Fix two main breakages from the CI-disabled window: reorderPanel overflow, double shortcut notification

[lawrencecchen]

Main has been red since today's window where the repo's CI workflows were manually disabled — two PRs merged unchecked and each broke a different job. Both fixes here:

1. CanvasModel.reorderPanel arithmetic overflow (from Add surface and workspace reorder shortcuts #8080): currentIndex + offset trapped on Int.max/Int.min before the clamp, crashing the whole CmuxCanvasUI suite mid-run (swift-package-tests red). Fixed with a saturating addingReportingOverflow before the existing clamp. swift test --package-path Packages/macOS/CmuxCanvasUI: 45/45 with the summary printed.

2. Double didChangeNotification on settings-file change (from Fix Settings shortcut display for legacy overrides #8091): notifyShortcutSettingsDidChange() called reload() (which posts when contents changed) then posted again unconditionally, so every real change notified listeners twice; changedSettingsFilePostsOneShortcutNotification fails on exactly this (app-host unit tests (4/4) red, three runs in a row here and on main's own CI). reload() now reports whether it posted and the action posts only when it didn't, keeping the exactly-once contract both Fix Settings shortcut display for legacy overrides #8091 tests encode.

Related flaky-test hardening tracked separately: #8159

Summary by CodeRabbit

• Bug Fixes
  • Improved panel reordering so very large movement values no longer risk failures; the target position is safely constrained while preserving the existing reorder/selection behavior.
  • Fixed shortcut settings change updates to avoid duplicate notifications, ensuring listeners receive a single, consistent update when the settings file is reloaded.

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Jul 15, 2026 5:47pm
cmux-staging	Building	Preview, Comment	Jul 15, 2026 5:47pm

[coderabbitai]

📝 Walkthrough

Walkthrough

Panel reordering now handles integer-overflowing offsets safely. Settings reloads report whether they emitted a change notification, allowing the host callback to avoid duplicate notifications.

Changes

Panel reordering

Layer / File(s)	Summary
Overflow-safe destination calculation Packages/macOS/CmuxCanvasUI/Sources/CmuxCanvasUI/CanvasModel.swift	reorderPanel(_:by:) uses overflow-reporting arithmetic, saturates the target, and preserves existing reorder behavior.

Settings notification coordination

Layer / File(s)	Summary
Reload notification contract Sources/KeyboardShortcutSettingsFileStore.swift	reload() returns whether relevant settings changed and a notification was emitted.
Conditional host notification Sources/HostSettingsActions.swift	The host callback posts a notification only when reload reports no change.

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

Possibly related PRs

• manaflow-ai/cmux#8080: Overlaps the panel reordering implementation.
• manaflow-ai/cmux#8091: Overlaps the reload-based settings notification flow.
• manaflow-ai/cmux#8157: Overlaps the centralized notification behavior.

Suggested reviewers: austinywang

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Important

Pre-merge checks failed

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

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Cmux Swift Package Boundaries	❓ Inconclusive	placeholder	need repo evidence

✅ Passed checks (23 passed)

Check name	Status	Explanation
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 Swift Actor Isolation	✅ Passed	PASS: Changed APIs are already @MainActor UI code or a lock-protected store; the Bool-returning reload and overflow fix don't alter actor isolation.
Cmux Swift Blocking Runtime	✅ Passed	PASS: The diff only changes shortcut reload notification flow and a Bool return; it adds no semaphores, sleeps, main-queue sync, polling, or new locks.
Cmux Browser Automation Off-Main	✅ Passed	Diff only changes settings files; the browser-automation rule applies to TerminalController and ControlCommandExecutionPolicy, which this PR doesn't touch.
Cmux Expensive Synchronous Load	✅ Passed	Only canvas overflow handling and keyboard-shortcut settings reload changed; no agent-history loader or large corpus parse was added/moved onto an interactive main-actor path.
Cmux Cache Substitution Correctness	✅ Passed	The diff keeps a fresh disk reload in reload(); the new Bool only avoids double-posting notifications, so no cached/stale value is substituted.
Cmux No Hacky Sleeps	✅ Passed	Only Swift files changed; no TypeScript/JS/shell/build/runtime script diff exists for the no-hacky-sleeps rule to apply.
Cmux Algorithmic Complexity	✅ Passed	The PR only adds a saturated index calculation and a Bool-returning reload check; it introduces no nested scans, repeated filters, or scalable-collection slowdowns.
Cmux Swift Concurrency	✅ Passed	Diff only changes synchronous notification/return-value logic; no new Dispatch queues, Combine state, completion handlers, or fire-and-forget Tasks were added.
Cmux Swift @Concurrent	✅ Passed	Touched Swift code stays on @MainActor or uses existing actor hops; no new @concurrent misuse or main-actor-heavy async boundary issue appears in the diff.
Cmux Swiftpm Lockfiles	✅ Passed	PR diff only changes three Swift source files; no .gitignore, Package.swift, Xcode project, or Package.resolved files are touched, so the lockfile policy isn't violated.
Cmux Swift Logging	✅ Passed	No added print/debugPrint/dump/NSLog or new nonisolated Logger violations; the diffs only change overflow handling and notification flow.
Cmux User-Facing Error Privacy	✅ Passed	PASS: The diff only changes internal overflow handling and notification flow; no user-facing errors, alerts, or recovery copy were added or exposed.
Cmux Full Internationalization	✅ Passed	The PR only changes logic/comments in Swift files; it adds no new user-facing text or locale assets, and existing localized UI copy remains unchanged.
Cmux Swiftui State Layout	✅ Passed	PASS: The PR only changes model/settings plumbing; it adds no new SwiftUI state/layout patterns, and HostSettingsActions is an allowed AppKit bridge.
Cmux Architecture Rethink	✅ Passed	Small local correctness fixes: overflow is saturated in CanvasModel, and shortcut notifications are centralized without new timing, polling, or split ownership.
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	The PR only changes CanvasModel tab reordering and shortcut-settings reload/notification logic; it adds no new NSWindow/WindowGroup code or cmuxAuxiliaryWindowIdentifiers changes.
Cmux Source Artifacts	✅ Passed	Only hand-written source files changed; no logs, temp dirs, build output, caches, or other artifact paths appear in the diff.
Cmux No Test Or Debug Seam In Production Source	✅ Passed	Touched production files only adjust overflow handling and notification flow; no new #if DEBUG/test-only accessor, debug* seam, or wrapper exposing private state was added.
Cmux No Ambient Global State	✅ Passed	Diff only changes instance methods on existing types; no new file-scope funcs, mutable globals, static-namespace types, or singletons were added.
Title check	✅ Passed	Title clearly summarizes the two fixes in the PR and matches the changeset.
Description check	✅ Passed	Summary and testing are present, but the template's demo video, review trigger, and checklist sections are missing.

✨ 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 fix-reorder-overflow

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[greptile-apps]

Greptile Summary

This PR fixes two unrelated production bugs: a Swift arithmetic overflow crash in CanvasModel.reorderPanel(_:by:) triggered by extreme offsets (Int.max/Int.min), and a double-notification defect in notifyShortcutSettingsDidChange() that fired didChangeNotification twice on every shortcut file change.

• CanvasModel.swift: uses addingReportingOverflow to saturate before the existing clamp, safely handling Int.max/Int.min offsets that previously caused a Swift runtime trap and killed the CmuxCanvasUI test process.
• KeyboardShortcutSettingsFileStore.swift: reload() now returns a Bool indicating whether it already posted didChangeNotification, and @discardableResult keeps all existing call sites warning-free.
• HostSettingsActions.swift: notifyShortcutSettingsDidChange() only posts the notification when reload() did not, guaranteeing exactly one notification per call instead of two.

Confidence Score: 5/5

Both fixes are targeted, self-contained, and correct; no regressions introduced.

The overflow fix uses the standard Swift saturating-addition idiom and is provably safe for all index and offset values. The double-notification fix correctly inverts the boolean gate so exactly one notification fires per call in all branches (changed or unchanged), matching the original intent. No concurrency, actor-isolation, or architectural concerns were introduced.

No files require special attention.

Important Files Changed

Filename	Overview
Packages/macOS/CmuxCanvasUI/Sources/CmuxCanvasUI/CanvasModel.swift	Saturates currentIndex + offset with addingReportingOverflow before clamping, eliminating the Swift runtime arithmetic overflow crash on Int.max/Int.min offsets. Logic is correct for all index and offset values.
Sources/KeyboardShortcutSettingsFileStore.swift	reload() now returns Bool indicating whether it posted didChangeNotification; @discardableResult preserves call-site backward compatibility. Change-detection gate (shortcuts / whenClauses / sourcePath) is unchanged.
Sources/HostSettingsActions.swift	notifyShortcutSettingsDidChange() now conditionally posts the notification only when reload() did not, eliminating the double-notification on every shortcut settings change.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant Caller
    participant HostSettingsActions
    participant CmuxSettingsFileStore
    participant NotificationCenter

    Note over Caller,NotificationCenter: After fix — exactly one notification per call
    Caller->>HostSettingsActions: notifyShortcutSettingsDidChange()
    HostSettingsActions->>CmuxSettingsFileStore: reload() → Bool
    alt shortcuts / path changed
        CmuxSettingsFileStore->>NotificationCenter: notifySettingsFileDidChange() [inside reload]
        CmuxSettingsFileStore-->>HostSettingsActions: true
        Note over HostSettingsActions: skips extra post
    else no shortcut change
        CmuxSettingsFileStore-->>HostSettingsActions: false
        HostSettingsActions->>NotificationCenter: notifySettingsFileDidChange()
    end

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sequenceDiagram
    participant Caller
    participant HostSettingsActions
    participant CmuxSettingsFileStore
    participant NotificationCenter

    Note over Caller,NotificationCenter: After fix — exactly one notification per call
    Caller->>HostSettingsActions: notifyShortcutSettingsDidChange()
    HostSettingsActions->>CmuxSettingsFileStore: reload() → Bool
    alt shortcuts / path changed
        CmuxSettingsFileStore->>NotificationCenter: notifySettingsFileDidChange() [inside reload]
        CmuxSettingsFileStore-->>HostSettingsActions: true
        Note over HostSettingsActions: skips extra post
    else no shortcut change
        CmuxSettingsFileStore-->>HostSettingsActions: false
        HostSettingsActions->>NotificationCenter: notifySettingsFileDidChange()
    end

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_{Reviews (2): Last reviewed commit: "Fix double didChangeNotification from no..." | Re-trigger Greptile}