#19148 fix: stop remote tmux detach adding a second replacement terminal

Main is red (#19109): LastSurfaceClosePreferenceTests remoteTmuxWindowCloseKeepsWorkspaceOpenWhenKeepWorkspaceOpenPreferenceIsEnabled, remoteTmuxWindowCloseKeepsWorkspaceOpenImmediatelyForShortcut and remoteTmuxWindowCloseCreatesReplacementWhenOnlyMainWindowWouldBeEmpty fail with panels.count → 2 == 1 in app-host shard 2/7.

Cause: #18645 (feat(cli): list and attach remote tmux sessions, @austinywang) added repairRetiredRemoteTmuxContainerPanelsAfterDetach() to detachRemoteTmuxMirrorKeptOpenLocallyIfNeeded(), which creates a replacement terminal whenever the workspace is empty. The last-surface close path calls detach on an already-empty workspace and then creates its own replacement, so a kept-open remote tmux workspace ends up with two terminals. The Dock surface-move path has the same double.

Fix: the repair only creates a replacement when it removed retired panels itself. detachingMirrorReplacesRetiredContainerWithUsableTerminal (the #18645 test) still gets its replacement; callers that detach an already-empty workspace keep creating exactly one.

Not built locally (machine rule); full CI dispatched on this branch.

🤖 Generated with Claude Code

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Summary by cubic

Fixes kept-open remote tmux workspaces ending up with two terminals when closing the last surface. Detaching an already-empty workspace (last-surface close, Dock surface moves) now creates only one replacement; the repair only adds its own replacement when it actually removed the last panels.

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[!NOTE]
Low Risk
Narrow change to remote tmux mirror detach and replacement-terminal creation; no auth or data-handling impact.

Overview
Fixes duplicate replacement terminals when a kept-open remote tmux mirror detaches on a workspace that is already empty.

repairRetiredRemoteTmuxContainerPanelsAfterDetach() now calls createReplacementTerminalPanel() only when it actually removed retired container panels (!retiredPanelIDs.isEmpty), not merely because panels is empty after detach. Last-surface close, Dock surface moves, and similar paths that detach an empty workspace and add their own shell no longer get a second terminal from this repair; the detach path that still clears stale retired containers continues to get one replacement when needed.

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Summary by CodeRabbit

• Bug Fixes
  • Prevented unnecessary replacement terminals from being created after detaching when no retired panels were removed.