test: stub user-preference fetches in the global setup to stop a cross-test leak (#60)

Admin surfaces load user preferences on mount (e.g. module-inserter
favourites via useModuleInserterPreference → getUserPreference), firing a
real fetch to /admin/api/cms/me/preferences/<key>. In tests that hits
localhost and rejects with ECONNREFUSED. The preference store is a
module-level singleton whose load promise can outlive the component that
triggered it, so the rejection surfaces during a LATER test's cleanup() as
an AggregateError — a render-timing-dependent cross-test flake.

It was masked while canvas frames mounted slowly (the tests timed out before
the preference fetch settled) and reappeared once frames mount synchronously
(#58), failing the release Verify step on canvasFrameMounting's first test.

Return the server's "never set" envelope ({ value: null }) for preference
GETs in the global test preload, so the load resolves cleanly to each
caller's own default with no network call. Tests that need specific
preference data still override globalThis.fetch in their own setup;
getUserPreference callers that inject a fetchImpl bypass this entirely.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: DavidBabinec

src/__tests__/setup.ts

@@ -115,6 +115,48 @@ for (const key of GLOBALS_TO_COPY) {
   }
 }
 
+// ---------------------------------------------------------------------------
+// Default user-preference fetches to the "never set" envelope.
+//
+// Admin surfaces load user preferences on mount (e.g. the module-inserter
+// favourites via `useModuleInserterPreference` → `getUserPreference`), which
+// fires a real `fetch` to `/admin/api/cms/me/preferences/<key>`. In tests that
+// hits `http://localhost` and rejects with ECONNREFUSED. Because the
+// preference store is a module-level singleton whose load promise can outlive
+// the component that triggered it, that rejection surfaces during a LATER
+// test's `cleanup()` as an `AggregateError` — a cross-test flake that depends
+// on render timing (it was masked while canvas frames mounted slowly, and
+// reappeared once they mount synchronously).
+//
+// Returning the server's "never set" signal (`{ value: null }`) makes every
+// such load resolve cleanly to the caller's own default, with no network call.
+// Tests that need specific preference data still override `globalThis.fetch`
+// in their own setup; `getUserPreference` callers that inject a `fetchImpl`
+// bypass this entirely.
+{
+  const realFetch = globalThis.fetch
+  const PREFERENCES_PATH = '/admin/api/cms/me/preferences/'
+  ;(globalThis as Record<string, unknown>).fetch = (async (
+    input: RequestInfo | URL,
+    init?: RequestInit,
+  ): Promise<Response> => {
+    const url =
+      typeof input === 'string'
+        ? input
+        : input instanceof URL
+          ? input.href
+          : (input as Request).url
+    const method = (init?.method ?? (input as Request).method ?? 'GET').toUpperCase()
+    if (method === 'GET' && url.includes(PREFERENCES_PATH)) {
+      return new Response(JSON.stringify({ value: null }), {
+        status: 200,
+        headers: { 'Content-Type': 'application/json' },
+      })
+    }
+    return realFetch(input, init)
+  }) as typeof globalThis.fetch
+}
+
 // ---------------------------------------------------------------------------
 // Tame DOM serialization in failure output.
 //