The spawn-time output tail (#93608) puts child stdout into flowing mode at
spawn. Both backend spawn paths in main.ts then await claimBackendChild
(whose Windows Get-Process probe cold-starts in 2-8s) and boot-progress IPC
BEFORE waitForDashboardPortAnnouncement attaches its stdout listener. Node
streams never replay consumed chunks to late listeners, so a READY sentinel
printed during that window was lost forever — the wait hit its 90s timeout
and a healthy backend was killed (deterministic on Windows, racy on
macOS/Linux; still firing on v0.21.0 incl. concurrent multi-profile boots).
Fix (belt and suspenders, both spawn paths — primary and profile pool):
- create the port-announcement promise immediately after spawn, before any
await
- new bufferedOutput option on waitForDashboardPortAnnouncement: after
attaching its own listener, waitForDashboardPort scans the output tail's
already-buffered text for the sentinel, making listener-attach ordering
irrelevant regardless of call-site shape
The readyFile path was already ordering-safe (it polls a file, not the
stream). Approach follows stale PR #60986 by @ParaWheeler, rebased onto the
output-tail/readyFile plumbing added since.
Fixes#60323
Teknium
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