fix: avoid double-borrow panic on rapid Ctrl+Tab tab switching

[ferdinankurnian]

Summary

Fixes a crash caused by a double-borrow panic on TabState's RefCell when rapidly switching tabs with Ctrl+Tab.

Root cause

activate_tab() in pane.rs held tab_state.borrow_mut() across the call to content_stack.set_visible_child_name(tab_id). That GTK call synchronously fires an unmap/map signal cascade on the old and new tab content — including hover/crossing signals on the terminal surface, whose callback calls tab_rename_active(&tab_state), which needs tab_state.borrow().

A single tab switch usually completes (and drops the borrow) before the next signal fires, so it goes unnoticed. But pressing Ctrl+Tab rapidly (2-4x in quick succession) can start a second activate_tab() call while the first switch's unmap cascade is still resolving, causing the reentrant .borrow() to panic while the outer .borrow_mut() is still held — and since this happens inside a GTK/glib signal callback (FFI boundary), the panic can't unwind and the process aborts (SIGABRT).

Fix

Narrowed the borrow_mut() scope so it's dropped before content_stack.set_visible_child_name() is called, removing the reentrancy window.

Testing

• Reproduced the crash consistently on the release build from AUR (limux-bin) before applying the fix — rapid Ctrl+Tab (2-4 presses) crashed every time
• Applied the fix, built v0.1.22 via this repo's Build Linux Release Packages workflow, downloaded and ran the resulting build locally — rapid Ctrl+Tab no longer crashes
• Rust Quality workflow (build, clippy, fmt) passes on the fix commit

Fixes #111

[ferdinankurnian]

Here's the recording confirming the fix, rapid Ctrl+Tab, no crash:

recording_2026-07-11_17-14-12.mp4

[bvolpato]

LGTM. Scoped RefCell borrow removes GTK reentrancy panic while preserving focus behavior.

[bvolpato]

Non-blocking: move child_by_name() below this scope. Current comment says content_stack is untouched until ts drops, but this query still runs under borrow_mut(). It is likely signal-free; keeping all stack calls outside makes reentrancy boundary explicit.

[bvolpato]

LGTM. activate_tab now drops mutable TabState borrow before set_visible_child_name() triggers synchronous GTK callbacks. Active-tab styling and deferred terminal/browser focus stay intact. No overlap with control-socket or Ghostty changes in #112 or #114.

(Review assisted by gpt-5.6-sol)