Dock.load_state() causes DrawList corruption, rendering blank main page

[ZhangHanDong]

Summary

Restoring the Dock layout from persisted state via Dock.load_state() corrupts Makepad's internal DrawList references, causing the entire main content area (rooms list + room tabs) to render as a blank grey page after app restart.

Symptoms

• Left navigation bar renders correctly
• Main content area (Dock with RoomsSideBar + room tabs) is completely blank/grey
• Console floods with Drawlist id generation wrong errors:

  [E] draw_list.rs:324: Drawlist id generation wrong index: 21 current gen:1 in pointer:0
  

Root Cause

Dock.load_state() (Makepad widgets/src/dock.rs:1310) destroys DrawList2d objects by calling self.tab_bars.clear() during event handling. The Makepad rendering pipeline still holds cached DrawListId references from the previous frame, causing generation mismatches when the freed pool entries are accessed.

Key sequence:

1. First draw creates tab_bars with DrawList2d at pool index N, generation 0
2. RestoreAppStateFromPersistentState triggers load_state() during event handling
3. tab_bars.clear() drops DrawList2d → pool[N].generation increments to 1
4. Next frame accesses stale DrawListId(N, gen=0) → generation mismatch → blank rendering

Reproduction

1. Run the app, log in, open some room tabs
2. Close the app (state persists to latest_app_state.json)
3. Restart → blank main page

Verification: Deleting latest_app_state.json → UI renders correctly with 0 DrawList errors.

Fix Applied

Replaced dock.load_state(dock_items) in load_dock_state_from() with programmatic tab recreation via close_all_tabs() + focus_or_create_tab(), which uses the Dock's normal widget API and avoids direct DrawList destruction.

See issues/001-dock-load-state-drawlist-corruption.md for full details.

Remaining Issues

• Splitter position not restored — custom sidebar width resets to 300px on restart
• Multi-pane layout not restored — drag-created split-view arrangements lost on restart
• Upstream Makepad bug — Dock.load_state() should properly handle DrawList lifecycle when called during event handling (needs fix in kevinaboos/makepad stack_nav_improvements branch)
• Unrelated: SETTINGS_BUTTON_HEIGHT undefined in account_settings.rs:63,86

Environment

• Makepad: kevinaboos/makepad@stack_nav_improvements (461b0513)
• Platform: macOS (Darwin 24.5.0)