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/kicad/utils/wait-beacons.ts

@@ -1,14 +1,14 @@
 // Wait-beacon extraction (JSPI-era successor of guard-beacons.ts; the
 // mailbox/scheduler migration doc is docs/features/async/17, step S0.3).
 //
-// Every legacy anti-collision guard announces itself on the console when it fires.
-// During the migration each superseded guard is kept as a TRIPWIRE: the mailbox is
-// only trusted once the guard it replaces is provably silent across the suite.
-// This module turns a TestLogger's consoleLogs into per-family counts so specs can
-// assert `expectGuardsSilent(...)` at the step that claims a family.
+// Every anti-collision guard announces itself on the console when it fires.
+// A superseded guard is kept as a TRIPWIRE: the mailbox is only trusted once
+// the guard it replaces is provably silent across the suite. This module turns
+// a TestLogger's consoleLogs into per-family counts so specs can assert
+// `expectGuardsSilent(...)` at the step that claims a family.
 //
-// Rate-limiting caveat: [wx-asyncify] and [collab-fcontext] beacons print the first
-// 10 occurrences, then every 100th, embedding "(occurrence N)". `linesSeen` is what
+// Rate-limiting caveat: the [wx-dispatch] ERASED beacon prints the first 10
+// occurrences, then every 100th, embedding "(occurrence N)". `linesSeen` is what
 // reached the console; `estimatedTotal` recovers the true count from the highest
 // occurrence number when present (else it equals linesSeen). Assertions on SILENCE
 // are exact either way: zero fires = zero lines.
@@ -24,32 +24,18 @@ export interface GuardBeaconCounts {
   timerRetry: BeaconFamilyCount;
   // wx dispatch interlock bookkeeping anomalies (evtloop.cpp)
   dispatchAnomaly: BeaconFamilyCount;
-  // asyncify-scheduler.js shim: nested-park / wake-aliasing / stale-fiber refusals
-  wxAsyncify: BeaconFamilyCount;
-  // libcontext swap-layer refusals + hot-main beacons ([collab-fcontext])
-  libcontext: BeaconFamilyCount;
   // open-settle gate giving up (open-flow.ts)
   openSettleFailed: BeaconFamilyCount;
-  // jspi-scheduler.js turnstile/containment beacons (JSPI builds)
+  // jspi-scheduler.js turnstile/containment beacons
   wxScheduler: BeaconFamilyCount;
   // libcontext JSPI backend ghost/refused-transition census
   libctxJspi: BeaconFamilyCount;
-  // scheduler build marker — identifies the dual-glue variant, not a guard
-  schedulerBuild: boolean;
 }
 
-const FAMILY_PATTERNS: Record<
-  Exclude<keyof GuardBeaconCounts, 'schedulerBuild'>,
-  RegExp
-> = {
+const FAMILY_PATTERNS: Record<keyof GuardBeaconCounts, RegExp> = {
   timerRetry: /\[wx-timer\] retry storm/,
   dispatchAnomaly: /\[wx-dispatch\] (ERASED|NEGATIVE)/,
-  wxAsyncify:
-    /\[wx-asyncify\] (concurrent-park|reentrant-state|aliased-wake-live|overlapped-wake|fiber-resume-refused)/,
-  libcontext:
-    /\[collab-fcontext\] (jump-refused|jump-refused-hot-main|hot-main-swap-out|jump-hot-into-main|jump-ghost|entry-orphaned)/,
   openSettleFailed: /\[open\] load chain never settled/,
-  // JSPI-era families (jspi-scheduler.js + libcontext's JSPI backend):
   wxScheduler:
     /\[wx-scheduler\] (force-clearing stuck window|job tick error|untracked promising entry|activation stack imbalance|resume window misnested)/,
   libctxJspi: /\[libctx-jspi\] ghost\/refused/,
@@ -66,19 +52,12 @@ export function countGuardBeacons(consoleLines: string[]): GuardBeaconCounts {
   const counts: GuardBeaconCounts = {
     timerRetry: emptyFamily(),
     dispatchAnomaly: emptyFamily(),
-    wxAsyncify: emptyFamily(),
-    libcontext: emptyFamily(),
     openSettleFailed: emptyFamily(),
     wxScheduler: emptyFamily(),
     libctxJspi: emptyFamily(),
-    schedulerBuild: false,
   };
 
   for (const line of consoleLines) {
-    if (line.includes('[wx-scheduler] scaffolding installed')) {
-      counts.schedulerBuild = true;
-      continue;
-    }
     for (const family of Object.keys(FAMILY_PATTERNS) as Array<
       keyof typeof FAMILY_PATTERNS
     >) {
@@ -94,24 +73,11 @@ export function countGuardBeacons(consoleLines: string[]): GuardBeaconCounts {
   return counts;
 }
 
-// Last-seen fcsTotal/rootHotTotal from a __wxAsyncifyDump()/STATE line, if any.
-// rootHotTotal must stay 0 post-v0.1.28 — the standing N8 assertion.
-export function parseAsyncifyCounters(
-  consoleLines: string[]
-): { fcsTotal: number; rootHotTotal: number } | null {
-  let result: { fcsTotal: number; rootHotTotal: number } | null = null;
-  for (const line of consoleLines) {
-    const m = /fcsTotal=(\d+) rootHotTotal=(\d+)/.exec(line);
-    if (m) result = { fcsTotal: parseInt(m[1], 10), rootHotTotal: parseInt(m[2], 10) };
-  }
-  return result;
-}
-
 // Assert the named guard families never fired. Throws with the offending sample
 // lines so the log points straight at the collision the mailbox failed to absorb.
 export function expectGuardsSilent(
   consoleLines: string[],
-  families: Array<Exclude<keyof GuardBeaconCounts, 'schedulerBuild'>>
+  families: Array<keyof GuardBeaconCounts>
 ): void {
   const counts = countGuardBeacons(consoleLines);
   const noisy = families