Port Snapmaker/OrcaSlicer #1004: stop backup thread wxPostEvent after shutdown

[aceRage]

Description

Port of Snapmaker/OrcaSlicer #1004 onto Edge main.

Upstream head SHA ported: 4f3e868732eef29a6372ecef0888b53a41361515 (open, unmerged; may still change).
Edge branch head: 53d3288785cd050bea2f324c5a763384cacff3e7
Edge base: 83267707adc757e9ca1f2e1c946084768cef1d41 (main)

The backup worker (_BBS_Backup_Manager::operator()) used to snapshot m_post_callback under m_mutex, drop the lock for process_task(), then invoke the stale copy. MainFrame::shutdown() — on quit and on language-switch recreate — calls set_backup_callback(nullptr) and destroys the frame. If that lands in the unlocked window, the worker wxPostEvents into a destroyed MainFrame (Sentry SNAPMAKER_ORCA-7R / #7134242393, EXC_BAD_ACCESS).

This port:

• Adds m_post_callback_mutex so callback swaps serialize against in-flight invokes (lock order m_mutex → m_post_callback_mutex).
• Re-reads m_post_callback at fire time instead of using a stale local.
• Catch-up: installing a non-null callback re-announces queued m_ui_tasks so language-switch recreate does not stall auto-backup (EVT_BACKUP_POST is edge-triggered on size()==1).

No public API change. process_ui_task()’s UI-thread callback(1) path is unchanged (same thread as the only writer).

Adapted, not cherry-picked: Edge bbs_3mf.cpp line numbers and Snapmaker extras around the worker are left as-is; only the callback swap/invoke path is touched.

Screenshots/Recordings/Graphs

N/A — shutdown race in the backup worker, no UI layout change.

Tests

Catch2 v2 in existing tests/libslic3r/test_3mf.cpp ([3mf][bbs-backup]). Upstream’s new test_bbs_backup.cpp + tests/libslic3r/CMakeLists.txt edit were not ported (Edge: existing test files only, no test CMake edits). Converted from Catch2 v3 (catch_test_macros.hpp) to v2 (catch.hpp).

libslic3r_tests "[bbs-backup]"

This cloud VM has no slicer deps/libslic3r_tests binary, so the case was not executed here. Edge CI is the gate.

Manual smoke (owed on a built app)

• Quit while a backup cycle is in flight (5 trials): no hang, no crash, process exits clean.
• Language switch (recreate GUI) while a backup is queued: auto-backup still fires after the new MainFrame is up; no stall until exit.
• Idle backup interval still writes .3mf under the project backup path after a period of edits.