wip: nested-asyncify fix, wxAuiToolBar registration, tests, research docs

Main-repo side of a multi-part WIP covering the KiCad WASM tool-selection
and nested-Asyncify work. Submodule commits are in kicad@f6e9239aaa
(libcontext hygiene) and wxwidgets@bb80f91e8b (auibar registration +
dialog diagnostics).

## scripts/common/inject-dyncall-shims.sh

Wrap Asyncify.handleSleep / allocateData to save-and-restore Asyncify.currData
around each EM_ASYNC_JS sleep. This fixes the nested Asyncify collision where
a fiber swap that fired during a modal's event loop clobbered currData, and
the modal's later doRewind used the fiber's buffer and hit "RuntimeError:
index out of bounds". Root cause documented as Emscripten Issue #9153
(wontfix upstream).

Diagnostic-rewind logging (forcedBottomOfCallStack, callStack traces) is
retained to help future debugging of Asyncify state corruption.

## tests/

- tests/playwright-kicad.config.ts: add `channel: 'chrome'` for the
  chromium project so --project=chromium --headed uses system Chrome
  (real GPU) instead of SwiftShader on ARM Mac. Also switch trace to
  retain-on-failure + screenshot on-failure for easier E2E debugging.
- tests/kicad/pcbnew.spec.ts: replace `tool.checked` assertions with a
  label-suffix check (`[checked]`) since our auibar registration encodes
  checked state in the label (no schema change to the registry).
- tests/apps/Makefile.wasm: add `coroutine-nested` build target + include
  it in the all: list.
- tests/apps/standalone/coroutine/: kicad_coroutine_harness.h + test app
  reproducing KiCad COROUTINE semantics against real libcontext.
- tests/apps/standalone/coroutine-nested/: nested_test.cpp reproduces the
  EM_ASYNC_JS-modal + fiber-swap nesting bug in isolation. 8 scenarios
  from baseline_modal_alone through nested_fibers_inside_modal.
- tests/e2e/coroutine.spec.ts + coroutine-nested.spec.ts: Playwright specs
  that load the standalone apps and assert all case cases pass via
  [COROUTINE_TEST] SUMMARY log parsing.

## research/ and features/browser-tools/

Three background docs capturing the investigation trajectory:

- features/browser-tools/0001-kicad-wasm-tool-activation-investigation.md
  Early investigation: why tools don't activate; initial dynCall-empty-
  callback hypothesis.
- features/browser-tools/0002-wasm-coroutine-deep-dive.md
  Deep dive on Asyncify internals, fiber API, QEMU's coroutine-wasm
  reference implementation.
- features/browser-tools/0003-wxauitoolbar-registration-fix.md
  The narrow fix: why wxAuiToolBar needs a registration block, where to
  add it, what the fallback plan is.
- research/threading_1.md: corrected root-cause analysis after reading
  runtime logs — nested-Asyncify currData collision, Emscripten #9153.
- research/threading_2.md: extended research on alternative approaches
  (JSPI/WasmFX/state-machines) and why they don't help here.

## Submodule pointer updates

kicad: f6e9239aaa (wip: libcontext WASM hygiene cleanup)
wxwidgets: bb80f91e8b (wip: wxAuiToolBar element-registry registration +
            dialog diagnostics)

## Open threads not yet in scope

- Firefox/Chrome divergent behavior: "indirect call signature mismatch"
  traps in Firefox vs renderer crash in system Chrome (tracked in
  plans/peaceful-hugging-pnueli.md and the research docs).
- E2E pixel-diff for Draw Lines fails because the test's diff region does
  not cover where the line is actually drawn; tool activation works, the
  line is visible in test-results/pcbnew-draw-lines-02-after-drawing.png.

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

tests/playwright-kicad.config.ts

@@ -55,7 +55,8 @@ export default defineConfig({
 
   use: {
     baseURL: `http://localhost:${port}`,
-    trace: 'on-first-retry',
+    trace: 'retain-on-failure',
+    screenshot: 'only-on-failure',
   },
 
   projects: [
@@ -68,11 +69,14 @@ export default defineConfig({
       },
     },
     {
-      // Chrome for headed debugging only (headless crashes on ARM Mac)
-      // Use --headed flag when running: npm run test:kicad:headed
+      // Uses the SYSTEM-installed Google Chrome (not the Playwright-bundled
+      // Chromium) so WebGL runs on the real GPU instead of SwiftShader.
+      // The bundled Chromium fails with canvas hidden on ARM Mac because of
+      // Chromium issues #1416283, #338414704 (SwiftShader WebGL bug).
+      // Run via: npm run test:kicad:headed
       name: 'chromium',
       use: {
-        ...devices['Desktop Chrome'],
+        channel: 'chrome',
         viewport: { width: 1280, height: 720 },
       },
     },