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-kicad.config.ts

@@ -139,17 +139,21 @@ export default defineConfig({
   outputDir: process.env.CI ? "pw-artifacts/kicad" : "test-results",
   fullyParallel: true,
   forbidOnly: !!process.env.CI,
-  // 1 local retry absorbs the known under-parallel-load flakes (same rationale
-  // as playwright.config.ts): the load-pcb post-load clipboard crash that can
-  // close the page on Firefox, and the calculator first-run-wizard timing race.
-  retries: process.env.CI ? 2 : 1,
+  // retries:0 — the suite is deterministic (no blind sleeps or "if element exists" branches;
+  // screenshots go through stableShot for the offline gate, not asserted inline), so a failure
+  // is a real failure rather than flake to mask 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.
+  // or a fixed count) if contention OOMs/flakes.
   workers: undefined,
   reporter: "html",
   timeout: 180000, // KiCad WASM needs more time to load (3 minutes)
 
+  // No expect.toHaveScreenshot block: screenshots are captured via stableShot() (render-settle +
+  // raw PNG to test-results/) and compared OFFLINE by tools/screenshots against the committed
+  // baselines on CI's deterministic Linux render — Playwright does no inline pixel comparison.
+
   use: {
     baseURL: `http://localhost:${port}`,
     trace: "retain-on-failure",