diff --git a/packages/fs/tool-fs/src/diff.ts b/packages/fs/tool-fs/src/diff.ts
index 273fe0b033..64f3c5c686 100644
--- a/packages/fs/tool-fs/src/diff.ts
+++ b/packages/fs/tool-fs/src/diff.ts
@@ -81,7 +81,8 @@ function isFileDiff(value: unknown): value is FileDiff {
  * hunks, or `undefined` when it is absent/malformed. `presentResult` runs on
  * arbitrary logged `meta` (possibly from an older shape or a hand-edited log), so
  * it validates defensively rather than trusting the payload — a bad `meta` yields
- * no diff card (the generic result rendering) instead of a thrown presenter.
+ * `undefined`, and the caller decides the fallback (edit → the generic result
+ * rendering; write → an args-derived whole-file diff), never a thrown presenter.
  */
 export function diffsFromMeta(meta: unknown): FileDiff[] | undefined {
   if (typeof meta !== 'object' || meta === null || Array.isArray(meta)) return undefined
diff --git a/packages/ui/acp/src/index.ts b/packages/ui/acp/src/index.ts
index 1c1f0f770a..ab784d2efd 100644
--- a/packages/ui/acp/src/index.ts
+++ b/packages/ui/acp/src/index.ts
@@ -1126,9 +1126,10 @@ function terminalExitMeta(callId: string, view: TerminalResultView): TerminalExi
  * (the terminal card consumes them and `content` is OMITTED — a
  * `tool_call_update.content` REPLACES the call's content collection in Zed, so
  * re-sending would clobber the terminal block the call installed) and otherwise
- * derives the fenced ```console fallback from `output`. A `diff` result emits the
- * applied-hunk `{ type: 'diff' }` content blocks, which replace the call-time
- * whole-file snippet in the editor.
+ * derives the fenced ```console fallback from `output`. A `diff` result emits its
+ * `{ type: 'diff' }` content blocks (an applied hunk, or a whole-file diff for a
+ * create), which replace the diff the call installed — so the model-facing result
+ * text can never clobber it.
  */
 function toolResultUpdate(callId: CallId, view: ToolResultView, isError: boolean, terminal: TerminalRendering): ToolCallSessionUpdate {
   const status = isError ? 'failed' as const : 'completed' as const
diff --git a/packages/ui/acp/tests/stream-update.spec.ts b/packages/ui/acp/tests/stream-update.spec.ts
index 0a9974e049..67cd95ccdd 100644
--- a/packages/ui/acp/tests/stream-update.spec.ts
+++ b/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',