The spawn-time output tail feeds stdout AND stderr into ONE buffer, so its
contents are not line-accurate. uvicorn logs to stderr in raw chunks, and a
chunk that ends without a newline is concatenated directly onto the stdout
sentinel that follows it:
INFO Started server process [4711]HERMES_BACKEND_READY port=65238
The late-attach seed scan added for #60323 matched that buffer with the
line-anchored `_READY_RE`, so `^` never lined up and the seed silently
recovered nothing. The live stdout listener cannot cover the gap either: the
sentinel was already consumed by the tail, and flowing-mode streams never
replay chunks to late listeners. The wait then runs out its full 90s deadline
and a healthy, listening backend is SIGTERMed — while desktop.log, which reads
both streams, plainly shows the READY line. That contradiction (READY logged,
boot timed out anyway) is the reported macOS regression.
Scan the tail with a boundary-guarded pattern instead of a line-anchored one.
`port=<digits>` keeps the token unambiguous, so prose naming the sentinel and
longer identifiers ending in it still do not match. The live per-line scanner
keeps `^`: individual stream chunks ARE line-accurate there, and loosening it
would let unrelated child output settle the boot on a bogus port.
Scope: the seed only. Watching stderr on the live path is #97086's change and
is deliberately untouched here — the two compose.
joaomarcos
4bbfdaf0b7