fix: refresh tmux sizing after display changes

[timonv]

Remote tmux panes can keep their old size after a display disconnects. AppKit geometry callbacks now refresh their region and scale so they fit again. Never-selected tabs also claim their first measured size before joining a window.

One measurement helper handles this; the production file is five lines shorter. The tests select window 0 explicitly and use 1200pt so the 99-column server resize fits within the client size.

A local test removed a virtual display and verified tmux shrank from 423×91 to 157×50, with matching pane grids and terminal content.

Vertical window resize recording

The test changes only height. Columns stay at 118; rows grow and shrink: 30 → 38 → 46 → 38 → 30.

Ordinary window resize recording

Validation

• All 61 focused native tests passed; the new windowless regression failed before the fix.
• All 17 live UI scenarios passed locally across a full run and focused reruns, including display disconnect, hidden tabs, and height resizing.
• All 17 scoped checks and the localization audit passed.

Changelog

Fixed: Remote tmux panes refresh their size when the window changes displays.

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Note

Medium Risk
Changes when and how tmux client size claims are derived (display disconnect, hidden tabs, scale moves); behavior is heavily tested but sizing is core to remote tmux UX.

Overview
Remote tmux mirror sizing no longer depends on SwiftUI onGeometryChange for the container region. MirrorHostProbe now pushes size and backing scale from AppKit (setFrameSize, layout, viewDidChangeBackingProperties, window attach) into a shared refreshContainerSizeFromHost path that calls noteContainerSize, including a first claim for hidden tabs before the probe has a window (seed scale from the representable).

Visibility and layout-structure handlers were rewired to refresh from the host and re-arm sizing passes instead of caching SwiftUI geometry locally. Stale or replaced probes are ignored so detached geometry cannot overwrite a good reading.

Tests and docs add focused native coverage for display moves, height-only resize, windowless initial claims, and backing-scale changes; UI tests gain display-disconnect, never-selected-window claim, and vertical resize sweeps, with tab focus via remote.tmux.pane_surfaces, stricter frame/claim oracles, and harness notes for virtual-display recording.

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Summary by CodeRabbit

• Bug Fixes
  • Remote tmux panes now refresh their row and column sizing when window dimensions or display scaling change, including when a display is disconnected.
  • Hidden mirrors retain their current sizing until they become visible again, while newly opened windows receive an initial size claim.
• Documentation
  • Updated guidance for running remote tmux sizing checks across display changes.

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Repository: manaflow-ai/cmux/.coderabbit.yaml
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📥 Commits

Reviewing files that changed from the base of the PR and between 4fe8a66 and 17a7a91.

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📒 Files selected for processing (6)

• Sources/RemoteTmuxWindowMirrorSplitView.swift
• cmuxTests/RemoteTmuxBonsplitImpositionRenderTests.swift
• cmuxUITests/RemoteTmuxSizingUITests+Oracle.swift
• cmuxUITests/RemoteTmuxSizingUITests+Socket.swift
• cmuxUITests/RemoteTmuxSizingUITests.swift
• skills/cmux-testing/references/remote-tmux-sizing-e2e.md

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📝 Walkthrough

Walkthrough

The mirror now reads container geometry and backing scale from its registered AppKit host probe. Probe and display changes refresh sizing measurements. Unit and UI tests cover geometry and scale changes, hidden sizing, stale callbacks, and display removal.

Changes

Remote tmux mirror sizing

Layer / File(s)	Summary
Host probe measurement and sizing Sources/RemoteTmuxWindowMirrorSplitView.swift, Sources/RemoteTmuxWindowMirror.swift, docs/remote-tmux-reconcile-design.md	The host probe reports its bounds with the window’s backing scale. Layout and visibility changes refresh measurements before sizing. Duplicate measurements matching pending or accepted values are ignored.
Measurement and sizing tests cmuxTests/RemoteTmuxBonsplitImpositionRenderTests.swift	Tests cover initial and subsequent probe geometry, backing-scale updates, grid requests, hidden sizing, and callbacks from replaced or detached probes.
Display and window sizing scenarios cmuxUITests/RemoteTmuxSizingUITests.swift, cmuxUITests/RemoteTmuxSizingUITests+Lab.swift, cmuxUITests/RemoteTmuxSizingUITests+Content.swift, cmuxUITests/RemoteTmuxSizingUITests+Socket.swift	UI tests cover display removal, initial sizing of an unselected window, height-resize sweeps, and window movement. Test helpers select tmux windows by pane surface window ID and select an initial window when activation is requested.
UI sizing checks and test harness cmuxUITests/RemoteTmuxSizingUITests+Oracle.swift, cmuxUITests/RemoteTmuxSizingUITests+Content.swift, skills/cmux-testing/references/remote-tmux-sizing-e2e.md	UI checks validate window and content heights, use per-window cell calibration, and read pushed columns and rows together. Timeout diagnostics, resize dimensions, and external-display test instructions are updated.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~30 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant UITest
  participant DisplayHarness
  participant MirrorWindow
  participant Tmux
  UITest->>MirrorWindow: Move window to virtual display
  UITest->>DisplayHarness: Request display removal
  DisplayHarness->>MirrorWindow: Remove virtual display
  MirrorWindow->>Tmux: Refresh pane grid sizing
  Tmux->>UITest: Report pane grids and content

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Possibly related PRs

• manaflow-ai/cmux#7315: Establishes the remote-tmux sizing pipeline that this change refreshes from AppKit host measurements.
• manaflow-ai/cmux#7938: Changes the same mirror sizing path and related host-probe and pane-grid tests.
• manaflow-ai/cmux#7996: Continues the same host-probe measurement and display-region sizing work.

Suggested reviewers: ejc3

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Merge Risk: ⚪ Minimal · up to 17a7a

The display-sizing change has no identified issue requiring a fix before merge; normal validation remains appropriate.

🚥 Pre-merge checks | ✅ 24 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 61.90% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 42 functions across 8 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (24 passed)

Check name	Status	Explanation
Title check		The title is concise, specific, and accurately identifies the primary change: refreshing tmux sizing after display changes.
Description check		The description explains the problem, resulting behavior, implementation approach, testing performed, changelog entry, and user-visible proof. It does not include the template's explicit Summary, Test…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Cmux Cloud Persistent Session And Early Input		PASS. The pull request changes remote tmux sizing, AppKit geometry probing, and sizing tests. The authoritative diff contains no Cloud terminal creation or transport changes, no new cmux-tui/client or…
Cmux Swift Actor Isolation		The production diff does not introduce a value model, service protocol, Sendable reference type, or background access to a UI store. RemoteTmuxWindowMirror is already explicitly @MainActor (Source…
Cmux Swift Blocking Runtime		PASS. The production diff adds no semaphore, blocking wait, sleep, timer, polling loop, main-queue sync, or manual lock. It replaces SwiftUI geometry callbacks with AppKit host callbacks in `Sources/R…
Cmux Browser Automation Off-Main		The check is not applicable to this pull request. The authoritative diff changes Remote tmux sizing, UI tests, and documentation only. Sources/TerminalController.swift and `Packages/macOS/CmuxContro…
Cmux Expensive Synchronous Load		The production diff changes tmux sizing measurement from SwiftUI geometry to an AppKit host probe. The added callbacks call refreshContainerSizeFromHost and noteContainerSize; they do not load age…
Cmux Cache Substitution Correctness		The production diff changes only transient tmux sizing UI state. It replaces SwiftUI geometry callbacks with event-driven AppKit probe callbacks that read probe.bounds.size and `probe.window?.backin…
Cmux No Hacky Sleeps		PASS: The pull request changes only Swift sources/tests and Markdown documentation. The applicable rule covers TypeScript, JavaScript, shell, and non-Swift build/runtime scripts. No covered non-Swift …
Cmux Algorithmic Complexity		The production diff adds host-measurement callbacks and a constant-time state comparison in Sources/RemoteTmuxWindowMirrorSplitView.swift (lines 132–220). It does not add nested scans, repeated sort…
Cmux Swift Concurrency		The production diff adds AppKit lifecycle callbacks and a synchronous host-geometry refresh. It adds no background Dispatch queue, Combine state, new completion-handler API, or fire-and-forget Task. T…
Cmux Swift @Concurrent		PASS: The production Swift diff adds only synchronous AppKit geometry callbacks and the synchronous refreshContainerSizeFromHost helper. RemoteTmuxWindowMirror and `RemoteTmuxWindowMirrorSplitView…
Cmux Swift Package Boundaries		PASS: The production diff is limited to Sources/RemoteTmuxWindowMirrorSplitView.swift plus a comment in RemoteTmuxWindowMirror.swift. The new sizing helper is AppKit/SwiftUI glue: it reads `NSView…
Cmux Swiftpm Lockfiles		PASS. The reviewed diff changes only Swift source, tests, documentation, and testing references. It changes no Package.swift, Package.resolved, .gitignore, workflow, or Xcode project package-reference…
Cmux Swift Logging		The production Swift diff changes only sizing and AppKit probe behavior in Sources/RemoteTmuxWindowMirror*.swift. It adds no print, debugPrint, dump, NSLog, ad hoc diagnostic logging, Logger…
Cmux User-Facing Error Privacy		The production diff changes tmux sizing measurement and AppKit probe callbacks only. It adds no user-facing error, alert, command-output, API-error, or recovery text. The added diagnostic strings and …
Cmux Full Internationalization		The production diff changes tmux sizing behavior and developer comments only. It adds no user-facing Swift text, localization keys, string-catalog entries, web UI text, metadata, API copy, rendered ma…
Cmux Swiftui State Layout		The PR removes the SwiftUI @State container size and onGeometryChange measurement. It adds no prohibited SwiftUI state, lazy-row store reference, or GeometryReader. The new measurement path is c…
Cmux Architecture Rethink		PASS. The production diff replaces SwiftUI geometry feedback with one refreshContainerSizeFromHost path. AppKit callbacks provide the required frame, bounds, layout, window, and backing-scale signal…
Cmux Swift Auxiliary Window Close Shortcuts		PASS: The production Swift diff changes MirrorHostProbeView sizing callbacks and RemoteTmuxWindowMirror state handling. It does not add or materially change a standalone cmux-owned NSWindow, `NS…
Cmux Source Artifacts		All 10 changed paths are intentional Swift source, native/UI tests, or durable design/testing documentation. The diff adds no artifact directories, binary media, logs, caches, build output, DerivedDat…
Cmux No Test Or Debug Seam In Production Source		The production diff adds refreshContainerSizeFromHost, but it is a normal internal sizing helper with multiple production callers: RemoteTmuxWindowMirrorSplitView, MirrorHostProbeView AppKit cal…

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Full details: Docstring Coverage

Explanation

Docstring coverage is 61.90% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 42 functions across 8 files. (1 skipped: 1 unsupported.)

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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 @Sources/RemoteTmuxWindowMirrorSplitView.swift:
- Line 160: Update the `didChangeScreenNotification` handler to call
`sourceWindow.layoutIfNeeded()` before sampling the probe view’s bounds, rather
than treating a main-queue turn as proof that layout has completed. Keep the
existing window and probe identity guards, and continue passing the settled size
to `noteContainerSize` as the sizing authority.

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📒 Files selected for processing (2)

• Sources/RemoteTmuxWindowMirrorSplitView.swift
• cmuxTests/RemoteTmuxBonsplitImpositionRenderTests.swift

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[timonv]

I have read the CLA Document v2.2 and I hereby sign the CLA

[teamleaderleo]

Thank you @timonv for tracking this down! Moving to the AppKit callbacks makes sense.

However, noteHostProbeGeometry now skips probes with no window, and a never-selected tmux window relies on that first measurement to claim its size. Could you confirm that still works, ideally with a test for a second window that's never selected?

Also, could the attachSession window-0 select and the 1000→1200pt change go in a separate PR (or get a quick note on why they're needed here)? And the didChangeScreenNotification posts in the unit tests can go, since nothing observes them anymore.

[timonv]

@teamleaderleo Thank you for the project and the way faster than expected reply, will take a look asap. Also need to check if vertical scaling also works.

[timonv]

Thanks @teamleaderleo, you are correct. The window check blocked that first measurement. I’ve fixed it and added a regression test plus a local UI test where the second tmux window is never selected. Both passed. Additional recording in the pr description

Updated the tests to reflect the change, and double checked vertical resizing and display disconnection locally.

I'm a bit rusty on Swift/macOS internals, FTR codex did most of it. If I understand correctly, onChange isn’t replacing onGeometryChange by itself. The AppKit callbacks now report size and display-scale changes directly to the tmux mirror, while onChange handles tab and pane-layout changes. This avoids reusing an old cached size. The local tests passed for never-selected tabs, vertical resizing, and display disconnect.