test(determinism): deterministic waits + stableShot screenshots; drop blind sleeps/ifs/retries

Make the Playwright e2e + kicad suites deterministic so screenshot flake stops
tracing to timing races.

- Blind page.waitForTimeout -> condition waits (expect.poll, web-first
  assertions, waitUntil) + readiness helpers (waitForWxApp, waitForCanvasApp).
  Remaining sleeps are documented interaction dwells (annotated).
- Defensive "if element exists" branches -> loud asserts; label-fallback chains
  -> normalized clickMenuItemByText. First-run wizard for/if loops removed by
  seeding calculator/gerbview/pcbnew HTMLs.
- Screenshots: new stableShot(page, name) settles the render in-page (canvas
  hash over rAF) then writes a raw PNG to test-results/ for the existing offline
  gate (tools/screenshots vs baseline-screenshots). Replaces toHaveScreenshot,
  which did inline compare + its own baselines and had decoupled the specs from
  the real gate. scale:'css' pinned.
- retries: 0 in both configs.
- Guard: tests/tools/lint-determinism.ts (npm run lint:determinism) bans blind
  sleeps / toHaveScreenshot / inline retries / swallowed catches in specs;
  documented exceptions carry a marker. Rules in tests/TESTING.md.

Assertions, coverage, and renders unchanged (semantic-equivalence reviewed;
captures pixel-identical modulo inherent timer/timestamp/3d-raytrace variance).
Both suites green at retries:0 (e2e 340, kicad 92); ~35-61% faster.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BVX1pHMvRPYHdp6ZfEawrk

tests/playwright.config.ts

@@ -76,9 +76,10 @@ export default defineConfig({
   outputDir: process.env.CI ? 'pw-artifacts/wx' : 'test-results',
   fullyParallel: true,
   forbidOnly: !!process.env.CI,
-  // 1 local retry absorbs transient `npx serve` connection refusals under heavy
-  // parallel load (many workers fetching large WASM bundles at once).
-  retries: process.env.CI ? 2 : 1,
+  // retries:0 — the suite is deterministic (no blind sleeps, no "if element exists"
+  // branches; screenshots are captured via stableShot for the offline gate, not asserted
+  // inline), so a failure is a real failure, not flake to paper over with a retry.
+  retries: 0,
   // Run parallel workers on CI too (Playwright default ≈ 50% of cores), same as
   // local — the serial CI run was the dominant wall-clock cost. Cap (e.g. '50%'
   // or a fixed count) if contention OOMs/flakes; retries:2 covers transient.
@@ -86,6 +87,10 @@ export default defineConfig({
   reporter: 'html',
   timeout: 60000,  // WASM can be slow to load
 
+  // No expect.toHaveScreenshot block: screenshots are captured via stableShot() (render-settle +
+  // raw PNG to test-results/) and compared OFFLINE by tools/screenshots against tests/baseline-
+  // screenshots on CI's deterministic Linux render — Playwright does no inline pixel comparison.
+
   use: {
     baseURL: `http://localhost:${port}`,
     trace: 'on-first-retry',