fix: wait for control socket dispatch sources before close

[austinywang]

Summary

Control-socket connections could close a borrowed descriptor before libdispatch finished cancelling its read or writable source. Connection teardown now awaits cancellation completion before shutdown/close, using async continuations rather than blocking executor threads. Read and authorization-revocation sources share a completion barrier; each one-shot writable wait joins its own cancellation. The socket loop explicitly runs off the calling actor.

The barrier documents its synchronous callback locking invariant. Reader, writer, and barrier implementations have separate files. No socket method or remote-relay allowlist changed.

Closes #12764. The reports contain no cmux frame identifying the vanished source, so reporter confirmation on macOS 26.6.2 remains outstanding; this fixes the reproduced control-socket lifetime violation.

Testing

• swift test --package-path Packages/macOS/CmuxControlSocket: 452 tests passed.
• Lifecycle coverage includes 1,024 read/revocation teardown cycles and a real backpressured writeAll task. A test-only executor observes the existing registration count after the task suspends before cancelling, then verifies teardown returns it to zero. No sleep, yield-count assumption, production factory hook, or helper bypass remains.
• The executor-specific case requires macOS 15+; other lifecycle cases retain macOS 14 coverage. Tests were run on macOS 26.4.
• Strict test-determinism guard, PBX test-wiring lint, package-lockfile policy, and diff whitespace checks passed.
• Current CI run. App-host test compilation passed on the prior head and was admitted for identical build inputs on this documentation-only merge. The PR lane does not execute the app-host suite.
• iOS connectivity soak coverage is not applicable: this changes the macOS local CLI socket transport, not mobile connectivity/auth/session state.
• Localization audit: no user-facing strings changed.

Exact-head developer build

• Head: 356006834d78990c1d627bae02d5de01b2b00ac3; includes main fff5bbcd4b1d5e450b16dd35e9663ddce4505f6f.
• Controller job: ecb7cd47041ad179dadb8556, worker cmuxs-Mac-mini-3.local, succeeded in 661.97s (492.50s build phase).
• Previous exact-head builds passed, including ae6ef2888f after all runtime changes. The latest commit adds explicit empty deinitializers required by the repository lint configuration; the lifecycle suite passed again.
• Issue-tag build will be refreshed with the current artifact when its verified receipt completes. No GUI dogfood claim.

Demo Video

Not applicable: background socket-lifecycle fix with no new UI. Evidence is the real-socket tests and build receipts above.

Review Trigger

Automatic repository review bots run on pushes. No additional second-model review was requested.

Checklist

• I tested the change locally (focused package tests)
• I added or updated tests for behavior changes
• Deterministic lifecycle coverage updated; iOS connectivity soak applicability explained
• I updated docs/changelog if needed (API/lifecycle documentation updated)
• Automatic review bots triggered by the latest push
• All code review bot comments are resolved
• All human review comments are resolved

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📥 Commits

Reviewing files that changed from the base of the PR and between 0c5af74 and d4bad80.

📒 Files selected for processing (3)

• Packages/macOS/CmuxControlSocket/Sources/CmuxControlSocket/Server/ControlClientAsyncWriter.swift
• Packages/macOS/CmuxControlSocket/Sources/CmuxControlSocket/Server/DispatchSourceCancellationBarrier.swift
• Packages/macOS/CmuxControlSocket/Tests/CmuxControlSocketTests/SocketWriterTestExecutor.swift

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📝 Walkthrough

Walkthrough

The transport now waits for dispatch source cancellation before socket teardown. The reader and writer expose asynchronous cancelAndWait(). TerminalController awaits cancellation before shutdown and close. Lifecycle tests cover reader, revocation, and blocked-writer cleanup.

Changes

Descriptor lifecycle synchronization

Layer / File(s)	Summary
Reader source cancellation Packages/macOS/CmuxControlSocket/Sources/CmuxControlSocket/Server/DispatchSourceCancellationBarrier.swift, Packages/macOS/CmuxControlSocket/Sources/CmuxControlSocket/Server/ControlClientAsyncTransport.swift, Packages/macOS/CmuxControlSocket/Tests/CmuxControlSocketTests/ControlClientSourceLifecycleTests.swift, Packages/macOS/CmuxControlSocket/Tests/CmuxControlSocketTests/SocketControlServerManagedPolicyTests.swift	The line reader uses DispatchSourceCancellationBarrier for read and revocation sources. cancelAndWait() now awaits source cancellation. Tests cover repeated cancellation, policy revocation, and teardown ordering.
Writer source cancellation Packages/macOS/CmuxControlSocket/Sources/CmuxControlSocket/Server/ControlClientAsyncWriter.swift, Packages/macOS/CmuxControlSocket/Tests/CmuxControlSocketTests/ControlClientSourceLifecycleTests.swift, Packages/macOS/CmuxControlSocket/Tests/CmuxControlSocketTests/SocketWriterTestExecutor.swift	The writer performs non-blocking writes and tracks one-shot writable sources with the barrier. It cancels and waits for each source before returning writable results or completing cancelAndWait(). The lifecycle test covers a blocked write that is cancelled before socket close.
Connection teardown integration Sources/TerminalController.swift	handleClientAsync retains the reader and writer through handleClientLoop, awaits both cancelAndWait() methods, and then shuts down and closes the socket.

Priority: ⬆️ High

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

Change: Bug fix · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant TerminalController
  participant ControlClientAsyncLineReader
  participant ControlClientAsyncWriter
  participant SocketDescriptor
  TerminalController->>ControlClientAsyncLineReader: run handleClientLoop
  TerminalController->>ControlClientAsyncWriter: run handleClientLoop
  TerminalController->>ControlClientAsyncLineReader: await cancelAndWait()
  TerminalController->>ControlClientAsyncWriter: await cancelAndWait()
  TerminalController->>SocketDescriptor: shutdown and close

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🚥 Pre-merge checks | ✅ 25

✅ Passed checks (25 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes meet the coding requirements in [#12764]. DispatchSourceCancellationBarrier tracks read, authorization-revocation, and one-shot writable source cancellation. cancelAndWait() awaits can…
Out of Scope Changes check	✅ Passed	The changes stay within [#12764]. The barrier, asynchronous writer cancellation, teardown ordering, call-site updates, test executor, and lifecycle tests directly support safe dispatch-source cancella…
Docstring Coverage	✅ Passed	Docstring coverage is 82.35% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 17 functions across 6 files.
Cmux Cloud Persistent Session And Early Input	✅ Passed	PASS. The authoritative PR diff changes local control-socket source teardown and socket ownership only. It adds cancellation barriers, awaits reader and writer teardown, and preserves the existing aut…
Cmux Swift Actor Isolation	✅ Passed	No changed production declaration matches the failure conditions. The new DispatchSourceCancellationBarrier is @unchecked Sendable and documents its NSLock protection and callback invariant. `Co…
Cmux Swift Blocking Runtime	✅ Passed	PASS. The production diff adds no semaphore, blocking wait, sleep, delayed dispatch, polling loop, or main-queue synchronous call. DispatchSourceCancellationBarrier.wait() is an async continuation-b…
Cmux Browser Automation Off-Main	✅ Passed	PASS. The authoritative PR diff changes socket transport teardown, writer/barrier implementations, lifecycle tests, and handleClientAsync/handleClientLoop in Sources/TerminalController.swift. It…
Cmux Expensive Synchronous Load	✅ Passed	The PR does not add or move an expensive synchronous agent-history load. The production diff changes control-socket DispatchSource cancellation, async writer backpressure, and socket teardown in `Cont…
Cmux Cache Substitution Correctness	✅ Passed	PASS: The changed production code only manages control-socket readers, writers, DispatchSource cancellation, and socket teardown. The diff does not replace an authoritative read with a cached or oppor…
Cmux No Hacky Sleeps	✅ Passed	PASS: The authoritative PR diff changes seven .swift files only. The checked rule applies to TypeScript, JavaScript, shell, and non-Swift build/runtime scripts; it explicitly excludes Swift. No cove…
Cmux Algorithmic Complexity	✅ Passed	The production diff does not introduce a prohibited complexity pattern. ControlClientAsyncWriter.writeAll uses a linear loop over the bytes being written, and that loop already existed in the base r…
Cmux Swift Concurrency	✅ Passed	PASS: The diff does not introduce a prohibited legacy async pattern. The production DispatchQueue.global(qos: .utility) and DispatchSource handlers already existed in the base transport; the write…
Cmux Swift @Concurrent	✅ Passed	The diff adds @concurrent to both changed nonisolated async socket lifecycle functions, handleClientAsync and handleClientLoop, with an @Sendable fallback for older compilers. These functions …
Cmux Swift Package Boundaries	✅ Passed	PASS. The new production transport and cancellation logic is under Packages/macOS/CmuxControlSocket/Sources/CmuxControlSocket, which has its own CmuxControlSocket SwiftPM target and test target. T…
Cmux Swiftpm Lockfiles	✅ Passed	PASS. The authoritative PR diff changes only Swift source and test files. It does not change any Package.swift, Package.resolved, .gitignore, Xcode project, or workspace file. The unchanged CmuxContro…
Cmux Swift Logging	✅ Passed	PASS. The authoritative PR diff changes seven Swift files, but the added or materially changed lines contain no print, debugPrint, dump, NSLog, Logger, os_log, FileHandle, stdout, or std…
Cmux User-Facing Error Privacy	✅ Passed	PASS. The authoritative diff changes socket lifecycle, dispatch-source cancellation, and tests. It adds no user-facing error, alert, command output, API error body, or recovery text. The only added qu…
Cmux Full Internationalization	✅ Passed	PASS. The authoritative diff changes only control-socket lifecycle code, comments, and tests. It adds no Swift UI, alert, command, API-response, web, metadata, changelog, or string-catalog text. The a…
Cmux Swiftui State Layout	✅ Passed	PASS: The pull request changes socket lifecycle and test code, not SwiftUI view state or layout. The authoritative diff adds no SwiftUI import, ObservableObject/@published state, @Observable state, Ge…
Cmux Architecture Rethink	✅ Passed	PASS. The diff is a local control-socket lifetime fix with clear ownership and invariants. handleClientAsync retains the reader and writer, awaits cancelAndWait(), and closes the borrowed descript…
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	PASS. The reviewed diff changes only control-socket transport, dispatch-source teardown, tests, and socket handling in Sources/TerminalController.swift. It adds or changes no NSWindow, NSPanel, …
Cmux Source Artifacts	✅ Passed	PASS. The review-scoped diff changes seven paths, all under established Swift source/test locations or Sources/TerminalController.swift. The four added files are ordinary 100644 Swift text blobs: pr…
Cmux No Test Or Debug Seam In Production Source	✅ Passed	No forbidden test/debug seam was introduced. The production diff adds no DEBUG, TESTING, or XCTest guard and no seam-named member. The lifecycle test uses @testable import CmuxControlSocket and read…
Title check	✅ Passed	The title clearly and concisely describes the main fix: waiting for control-socket dispatch sources before closing the descriptor.
Description check	✅ Passed	The description includes the required Summary, Testing, Demo Video, Review Trigger, and Checklist sections. It explains the problem, implementation, test coverage, applicability decisions, and review …

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Confidence Score: 5/5

The PR appears safe to merge; the previously reported teardown, coverage, locking-documentation, and test-seam concerns are resolved in the current code.

Summary

The PR fixes control-socket descriptor teardown by asynchronously joining dispatch-source cancellation before the connection owner shuts down and closes the socket.

• Adds a continuation-based barrier shared by the reader’s read and authorization-revocation sources.
• Moves writer logic into its own file and joins each one-shot writable source after readiness or task cancellation.
• Runs the socket loop away from the calling actor and retains reader/writer ownership through teardown.
• Adds deterministic lifecycle coverage for repeated reads, authorization revocation, and real socket backpressure.

_{Reviews (14) · Last reviewed commit: "Merge branch 'main' of https://github.co..."}

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
In
`@Packages/macOS/CmuxControlSocket/Tests/CmuxControlSocketTests/ControlClientSourceLifecycleTests.swift`:
- Around line 94-96: Update the lifecycle test around the pending write and
repeated Task.yield calls to wait for an explicit writable-source registration
signal before invoking pending.cancel(). Ensure cancellation occurs only after
writeAll has reached waitForWritable(), so the test always exercises
cancellation of a registered source rather than the early cancellation guard.

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📒 Files selected for processing (4)

• Packages/macOS/CmuxControlSocket/Sources/CmuxControlSocket/Server/ControlClientAsyncTransport.swift
• Packages/macOS/CmuxControlSocket/Tests/CmuxControlSocketTests/ControlClientSourceLifecycleTests.swift
• Packages/macOS/CmuxControlSocket/Tests/CmuxControlSocketTests/SocketControlServerManagedPolicyTests.swift
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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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In
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- Line 5: Add explicit empty deinit declarations to the four classes
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