Checkpoint before line-grid scrolling refactor

CLIENT_TODO.md

@@ -40,6 +40,7 @@ Required module rules:
 - Every app module declares all required dependencies in its `dependencies` list.
 - The loader loads module scripts, resolves the dependency graph, initializes modules in dependency order, awaits async initialization, and only then hides the loading overlay.
 - Modules must rely on the loader for dependency readiness. Do not add fallback paths for missing dependencies inside modules.
+- Do not add fallback code that bypasses an authoritative module, service, parser, state store, or API to hide an architectural problem. If such a fallback already exists or seems tempting, stop and report the architectural mismatch before changing code.
 - Module states are `PENDING`, `LOADING`, `WAITING`, `INITIALIZING`, `FINISHED`, and `ERROR`.
 - Modules must report real state transitions. A module must not report `FINISHED` until its critical initialization is actually ready.
 - `setTimeout` must not be used to paper over dependency or async ordering bugs. It is acceptable inside isolated scheduling systems such as animation timing, debounce, throttle, or browser rendering workarounds when documented by context.