tools/serve.py: build, serve and rebuild on change (t9)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/PROJECT_MAP.md

@@ -20,9 +20,10 @@ src/ui/               the browser shell: input, HUD, build menu, notebook, setti
                       audio, the frame loop
 test/                 headless suites (t_*.js) and their harness; browser tests (play.py,
                       t_smooth.py); run_all.py
-tools/                shot.py (screenshots), where.py, map.py, perf.py, playthrough.py,
-                      use_venv.py (switches browser scripts to .venv), scenes/ (screenshot
-                      setups), experiments/ (measurements and reports)
+tools/                serve.py (build, serve, rebuild on change), shot.py (screenshots),
+                      where.py, map.py, perf.py, playthrough.py, use_venv.py (switches browser
+                      scripts to .venv), scenes/ (screenshot setups), experiments/
+                      (measurements and reports)
 docs/                 this map, DESIGN.md, TESTING.md, systems/ (notes per system),
                       history/ (the owner's requests), agent-log.md
 dist/, shots/         build output and screenshots (not committed)
@@ -456,6 +457,7 @@ The frame loop and boot.
 - `tools/map.py`: Regenerate the file and symbol index at the end of docs/PROJECT_MAP.md.
 - `tools/perf.py`: Times the renderer and the simulation in a headless browser: light, drawWorld (with and without light and glow), the pixel upload and blit, and one simulation tick, in ms. Rebuild first.
 - `tools/playthrough.py`: Headless browser run: load the page, start a world, play a little, take screenshots.
+- `tools/serve.py`: Build, serve and rebuild when sources change: python3 tools/serve.py [--port 8000].
 - `tools/shot.py`: Screenshot the game in a headless browser, after setting up a scene with JavaScript.
 - `tools/use_venv.py`: Let browser scripts run with plain python3 by switching to the repo's .venv.
 - `tools/where.py`: Turn a line number in dist/index.html into the source file and line it came from.