remote-tmux: let a failed socket request say what failed by ejc3 · Pull Request #17134 · manaflow-ai/cmux

ejc3 · 2026-10-03T08:24:02Z

Summary

Every remote tmux request that fails reports the same thing from the CLI, whatever went wrong:

$ cmux ssh-tmux build-box --new-window
Connecting to build-box…
Error: The Cloud VM request failed. Retry, or check the machine's status with `cmux vm ls`.

The host is an ssh host and no Cloud VM is involved. The real error in that run was "host unreachable: app not ready".

Remote tmux socket methods run through v2VmCall, the wrapper Cloud VM requests use. Its last fallback, cloudVMSafeErrorMessage, returns the Cloud VM line for any error it does not recognise, and RemoteTmuxError is not one it recognises. RemoteTmuxError.message is app-owned wording, and it already flattens and caps any remote text it includes, so the fallback now returns it as it is. The comment on RemoteTmuxError's CustomStringConvertible conformance says the socket path was meant to surface that message.

Testing

RemoteTmuxSocketErrorTextTests throws three RemoteTmuxError cases through v2VmCall and reads the message out of the encoded reply.

Run with xcodebuild test-without-building -scheme cmux-unit -only-testing:cmuxTests/RemoteTmuxSocketErrorTextTests:

fa61c07, the test alone: all three cases fail, each returning the Cloud VM line.
c9b0c25, with the fix: passes, along with RemoteTmuxMirrorCloseDetachTests, RemoteTmuxAuthTests and RemoteTmuxMissingTmuxTests (46 tests in 4 suites).

I also checked it from the CLI against a live tmux server on a local build that carries this change on top of other branches of mine. A failing cmux ssh-tmux printed the Cloud VM line before and its own reason after.

Changelog

Fixed: A failed cmux ssh-tmux now reports why it failed instead of a Cloud VM error.

Checklist

Behavior changes have added or updated tests, or Testing says why not

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

Summary by cubic

Fixed failed remote tmux requests reporting the Cloud VM error line instead of their own reason.

Remote tmux socket methods run through v2VmCall, the wrapper Cloud VM requests use, and its fallback returns "The Cloud VM request failed" for any error it does not recognize. RemoteTmuxError was unrecognized, so a failing cmux ssh-tmux pointed users at cmux vm ls even when no Cloud VM was involved. The wrapper now returns RemoteTmuxError.message as-is, since it already flattens and caps any remote text it includes.

Added RemoteTmuxSocketErrorTextTests covering three RemoteTmuxError cases routed through v2VmCall.

^{Written for commit 30da6b1. Summary will update on new commits.}

Summary by CodeRabbit

Bug Fixes
- Remote tmux errors now display their specific message instead of being formatted as a Cloud VM error.

…line Remote tmux requests share a socket wrapper with Cloud VM requests. Its fallback answers any error it does not recognise with "The Cloud VM request failed", so every remote tmux failure reached the CLI as that.

The wrapper remote tmux requests share with Cloud VM requests answered any error it did not recognise with the Cloud VM line. RemoteTmuxError carries app-owned wording with remote text already flattened and capped, so it is returned as it is.

github-actions · 2026-10-03T08:24:17Z

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coderabbitai · 2026-10-03T08:24:55Z

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Reviewing files that changed from the base of the PR and between c9b0c25 and 30da6b1.

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cmux.xcodeproj/project.pbxproj

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📝 Walkthrough

Walkthrough

Error formatting now returns RemoteTmuxError.message directly. New tests check the JSON error message for three remote tmux failure cases.

Changes

Remote tmux error text

Layer / File(s)	Summary
Format and test remote tmux errors `Sources/TerminalController.swift`, `cmuxTests/RemoteTmuxSocketErrorTextTests.swift`, `cmux.xcodeproj/project.pbxproj`	`TerminalController` returns the message from `RemoteTmuxError`. Tests check that three failure cases produce their own message and exclude “Cloud VM,” ignoring case. The Xcode project includes the test file in the test target.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 30da6

Remote tmux failures retain their intended error messages, with no identified issue blocking the change from merging.

Architecture Summary

Architecture risk: 🔵 Low · up to 30da6

The change affects 3 systems.

Changed systems: cmux.xcodeproj, cmuxTests, Sources

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

observed — cmux.xcodeproj (service) was modified; 1 changed file maps to changed impact.
observed — cmuxTests (service) was modified; 1 changed file maps to changed impact.
observed — Sources (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

observed — Modified behavior in Sources/TerminalController.swift: Adds a RemoteTmuxError case that returns its message directly; other errors continue to the existing handling.
observed — Modified behavior in cmuxTests/RemoteTmuxSocketErrorTextTests.swift: Adds Foundation and Testing imports and conditionally imports cmux_DEV or cmux for test access.
observed — Modified behavior in cmuxTests/RemoteTmuxSocketErrorTextTests.swift: Adds a parameterized test for unreachable, launch-failed, and window-creation failures. It extracts the reply’s JSON error message and expects it to equal failure.message and exclude “Cloud VM” case-insensitively.
observed — Modified behavior in cmux.xcodeproj/project.pbxproj: Adds the test file’s build-file entry for the Sources build phase.

Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error, 1 warning)

Check name	Status	Explanation	Resolution
Cmux User-Facing Error Privacy	❌ Error	The diff exposes raw remote command errors to cmux end users. `RemoteTmuxError.commandFailed` stores SSH/tmux stderr, and its `message` interpolates that stderr after only flattening control character…	Change the production socket formatter so it does not return remote stderr or other unreviewed upstream text in user-facing errors. Use app-authored, safe error copy for `RemoteTmuxError.commandFailed` and related cases. Keep raw diagnostic…
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files. (1 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (23 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: remote tmux socket failures now report the reason for the failure.
Description check	✅ Passed	The description includes the problem and resulting behavior, test coverage and results, a changelog entry, and the applicable behavior-test checklist item. It omits the demo video or screenshot reques…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Cmux Cloud Persistent Session And Early Input	✅ Passed	The check does not apply to this diff. The only production change adds RemoteTmuxError.message handling in cloudVMSafeErrorMessage; the other changes add a focused error-text test and register it in t…
Cmux Swift Actor Isolation	✅ Passed	The only production Swift change adds a `RemoteTmuxError` cast and reads its `message` in `cloudVMSafeErrorMessage`, an existing `private nonisolated static` formatter. `RemoteTmuxError` is an existin…
Cmux Swift Blocking Runtime	✅ Passed	The production diff only adds a `RemoteTmuxError` type check and returns its message from the existing error formatter. It adds no blocking wait, sleep, delayed dispatch, polling, sync dispatch, or lo…
Cmux Browser Automation Off-Main	✅ Passed	The pull request changes only error formatting for `RemoteTmuxError` and adds a test for that message. It does not change browser command routing, actor hops, or worker-lane behavior. The browser auto…
Cmux Expensive Synchronous Load	✅ Passed	The production diff adds only a `RemoteTmuxError` type check and returns its `message` in `cloudVMSafeErrorMessage`. `RemoteTmuxError.message` sanitizes and caps error text; the change adds no agent-h…
Cmux Cache Substitution Correctness	✅ Passed	The changed production code adds a `RemoteTmuxError` formatting branch in `cloudVMSafeErrorMessage`. `v2VmCall` uses that helper to encode an error reply. The patch does not replace an authoritative r…
Cmux No Hacky Sleeps	✅ Passed	The diff changes only Swift source, a Swift test, and Xcode project configuration. It adds no production TypeScript, JavaScript, shell, or build/runtime script changes covered by this check. The added…
Cmux Algorithmic Complexity	✅ Passed	The production diff adds one `RemoteTmuxError` type check and returns its `message`. That property sanitizes one error string in a single linear pass. The change adds no nested scans, repeated collect…
Cmux Swift Concurrency	✅ Passed	The diff adds only a `RemoteTmuxError` message branch to error formatting and a test that invokes `v2VmCall` synchronously. It introduces no background Dispatch work, Combine state, completion-handler…
Cmux Swift `@Concurrent`	✅ Passed	The changed implementation adds only a synchronous `RemoteTmuxError` formatting branch inside `cloudVMSafeErrorMessage`, which is `nonisolated` and synchronous. The added test calls the existing synch…
Cmux Swift Package Boundaries	✅ Passed	The production diff adds only a `RemoteTmuxError` case to `TerminalController.cloudVMSafeErrorMessage`, the app's socket error-formatting wrapper. It returns the existing error's `message`; it does no…
Cmux Swiftpm Lockfiles	✅ Passed	The PR changes only `Sources/TerminalController.swift`, `cmux.xcodeproj/project.pbxproj`, and a new test file. The project-file additions only register the test source; they do not change SwiftPM pack…
Cmux Swift Logging	✅ Passed	The Swift diff adds no logging statements or diagnostic output. It returns `RemoteTmuxError.message` in the socket error response through `v2VmCall`; this is user-facing error text, not logging. The t…
Cmux Full Internationalization	✅ Passed	The production diff only adds a branch that returns `RemoteTmuxError.message`; it adds no user-facing text or catalog changes. `RemoteTmuxError.message` already uses `String(localized:defaultValue:)` …
Cmux Swiftui State Layout	✅ Passed	The pull request does not introduce SwiftUI state or layout changes. Its Swift changes add RemoteTmuxError message handling in TerminalController and add socket-error tests; no changed Swift lines mat…
Cmux Architecture Rethink	✅ Passed	The PR adds only a `RemoteTmuxError` formatting branch and test registration. `RemoteTmuxError.message` owns user-facing wording and sanitizes remote details. The change adds no timing repair, mutable…
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	The PR changes only error formatting in `TerminalController.swift`, Xcode test-target registration, and a new test fixture. The added implementation returns `RemoteTmuxError.message`; it does not add …
Cmux Source Artifacts	✅ Passed	The three changed paths are `Sources/TerminalController.swift`, `cmux.xcodeproj/project.pbxproj`, and `cmuxTests/RemoteTmuxSocketErrorTextTests.swift`. The diff adds application source, registers a te…
Cmux No Test Or Debug Seam In Production Source	✅ Passed	The production-source diff only adds a `RemoteTmuxError` case to `cloudVMSafeErrorMessage` and returns its existing `message` for request-error formatting. It adds no debug/test guard, test- or debug-…

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files. (1 skipped: 1 unsupported.)

Full details: Cmux User-Facing Error Privacy

Explanation

The diff exposes raw remote command errors to cmux end users. RemoteTmuxError.commandFailed stores SSH/tmux stderr, and its message interpolates that stderr after only flattening control characters and capping length (Sources/RemoteTmuxError.swift:35-58). Failed SSH commands construct this case with result.stderr (Sources/RemoteTmuxSSHTransport.swift:58-63; Sources/RemoteTmuxSSHTransport+MissingTmux.swift:12-18). The changed branch returns RemoteTmuxError.message from the production socket error formatter (Sources/TerminalController.swift:4090-4094), and v2VmCall places it in the API error body (Sources/TerminalController.swift:4030-4035). The product CLI calls remote.tmux.mirror or remote.tmux.window (CLI/cmux.swift:12144-12151), decodes the error message (CLI/SocketClient+V2.swift:67-85), and prints it to stderr (CLI/cmux.swift:42908-42915). The new code therefore makes raw upstream stderr user-visible. Flattening and truncating do not redact raw messages, which the policy explicitly prohibits.

Resolution

Change the production socket formatter so it does not return remote stderr or other unreviewed upstream text in user-facing errors. Use app-authored, safe error copy for RemoteTmuxError.commandFailed and related cases. Keep raw diagnostics in sanitized internal logs or telemetry, not in the API error body or CLI output. Add a regression test that throws a RemoteTmuxError.commandFailed containing a recognizable upstream diagnostic and verifies that the socket reply does not include it.

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github-actions · 2026-10-03T20:46:02Z

CI failure attribution

CI failed on 30da6b15ce (run 37155148040 attempt 2): 1 code, 1 unknown.

Job	Verdict	Why
Fast static checks	code	a static check failed
guards / workflow-guard-tests / ci	unknown	no known signature; failed step: `Propagate failed independent fast guard`

Matched log lines

Fast static checks: FAILED localization (1.27s)

Not re-run automatically: Fast static checks, guards / workflow-guard-tests / ci are not machine failures.

Written by scripts/ci/classify_failures.py (ci-failure-attribution.yml); signatures are its SIGNATURES table. A machine verdict is the runner's fault, not this PR's.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cursor · 2026-10-03T21:27:09Z

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github-actions · 2026-10-03T21:33:05Z

CI fast guards failed on 30da6b15ce (https://github.com/manaflow-ai/cmux/actions/runs/37155147931). It does not block the merge; a red guard merged into main breaks it for every open PR.

`Validate macOS jobs select a pinned Xcode` (red on main too, not this PR)

Main has failed this step since #17206 by @teamleaderleo (self-merged) (#17169). Merge main again once the fix lands there.

`Validate owned Mac build state` (red on main too, not this PR)

Main has failed this step since #17168 by @teamleaderleo (self-merged) (#17169). Merge main again once the fix lands there.

`Validate fork runner routing` (red on main too, not this PR)

Main has failed this step since #17206 by @teamleaderleo (self-merged) (#17169). Merge main again once the fix lands there.

`Run canonical CMUX CI guard profile` (red on main too, not this PR)

Main has failed this step since #17206 by @teamleaderleo (self-merged) (#17169). Merge main again once the fix lands there.

Agents: python3 scripts/ci/guard_attribution.py fix applies the mechanical fixes locally. This comment is updated in place on each push.

teamleaderleo · 2026-10-03T21:42:08Z

Merged, thank you @ejc3! :D

github-actions · 2026-10-03T21:42:18Z

Merge receipt for 30da6b15ce, merged 2026-10-03 21:42:06 UTC

Not verified at merge: ci-status (failure), CI fast guards (failure), Fast static checks (failure), guards (18) (failure), linux-preflight (failure), tests (failure)
Verified: backend migrations applied, CI timing, GhosttyKit release check, plan, Web complexity, web-validation
Skipped by policy: apply-production, apply-staging, browser, Claude wrapper regressions, Dogfood build #${{ github.event.pull_request.number }}, full-suite-coverage, macos, macOS admission gate, remote-daemon, suite-coverage, ui-tests, web, and 3 more
Full suite: runs on main after merge.

Labeled merged-unverified: if main breaks near this merge, look here first.

github-actions · 2026-10-03T22:08:27Z

main no longer compiles after this merge

@teamleaderleo @ejc3: after 46b5f9c4ea landed on main, the app-host test product (the app and cmuxTests, build-for-testing) stops compiling. These errors first show up in a range of 4 merges (9c41d59d65..d8ef7e7fab), and this pull request's diff is the one that reaches them. The other merges in that range (984baea12f, e88d636d7b, d8ef7e7fab) are being compiled on their own to confirm.

Evidence: https://github.com/manaflow-ai/cmux/actions/runs/37156042656/job/111299626496

/tmp/cmux-ci-blacksmith-6vcpu-macos-15-Runner-cb61267037/src/cmuxTests/RightSidebarTabCustomizationTests.swift:126: error: cannot find 'RightSidebarModeBarDragLayout' in scope
/tmp/cmux-ci-blacksmith-6vcpu-macos-15-Runner-cb61267037/src/cmuxTests/RightSidebarTabCustomizationTests.swift:126: error: generic parameter 'T' could not be inferred
/tmp/cmux-ci-blacksmith-6vcpu-macos-15-Runner-cb61267037/src/cmuxTests/RightSidebarTabCustomizationTests.swift:144: error: type 'Any' cannot conform to 'Equatable' [#ProtocolTypeNonConformance]
/tmp/cmux-ci-blacksmith-6vcpu-macos-15-Runner-cb61267037/src/cmuxTests/RightSidebarTabCustomizationTests.swift:146: error: reference to member 'files' cannot be resolved without a contextual type
/tmp/cmux-ci-blacksmith-6vcpu-macos-15-Runner-cb61267037/src/cmuxTests/RightSidebarTabCustomizationTests.swift:146: error: reference to member 'sessions' cannot be resolved without a contextual type
/tmp/cmux-ci-blacksmith-6vcpu-macos-15-Runner-cb61267037/src/cmuxTests/RightSidebarTabCustomizationTests.swift:146: error: reference to member 'find' cannot be resolved without a contextual type
/tmp/cmux-ci-blacksmith-6vcpu-macos-15-Runner-cb61267037/src/cmuxTests/RightSidebarTabCustomizationTests.swift:146: error: reference to member 'machines' cannot be resolved without a contextual type

Nothing blocks merging meanwhile. A fix-forward (or, failing that, a revert) is attempted automatically unless an open pull request already fixes this.

_{main_compile_attribution.py: post-merge, nothing here gates a merge.}

00f182f Set Claude idle after reentrant stop without work (manaflow-ai#16635) d8ef7e7 Reject unknown and valueless options in cmux hooks setup (manaflow-ai#17183) 46b5f9c remote-tmux: let a failed socket request say what failed (manaflow-ai#17134) e88d636 remote-tmux: re-read a pane from tmux when its width changes, not only when it grows (manaflow-ai#17140) 984baea remote-tmux: close a window emptied by gathering its mirrors into a new one (manaflow-ai#17141) 9c41d59 fix: recover hidden terminal renderer after window attach (manaflow-ai#16548) 70854a5 ci: publish dogfood artifacts from red CI runs (manaflow-ai#17210) db77e58 fix(cli): reject missing notify text values (manaflow-ai#16778) 76ccbfc ci: activate org-member dogfood artifact publisher (manaflow-ai#17206)

ejc3 added 2 commits October 3, 2026 00:03

Merge main

30da6b1

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

teamleaderleo merged commit 46b5f9c into manaflow-ai:main Oct 3, 2026
60 of 67 checks passed

github-actions Bot added the merged-unverified A judging check was not green at merge; see the merge receipt comment label Oct 3, 2026

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remote-tmux: let a failed socket request say what failed - #17134

remote-tmux: let a failed socket request say what failed#17134
teamleaderleo merged 3 commits into
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ejc3:fix/remote-tmux-socket-error-text

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github-actions Bot commented Oct 3, 2026

Validate macOS jobs select a pinned Xcode (red on main too, not this PR)

Validate owned Mac build state (red on main too, not this PR)

Validate fork runner routing (red on main too, not this PR)

Run canonical CMUX CI guard profile (red on main too, not this PR)

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main no longer compiles after this merge

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ejc3 commented Oct 3, 2026 •

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`Validate macOS jobs select a pinned Xcode` (red on main too, not this PR)

`Validate owned Mac build state` (red on main too, not this PR)

`Validate fork runner routing` (red on main too, not this PR)

`Run canonical CMUX CI guard profile` (red on main too, not this PR)