Fix terminal blank when last pane closes (#2665)

[austinywang]

Summary

• When closing terminal panes in a workspace down to the last remaining pane, the surviving terminal went blank and stopped accepting input
• Root cause: the SwiftUI split-to-single-pane rebuild transiently detaches the terminal surface view, causing the first responder to be lost. The one-shot async focus reconcile fires before the view is reattached, and no further retry occurs
• Fix: include the surviving panel in the layout follow-up as terminalFocusPanelId, so the existing retry loop (triggered by terminalSurfaceHostedViewDidMoveToWindow) keeps calling ensureFocus until the surface view successfully becomes first responder after reattachment

Test plan

• Open a workspace with 2+ split panes
• Close panes one by one until only 1 remains
• Verify the surviving terminal is not blank and accepts keyboard input
• Verify closing panes in a 3+ pane split (leaving 2+ remaining) still works correctly
• Verify detaching a pane (drag to new workspace) still works correctly

Closes #2665

🤖 Generated with Claude Code

---

Note

Medium Risk
Moderate risk because it changes focus/first-responder and layout-follow-up timing around SwiftUI split-view rebuilds, which could impact keyboard focus behavior across panel types.

Overview
Prevents the surviving terminal from going blank/losing input when split panes collapse to a single pane by re-running the existing event-driven layout follow-up until the terminal surface is reattached and becomes first responder.

This also broadens when terminal focus follow-ups are started during focusPanel: they now run whenever the terminal isn’t first responder (or for .terminalFirstResponder triggers), and pane-close paths now prefer beginEventDrivenLayoutFollowUp(..., includeGeometry: true) for surviving terminals instead of a one-shot scheduleTerminalGeometryReconcile.

^{Reviewed by Cursor Bugbot for commit 9c7cb55. Bugbot is set up for automated code reviews on this repo. Configure here.}

---

Summary by cubic

Fixes blank terminals when collapsing to a single pane and when creating a new workspace (Cmd+T), ensuring the terminal keeps focus and accepts input (fixes #2665).

• Bug Fixes
  • On pane collapse, start an event-driven layout follow-up with the surviving panel as terminalFocusPanelId so the retry loop re-applies focus after the split view rebuild; applies to both tab-close and pane-collapse; skipped on detach.
  • When focusing a terminal, start the same follow-up if the terminal isn’t first responder (not just on .terminalFirstResponder), covering new workspace creation where the surface isn’t attached yet.

^{Written for commit 9c7cb55. Summary will update on new commits.}

Summary by CodeRabbit

• Bug Fixes
  • Improved terminal focus handling when closing or collapsing panes so the remaining terminal reliably regains focus.
  • Reduced layout/geometry glitches after pane collapse by using a targeted layout follow-up when possible, with a safe fallback to a full geometry reconcile when needed.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Apr 7, 2026 9:00am

[cubic-dev-ai]

This review could not be run because your cubic account has exceeded the monthly review limit. If you need help restoring access, please contact contact@cubic.dev.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adjusted Workspace/Bonsplit pane-close handling to avoid unconditional terminal geometry reconciliation. Now, when a pane collapse closes a pane and a surviving focused panel maps to a terminal, an event-driven layout follow-up targeting that terminal is scheduled; otherwise the code falls back to the existing geometry reconcile path.

Changes

Cohort / File(s)

Summary

Workspace Bonsplit / Terminal follow-up Sources/Workspace.swift

Replaced unconditional scheduleTerminalGeometryReconcile() in splitTabBar(_:didCloseTab:fromPane:) and splitTabBar(_:didClosePane:) with conditional logic: when not detaching and a surviving focusedPanelId resolves to a TerminalPanel, call beginEventDrivenLayoutFollowUp(reason: "workspace.paneCollapse", terminalFocusPanelId: ..., includeGeometry: true); otherwise call scheduleTerminalGeometryReconcile(). Also broadened terminal-first-responder follow-up condition in Workspace.focusPanel(_:trigger:) to use a TerminalPanel cast and to trigger when the hosted surface is not first responder.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• Fix workspace layout follow-up spin loop #1633: Related — also modifies layout follow-up scheduling and terminal geometry reconcile interactions.
• Fix split ghost terminal render and focus recovery #1148: Related — touches Bonsplit/Workspace terminal focus handling during pane state changes.
• Fix terminal drag hover overlay flicker #1050: Related — adjusts terminal hosting/geometry behavior that intersects with when reconcilers and portals are stabilized.

Poem

🐰 I nudge the panes when they tumble low,
I whisper to terminals where cursors go,
A tiny hop, a follow-up call,
No blank screens lurking after the fall,
Hooray — the prompt is back for all!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main bug fix: terminal becomes blank when the last pane closes.
Linked Issues check	✅ Passed	The PR directly addresses issue #2665 by fixing the terminal blank/unresponsive state when panes collapse to one. The fix uses event-driven layout follow-up to restore focus after view reattachment, matching the core requirement.
Out of Scope Changes check	✅ Passed	All changes are focused on the terminal focus/first-responder issue during pane collapse. The modifications to focusPanel and BonsplitDelegate handling are directly scoped to address the blank terminal problem.
Description check	✅ Passed	The pull request description provides a clear summary of the problem, root cause, and solution. It includes a test plan with specific verification steps and links to the related issue #2665.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ 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-2665-last-pane-blank

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[greptile-apps]

Greptile Summary

This PR fixes a terminal blank/input-loss bug (#2665) that occurred when closing split panes down to the last remaining pane. The root cause was the SwiftUI split-to-single-pane rebuild transiently detaching the terminal surface mid-focus-reconcile; the fix passes the surviving panel as terminalFocusPanelId to beginEventDrivenLayoutFollowUp in both didCloseTab and didClosePane, arming the existing retry loop so focus is re-applied once the view is reattached. The includeGeometry: true flag preserves the geometry reconcile that scheduleTerminalGeometryReconcile() previously provided.

Confidence Score: 5/5

Safe to merge; fix is surgical, well-commented, and handles all relevant edge cases

No P0 or P1 findings. The two change sites are symmetric and correct: pane-collapse detection in didCloseTab uses the explicit !bonsplitController.allPaneIds.contains(pane) guard while didClosePane implicitly implies a pane was removed. The includeGeometry flag preserves the prior geometry-reconcile behavior. No double-fire risk is introduced—the trailing scheduleFocusReconcile() calls were already present before this PR.

No files require special attention.

Important Files Changed

Filename	Overview
Sources/Workspace.swift	Correctly replaces the one-shot scheduleTerminalGeometryReconcile with a retry-loop beginEventDrivenLayoutFollowUp (includeGeometry:true) in both delegate callbacks; condition guards are appropriate and geometry coverage is preserved

Sequence Diagram

sequenceDiagram
    participant User
    participant BonsplitController
    participant Workspace
    participant SwiftUI
    participant TerminalSurface

    User->>BonsplitController: Close last tab in pane
    BonsplitController->>Workspace: didCloseTab(pane collapsed)
    Workspace->>Workspace: applyTabSelection(survivingPane)
    note over Workspace: isDetaching=false,<br/>pane no longer in allPaneIds
    Workspace->>Workspace: beginEventDrivenLayoutFollowUp(<br/>terminalFocusPanelId=survivingPanelId,<br/>includeGeometry=true)
    Workspace->>SwiftUI: layout observers installed
    SwiftUI-->>Workspace: split view rebuilds (detaches surface)
    TerminalSurface-->>Workspace: terminalSurfaceHostedViewDidMoveToWindow
    Workspace->>Workspace: scheduleLayoutFollowUpAttempt()
    Workspace->>TerminalSurface: ensureFocus() [retry loop]
    TerminalSurface-->>User: first responder restored ✓

Loading

_{Reviews (1): Last reviewed commit: "Fix terminal blank when last pane closes..." | Re-trigger Greptile}