selfcheck: --no-wasm-dynamic-tiering, so Windows no longer aborts checks at exit - #56

The crash

On Windows, a selfcheck that calls process.exit right after loading its .ts files sometimes died with libuv's Assertion failed: !(handle->flags & UV_HANDLE_CLOSING), file src\win\async.c, line 94 (exit 3221226505), after all its checks had passed. Today it turned four runs red and refused one push.

Cause

Node's TypeScript type-stripper is WebAssembly. When V8 is still recompiling the stripper's hot functions in the background (dynamic tiering), process.exit closes the libuv handle that task reports back on. This is nodejs/node#56645, fixed by #61999, which isn't in Node 26.2.

How it was pinned down:

• Bisected to env/update.ts's module: a two-line file that imports it and calls process.exit(0) crashed 30 of 30 times, run one at a time.
• It's not one part of the file: each half alone doesn't crash, and neither does padding a non-crashing variant to the same size. It needs both install and autoUpdate.
• It disappears under --jitless, --liftoff-only, --no-liftoff and --no-wasm-dynamic-tiering. Turning off the background compile-task threads doesn't help.

Fix

src/selfcheck.ts starts each check with --no-wasm-dynamic-tiering. That's one line, the 33 check files stay as they are, and real wf commands are untouched.

Measured

• env/update.selfcheck.ts one at a time: 10 of 30 crashed before, 0 of 30 after.
• The whole selfcheck, 30 runs: 6 red before, 0 after. Each run takes 0.89 s → 1.16 s.
• Real wf commands (status, next, an unknown command, through both entries): none crashed in 40 runs. They do more work before they exit. If one ever does, the same flag or setting process.exitCode instead of calling process.exit is the fix.