Bun keeps the parent event loop alive when an unref'd child has a piped
stderr stream. The first #4324 fix started with stderr: "pipe", so a
long-lived idle TTS/STT/tiny/mnemopi worker could keep short CLI commands
alive even after proc.unref().
Switch worker stderr capture to a temp-file fd target instead of a Bun
ReadableStream pipe. The parent does not start any JS read while the
worker is alive; after onExit it reads the bounded tail from the file,
logs captured lines, appends the tail to the surfaced worker Error, then
closes and removes the temp capture.
Add a regression that spawns a non-test wrapper process with an idle
unref'd worker and asserts the wrapper exits immediately. Existing stderr
capture, truncation, and intentional SIGKILL behavior remain covered.
Fixes#4324
roboomp
b0e52a13ac