fix(rectification): keep opening greeting across set-focus

set-focus only attaches the question stem. Retracting live Chinese before
it wiped the opening hello with an empty replace. Other public tools still
retract planning prose.

BUG-533.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/tests/rectification-step-answer.test.ts

@@ -106,6 +106,42 @@ test("retracts a live spoken prefix if that step later calls a public tool", ()
   assert.deepEqual(spoken, { kind: "live", text: "诊断已经看过。接下来确认入职年份。" });
 });
 
+test("keeps a live opening greeting when the next public tool is set-focus", () => {
+  const state = createStepAnswerState();
+  assert.deepEqual(
+    applyStepAnswerChunk(
+      state,
+      chunk("text-delta", { text: "你好，我们从你最容易想起的经历开始就行。" }),
+      isPublicTool,
+    ),
+    { kind: "live", text: "你好，我们从你最容易想起的经历开始就行。" },
+  );
+  assert.equal(
+    applyStepAnswerChunk(
+      state,
+      chunk("tool-call", { toolName: "rectification-set-focus" }),
+      isPublicTool,
+    ).kind,
+    "none",
+  );
+  assert.equal(
+    applyStepAnswerChunk(
+      state,
+      chunk("tool-result", { toolName: "rectification-set-focus" }),
+      isPublicTool,
+    ).kind,
+    "none",
+  );
+  assert.deepEqual(
+    applyStepAnswerChunk(
+      state,
+      chunk("text-delta", { text: "我们慢慢来就好——想到哪件就聊哪件，不用一次说完。" }),
+      isPublicTool,
+    ),
+    { kind: "live", text: "我们慢慢来就好——想到哪件就聊哪件，不用一次说完。" },
+  );
+});
+
 test("does not live-publish English planning before a tool-call", () => {
   const state = createStepAnswerState();
   assert.equal(