jspi: migration phases 0-7 — build knob, scheduler shim, test successor suite

Toolchain: emsdk 6.0.6 (versions.sh; cache-hash keys on it). Build knob
PCBJAM_ASYNC_BACKEND=jspi|asyncify: build-kicad-target.sh links editors with
-sJSPI + -sJSPI_EXPORTS=@scripts/common/jspi-exports.txt + --pre-js
jspi-scheduler.js (no DYNCALLS, no post-link asyncify pipeline); wx build
stamps the backend and forces clean on flip or unknown provenance;
docker/build.sh passes the knob, seeds the emscripten ports cache from the
volume every launch, jspi postprocess = patch-env-shim only.

scripts/common/shims/jspi-scheduler.js: the JSPI successor scheduler —
token-wait registry, resume turnstile (one armed resume between engine
re-entries, SP swaps only at microtask boundaries), green-region spill
stacks (16-aligned tops), S1 embind mutator FIFO lane + parker wraps, S6
shutdown, libctx integration hooks (suspend/end/quarantine + g_current
arm/clear), SuspendError attributor, lost-wake + stuck-window watchdogs,
__wxWaitDump observability.

Embind: PARKER registrations get emscripten::async() under PCBJAM_JSPI
(wasm/bindings/pcbjam_async_policy.h). nanosleep yields route via the shim.

Tests: tests/asyncify -> tests/jspi successor suite (jspi-stack red/green
shadow-stack battery, jspi-coroutine MiniCoro harness, suspend-races
semantic scenarios + __wxWaitDump books coherence); projects jspi-firefox/
jspi-chrome (asyncify-webkit retired — no JSPI in WebKit); unconditional
Firefox JSPI pref; guard-beacons -> wait-beacons (+wxScheduler/libctxJspi
families); Makefile.wasm links test apps against JSPI with the shim as a
tracked link prerequisite.

Web: WasmTool setRo await + __wxWaitDump forensics, open-flow contained
promise, scheduler-shim.test.ts retargeted (8 green).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NDeBaKKhQztd8KiVtHuyXr

tests/jspi/jspi-stack.spec.ts

@@ -0,0 +1,67 @@
+import { test, expect } from '../e2e/utils/fixtures';
+
+// The permanent regression tripwire for the JSPI shadow-stack hazard
+// (emscripten #27364): JSPI switches the native stack per activation but NOT
+// the C spill stack (__stack_pointer), so concurrently-suspended activations
+// corrupt each other unless a discipline is applied. The harness
+// (tests/apps/standalone/jspi-stack, browser battery in its index.html) runs:
+//
+//   red/single           mitigation OFF  → MUST detect corruption (the
+//                        harness can still see the bug; a silent red means
+//                        the tripwire itself broke)
+//   green-copy/single    per-suspension [sp, entrySp] snapshot+restore — the
+//                        discipline jspi-scheduler.js applies to wx entries
+//   green-region/single  per-activation stack region + SP swap — the
+//                        discipline libcontext's JSPI backend applies to
+//                        KiCad coroutines
+//   green-copy/pthread   both disciplines again with cross-thread allocator
+//   green-region/pthread churn running during the parks
+//
+// Output contract per combo:
+//   [JSPI_STACK] SCENARIO <mode>/<variant> corruptA=.. corruptB=.. corruptNested=.. verdict=<RED|GREEN|UNEXPECTED>
+
+const COMBOS = [
+  { name: 'red/single', verdict: 'RED' },
+  { name: 'green-copy/single', verdict: 'GREEN' },
+  { name: 'green-region/single', verdict: 'GREEN' },
+  { name: 'green-copy/pthread', verdict: 'GREEN' },
+  { name: 'green-region/pthread', verdict: 'GREEN' },
+];
+
+test.describe('JSPI shadow-stack red/green battery', () => {
+  test('red detects corruption; both mitigations hold, incl. pthread churn', async ({
+    page,
+    testLogger,
+  }) => {
+    test.setTimeout(120000);
+    await page.goto('/standalone/jspi-stack/');
+
+    await expect
+      .poll(
+        () =>
+          testLogger.consoleLogs.find((l) => l.includes('[JSPI_STACK] DONE')) ??
+          testLogger.consoleLogs.find((l) => l.includes('[JSPI_STACK] FATAL')) ??
+          null,
+        {
+          timeout: 90000,
+          message: 'battery should emit DONE (FATAL/silence = harness wedge)',
+        },
+      )
+      .not.toBeNull();
+
+    const fatal = testLogger.consoleLogs.filter((l) => l.includes('[JSPI_STACK] FATAL'));
+    expect(fatal, `harness fatal: ${fatal.join(' || ')}`).toHaveLength(0);
+
+    for (const combo of COMBOS) {
+      const line = testLogger.consoleLogs.find((l) =>
+        l.includes(`[JSPI_STACK] SCENARIO ${combo.name} `),
+      );
+      expect.soft(line, `combo ${combo.name} should have run`).toBeTruthy();
+      if (line) {
+        expect
+          .soft(line, `combo ${combo.name} verdict`)
+          .toContain(`verdict=${combo.verdict}`);
+      }
+    }
+  });
+});