every control writes itself

The Save button is gone, and so is the SaveTarget context that announced it.
Every screen here is a preview of the thing being edited, so a change is already
visible before it is written — a button then asks somebody to confirm what they
can see.

useAutosave debounces a burst into one request. It takes the unsaved state as a
string rather than a flag, so a failed save is not retried on the next render,
and it flushes on unmount so a section change loses nothing.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

web/sections/LayoutPanel.tsx

@@ -4,7 +4,7 @@ import { useSearchParams } from 'react-router';
 import { useClient } from 'hooks/useClient';
 import { readableError } from '../errors';
 import { useFlash } from '../useFlash';
-import { useSaveTarget } from '../SaveTarget';
+import { useAutosave } from '../useAutosave';
 import { usePreviewable, useViewMode } from '../ViewMode';
 import { applySpacing, paintMeasure, type SpacingDraft } from '../canvas';
 import { SitePreview, useDevPort } from '../SitePreview';
@@ -203,7 +203,8 @@ export const LayoutPanel = () => {
     }
   };
 
-  useSaveTarget(dirty, busy, save);
+  // The serialised draft, or null when it matches what the server has. See useAutosave.
+  useAutosave(dirty ? only(draft) : null, busy, save);
   // This section has a preview, so the bar offers Edit/View and the three widths.
   usePreviewable();
   const { device } = useViewMode();