Restore native Window menu move controls

[austinywang]

Summary

• keep normal cmux main windows movable so AppKit enables its native Window menu move and resize commands
• keep background dragging disabled and preserve the shared pane-tab/folder drag suppression lifecycle
• retain the existing frame-reconciliation safeguards for disconnected displays

Fixes #7446

Testing

• Red regression proof at test-only commit 4ae7bec5ae: ./scripts/reload-cloud.sh xctest --tag sym7446-red-unit --only-testing cmuxTests/MainWindowDragBehaviorTests (sym7446-red-unit-6b28fc63f950) failed the two new movability assertions as expected.
• Green focused proof at f7e50e3b24: ./scripts/reload-cloud.sh xctest --tag sym7446-green-unit with MainWindowDragBehaviorTests, FolderWindowMoveSuppressionTests, WindowMoveSuppressionHitPathTests, TitlebarInteractiveControlTests, CmuxMainWindowConstrainFrameTests, and AppDelegateWindowFrameReconcileTests (sym7446-green-unit-2fbb500a73f0) passed 33 XCTest cases and 6 Swift Testing cases.
• Dev build: ./scripts/reload-cloud.sh --tag sym7446 --builder blacksmith --launch succeeded on Blacksmith macOS 26 run 30959268214; no local-build fallback was used. The downloaded app embedded ephemeral build commit cb3d7566d, whose parent is exact PR HEAD f7e50e3b24. /tmp/cmux-debug-sym7446.sock returned PONG. With the tagged app active and its CmuxMainWindow both main and key on Studio Display XDR, runtime inspection saw both Studio Display XDR and Built-in Retina Display, isMovable == true, isMovableByWindowBackground == false, and the tracked Window menu reported Fill, Center, Move & Resize, and Move to Built-in Retina Display all enabled. The tagged app was stopped with pkill -f "DerivedData/cmux-sym7446"; PID 82759 exited and the tagged socket was removed.
• Localization audit: no user-facing strings or localization catalogs changed; a diff scan found no new Swift UI string candidates.

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Summary by cubic

Restores native Window menu move controls for main windows by keeping them movable except during explicit suppression. Background dragging stays off, and off‑screen/titlebar safety remains in place.

• Bug Fixes
  • Set isMovable = true unless isWindowDragSuppressed to re-enable Window > Fill, Center, and Move & Resize.
  • Keep isMovableByWindowBackground = false so titlebar drag zones control movement and pane-tab/folder drags can suppress it.
  • Preserve frame clamping and reactive reconcile to keep the titlebar reachable after display changes.
  • Updated tests to cover movability, suppression lifecycle, and frame safety.

^{Written for commit f7e50e3. Summary will update on new commits.}

Summary by CodeRabbit

• Enhancements

  • Main windows now remain natively movable while background dragging stays disabled.
  • Pane-tab and folder drag operations temporarily suppress window movement, then restore the prior behavior.
  • Window positioning remains safeguarded when display configurations change.

• Tests

  • Updated coverage verifies native movability, controlled drag suppression, restoration behavior, and display-change positioning.

[coderabbitai]

📝 Walkthrough

Walkthrough

The main window now remains natively movable while background dragging stays disabled. Active pane-tab and folder drags suppress movability through shared state. Documentation and tests describe this behavior and frame reconciliation after display changes.

Changes

Window drag behavior

Layer / File(s)	Summary
Native movability and drag suppression Sources/App/CmuxMainWindow.swift, Sources/ContentView.swift, cmuxTests/TitlebarInteractiveControlTests.swift, cmuxTests/WindowAndDragTests.swift	Main-window configuration preserves native movability unless drag suppression is active. Tests cover disabled background dragging and suppression across configuration reapplication.
Frame reachability and reconciliation Sources/App/CmuxMainWindow.swift, Sources/AppDelegate+WindowFramePolicy.swift, cmuxTests/AppDelegateWindowFrameReconcileTests.swift, cmuxTests/CmuxMainWindowConstrainFrameTests.swift	Comments describe titlebar drag handling and AppKit’s unreliable frame re-constraining for custom full-size-content windows after display changes.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
  participant BonsplitPaneTabDrag
  participant configureCmuxMainWindowDragBehavior
  participant isWindowDragSuppressed
  participant NSWindow
  BonsplitPaneTabDrag->>NSWindow: Begin pane-tab drag
  configureCmuxMainWindowDragBehavior->>isWindowDragSuppressed: Check suppression state
  isWindowDragSuppressed->>NSWindow: Preserve suppressed movability
  BonsplitPaneTabDrag->>NSWindow: Finish pane-tab drag

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Possibly related PRs

• manaflow-ai/cmux#8559: Modifies the same window-drag configuration and movability tests.
• manaflow-ai/cmux#8675: Updates related main-window frame reachability and restoration behavior.
• manaflow-ai/cmux#8845: Adds pane movement functionality associated with pane-tab dragging.

Suggested reviewers: lawrencecchen

🚥 Pre-merge checks | ✅ 25

✅ Passed checks (25 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes satisfy issue #7446 by restoring native movability while preserving drag suppression and multi-display safeguards.
Out of Scope Changes check	✅ Passed	All code, documentation, and test changes support the linked issue objectives and contain no unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Cmux Swift Actor Isolation	✅ Passed	Production diff keeps window configuration @MainActor and changes only movability logic/comments; no new models, protocols, Sendable references, or background UI access. Changed tests are @MainActor.
Cmux Swift Blocking Runtime	✅ Passed	The PR diff adds no blocking or timing primitive. Production changes only movability and comments; existing ContentView asyncAfter calls are unchanged, and test changes are deterministic.
Cmux Browser Automation Off-Main	✅ Passed	The commit changes only window movement/frame-policy comments and tests; it adds or moves no browser.* socket command, WebKit wait, worker route, or browser policy test.
Cmux Expensive Synchronous Load	✅ Passed	The PR adds only window movability and documentation changes; production additions contain no agent-history loader, file scan, JSON parse, transcript, or JSONL operation.
Cmux Cache Substitution Correctness	✅ Passed	The diff changes NSWindow movability plus comments/tests only; it does not replace authoritative reads in persistence, history, undo, or snapshot paths. Suppression state is transient AppKit state.
Cmux No Hacky Sleeps	✅ Passed	The PR changes only Swift source and Swift test files; it introduces no covered TypeScript, JavaScript, shell, or build/runtime-script sleeps or timers.
Cmux Algorithmic Complexity	✅ Passed	The production diff adds only an O(1) suppression-state lookup and a boolean assignment; no scalable collection scan or hot-path algorithm changed. Other executable changes are test-only.
Cmux Swift Concurrency	✅ Passed	The Swift diff adds no DispatchQueue, Task, Combine, completion-handler, or other legacy async pattern; production changes only update NSWindow movability, and tests cover suppression state.
Cmux Swift @Concurrent	✅ Passed	The PR changes only synchronous window-drag configuration, comments, and tests; no async, nonisolated, @concurrent, or async call-site changes were introduced.
Cmux Swift Package Boundaries	✅ Passed	The production diff changes only NSWindow movability, background-drag configuration, and related comments. It uses the existing suppression lifecycle, so it is allowed AppKit/UI glue, not reusable...
Cmux Swiftpm Lockfiles	✅ Passed	The complete PR diff contains only seven Swift source/test files; no Package.swift, Package.resolved, .gitignore, workflow, or Xcode project files changed.
Cmux Swift Logging	✅ Passed	The PR adds or changes no Swift logging; added lines contain only window behavior, comments, and test assertions, with no print, NSLog, Logger, or ad hoc diagnostic output.
Cmux User-Facing Error Privacy	✅ Passed	The full PR diff adds window behavior, comments, and test assertions only; it adds no user-facing errors, alerts, command output, API bodies, recovery copy, or sensitive diagnostics.
Cmux Full Internationalization	✅ Passed	The PR changes window behavior and developer comments/tests only; it adds no production user-facing text, localization keys, catalogs, or web messages.
Cmux Swiftui State Layout	✅ Passed	The PR adds no SwiftUI state or layout patterns. ContentView changes are comment-only, and CmuxMainWindow changes are in an AppKit NSHostingView/window bridge.
Cmux Architecture Rethink	✅ Passed	The diff adds no timing, blocking, observer, or duplicate lifecycle wiring; it uses the existing suppression owner and tests the movable/immovable invariant during reconfiguration.
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	The diff changes only the CmuxMainWindow workspace window and related comments/tests; it adds no standalone auxiliary window. The auxiliary-window lint also passes.
Cmux Source Artifacts	✅ Passed	The cumulative PR changes only seven intentional Swift source and test files; no logs, screenshots, caches, temp directories, build output, or other artifact paths appear in the diff.
Cmux No Test Or Debug Seam In Production Source	✅ Passed	The production diff changes window behavior and comments only; it adds no DEBUG/test guard, test/debug-named member, visibility widening, or test accessor.
Cmux No Ambient Global State	✅ Passed	The PR adds no production global state or declarations; it only changes the pre-existing configureCmuxMainWindowDragBehavior body and updates comments/tests.
Title check	✅ Passed	The title clearly identifies the primary change: restoring native Window menu movement controls.
Description check	✅ Passed	The description clearly explains the change and includes detailed testing evidence, but omits the template's demo video, review trigger, and checklist sections.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch issue-7446-window-menu-move-to-display-fill-center

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