countTurns-then-appendFileSync is read-then-write. N callers that all
observe used == budget-1 all decide to grant, and the bound is exceeded
by N-1. The comment above allowTurn asserted "Append-only: never
read-modify-write" and named the concurrent case - Phase 4.5/5 may spawn
several agents in a single message - as the reason it had to be. The
decision path was exactly what the comment denied, so the concurrency
claim had nothing under it.
Each grant now creates <data root>/trekresearch-loop-claims/<runId>-<slot>.claim
with flag 'wx' (O_CREAT|O_EXCL) before appending. The kernel picks the
winner per slot, slot numbers are bounded by the budget, and each can be
created exactly once - so total grants for a run cannot exceed the budget
however many callers arrive together. The ledger count now only says
where to start looking for a free slot.
Two of the three tests are deterministic and do not race anything: they
assert the invariant directly by pre-creating claims, including the state
a mid-append competitor leaves behind (ledger 7, slots 1-8 claimed, budget
8 -> deny). That matters because the third test - six real concurrent shim
processes at the boundary - passed even BEFORE the fix, since process
startup jitter serialised them. A race test that passes by luck is not
evidence, so it ships as a real-world regression guard next to the two
that are.
Stated rather than left to be discovered: claim files are empty, at most
budget per run, and never cleaned - the same standing as the ledger, which
also grows for the life of the data root. Reusing a runId across runs, or
two runIds colliding after filename sanitisation, both deny a turn, which
is the safe direction for a budget control.
Review finding 3994491ef1fdba6e0e3645b5b713cbdbdeb2b328 (MINOR).
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LuGhWAbWyRFBFeemfhxoVv
Kjell Tore Guttormsen
156539204a