Add WASI runtime configuration

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Summary

• add a WASI-specific single-P cooperative scheduler with no threads, signals, NUMA pinning, or stack switching
• add WASI fallbacks for runtime memory/NUMA/CPU APIs and single-threaded channel/poller locking
• compile the libxev WASI poll backend on Zig 0.16, including direct WASI fd read/write shims
• add a runtime-wasi-smoke module and test-wasi-runtime wasmtime step

Fixes #408

Notes

• zig build -Dtarget=wasm32-wasi installs the runtime artifacts and smoke module instead of trying to build the host compiler for WASI.
• The local machine does not have wasmtime, so the smoke run itself was not executed locally; the build step reports that dependency explicitly.

Validation

• zig fmt build.zig src/runtime/run_xev_bridge.zig zig-pkg/libxev-0.0.0-86vtcwIRFACVrx54GaHsMFFlyC4dTi0tcVh10V7btRUc/src/backend/wasi_poll.zig
• clang-format -i src/runtime/run_scheduler.h src/runtime/run_scheduler_wasi.c src/runtime/run_chan.c src/runtime/run_xev.c src/runtime/run_vmem.c src/runtime/run_numa.c src/runtime/run_runtime_api.c src/runtime/run_debug_api.c src/runtime/tests/wasi_smoke.c
• zig build -Dtarget=wasm32-wasi
• zig build
• zig build test (passes; emits the expected bad_check.run missing-symbol diagnostic)
• zig build test-runtime (82/82)
• zig build -Dtarget=wasm32-wasi test-wasi-runtime (not run: wasmtime is not installed locally)

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	runlang	ae5ed8e	Commit Preview URL Branch Preview URL	Apr 28 2026, 08:40 PM