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

scripts/kicad/build-kicad-target.sh

@@ -296,11 +296,10 @@ else
     log_info "Building KiCad in RELEASE mode (skipping wasm-opt due to memory limits)"
 fi
 
-# Suspension backend: JSPI (native stack switching) since the migration.
-# The headless CLIs (kicad_tools, occ_service) get NO suspension backend at
-# all — their targets pin -sASYNCIFY=0 and run in node/worker where nothing
-# may suspend. coroutine.h/libcontext key on __EMSCRIPTEN__ directly, so no
-# ABI define is threaded through the TU flags anymore.
+# Suspension backend: JSPI (native stack switching). The headless CLIs
+# (kicad_tools, occ_service) get no suspension backend — they run in
+# node/workers where nothing may suspend. coroutine.h/libcontext key on
+# __EMSCRIPTEN__ directly, so no ABI define is threaded through the TU flags.
 
 # Step 6: Create build directory
 mkdir -p "${KICAD_BUILD}"
@@ -365,23 +364,11 @@ fi
 
 log_info "Stub libraries built"
 
-# Step 6.2/6.3: wasm-opt + wasm-emscripten-finalize handling.
-# For the editor apps these tools OOM on the huge debug wasm, so we stub them in
-# the container and run them on the host (docker/build.sh phase 2). The small,
-# debug-stripped (-g0) CLI finalizes fine in-container, so for kicad_tools
-# we restore/keep the real tools and skip host post-processing entirely.
+# EMSDK is needed below (emscripten sysroot paths in the CMake invocation).
 if [ -z "${EMSDK}" ]; then
     log_error "EMSDK environment variable is not set."
     exit 1
 fi
-EMSDK_WASM_OPT="${EMSDK}/upstream/bin/wasm-opt"
-EMSDK_FINALIZE="${EMSDK}/upstream/bin/wasm-emscripten-finalize"
-
-# JSPI has no post-link asyncify pass: every app finalizes in-container with
-# the REAL tools. The .real backups exist on containers that ran the retired
-# asyncify stub dance — restore them if present.
-[ -f "${EMSDK_WASM_OPT}.real" ] && cp "${EMSDK_WASM_OPT}.real" "${EMSDK_WASM_OPT}"
-[ -f "${EMSDK_FINALIZE}.real" ] && cp "${EMSDK_FINALIZE}.real" "${EMSDK_FINALIZE}"
 
 # Step 6.5: Verify WASM support is in KiCad fork
 # The kicad submodule should already have WASM port detection and kiplatform support
@@ -531,16 +518,16 @@ fi
 # (scripts/common/jspi-exports.txt: the wx KEEPALIVE entries that can park +
 # pcbjam_libctx_entry; regenerate by grep, not memory), the jspi-scheduler
 # pre-js, and the runtime methods its spill-stack discipline needs
-# (stackSave/stackRestore/HEAPU8). Headless CLIs: nothing — their targets pin
-# -sASYNCIFY=0 and nothing in them may suspend.
+# (stackSave/stackRestore/HEAPU8). Headless CLIs: nothing — no suspension
+# backend; nothing in them may suspend.
 case "${APP_NAME}" in
     kicad_tools|occ_service)
-        ASYNC_LINK_FLAGS=""
-        ASYNC_RUNTIME_METHODS="-sEXPORTED_RUNTIME_METHODS=['ccall','cwrap','UTF8ToString','stringToUTF8','lengthBytesUTF8']"
+        JSPI_LINK_FLAGS=""
+        JSPI_RUNTIME_METHODS="-sEXPORTED_RUNTIME_METHODS=['ccall','cwrap','UTF8ToString','stringToUTF8','lengthBytesUTF8']"
         ;;
     *)
-        ASYNC_LINK_FLAGS="-sJSPI -sJSPI_EXPORTS=@${PROJECT_ROOT}/scripts/common/jspi-exports.txt --pre-js ${PROJECT_ROOT}/scripts/common/shims/jspi-scheduler.js"
-        ASYNC_RUNTIME_METHODS="-sEXPORTED_RUNTIME_METHODS=['ccall','cwrap','UTF8ToString','stringToUTF8','lengthBytesUTF8','stackSave','stackRestore','HEAPU8','HEAP8','HEAP32']"
+        JSPI_LINK_FLAGS="-sJSPI -sJSPI_EXPORTS=@${PROJECT_ROOT}/scripts/common/jspi-exports.txt --pre-js ${PROJECT_ROOT}/scripts/common/shims/jspi-scheduler.js"
+        JSPI_RUNTIME_METHODS="-sEXPORTED_RUNTIME_METHODS=['ccall','cwrap','UTF8ToString','stringToUTF8','lengthBytesUTF8','stackSave','stackRestore','HEAPU8','HEAP8','HEAP32']"
         ;;
 esac
 
@@ -556,7 +543,7 @@ emcmake cmake "${KICAD_DIR}" \
     -DCMAKE_POLICY_VERSION_MINIMUM=3.5 \
     -DCMAKE_CXX_FLAGS="${EXTRA_FLAGS} -Xclang -fno-pch-timestamp -pthread --use-port=zlib -DKICAD_USE_PLATFORM_WASM=1${DIAG_DEFINES} -I${SYSROOT}/include -I${STUBS_DIR} -include ${STUBS_DIR}/char_traits_uint16_workaround.h" \
     -DCMAKE_C_FLAGS="${EXTRA_FLAGS} -pthread --use-port=zlib -I${SYSROOT}/include -I${STUBS_DIR}" \
-    -DCMAKE_EXE_LINKER_FLAGS="${LINKER_DEBUG_FLAGS} -pthread ${ASYNC_LINK_FLAGS} -sUSE_PTHREADS=1 -sMALLOC=mimalloc -sPTHREAD_POOL_SIZE='${PTHREAD_POOL_EXPR}' -sPTHREAD_POOL_SIZE_STRICT=0 -sALLOW_MEMORY_GROWTH=1 -sINITIAL_MEMORY=256MB -sMAXIMUM_MEMORY=4GB -sMAX_WEBGL_VERSION=2 ${GL3D_LINK_FLAGS} ${NANOSLEEP_YIELD_LINK} ${MALLINFO_STUB_LINK} ${ASYNC_RUNTIME_METHODS} ${EMBIND_LINK_FLAG} -L${SYSROOT}/lib -L${KICAD_BUILD}/common -L${KICAD_BUILD}/common/gal ${STUBS_BUILD}/libgit2_stub.a ${STUBS_BUILD}/libcurl_stub.a${APP_STUB_LINK} ${STUBS_BUILD}/libnng_stub.a ${EMBIND_OBJ}" \
+    -DCMAKE_EXE_LINKER_FLAGS="${LINKER_DEBUG_FLAGS} -pthread ${JSPI_LINK_FLAGS} -sUSE_PTHREADS=1 -sMALLOC=mimalloc -sPTHREAD_POOL_SIZE='${PTHREAD_POOL_EXPR}' -sPTHREAD_POOL_SIZE_STRICT=0 -sALLOW_MEMORY_GROWTH=1 -sINITIAL_MEMORY=256MB -sMAXIMUM_MEMORY=4GB -sMAX_WEBGL_VERSION=2 ${GL3D_LINK_FLAGS} ${NANOSLEEP_YIELD_LINK} ${MALLINFO_STUB_LINK} ${JSPI_RUNTIME_METHODS} ${EMBIND_LINK_FLAG} -L${SYSROOT}/lib -L${KICAD_BUILD}/common -L${KICAD_BUILD}/common/gal ${STUBS_BUILD}/libgit2_stub.a ${STUBS_BUILD}/libcurl_stub.a${APP_STUB_LINK} ${STUBS_BUILD}/libnng_stub.a ${EMBIND_OBJ}" \
     -DCMAKE_SHARED_LINKER_FLAGS="-Wl,--allow-multiple-definition" \
     -DCMAKE_MODULE_LINKER_FLAGS="-Wl,--allow-multiple-definition" \
     -DZLIB_LIBRARY="${EMSDK}/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libz.a" \