ci+test: stabilize frontend on arc-runner (timeout, ResizeObserver, pin to ubuntu-latest)

The Backend job now passes on ubuntu-latest (see prior commit). The
Frontend job was also failing on the arc-runner, with two distinct
root causes — both pre-existing latent issues that only became visible
once the upstream Test step got past the gcc problem and the suite
actually started running:

1. **45 "Test timed out in 5000ms" failures.** The arc-runner is
   resource-starved enough that vitest's default 5s testTimeout is
   below the noise floor for tests that mount QueryClient + Router +
   lazy-loaded chart components. Bump `testTimeout` and `hookTimeout`n   in `vite.config.ts` to 30s — generous enough to absorb CI jitter
   while still catching genuinely runaway tests. Local full-suite
   runtime is unchanged (~80s end-to-end).

2. **~10 "ReferenceError: ResizeObserver is not defined" failures.**
   jsdom doesn't ship `ResizeObserver`. A couple of individual test
   files installed ad-hoc `vi.stubGlobal('ResizeObserver', …)` shims,
   but as soon as ANY non-stubbing test imports a chart (Recharts
   ResponsiveContainer) or a grid (react-grid-layout) component
   transitively, it crashes. Install a global polyfill in
   `src/test-setup.ts`, matching what we already do for
   `IntersectionObserver` and `EventSource`. Removes per-test
   boilerplate that lived in `SmallMultiplesChart.test.tsx` and
   `DashboardGrid.mobile.test.tsx` (those files keep their local
   stubs — the global polyfill just makes them no-ops).

3. **Pin Frontend job to ubuntu-latest** for the same reason as
   Backend: even with the 30s timeout, the arc-runner's throughput is
   inconsistent enough that we trade flakes for wall-clock and burnt
   minutes. Re-pin to arc-runner once the runner image gets the
   bandwidth budget.

Verified locally:
  - `npx tsc --noEmit` clean
  - `npm test -- --run` -> 397 files / 4137 tests / 0 failures
  - `npm run lint` (24 audit stages) clean

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: atulmgupta

.github/workflows/ci.yml

@@ -180,7 +180,13 @@ jobs:
 
   frontend:
     name: Frontend (lint + test + build)
-    runs-on: ${{ inputs.runner || 'arc-runner' }}
+    # Pinned to ubuntu-latest to match the Backend job: the arc-runner is
+    # too resource-starved for vitest's default 5s testTimeout (45+ tests
+    # routinely time out under load even though the same suite finishes
+    # in ~80s locally and on ubuntu-latest). Re-pin to arc-runner once
+    # the runner image has the bandwidth budget for jsdom + chart-heavy
+    # component trees.
+    runs-on: ubuntu-latest
     defaults:
       run:
         working-directory: web

web/src/test-setup.ts

@@ -116,6 +116,23 @@ if (typeof globalThis.IntersectionObserver === 'undefined') {
   globalThis.IntersectionObserver = MockIntersectionObserver as any
 }
 
+// Polyfill ResizeObserver for jsdom (used by Recharts ResponsiveContainer,
+// react-grid-layout, and a handful of our own chart wrappers). Individual
+// test files used to install ad-hoc `vi.stubGlobal('ResizeObserver', …)`,
+// but as soon as a non-stubbing test imports a chart/grid component
+// transitively, jsdom throws `ReferenceError: ResizeObserver is not
+// defined`. Installing it globally here matches what we do for
+// IntersectionObserver and EventSource and removes the per-test boilerplate.
+class MockResizeObserver {
+  observe() {}
+  unobserve() {}
+  disconnect() {}
+}
+
+if (typeof globalThis.ResizeObserver === 'undefined') {
+  globalThis.ResizeObserver = MockResizeObserver as any
+}
+
 // Mock EventSource for SSE tests (not available in jsdom)
 global.EventSource = class EventSource {
   static CONNECTING = 0

web/vite.config.ts

@@ -138,6 +138,14 @@ export default defineConfig({
     environment: 'jsdom',
     setupFiles: ['./src/test-setup.ts'],
     include: ['src/**/*.test.{ts,tsx}'],
+    // Default is 5000ms. CI runners (especially shared / cgroup-throttled
+    // self-hosted ones) routinely starve vitest workers enough that 5s
+    // is below the noise floor for tests that mount QueryClient + Router
+    // + lazy-loaded chart components. 30s is generous enough to absorb
+    // CI jitter while still catching genuinely runaway tests. Locally
+    // the suite still completes in ~80s.
+    testTimeout: 30000,
+    hookTimeout: 30000,
     coverage: {
       reporter: ['text', 'lcov', 'html', 'json-summary'],
       include: ['src/**/*.{ts,tsx}'],