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

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Note

Medium Risk
Adjusts workspace focus/layout follow-up logic around terminal first-responder handling and split-view rebuilds; regressions could leave focus stuck or cause extra layout retries in terminal panels.

Overview
Prevents the surviving terminal from going blank after collapsing split panes by starting an event-driven layout follow-up that keeps re-applying ensureFocus until the terminal’s preferred keyboard target is active.

This expands terminal focus follow-up beyond the .terminalFirstResponder trigger, adds terminalPanelKeyboardFocusNeedsFollowUp (checks window first responder vs. terminal preferred focus), and uses it to gate both follow-up scheduling and clearing. Pane close/collapse paths now prefer beginEventDrivenLayoutFollowUp(... includeGeometry: true) for the surviving terminal (skipping detach flows), falling back to the existing geometry reconcile otherwise.

^{Reviewed by Cursor Bugbot for commit f8e480a. Bugbot is set up for automated code reviews on this repo. Configure here.}

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Summary by cubic

Fixes blank terminals and lost input when collapsing to a single pane or creating a new workspace (Cmd+T). Keeps the surviving terminal—or its find field—in focus so input works (fixes #2665).

• Bug Fixes
  • On pane collapse, start an event-driven layout follow-up with the surviving panel as terminalFocusPanelId so focus is reapplied after the split rebuild; applies to tab-close and pane-collapse; skipped on detach.
  • Trigger the same follow-up whenever the terminal isn’t at its preferred keyboard target (surface or find field), not only on .terminalFirstResponder; covers new workspace creation.
  • In the follow-up loop, stop only after the preferred keyboard target is focused to preserve terminal find focus when active.

^{Written for commit f8e480a. Summary will update on new commits.}

Summary by CodeRabbit

• Bug Fixes
  • Improved terminal focus recovery after pane closes or collapses so the remaining terminal reliably regains keyboard focus.
  • Reduced layout/geometry glitches after pane collapse by using a targeted, event-driven layout follow-up when possible, with a safe fallback to a full geometry reconcile when needed.

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Apr 10, 2026 1:31am

[cubic-dev-ai]

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[coderabbitai]

📝 Walkthrough

Walkthrough

Broadened Workspace terminal follow-up and pane-collapse logic: focus convergence is now checked via a new helper and, when a surviving focused panel is a terminal, Workspace schedules an event-driven layout follow-up targeting that terminal; otherwise it falls back to the existing geometry reconcile path. (50 words)

Changes

Cohort / File(s)

Summary

Workspace / Bonsplit focus & follow-up Sources/Workspace.swift

Refined terminal follow-up logic: added terminalPanelKeyboardFocusNeedsFollowUp helper and switched Workspace.focusPanel(_:trigger:) to use a TerminalPanel cast/path that schedules beginEventDrivenLayoutFollowUp when keyboard-focus convergence is needed. In BonsplitDelegate pane/tab-close handlers, replaced unconditional scheduleTerminalGeometryReconcile() with conditional beginEventDrivenLayoutFollowUp(reason: "workspace.paneCollapse", terminalFocusPanelId: ..., includeGeometry: true) when a surviving focused panel is a terminal; otherwise falls back to scheduleTerminalGeometryReconcile().

Sequence Diagram(s)

sequenceDiagram
    participant Split as BonsplitDelegate
    participant WS as Workspace
    participant Panel as TerminalPanel
    participant Win as Window / FirstResponder

    Split->>WS: pane/tab closed (didClosePane/didCloseTab)
    WS->>WS: determine surviving focusedPanelId
    alt surviving panel is TerminalPanel && not detaching
        WS->>Panel: beginEventDrivenLayoutFollowUp(reason: "workspace.paneCollapse", includeGeometry: true)
        Panel->>Win: query preferredKeyboardFocus
        Win-->>Panel: current firstResponder
        Panel->>WS: terminalPanelKeyboardFocusNeedsFollowUp? (compare)
        alt needs follow-up
            WS->>Panel: schedule focus re-apply / follow-up completion
        else
            WS->>WS: clear follow-up state
        end
    else
        WS->>WS: scheduleTerminalGeometryReconcile()
    end

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• Fix workspace layout follow-up spin loop #1633: Modifies Workspace follow-up/focus logic and scheduling paths similar to this change.
• Fix split ghost terminal render and focus recovery #1148: Alters terminal-first-responder and Bonsplit/Workspace focus reassertion behavior.
• Fix browser pane flicker during multi-split resize #2574: Related to terminal geometry reconciliation and split-resize/portal stabilization interactions.

Poem

🐰 I hop where panes once lost their spark,
I poke the terminal, nudge out the dark,
A gentle follow-up, a tidy little fix,
Cursors return with nimble rabbit tricks,
Hooray — the prompt resumes its lark!

🚥 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 accurately and concisely describes the main fix: preventing terminal blank when closing panes to a single remaining one, directly addressing issue #2665.
Linked Issues check	✅ Passed	The pull request directly addresses issue #2665 by fixing the terminal blank/unresponsive state when collapsing splits to a single pane, and maintains correct behavior for multi-pane and detach scenarios.
Out of Scope Changes check	✅ Passed	All changes are scoped to terminal focus and layout follow-up logic directly related to fixing #2665; no unrelated modifications detected in the file changes.
Description check	✅ Passed	The PR description is comprehensive and covers the required template sections: Summary (what/why), Test plan (how tested), and includes generated AI summaries and context.

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✨ 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

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[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 ✓

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