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

scripts/build-wasm-test.sh

@@ -101,8 +101,16 @@ fi
 # submodule (version_130 + hoist pass) via apply-asyncify.sh.
 EMSDK_WASM_OPT="$PROJECT_ROOT/tools/emsdk/upstream/bin/wasm-opt"
 WASMOPT_STUB="$PROJECT_ROOT/wasm/stubs/wasm-opt-stub.sh"
-_eh_restore_wasmopt() { [ -f "${EMSDK_WASM_OPT}.ehbak" ] && mv -f "${EMSDK_WASM_OPT}.ehbak" "${EMSDK_WASM_OPT}"; }
+_eh_restore_wasmopt() { if [ -f "${EMSDK_WASM_OPT}.ehbak" ]; then mv -f "${EMSDK_WASM_OPT}.ehbak" "${EMSDK_WASM_OPT}"; fi; }
 EH_MARKER="$(mktemp)"   # created before the build so 'find -newer' below selects freshly-linked apps
+if [ "${PCBJAM_ASYNC_BACKEND:-asyncify}" = "jspi" ]; then
+    # JSPI: no binaryen instrumentation exists — no fork build, no stub dance,
+    # no post-link pass, no dyncall/scheduler injection (the jspi-scheduler
+    # ships as a --pre-js from Makefile.wasm). emcc's real wasm-opt runs
+    # in-link like any normal build.
+    echo ""
+    echo "=== JSPI backend: in-link build, no post-link instrumentation ==="
+else
 echo ""
 echo "=== Building the Binaryen submodule (version_130 + hoist pass) ==="
 # One binaryen everywhere: the submodule fork is version_130 (asyncify unchanged) + our hoist
@@ -114,6 +122,7 @@ echo "Stubbing in-link Asyncify (will run post-link instead)..."
 cp "$EMSDK_WASM_OPT" "${EMSDK_WASM_OPT}.ehbak"
 cp "$WASMOPT_STUB" "$EMSDK_WASM_OPT"; chmod +x "$EMSDK_WASM_OPT"
 trap _eh_restore_wasmopt EXIT
+fi
 
 # Build (pass DEBUG flag if requested). App links are independent, so honor
 # JOBS/PARALLEL_JOBS from env.sh (each emcc link is slow due to Asyncify).
@@ -139,6 +148,12 @@ fi
 # it for the coroutine apps; inject-dyncall-shims.sh is idempotent (skips an already-shimmed glue),
 # so re-running it here is safe. The .wasm gets post-link hoist + asyncify first.
 _eh_restore_wasmopt; trap - EXIT
+if [ "${PCBJAM_ASYNC_BACKEND:-asyncify}" = "jspi" ]; then
+    rm -f "$EH_MARKER"
+    echo ""
+    echo "=== Build complete (jspi backend) ==="
+    exit 0
+fi
 echo ""
 echo "=== Post-link --hoist-cpp-catches + --asyncify (${JOBS:-1}-wide) ==="
 # The apps are independent here too (apply-asyncify rewrites each wasm in place; the shim