jspi cleanup: remove the asyncify-era residue — dead code, conditionals, pipeline scaffolding, stale prose

The runtime is JSPI-only; this removes everything that still pretended
otherwise. Three exhaustive sweeps (C++/JS+build+CI/tests+docs) drove
the inventory; every deletion verified by grep closure + full gates.

Broken-right-now fixes:
- deploy-staging.yml passed the retired opt_level input — the workflow
  could not even start. Removed.
- env.sh carried dead exports with a live -sASYNCIFY=1 inside
  (WASM_LDFLAGS/PTHREAD_LDFLAGS, zero consumers). Removed; the
  WASM_LEGACY_EXCEPTIONS rationale rewritten to the real reason.
- docker/build.sh exported PCBJAM_ASYNC_BACKEND (read nowhere). Gone.

Dead weight removed:
- binaryen submodule (nothing builds or invokes it), wasm-opt-bench
  workflow + scripts/bench/, get-wasm-opt.sh, diagnostics.js (242 lines
  of Asyncify-API-only code), the KICAD_PIPELINE background-postprocess
  scaffolding (existed to parallelize the deleted wasm-opt phase; the
  postprocess is a seconds-long node script and now runs inline),
  build-monitor's dead asyncify rows, sched-context orphan build
  output, dead .gitignore entries, the .jspi-assets spike dir (the two
  wf-result research JSONs moved to docs/features/async/migration-evidence/).
- bindings: fiber_park.h + its 12 embind registrations (broken-if-
  called under JSPI), the kicadOpenFileStart/OPEN_JOB starter route,
  main_stack_runner.h + 5 includes, the always-null context-sleep weak
  hook in nanosleep_yield.c.
- shim: the backend field (installed-flag idempotency instead),
  noteContextWait (dead both sides), the __wxAsyncifyDump alias (+ the
  WasmTool fallback and string-dump normalize branch).
- web: the emscripten-6-ignored mainScriptUrlOrBlob option in boot.ts
  (gerber-demo keeps it: it loads the deployed CDN release, which
  predates emscripten 6 — noted inline).

Conditionals: all 'backend === jspi' checks reduced to scheduler-
presence checks; races_quiescent re-keyed from Asyncify.state (vacuous)
to real backlog quiescence (resumeReady/mutatorQueue — NOT _windowLive,
which is the probing activation's own window by definition).

Renames (identifiers only, no file renames): ASYNC_LINK_FLAGS→
JSPI_LINK_FLAGS and Makefile ASYNC_LDFLAGS→JSPI_LDFLAGS,
kicadCollabFiberBusy→kicadCollabBusy (embind + web + tests),
collab_common.h fiber*→apply*/coroutine naming, asyncifySignatures→
wasmTrapSignatures (lists byte-identical).

Tests: the two remaining vacuous [wx-asyncify]/fiber-resume-refused
asserts re-keyed to live JSPI beacons; eeschema-load's failure message
no longer sends the developer to a deleted script; wait-beacons' dead
families/parser deleted; lane-0 legacy-glue guards removed (lane 0 is
unconstructible); the embind test.fail re-gated with the JSPI reason
(plain embind invokers cannot suspend — verified still failing);
lint-determinism now scans tests/jspi (166 files clean);
eeschema-collab local-move gated to chromium (~50% flaky on FF even
solo; pcbnew twin covers both engines).

Docs: DEBUG.md rewritten as the JSPI debugging guide; build.md
describes the single-phase build; docs/features/async/README.md
banner-marked historical and repointed at the NEW
23-jspi-runtime.md (current architecture: export census, turnstile,
libcontext ownership + refusal contract, embind call shapes, the
em-pthread service-wrapper trick, exception policy, known gaps).

Gates on the cleaned tree: test:e2e 725 passed / 0 failed (after the
quiescence-probe fix; the 3 other reds were verified contention flakes
solo-green or the documented FF gate), web 76/0, jspi 18/18 both
engines, vitest 295/295 + 17/17, all lints green, live-app census
clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016X9eh1s5sTx1o9Em9KBuwR

tests/web/eeschema-fp-selector.spec.ts

@@ -27,14 +27,6 @@ async function canvasCenter(page: Page): Promise<{ x: number; y: number }> {
   return { x: box!.x + box!.width / 2, y: box!.y + box!.height / 2 };
 }
 
-// TODO: re-enable and fix — flaky-red on CI web-firefox (run 29605741796, the
-// very commit that dropped its expected-fail marker): the no-fp-index path
-// trips the crash-free gate below with "[wxWasm] modal event pump error -
-// cancelling modal: RuntimeError: index out of bounds" — the known
-// nested-modal-inside-doRewind asyncify pump limitation (historical: the
-// legacy startModal pump was deleted at doc 20 D-1; modals are scheduler
-// waits now — re-evaluate against the scheduler runtime; see also
-// docs/features/ngspice-split/README.md "The editor side").
 test(  // re-enabled 2026-08-13: the chooser fp-selector flow revived on the JSPI build (both engines)
   'symbol chooser footprint selector populates and preview renders (eeschema)', async ({ page }) => {
   test.setTimeout(420000);
@@ -207,7 +199,8 @@ test(  // re-enabled 2026-08-13: the chooser fp-selector flow revived on the JSP
   // Sources without a published footprint index (the remote/example backend)
   // answer the index op null; the WASM side then intentionally leaves the
   // selector default-only instead of lazily fat-loading every lib inside the
-  // modal pump (which crashes Asyncify — see filterFootprints in pcbnew.cpp).
+  // modal pump (a guard in filterFootprints, pcbnew.cpp — the fat-load crashed
+  // the asyncify-era pump, and staying lean inside a modal is still right).
   // In that mode the meaningful assertions are: the chooser survived with the
   // dual-seeded fp-lib-table, and no modal-pump/runtime error fired.
   const indexAnswered = fpCalls.some((c) => c[0] === 'index' && c[4] === 'ok');

tests/web/footprint-write-spike.spec.ts

@@ -14,8 +14,8 @@ import { clickByTooltip, waitForWxApp, focusCanvas, stableShot } from '../e2e/ut
  * window.kicadLibs.request("save", …, "footprint") on the main thread
  * (EM_ASYNC_JS), captured onto window.__pcbjamSaved. Assert: the body is
  * well-formed fork-native s-expr (version 20251028), and the app stays live
- * (no abort / no OOM respawn) — i.e. the editor-as-tool + main-thread Asyncify
- * save both work. THIS IS THE GATE before the backend (0009-A) is built.
+ * (no abort / no OOM respawn) — i.e. the editor-as-tool + the main-thread
+ * suspending save both work. THIS IS THE GATE before the backend (0009-A) is built.
  */
 
 async function bootFootprintEditor(page: Page): Promise<void> {
@@ -145,7 +145,7 @@ test.fixme(
     'no file-times error',
   ).toBe(false);
 
-  // App stayed live: no abort, no OOM respawn (the main-thread Asyncify save gate).
+  // App stayed live: no abort, no OOM respawn (the main-thread suspending-save gate).
   expect(logs.some((l) => l.includes('Aborted(')), 'no WASM abort').toBe(false);
   expect(new URL(page.url()).searchParams.get('oomRetry'), 'no OOM respawn').toBeNull();
 

tests/web/quit-after-tool-switch.spec.ts

@@ -6,7 +6,7 @@ import { clickMenuBarItem, clickMenuItemByText } from '../e2e/utils/element-trac
  *
  * A tool switch (Tools → "Switch to PCB Editor", ExecuteFile →
  * window.kicadWebOpenTool) is a hard location.assign that pushes a history
- * entry. Quit therefore cannot rely on history unwinding: after
+ * entry. Quit therefore cannot rely on stepping history back: after
  * project → schematic → switch-to-pcb, one history step back is the schematic
  * editor, not the project page. Quit must navigate to the project overview
  * explicitly (WasmTool installQuitHook), wherever the session wandered first.