Depends on #2192 and #2208.

Part of #2152.

Problem

GOOS=wasip1 GOARCH=wasm llgo build can produce a module after #2192, but goroutines still select the pthread runtime. The resulting executable imports shared host memory and WASI pthread facilities, so ordinary single-worker Wasmtime execution cannot run Go scheduler behavior.

The continuation implementation also needs a clear ownership boundary. Scheduler code should not know whether a backend uses Emscripten Fiber, a raw Asyncify save area, a future resumable ABI, or standardized stack switching.

Implementation

• Make WASI pthread scheduling an explicit LLGO_WASI_THREADS=1 compatibility mode.
• Add a raw wasm32 execution-context backend and a one-M/one-P FIFO scheduler for default WASI Preview1 builds.
• Run package initialization and main.main as the first schedulable task while keeping the host entry on the system stack.
• Put backend-specific stack and Asyncify storage ownership in runtime/internal/wasmcontext.
• Let the runtime supply root-aware allocate/free callbacks only during cold context creation and destruction. The callbacks are not retained per G; Swap, Resume, and Suspend remain direct concrete hot-path calls.
• Keep queue ownership and scheduling policy in runtime/internal/runtime; the continuation package does not inspect G/M/P state.
• Declare Asyncify as a typed target capability; executable linking writes a temporary core module, runs pinned Binaryen instrumentation, and atomically publishes the final module. Archives and shared libraries are unchanged.
• Compile LLVM 19 SjLj with legacy wasm EH, apply Asyncify, then translate the final module to standardized exnref EH.
• Keep the existing JS wasm scheduler behavior behind the same internal context boundary.
• Preserve the historical pthread source selection and fatal behavior when LLGO_WASI_THREADS=1 is set.
• Depend on ssa/wasm: use static defer continuation dispatch #2208 for static wasm defer continuation dispatch; without it, LLVM 19 crashes while selecting runtime.EnsureLocalInitializer after compiler/runtime: add //llgo:tls and //llgo:gls package variables #2079.

The implementation is intentionally limited to the scheduler/context foundation. Channel blocking, timers and host async integration, wasm GC integration, root/safepoint work, and optional WASI Preview2 support remain follow-up work tracked by #2152.

Validation

All local commands use GOMAXPROCS=2 and -p=1 where applicable.

• macOS arm64, Go 1.26.5: J32, J64, and P1 scheduler fixtures pass, including deadlock exit status and 5,000 serial goroutine lifecycles.
• macOS: default P1 selects fatal_wasm + proc_wasip1; LLGO_WASI_THREADS=1 selects fatal_default + proc_pthread. Both build, and default P1 validates and runs under Wasmtime 39.0.1.
• macOS: focused build/crosscompile/SSA tests, the complete runtime module, and native llgo test -p=1 ./test/llgoext pass.
• runtime/internal/wasmcontext and runtime/internal/runqueue each have 100% statement coverage.
• Ubuntu 24.04 amd64 container, capped below 15 GiB and at 2 CPUs with no network or swap: the changed runtime packages retain 100% coverage and both default/threads P1 source selections pass under Go 1.26.5.
• Earlier branch validation also covers P1 -O0, -O3, ThinLTO, post-link validation/execution, no default pthread/shared-memory imports, the external-module _demo/c/helloc path, and the full Ubuntu/macOS CI matrix.
• Full LTO still hits the existing LLVM 19 SelectionDAG crash in runtime.printany; the same failure reproduces on the unmodified runtime/wasm: add single-worker Asyncify scheduler #2192 base.

The lifecycle abstraction changes final scheduler modules by +2,991 bytes for J32 and +1,567 bytes for J64 against the same pre-lifecycle #2192/W tree. Binaryen reports six additional functions, two table entries, and seven indirect calls from the cold allocation callbacks. This is artifact size, not per-G memory; the existing 64 KiB stack and 64 KiB Asyncify reservations are unchanged. The measured P1 +172-byte integration delta uses an older W baseline and is not presented as a pure lifecycle comparison.

Independent diff over the current #2192 and #2208 merge tree: 31 files, +1,402/-101. The new lifecycle commit removes scheduler-owned backend buffers while adding focused storage failure/cleanup coverage. No previously runnable test is skipped or ignored.