Coordinator: keep the first minted pending payload on concurrent next() - #152
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Two concurrent next() calls for the same role can both observe no pending payload and each mint a fresh one; the last store.update wins, so the losing caller holds a signing request over bytes the coordinator no longer stores. Any checkpoint signed from that stale request then fails artifact_signer on submit — deterministically, on every retry. Serialize the decision inside the update callback: if a pending payload is already stored, keep it and build the response signing request from the stored bytes. Covers proposal, acceptance, evidence, and the proposal-window renewal path. Also extend the checkpoint failure detail tags with the recovered signer address prefix and the pending bytes hash prefix (session-scoped public data) so a residual artifact_signer failure separates wrong-key from wrong-bytes in one log line.
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Summary
agent_handshake_next: two concurrent polls for the same role could both observe no pending payload and mint different proposals/acceptances/evidence; the laststore.updatewon, stranding signatures made over the loser's request bytes (artifact_signeronsubmit_checkpoint, deterministic on retry).store.updatecallback — an existing stored pending is kept, and the response's signing request is always built from the stored bytes. Applied to proposal, acceptance, evidence, and the proposal-window renewal path.artifact_signer.<recovered12>.<bytesHash8>,artifact_digest.<expected8>,checkpoint_signer.<recovered12>) in the server-sideagent_handshake_tool_failurelog only — public errors staycoordination_failed.Evidence
9eeb53e9showeddetail: "artifact_signer"on all three acceptancesubmit_checkpointretries.Test plan
npm run build(mcp-server)npm test— 550/550/nextto VERIFIED after deploy