Related to #4777 (closed). Still crashing with both fixes applied:

• 2c7f73f ("Do not use recallocarray...")
• 035a2f3 ("Clear trimmed lines after moving...")

The crash is POINTER_BEING_FREED_WAS_NOT_ALLOCATED in grid_clear_lines, triggered when entering
copy mode after a long session (~9 hours uptime).

Stack trace:
grid_clear_lines+140
screen_reinit+256
window_copy_clone_screen+236
window_copy_init+88
window_pane_set_mode+196
cmd_copy_mode_exec+348

Environment:

• tmux next-3.7 (pinned to d0caf0a, 2026-03-06)
• macOS 26.3.1 (25D2128), Apple Silicon (MacBookPro18,2)
• Terminal: Ghostty

Full crash report (macOS .ips):

{"app_name":"tmux","timestamp":"2026-03-28 16:00:19.00
-0600","app_version":"","slice_uuid":"fa45b2ee-8c88-3e40-bd0c-ab9654d2b6cf","build_version":"","p
latform":1,"share_with_app_devs":0,"is_first_party":1,"bug_type":"309","os_version":"macOS 26.3.1
(25D2128)","roots_installed":0,"incident_id":"4D27E921-A851-4850-B911-F34D2B2C51A2","name":"tmux
"}
{
"uptime" : 290000,
...
}

{"app_name":"tmux","timestamp":"2026-03-28 16:00:19.00 -0600","app_version":"","slice_uuid":"fa45b2ee-8c88-3e40-bd0c-ab9654d2b6cf","build_version":"","platform":1,"share_with_app_devs":0,"is_first_party":1,"bug_type":"309","os_version":"macOS 26.3.1 (25D2128)","roots_installed":0,"incident_id":"4D27E921-A851-4850-B911-F34D2B2C51A2","name":"tmux"}
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