step 6: add stable overlays and live update stress tests

AGENTS.md

@@ -2,7 +2,7 @@
 
 ## Current status
 
-Step 5 complete.
+Step 6 complete.
 
 ## Completed steps
 
@@ -11,10 +11,11 @@ Step 2 - Thread-safe state, commands, overlays, and cache model.
 Step 3 - Widget shell, sizing system, and GUI-thread frame pump.
 Step 4 - Tile manager, persistent cache, and asynchronous loading.
 Step 5 - Interaction: pan, zoom, and view commands.
+Step 6 - Overlay rendering and runtime update stress tests.
 
 ## Current step
 
-Step 6 - Overlay rendering and runtime update stress tests.
+Step 7 - Layers, provider switching, and clearing APIs.
 
 ## Design decisions
 
@@ -81,7 +82,19 @@ None yet.
 - Ran `uv run ruff format --check .`.
 - Ran `uv run pyright`.
 - Ran a Dear PyGui context smoke check for `map_widget` child-window/drawlist/texture-registry/handler-registry creation.
+- Implemented Dear PyGui draw-layer bookkeeping for background, tiles, overlays, and attribution.
+- Rendered markers, polylines, and trajectories from GUI-thread overlay snapshots.
+- Isolated overlay redraws so they clear only the overlay draw layer and do not clear tile draw commands or textures.
+- Added live background-thread marker and trajectory stress examples.
+- Added Step 6 tests for overlay draw-layer isolation, overlay-only dirty flags, threaded update coalescing, and view/drag-state isolation.
+- Updated `README.md` with Step 6 overlay rendering behavior and examples.
+- Ran `uv run ruff format .`.
+- Ran `uv run pytest`.
+- Ran `uv run pyright`.
+- Ran `uv run ruff check .`.
+- Ran `uv run ruff format --check .`.
+- Ran a Dear PyGui context smoke check for `map_widget` with marker, polyline, and trajectory overlays.
 
 ## Next action
 
-Implement Step 6.
+Implement Step 7.