fix(ssh): keep remote agents running across reconnects

[luke2x]

Problem

SSH reconnect can kill the managed remote server and its running agents. The local forward often goes stale across laptop sleep, and the 2-second reuse probe misses on a loaded host. In the reported case, macOS DarkWake reconnects killed a busy server about every 15 minutes overnight and no agent work survived.

Change

• Reconnect closes a stale local forward without running the managed-server stop; explicit Disconnect/Remove keeps the stop path.
• The launch script reuses a live managed server instead of killing it: a readiness failure leaves the server running and returns a retryable error, and the reuse path gets the existing 60-second cold-start budget. Newly launched processes still clean up when they fail to start.
• The update path is unchanged: a changed downloaded runner (RUNNER_CHANGED) still restarts the managed server, as on main. Whether to defer an update while runs are active is left to maintainers, per the triage on [Bug]: SSH reconnect kills a busy remote server, cancelling all running agents (2s reuse probe) #16477.

Scope and approval

One underlying problem: the SSH reconnect lifecycle in packages/ssh. It covers the stale-forward stop and the readiness-timeout kill; the RUNNER_CHANGED restart and the pairing script are untouched.

Fixes #16477. The failure is established in maintainer triage.

Verification

• vp test run packages/ssh/src/tunnel.test.ts --maxWorkers 1 --no-file-parallelism: 24 tests pass.
• The regressions fail on unchanged upstream: the captured fixture server processes are killed on an unchanged runner and stale-forward cleanup invokes remote stop. With this fix the processes stay alive and the stop command is not called.
• A fourth case writes a different runner to the state directory and asserts the managed server is stopped and replaced, so the update path stays covered.
• vp run --filter @t3tools/ssh typecheck, vp lint packages/ssh/src/tunnel.ts packages/ssh/src/tunnel.test.ts, and vp fmt --check on both files pass.
• Not exercised: actual laptop sleep and a production remote host. The tests use real temporary-home shell fixtures and captured process IDs.

Implemented and tested with OpenAI Codex (gpt-6.1-sol) in T3 Code. Review follow-ups by DeepSeek V4.1 Flash, coordinated and checked by Claude Opus 5.5.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-10T21:36:53.693392Z	d3258a2	PR opened

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[macroscopeapp]

Approvability

Verdict: Approved at d3258a2

Macroscope's review found this PR approvable — This is a focused SSH reconnect bug fix that preserves live remote agents while replacing stale local forwards, without changing explicit disconnect behavior. Production logic is localized and supported by targeted regression tests; no defaults or static-analysis controls are changed.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 91a316d and b0c31ab.

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📒 Files selected for processing (2)

• packages/ssh/src/tunnel.test.ts
• packages/ssh/src/tunnel.ts

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📝 Walkthrough

📝 Walkthrough

Walkthrough

The SSH launch script now checks live recorded servers before default runtimes. It waits for full readiness without stopping a recorded server on timeout. Stale tunnel cleanup removes the tunnel entry before closing it.

Changes

SSH reconnect recovery

Layer / File(s)	Summary
Reconnect server selection and readiness packages/ssh/src/tunnel.ts, packages/ssh/src/tunnel.test.ts	Reconnect checks a live recorded server before the default runtime. A changed runner stops the recorded server. Otherwise, a readiness timeout reports failure and leaves the server running. When no recorded server is live, the script adopts the default runtime as external after full readiness. Tests cover readiness, process metadata, runner changes, and launch-script assertions.
Stale tunnel replacement packages/ssh/src/tunnel.ts, packages/ssh/src/tunnel.test.ts	Stale cleanup removes the tunnel entry before closing it. Tests verify that replacement does not stop the remote server and that a later disconnect does.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: juliusmarminge

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Merge Risk: 🔵 Low · up to b0c31

Reconnects can remain blocked when saved server state points to an unrelated live process. This uncommon case needs a safe stale-state cleanup, but the PR is otherwise mergeable with owner awareness.

Security Architecture Review

Security architecture risk: 🔵 Low · up to b0c31

Reconnect preserves running work, and explicit disconnect retains the shutdown path. However, stale process identity can repeatedly block reconnection and complicate safe cleanup. No expansion of remote privileges was established.

Retained concerns

• Medium · reliability · inferred: Stale live PID state can strand reconnect recovery. After an unclean server exit and PID reuse, the head selects the unrelated live PID and recorded port, then exits on readiness failure without clearing ownership. Repeated reconnects select the same state, even when another default runtime is available. The base instead proceeded toward replacement after failed reuse. Explicit disconnect can recover only if its recorded-PID stop succeeds, and may signal the unrelated process. That signaling hazard predates the PR; the introduced regression is persistent stale-state selection without a non-destructive recovery transition.

Security review details

Security Blast Radius

• inferred — The demonstrated exposure is the selected SSH target’s launch state, remote server and agent work. Stop commands operate with the remote account’s signaling privileges, so stale identity can also affect unrelated processes signalable by that account. Broader tenant, service or environment propagation was not established.

Security Findings and Attack Paths

• inferred — PID reuse can cause the retained recovery concern without an attacker. Deliberate manipulation would require control over the selected remote launch state or relevant process/listener state. The inspected change does not establish an unauthenticated network-only path or newly gained privileges; the base already trusted recorded PIDs for termination.

Trust Boundaries and Controls

• observed — Pairing still runs through the selected SSH target and the shared remote base directory. The pairing command creates persisted credentials; consumption checks single use, expiry, revocation, requested scopes and any configured proof-key binding through a conditional database update. These controls are not replaced by readiness checks.

Resilience and Maintainability Implications

• observed — Removing stale local ownership before closing the forward prevents accidental remote shutdown. Explicit disconnect remains available after a failed reconnect, but failed process termination preserves ownership files and reports failure, limiting automatic recovery from an invalid recorded identity.

Hardening Proposals

• proposed — Consider durable process provenance and a non-destructive stale-state recovery transition that distinguishes a temporarily unready owned server from a reused PID or mismatched listener, without making readiness timeout terminate active work.

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Pre-merge checks | 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check		The PR meets the coding requirements in directly linked issue [#16477]. In packages/ssh/src/tunnel.ts, a live managed PID uses T3_READY_TIMEOUT_MS instead of the 2-second reuse probe. A readiness …
Out of Scope Changes check		The production changes stay within [#16477]. They modify SSH launch recovery and stale-forward lifecycle handling in packages/ssh. The tests directly verify reconnect preservation, update behavior, …
Title check		The title clearly and concisely describes the main SSH reconnect change: keeping remote agents running across reconnects.
Description check		The description includes all required sections: Problem, Change, Scope and approval, and Verification. It explains the failure, implementation, issue and maintainer-triage reference, test results, unt…

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[coderabbitai]

Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @packages/ssh/src/tunnel.ts:
- Around line 639-643: Track a launch-specific identity for the managed process
and validate it wherever REMOTE_PID is reused or stopped, including the stop
path. If the identity does not match, clear the stale PID and managed ownership
state without signaling that PID; keep ownership intact when wait_ready fails or
the port has no listener, since the managed process may still be starting.

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ℹ️ Review info

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• packages/ssh/src/tunnel.test.ts
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Reviewed commit: d3258a2e67

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[juliusmarminge]

Note

This comment is posted by Julius' dot

#16477 leaves the RUNNER_CHANGED update path for a separate maintainer decision. This PR also removes that restart, so a downloaded update waits for a deliberate restart. Can a maintainer confirm that behavior, or can the reconnect fix preserve the existing update path? See the scope policy.

[luke2x]

Yes, the reconnect fix can keep the existing update path, and 785eda8270 does that. Thanks for catching it; removing that restart went beyond what #16477 scoped.

• RUNNER_CHANGED is back: a live managed server is still stopped and replaced when the downloaded runner differs, exactly as on main. Deferring an update while runs are active stays a separate maintainer decision.
• With that restored, a preserved server never runs behind a newer runner, so the started-runner pairing workaround from 91a316dacc is reverted. The pairing script is identical to main again.
• The PR now only changes the two reconnect kills from the triage: the stale-forward finalizer stop and the readiness-timeout kill.

tunnel.test.ts passes (24 tests). The reconnect cases now run with an unchanged runner, and a new case asserts that a changed runner still replaces the server. The description is updated to match.