collectionId } = useParams()
-  return collectionId || DEFAULT_COLLECTION
+  const { pathname } = useLocation()
+  const fromPath = pathname.match(/\/c\/([^/]+)/)
+  return collectionId || (fromPath && fromPath[1]) || DEFAULT_COLLECTION
 }
diff --git a/frontend/src/lib/useCollectionId.test.jsx b/frontend/src/lib/useCollectionId.test.jsx
new file mode 100644
index 0000000..8b31a5a
--- /dev/null
+++ b/frontend/src/lib/useCollectionId.test.jsx
@@ -0,0 +1,42 @@
+// Regression: useCollectionId must resolve the /c/<id>/ segment even when the
+// component renders ABOVE the `c/:collectionId` route (the Catalog's position
+// at `/p/:projectId/*`), where useParams() does not expose collectionId. A bug
+// here makes the faceted/bulk catalog silently scope to the default collection.
+import { describe, it, expect } from 'vitest'
+import { renderHook } from '@testing-library/react'
+import { MemoryRouter, Routes, Route } from 'react-router-dom'
+import { useCollectionId } from './entryPaths.js'
+
+function wrapperFor(initialPath, routePath) {
+  return ({ children }) => (
+    <MemoryRouter initialEntries={[initialPath]}>
+      <Routes>
+        <Route path={routePath} element={children} />
+      </Routes>
+    </MemoryRouter>
+  )
+}
+
+describe('useCollectionId', () => {
+  it('reads the /c/<id>/ segment from the path at the Catalog level (no param in scope)', () => {
+    // The Catalog matches `/p/:projectId/*` — collectionId is NOT a param here.
+    const { result } = renderHook(() => useCollectionId(), {
+      wrapper: wrapperFor('/p/ohm/c/bdd/e/checkout', '/p/:projectId/*'),
+    })
+    expect(result.current).toBe('bdd')
+  })
+
+  it('honours the route param when in scope', () => {
+    const { result } = renderHook(() => useCollectionId(), {
+      wrapper: wrapperFor('/p/ohm/c/features/e/login', '/p/:projectId/c/:collectionId/*'),
+    })
+    expect(result.current).toBe('features')
+  })
+
+  it('falls back to the default collection when there is no /c/ segment', () => {
+    const { result } = renderHook(() => useCollectionId(), {
+      wrapper: wrapperFor('/p/ohm', '/p/:projectId/*'),
+    })
+    expect(result.current).toBe('default')
+  })
+})