Port of upstream grok-build 1.0.1 (landed upstream 2026-08-06). The
coordinator fire-and-forgot every spawn, so a wide fan-out (graph
waves, swarm bursts, model-driven Task storms) could exhaust file
descriptors.
- kigi-tools task/admission: SubagentLimits — 32 concurrent per session
by default (KIGI_MAX_CONCURRENT_SUBAGENTS), queue|fail behavior
(KIGI_SUBAGENT_LIMIT_BEHAVIOR), zero clamped to 1, read once at the
composition root; parse_positive_env helper.
- Each parent session gets one spawn semaphore (map entries live for
the process so a resumed session shares its predecessor's limit);
handle_subagent_request holds an owned permit for the whole child
run — queue awaits FIFO with a unified-log notice at saturation,
fail routes through send_pre_spawn_failure. After a queued wait, a
closed parent command channel (teardown) fails the spawn instead of
running against a dead parent.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KSy9S31pZNWXtRZNVJ1sDf