fix(acp): treat session/prompt ack timeout as delivered#4812
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POST /v1/sessions/:id/send to an idle session returned a false-negative 422 PROMPT_DELIVERY_FAILED even though the prompt was delivered and the agent replied — the dashboard surfaced an error toast for a message that went through. Root cause: sendPrompt treated an AcpJsonRpcTimeoutError as "not delivered" (#4705). Empirically the request is written to a live JSON-RPC pipe and claude-agent-acp (single-threaded, in-order) processes the queued prompt; the ack merely lags past the 5s window on idle/cold-resumed sessions. A dead pipe rejects with a transport error, never a timeout — so a timeout is a slow ack, not a non-delivery. Reverses the #4705 assumption: timeout now returns delivered:true; the transcript remains the source of truth. Actual JSON-RPC errors (e.g. -32601) are still thrown. Updated the 3 test sites that asserted the old delivered:false / prompt_ack_timeout behavior. Verified live: /send on an idle session returns {"ok":true,"delivered":true,"attempts":1} and the reply appears in the transcript. Generated by Hephaestus (Aegis dev agent)
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✅ Approved.
Review summary:
- Correctness: Reverses the #4705 assumption with empirical justification. Timeout on a live JSON-RPC pipe = slow ack, not non-delivery. Dead pipes reject with transport errors, never timeouts. The reasoning is sound.
- Security: No new attack surface. No secrets, no input validation changes.
- Tests: 3 test sites updated (acp-backend.test.ts, acp-sendprompt-timeout-4705.test.ts). New direct sendPrompt test covers the continue-conversation case. All assertions match the new behavior.
- Patterns: Follows existing error handling patterns. Log operation renamed from
promptAckTimeout→promptAckTimeoutAcceptedfor audit clarity. - PR Hygiene:
fix(acp):title correct. Targetsdevelop. Issue #4705 linked in body. +53/-18, 3 files — focused scope. - CI: 16/17 green, 1 pending (helm-smoke). All critical checks pass (test ubuntu-20/22, lint, dashboard-e2e, platform-smoke, CodeQL, security scans).
9-gate sweep: All gates pass. Squash merging now.
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Jun 27, 2026
…emantics PR #4812 reverses the #4705 assumption: a session/prompt timeout is now treated as delivered:true (slow ack on a live pipe, not non-delivery). Update the error-values note in the POST /v1/sessions/:id/send section to reflect the new semantics and clarify when prompt_ack_timeout still surfaces in the 422 response. Refs: #4812, #4705
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Aegis version
Developed with: v0.6.7
Problem
POST
/v1/sessions/:id/sendto an idle session returned a false-negative422 PROMPT_DELIVERY_FAILED(prompt_ack_timeout) even though the prompt was delivered and the agent replied. The dashboard showed an error toast for a message that went through — continue-conversation appeared broken.Root cause
sendPrompttreatedAcpJsonRpcTimeoutErroras "not delivered" (#4705). Empirically the request is written to a live JSON-RPC pipe andclaude-agent-acp(single-threaded, in-order) processes the queued prompt; the ack merely lags past the 5s window on idle/cold-resumed sessions. A dead pipe rejects with a transport error, never a timeout — so a timeout is a slow ack, not a non-delivery.Change
Reverses the #4705 assumption: on
session/prompttimeout, returndelivered: true; the transcript remains the source of truth. Actual JSON-RPC errors (e.g.-32601) are still thrown.src/services/acp/backend/prompts.ts— timeout →{ delivered: true, attempts: 1 }.delivered: false/prompt_ack_timeoutbehavior (acp-sendprompt-timeout-4705.test.ts,acp-backend.test.ts).Verification
npx tsc --noEmitclean./sendon an idle session →{"ok":true,"delivered":true,"attempts":1}, reply appears in transcript (was 422).Notes
npm run gatehas pre-existing Windows-only flakes (path-separator inworktree-4694, ENOENT temp races) unrelated to this change; CI runs on Linux where those pass.