Harden historical anchor hydration edges

static/assistant_turn_anchors.js

@@ -928,6 +928,7 @@
     );
     const done=_activityRowToolDone(kind,status,payload);
     const isError=_activityRowToolIsError(status,payload);
+    const isDiff=_own(payload,'is_diff')===true||_own(payload,'isDiff')===true;
     const signatureParts=[
       toolName,
       toolCallId||'',
@@ -943,6 +944,7 @@
       output:_sanitizePayload(_own(payload,'output'))??null,
       done,
       is_error:isError,
+      ...(isDiff?{is_diff:true}:{}),
       duration:_activityPayloadFirst(payload,['duration','duration_seconds','elapsed'])??null,
       started_at:_activityPayloadFirst(payload,['started_at','startedAt'])??null,
       signature:signatureParts.join('|'),