Docs: trim arch 05 debounced-renderer sketch to its generation-guard insight

docs/architecture/05-rendering-theming-preview.md

@@ -384,49 +384,23 @@ export interface DebouncedRenderer {
   cancel(): void;
 }
 
-export function createDebouncedRenderer(opts: {
-  /** Current debounce delay in ms; read fresh each schedule so settings apply live. */
-  delayMs: () => number;
-  /** Performs one render. Reads the current spec/theme; awaits the embed. */
-  render: () => Promise<void>;
-  /** Toggle the non-blocking busy indicator. */
-  setBusy: (busy: boolean) => void;
-}): DebouncedRenderer {
-  let timer: ReturnType<typeof setTimeout> | null = null;
-  let generation = 0; // guards against a stale in-flight render finishing late
-
+// The factory wires the three operations over one timer. schedule() does
+// `setTimeout(run, delayMs())`, clearing any pending timer first (delayMs read fresh
+// so a settings change applies live); flush() clears the timer and runs now; cancel()
+// clears it and bumps `generation`. The non-obvious part is out-of-order protection:
+function createDebouncedRenderer(opts): DebouncedRenderer {
+  let generation = 0;
   const run = async () => {
-    timer = null;
-    const mine = ++generation;
+    const mine = ++generation; // capture this render's turn
     opts.setBusy(true);
     try {
       await opts.render();
     } finally {
-      // Only the most recent render clears the indicator.
-      if (mine === generation) opts.setBusy(false);
+      if (mine === generation) opts.setBusy(false); // only the latest render clears it
     }
   };
-
-  return {
-    schedule() {
-      if (timer) clearTimeout(timer); // cancel the pending render
-      timer = setTimeout(run, opts.delayMs());
-    },
-    flush() {
-      if (timer) {
-        clearTimeout(timer);
-        timer = null;
-      }
-      void run();
-    },
-    cancel() {
-      if (timer) {
-        clearTimeout(timer);
-        timer = null;
-      }
-      generation++; // abandon any in-flight result
-    },
-  };
+  // …schedule/flush/cancel as above. A slow render that resolves after a newer one
+  // fails the `mine === generation` check, so it can't clobber the fresh view/indicator.
 }
 ```