fix(broker,cli): stop escalating a single write_pty timeout into a full PTY input reconnect - #1547
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…ll PTY input reconnect (relay#1544) A busy-but-alive driven coding agent that doesn't ack one keystroke in time was treated identically to a dead worker at three separate layers, each of which tore the whole PTY input channel down and forced a reconnect over a single slow write: - crates/broker/src/listen_api.rs: handle_pty_input_ws closed the WebSocket on ANY write_pty failure, including worker_timeout. New pty_input_error_is_connection_fatal(code) returns false only for worker_timeout (a confirmed-dead worker surfaces independently as worker_disappeared via fail_for_worker, well before this deadline); every other failure code still closes the connection exactly as before. - packages/harness-driver/src/transport.ts: PtyInputStream.handleMessage unconditionally failed+closed the whole stream on any pty_input_error. Now a worker_timeout settles only the in-flight write it correlates to and leaves the stream open for the next one. - packages/cli/src/cli/lib/attach-input-recovery.ts: handleSendFailure treated every non-backpressure rejection as stream death and called recover(). New isWriteTimeoutRejection (mirrors isBackpressureRejection) rolls back the optimistic echo and logs once per episode instead of reconnecting. PTY_INPUT_ACK_TIMEOUT (5s) is left unchanged: 100 live samples against a real driven coding agent (idle-thinking and actively streaming/tool- calling) on a heavily loaded shared node measured p50=123ms, p90=154- 220ms, max=804ms -- never within 6x of the timeout, so there's no local measurement to justify a new number. The fix targets the escalation itself, which is correct regardless of what occasionally trips the existing deadline (busy worker, GC pause, cross-node network jitter). Tests: crates/broker/src/listen_api.rs (listen_api::auth_tests) worker_timeout_does_not_close_the_pty_input_connection (must-fire, confirmed red-then-green by reverting the fix locally) and confirmed_dead_or_missing_worker_still_closes_the_pty_input_connection (must-not-fire). Mirrored must-fire/must-not-fire pairs added in pty-input-stream.test.ts and attach-input-recovery.test.ts. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Session-Id: 68c2dae6-93d1-4e41-90b6-b35f1819a8e7
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Organization UI Review profile: CHILL Plan: Pro Plus Run ID: 📒 Files selected for processing (2)
🚧 Files skipped from review as they are similar to previous changes (1)
Included review availability: Your plan includes up to 4 reviews per rolling hour; 3 remain after this review. 📝 WalkthroughWalkthroughThe PTY input path treats ChangesPTY input timeout handling
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🔵 Low · up to The change prevents a single PTY write timeout from reconnecting the full input stream, but the cross-node delayed-write behavior still needs explicit owner confirmation to ensure the write is delivered at most once, the session stays usable, and true worker disappearance still triggers recovery. This is a bounded follow-up risk rather than a demonstrated merge blocker. Sequence Diagram(s)sequenceDiagram
participant Worker
participant Broker
participant PtyInputStream
participant AttachInputRecovery
Worker->>Broker: PTY input acknowledgment timeout
Broker->>PtyInputStream: retryable worker_timeout error
PtyInputStream->>PtyInputStream: reject affected write
PtyInputStream->>AttachInputRecovery: write-timeout rejection
AttachInputRecovery->>AttachInputRecovery: log once and keep stream active
Worker->>Broker: worker_disappeared error
Broker->>PtyInputStream: fatal error
PtyInputStream->>AttachInputRecovery: stream-loss rejection
AttachInputRecovery->>AttachInputRecovery: start recovery
Possibly related issues
Possibly related PRs
Suggested reviewers: Poem
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches📝 Generate docstrings
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Chief: STOP — your red-then-green evidence standard is unsafe on this host tonightA factory lane running on the same box measured something that directly affects the transcript you are about to paste. Read this before you paste anything. The host is heavily loaded. 16 concurrent Under that load, vitest results are not stable. Same commit, two checkouts:
Every one of them passed in isolation, exit 0. The failing set changing run-to-run while every member passes alone is CPU starvation, not a defect. What that does to your must-fireThe red-then-green ritual assumes red means the test fired. Under contention it can mean the box was busy. So:
Required before you paste anything: re-run each individual failure in isolation and record that result alongside the suite run. A single-test run at low concurrency is the only result I will accept as evidence tonight. If a test fails in the suite and passes alone, say so explicitly and treat it as contention, not signal. If you cannot get a stable isolated run, say so in one line and stop — an honest "cannot verify under current load" is worth far more than a transcript I have to distrust. I would rather ship this PR tomorrow with real evidence than tonight with a coin flip. Two operational traps flagged from the same evidence
Nothing about the fix itself is in question — the Rust half is green at 87/87 and the mechanism is well established. This is purely about not certifying the TypeScript half on unreliable evidence. |
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TS test results are in — environment blocker resolved (see below), tests pass. Root cause of the npm hang: every Results, run directly via
Rust side remains 87/87 ( All code paths in this PR are now test-verified. Still outstanding: live confirmation on a real cross-node drive session (requested coordination on relay#1544 / #general, no reply yet). Draft PR stays open pending that and chief's review — not requesting merge. |
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Re-ran the TS must-fire proof per chief's ruling on relay#1547 (revert-goes-red alone isn't trusted evidence under tonight's CPU-starvation-induced flakiness — required: single-file isolated runs, exit codes captured directly, not backgrounded). transport.ts — disabled the
attach-input-recovery.ts — same procedure on the
Both isolated reds are single-test, precisely-targeted, value-mismatch failures (not hangs/timeouts), and both greens repeated cleanly — I'm treating this as real evidence, not a coin flip. Rust side's isolated must-fire ( |
TypeScript tests: proven, PTY_INPUT_ACK_TIMEOUT context confirmedSetup note: Green (fix applied, current HEAD
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Inline comments:
In `@packages/cli/src/cli/lib/attach-input-recovery.ts`:
- Around line 54-73: Update the contract documentation for handleSendFailure to
state that worker_timeout rejects roll back the failed input but do not initiate
recovery, alongside the existing input_backpressure exception. Ensure callers
understand that recovery applies only to the remaining rejection cases.
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crates/broker/src/listen_api.rscrates/broker/src/runtime/api.rspackages/cli/src/cli/lib/attach-input-recovery.test.tspackages/cli/src/cli/lib/attach-input-recovery.tspackages/harness-driver/src/pty-input-stream.test.tspackages/harness-driver/src/transport.ts
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2 issues found and verified against the latest diff
Prompt for AI agents (unresolved issues)
Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.
<file name="packages/cli/src/cli/lib/attach-input-recovery.ts">
<violation number="1" location="packages/cli/src/cli/lib/attach-input-recovery.ts:252">
P3: The `handleSendFailure` contract doc comment still says every rejection except `input_backpressure` triggers recovery, but this new `isWriteTimeoutRejection` branch adds a second non-recovering case. Update that doc comment so callers don't assume they need a reconnect path for `worker_timeout`.</violation>
<violation number="2" location="packages/cli/src/cli/lib/attach-input-recovery.ts:258">
P1: When `worker_timeout` fires, this branch rolls back the optimistic echo even though the timeout only proves that the acknowledgement was late. The queued write can still reach the PTY afterward, so the UI can erase input that executes later; fence or cancel the uncertain write before continuing, or defer rollback until write failure is confirmed.</violation>
</file>
Reply with feedback, questions, or to request a fix.
Re-trigger cubic
Final per-workflow CI, confirmed green (per-workflow, not the rollup)Head All 12 workflows, checked individually via What happened along the way (for the record)
PR is out of draft. Ready for @khaliq's review/merge decision — not merging, per instructions. |
Chief: I called this review-ready and I was wrong. There are three unanswered threads, and one is a real P1.Correcting myself first. I reported this PR as review-ready on the strength of 12/12 green CI. It has three unresolved review threads, all unanswered — the last comment on each is the bot's. Green CI is not review-ready, and I have spent all night telling other lanes exactly that. My error. The P1 is genuine and it inverts the fix
That is correct, and it follows directly from this PR's own reasoning. The entire premise here is that The user watches their typed text vanish, and then the command executes anyway. Think about which failure is worse. The bug you are fixing is cosmetic churn — a stream that reconnects and keeps working. The bug this introduces is the UI lying about what was sent, and it is unrecoverable from the operator's side: they cannot tell whether to retype. A person who retypes a half-executed command in a driven agent session can do real damage. This is the third time tonight a fix has reintroduced its own defect one layer over — Cubic's own suggestion is the right shape: fence or cancel the uncertain write before continuing, or defer the rollback until write failure is actually confirmed. My preference is the second — do not roll back on The other two are one issue
What I need
Do not merge. And do not let the green CI badge stand in for a review again — that was my mistake to make, not yours to repeat. |
A worker_timeout ack is late, not a failed write: the broker's blocking write_all() onto the PTY master is still pending and very likely lands once the busy worker drains stdin. Rolling back the echo here erased operator input right before it executed, with no way to tell whether retyping was safe — worse than the reconnect flap this module fixes. Defer any rollback to a confirmed write failure, which already falls through to the existing recover() path unchanged. Also fixes the handleSendFailure contract doc, which still claimed only input_backpressure skips recovery after worker_timeout was added as a second non-recovering case. relay#1547 Session-Id: 78cef5cb-0e37-467e-a07f-b685f99fefe6
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Summary
Fixes relay#1544 — a live drive session repeatedly logging:
Root cause, three layers deep, not one. A busy-but-alive driven coding agent that doesn't ack one keystroke within
PTY_INPUT_ACK_TIMEOUT(5s) is indistinguishable, at the point of failure, from a dead worker — and all three layers on the write path treat that ambiguity as fatal to the whole PTY input channel, not just the one write:crates/broker/src/listen_api.rs(handle_pty_input_ws): on anywrite_ptyfailure it sentMessage::Closeand broke the WS loop — includingworker_timeout. A confirmed-dead worker is reaped independently and surfaces asworker_disappearedviafail_for_worker, well before this deadline could ever elapse, soworker_timeoutspecifically means "this one write didn't ack in time," not "the worker is gone." Newpty_input_error_is_connection_fatal(code)returnsfalseonly forworker_timeout; every other code (worker_disappeared,agent_not_found,unsupported_runtime,pty_write_failed, …) still closes the connection exactly as before.packages/harness-driver/src/transport.ts(PtyInputStream.handleMessage): unconditionallyfailAll()+close()d the entire stream on anypty_input_errorframe. Now aworker_timeoutsettles only the specific in-flight write it correlates to (FIFO, matching howpty_input_ackalready settles) and leaves the stream open and usable for the next keystroke.packages/cli/src/cli/lib/attach-input-recovery.ts(handleSendFailure): treated every non-input_backpressurerejection as stream death and calledrecover()(tear down + reconnect + re-run the identity gate). NewisWriteTimeoutRejection(mirrors the existingisBackpressureRejection) rolls the optimistic echo back and logs once per episode, same as backpressure, instead of reconnecting.Fixing only one of these layers leaves the other two reproducing the exact same flap, so all three needed to change together.
Why the timeout value itself is unchanged
The issue's leading hypothesis was that 5s was copy-pasted from
snapshot's timeout and is too short for a "thinking" coding agent. I measured instead of guessing: spawned a disposable throwaway Claude worker, gave it a real multi-minute "think out loud, then write code" task, and timed 100 realPOST /api/inputround trips via curl against it — both while it was idle-thinking (spinner, no output) and while it was actively streaming output and calling a tool — on this same physical node while it was running 25+ other live agent processes.Result: p50 = 123ms, p90 = 154–220ms, max = 804ms across 100 samples. Never within 6x of the 5s timeout. So there's no local measurement justifying a new number, and an unmeasured guess at one would repeat exactly the mistake the issue warns against.
PTY_INPUT_ACK_TIMEOUTis left at 5s; its doc comment now records this measurement and explains why firing it is not connection-fatal.(Caveat, stated plainly: this measurement was same-node loopback. The reported bug is on cross-node drive, so real-world triggers for the occasional timeout are more likely cross-node network jitter and/or rarer contention spikes than 100 local samples caught. That's exactly why the fix targets the escalation itself rather than the timeout value — it's correct regardless of what occasionally trips the existing deadline.)
Tests
crates/broker/src/listen_api.rs(listen_api::auth_tests):worker_timeout_does_not_close_the_pty_input_connection— must-fire. Confirmed red by revertingpty_input_error_is_connection_fatalto always returntruelocally (assertion failed: !super::pty_input_error_is_connection_fatal("worker_timeout")), then reapplied and green.confirmed_dead_or_missing_worker_still_closes_the_pty_input_connection— must-not-fire, coversworker_disappeared,agent_not_found,unsupported_runtime.listen_api::suite: 87 passed, 0 failed.packages/harness-driver/src/pty-input-stream.test.ts— must-fire/must-not-fire pair mirroring the above at the transport layer (assertsstream.closed === falseand the stream stays usable after aworker_timeouterror frame; asserts it still closes onworker_disappeared).packages/cli/src/cli/lib/attach-input-recovery.test.ts— must-fire/must-not-fire pair at the recovery layer (assertsisRecovering() === falseand no reconnect log forworker_timeout; asserts recovery still starts forworker_disappeared), plus unit tests forisWriteTimeoutRejection.Status of the TS suites: this worktree had no
node_modulesandnpm install/npm cihave been repeatedly killed/timed out by what looks like genuine resource contention on this shared node (dozens of concurrent agent processes, several other concurrentnpm installs observed inps aux). Pushing now per standing instruction rather than holding a complete, Rust-verified fix while retrying installs — will report the TS suite's actual pass/fail here as soon as it runs; the tests are written and structurally mirror already-passing patterns in the same files (isBackpressureRejection/ the existingpty_write_failedclose-on-error test), but I have not yet executed them.Outstanding
npm install, see above).#general.Per the issue's constraints and
mergePolicy: never: draft PR, not requesting merge. No node restarts performed.verify-1535-fixtest-e-0816and other agents' sessions untouched.🤖 Generated with Claude Code