_run_claim_guards read the agent's other tasks via unlocked SELECTs
before claim() took its row lock, and claim()'s FOR UPDATE locked only
the TARGET row — so two concurrent i_will_work_on by the SAME agent on
TWO DIFFERENT pending tasks each locked their own row, each read an
empty in_progress set, each passed already_active, each claimed+started
→ the agent ended with two in_progress tasks (the in-process asyncio
Lock is lost on orchestrator-restart split-brain, so it wasn't a
DB-level guarantee).
Fix: TaskService.acquire_claim_lock takes a transaction-scoped
pg_advisory_xact_lock keyed by hashtextextended(agent_id). The gate
acquires it BEFORE the guard reads (for non-coordinator roles only) so
the second concurrent claim's read sees the first's committed
in_progress task and is rejected. Tx-scoped → auto-releases on
commit/rollback, can't outlive the request.
Coordinator exemption (the key logical-regression guard): cell_pm /
main_pm do NOT take the lock — the PM coordinator concurrency feature
lets a PM plan+delegate many roots in parallel, and a per-agent lock
would serialize those claims and regress it. Matches the existing
_COORDINATOR_ROLES already_active/paused guard exemption. A hash
collision only causes benign false serialization, never a false
negative.
Tests: unit (dev acquires lock before guard read; coordinator does
not) + real-PG integration (same-agent serializes, different-agent
does not, releases on rollback).
Renn F
02984b996f