step 3: add widget shell sizing and frame pump

README.md

@@ -2,7 +2,7 @@
 
 `dpg-map` is a Dear PyGui map widget package under rebuild.
 
-The Step 2 logical runtime model is in place:
+The Step 3 widget shell is in place:
 
 ```python
 import dpg_map as dpgm
@@ -29,7 +29,21 @@ Implemented so far:
 - command queue with coalescing for overlay and view updates
 - logical marker, polyline, trajectory, and layer models
 - persistent disk cache path, metadata, scanning, and prune planning
+- Dear PyGui `child_window` + measured-size `drawlist` widget shell
+- GUI-thread frame pump that drains commands and redraws a placeholder background
+- sizing helpers that preserve the last non-zero size across hidden layouts
+- interaction hit-rectangle calculation for the measured map area
 
-Dear PyGui rendering is not implemented yet. The current `map_widget` is a logical
-context manager used to register state; Step 3 will add the real child window,
-drawlist, sizing, and GUI-thread frame pump.
+Real tile loading and overlay drawing are not implemented yet. Step 4 will add
+the asynchronous tile manager, persistent tile loading, and GUI-thread texture
+creation.
+
+Examples:
+
+```bash
+uv run python examples/basic_map.py
+uv run python examples/sizing_window.py
+uv run python examples/sizing_child.py
+uv run python examples/sizing_table.py
+uv run python examples/hidden_tab.py
+```