The single spawn-armed timer charged API queue latency to the work budget:
the recurring '0 turns / $0.00 / x3 attempts' failure with four budget-bump
receipts (180->300s, 240->360s, 300->420s, 90->300s). Split: startup phase
(no NDJSON byte yet) kills EARLY at min(grace, timeout) with the distinct
exitReason 'timeout_startup' — an availability verdict, not transcript
archaeology — and the work phase arms on the first byte for the REMAINING
budget, so total wall never exceeds the timeout (tier envelopes are
margin-free: tests pass timeout: CAPTURE_MS and bun-budget the same tier).
Local grace 90s (observed queue latency 60-90s), CI floor 300s (TODOS-filed;
shared runners queue harder), both pinned by the new grace tests with fake
-claude shims covering the late-first-byte and silent-API paths.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
All three provider runners (claude/codex/gemini) killed only the direct
child on timeout: tool subprocesses the CLI spawned survived as orphans
holding our pipes open and burning shared API rate (observed: a 600s
timeout stretching past 1400s; a stalled run once burned a core for 15
hours). gstack-detach's watchdog had the same shape one level up — killpg
SIGTERM, 5s grace, then a direct-child proc.kill() that orphaned
grandchildren.
Fix: spawn provider children via node:child_process with detached (own
process group) and killProcessGroup(SIGKILL) in the timeout handler —
runShardChild's proven pattern, EPERM/ESRCH fallbacks included. The codex
and gemini copies also gain the reader.cancel() + stderr Promise.race
hardening only the claude copy had (they still carried the blocked-drain
hang it fixed). gstack-detach's watchdog now group-SIGKILLs after the
grace.
Regression net: test/session-runner-groupkill.test.ts drives the REAL
runSkillTest against a fake claude shim (PATH override) that spawns a
grandchild and wedges — the run must classify timeout within budget and
leave neither shim nor grandchild alive — plus source pins on all three
runners (detached + killProcessGroup, no bare timeout kill, no Bun.spawn
reversion).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
