fix(cursor): retry prompts that only returned a transport failure - #11225
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Cursor's ACP emits transient transport failures as assistant text and then reports a successful turn. Since pingdotgg#10337 the adapter fails such turns, but every blip still costs the user a manual resend. When the failed attempt produced nothing but the diagnostic (no tool calls, no requests to the user, no other assistant text) a replay cannot duplicate work, so retry the prompt with a bounded backoff before failing the turn. Interrupting the turn during the backoff settles it as cancelled, a steer takes the turn over, and any observed work keeps the existing fail-fast behavior. The mock agent gains T3_ACP_PROMPT_RESPONSE_TEXT_PROMPT_LIMIT so only the first N prompts answer with the scripted text.
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| delayMs: Duration.toMillis(delay), | ||
| }, | ||
| ); | ||
| const interrupted = yield* Deferred.await(ctx.turnInterrupted).pipe( |
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🟡 Medium Layers/CursorAdapter.ts:1146
Stopping a session does not wake a sendTurn waiting in the transport-failure retry backoff, so the call waits for the 1s/3s timeout and then returns the old transport failure instead of settling as cancelled. stopSessionInternal should signal ctx.turnInterrupted before removing the session, just as interruptTurn does.
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In file @apps/server/src/provider/Layers/CursorAdapter.ts around line 1146:
Stopping a session does not wake a `sendTurn` waiting in the transport-failure retry backoff, so the call waits for the 1s/3s timeout and then returns the old transport failure instead of settling as cancelled. `stopSessionInternal` should signal `ctx.turnInterrupted` before removing the session, just as `interruptTurn` does.
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Fixed in e0628a0: stopSessionInternal now settles turnInterrupted right after marking the session stopped, and the retry wait treats that wake the same as an interrupt (the turn settles as cancelled, matching a stop during the prompt itself). Covered by the new "settles as cancelled when the session stops while waiting to retry" test, which joins the turn without pumping the test clock.
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| Effect.timeoutOrElse({ duration: delay, orElse: () => Effect.succeed(false) }), | ||
| ); | ||
| // A stop or a steer that landed during the backoff owns the turn now. | ||
| if (ctx.stopped || ctx.promptsInFlight !== 1) { |
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🟠 High Layers/CursorAdapter.ts:1151
A quick steer during the retry backoff causes the superseded invocation to resend the original prompt. The steering sendTurn temporarily increments promptsInFlight, but its ensuring decrement can restore the value to 1 before line 1151 checks it, so the stale invocation passes the guard and replays prompt at line 1160. Track a persistent per-turn generation or steer marker and check it before retrying, rather than relying on the transient promptsInFlight count.
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In file @apps/server/src/provider/Layers/CursorAdapter.ts around line 1151:
A quick steer during the retry backoff causes the superseded invocation to resend the original prompt. The steering `sendTurn` temporarily increments `promptsInFlight`, but its `ensuring` decrement can restore the value to `1` before line 1151 checks it, so the stale invocation passes the guard and replays `prompt` at line 1160. Track a persistent per-turn generation or steer marker and check it before retrying, rather than relying on the transient `promptsInFlight` count.
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Fixed in e0628a0: sendTurn now bumps a persistent per-session promptSequence alongside promptsInFlight, and the retry loop checks it both before waiting and after waking, so a steer that completed during the backoff blocks the replay even though the in-flight count is back at 1. Covered by the new "lets a steer during the backoff take the turn instead of replaying the prompt" test: the steer finishes inside the backoff and exactly two prompts reach the mock.
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ApprovabilityVerdict: Would Approve Macroscope's review found this PR approvable — This is a focused Cursor adapter bug fix with bounded transport-failure retries and dedicated coverage for success, exhaustion, work detection, and interruption. Unresolved findings still flag cancellation and steer-concurrency risks in the retry path. Not approved because:
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Included review availability: Your plan provides up to 10 included reviews per hour; 8 remain after this review. 📝 WalkthroughWalkthroughThe Cursor ACP adapter now retries transport failures that occur before prompt work. It tracks prompt activity, uses backoffs, cancels pending retries on interruption or session stop, and handles superseding steers. Tests cover retry outcomes. ChangesCursor transport failure retries
Priority: ⬇️ Low Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Suggested reviewers: Sequence Diagram(s)sequenceDiagram
participant CursorAdapter
participant ACPSession
participant MockACPAgent
CursorAdapter->>ACPSession: Send prompt
ACPSession->>MockACPAgent: Request prompt response
MockACPAgent-->>ACPSession: Return transport diagnostic
ACPSession-->>CursorAdapter: Return prompt result
CursorAdapter->>CursorAdapter: Wait for retry backoff or interruption
CursorAdapter->>ACPSession: Retry prompt
Merge Risk: ⚪ Minimal · up to The bounded retry behavior preserves cancellation and steering semantics, with coverage for successful retries, exhaustion, prior work, interruption, session shutdown, and steers. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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In `@apps/server/src/provider/Layers/CursorAdapter.test.ts`:
- Around line 339-351: Update the test around sawDiagnostic and
adapter.interruptTurn to add a deterministic signal for entry into the retry
backoff, then await that signal before interrupting the turn. Ensure the signal
is emitted by the mock adapter or backoff path only after the initial
session/prompt completes and backoff begins, so the test exercises the
turnInterrupted branch rather than cancelling an active prompt.
In `@apps/server/src/provider/Layers/CursorAdapter.ts`:
- Around line 1146-1149: Update sendTurn’s Deferred.await(ctx.turnInterrupted)
retry-backoff flow so session shutdown wakes the wait immediately: settle a
shared lifecycle signal from both interruptTurn and stopSessionInternal, and
have the final failure path check ctx.stopped before propagating the retained
transport error.
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apps/server/scripts/acp-mock-agent.tsapps/server/src/provider/Layers/CursorAdapter.test.tsapps/server/src/provider/Layers/CursorAdapter.ts
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Stopping a session left a sendTurn waiting out its transport-failure backoff and then returning the stale failure; it now settles as cancelled at once, like a stop during the prompt itself. A steer that finished during the backoff could also restore the in-flight count to one before the retry re-checked it and so replay the original prompt; sendTurn now bumps a persistent per-session prompt sequence and the retry only proceeds while no later prompt has arrived. Tests synchronize on the warning the adapter logs right before it waits, via a test-scoped logger, instead of racing the first streamed delta.
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Thanks for the PR. We're not taking changes to the orchestration and provider layers right now: that part of the server is being rewritten for V2, and merging into the current code would either conflict with or be thrown away by that work. Closing for now. If this is still an issue once V2 lands, please reopen (or open a fresh PR against the new code) and we'll take a proper look. |
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Refs #7830. Cursor's ACP leaks transient transport failures (
Error: RetriableError: [unavailable] …,ConnectError: [unavailable], …) as assistant text and then reportsend_turn. Since #10337 T3 fails those turns instead of accepting them as answers, but every blip still costs the user a manual resend, while Cursor's own interactive agent retries these internally. A retry was also asked for in the follow-up on #10337.#10337 left retries out because a failed turn may already have done work a replay would repeat. This retries only when the failed attempt provably did no work: no tool calls, no approval, question, or plan-proposal requests, and no assistant text other than the diagnostic. Steers, cancels, and anything that ran a tool keep the existing fail-fast path. Retries are bounded to two (1s, then 3s) in the same ACP session; interrupting the turn or stopping the session during the backoff settles it as cancelled without sending the prompt again, and a steer landing during the backoff takes over the turn instead (tracked with a per-session prompt sequence, since the in-flight count can already be back at 1 by the time the retry fires). Plan and todo updates do not block a retry: they are progress notes the replay regenerates, not side effects.
The leaked diagnostic stays visible in the thread ahead of the retried answer; hiding it would mean buffering the assistant stream, which is out of scope here. This does not change the matcher breadth discussed in #10480:
[internal] Failed to run step, exceeded max retriesis still classified as a transport failure, and since it carries no tool calls it now gets the same two retries before the turn fails.Reproduced on 0.0.40 with cursor-agent 2026.09.08-6caf4ff (macOS): the first prompt of a fresh session came back after three seconds with
Error: RetriableError: [unavailable] Erroras the only output, and the adapter failed the turn. Server trace:Tests: six mock-provider tests in
CursorAdapter.test.tsreplace the previous transport-error test (retry succeeds, retries exhaust, prior work blocks the retry, interrupt or stop during the backoff settles as cancelled, a steer during the backoff takes over without a replay). The backoff tests synchronize on the warning the adapter logs right before it waits, captured by a test-scoped logger. The mock agent gainsT3_ACP_PROMPT_RESPONSE_TEXT_PROMPT_LIMITso only the first N prompts answer with the scripted text.vp test runon the file (26 tests, several consecutive runs),vp lintandvp fmt --checkon the changed files, andvp run --filter t3 typecheckpass.Model: Claude Fable 5.1. Harness: Claude Code.
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