docs: correct three more result-diff comments to the whole-file case

Three comments still implied the result diff is always an applied hunk or
that write returns undefined on no-hunk: the toolResultUpdate JSDoc (a diff
result "emits the applied-hunk blocks, which replace the call-time snippet"),
the empty-diffs test comment ("an empty write returns undefined" — write now
falls back to a whole-file diff), and diffsFromMeta's JSDoc ("a bad meta
yields no diff card" — only true for edit; write falls back to a whole-file
diff). Each now states the write whole-file fallback. Regenerate the catalog.

packages/ui/acp/tests/stream-update.spec.ts

@@ -677,9 +677,10 @@ describe('result-time diff card (REAL fs edit tool → tool_call_update diff blo
 
   it('a diff result with an EMPTY diffs array and no title omits both keys (nothing to send)', () => {
     // A synthetic tool whose presentResult yields a `diff` card with no hunks and
-    // no title — the shipping fs tools never emit this (edit always has a hunk; an
-    // empty write returns undefined), so a stand-in is the only way to exercise
-    // the empty-content AND absent-title branches of the result-side diff arm.
+    // no title — the shipping fs tools never emit this (edit always has a hunk;
+    // write always falls back to a whole-file diff), so a stand-in is the only way
+    // to exercise the empty-content AND absent-title branches of the result-side
+    // diff arm.
     const emptyDiffTool: ToolDefinition = {
       name: 'writer',
       description: 'writes a file',