test(runtime-fallback): tighten quota regression fixtures so new paths actually fire

Addresses cubic-dev-ai bot review on #4113 (P2): the RESOURCE_EXHAUSTED
and snake_case insufficient_quota fixtures contained quota-shaped
messages that already matched pre-existing message regexes, so the tests
passed even without the new errorName allow-list entry and the
underscore normalization respectively.

Replace both fixture messages with a generic "Request failed." so the
only path to a `quota_exceeded` classification is via the new code:

- RESOURCE_EXHAUSTED: only the new `errorName?.includes("resourceexhausted")`
  match on the normalized name can fire.
- insufficient_quota (snake_case): only the new underscore-stripping
  normalization can route the name to `insufficientquota` and match the
  existing allow-list entry.

The third new test (Google ResourceExhausted message-only) is unchanged
because its message uniquely matches only the new
`/resource.?exhausted/i` pattern and not any existing quota regex.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/hooks/runtime-fallback/quota-error-classifier.regression.test.ts

@@ -90,11 +90,14 @@ describe("runtime-fallback quota error regressions", () => {
     expect(retryable).toBe(true)
   })
 
-  test("classifies Google RESOURCE_EXHAUSTED (gRPC code 8) as quota_exceeded", () => {
+  test("classifies Google RESOURCE_EXHAUSTED (gRPC code 8) as quota_exceeded via error name only", () => {
     //#given
+    // Bare provider error: only the error name carries the quota signal.
+    // Message is intentionally generic so the test fails if the new
+    // `resourceexhausted` name allow-list entry is removed.
     const error = {
       name: "RESOURCE_EXHAUSTED",
-      message: "Quota exceeded for quota metric 'Generate Content' and limit 'Generate Content quota per minute'.",
+      message: "Request failed.",
     }
 
     //#when
@@ -122,11 +125,14 @@ describe("runtime-fallback quota error regressions", () => {
     expect(retryable).toBe(true)
   })
 
-  test("classifies snake_case OpenAI insufficient_quota error name as quota_exceeded", () => {
+  test("classifies snake_case OpenAI insufficient_quota error name as quota_exceeded via name only", () => {
     //#given
+    // Bare provider error: only the snake_case error name carries the quota signal.
+    // Message is intentionally generic so the test fails if the underscore
+    // normalization (`insufficient_quota` -> `insufficientquota`) regresses.
     const error = {
       name: "insufficient_quota",
-      message: "You exceeded your current quota, please check your plan and billing details.",
+      message: "Request failed.",
     }
 
     //#when