fix: prefer final-answer text in web chat previews

src/shared/chat-message-content.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { extractFirstTextBlock } from "./chat-message-content.js";
+import { extractAssistantVisibleText, extractFirstTextBlock } from "./chat-message-content.js";
 
 describe("shared/chat-message-content", () => {
   it("extracts the first text block from array content", () => {
@@ -47,3 +47,66 @@ describe("shared/chat-message-content", () => {
     expect(extractFirstTextBlock({ content: [{ text: 1 }, { text: "later" }] })).toBeUndefined();
   });
 });
+
+describe("extractAssistantVisibleText", () => {
+  it("prefers final_answer text over commentary text", () => {
+    expect(
+      extractAssistantVisibleText({
+        role: "assistant",
+        content: [
+          {
+            type: "text",
+            text: "thinking like caveman",
+            textSignature: JSON.stringify({ v: 1, id: "msg_commentary", phase: "commentary" }),
+          },
+          {
+            type: "text",
+            text: "Actual final answer",
+            textSignature: JSON.stringify({ v: 1, id: "msg_final", phase: "final_answer" }),
+          },
+        ],
+      }),
+    ).toBe("Actual final answer");
+  });
+
+  it("does not fall back to commentary-only text", () => {
+    expect(
+      extractAssistantVisibleText({
+        role: "assistant",
+        content: [
+          {
+            type: "text",
+            text: "thinking like caveman",
+            textSignature: JSON.stringify({ v: 1, id: "msg_commentary", phase: "commentary" }),
+          },
+        ],
+      }),
+    ).toBeUndefined();
+  });
+
+  it("falls back to unphased legacy text", () => {
+    expect(
+      extractAssistantVisibleText({
+        role: "assistant",
+        content: [{ type: "text", text: "Legacy answer" }],
+      }),
+    ).toBe("Legacy answer");
+  });
+
+  it("does not mix unphased legacy text into final_answer output", () => {
+    expect(
+      extractAssistantVisibleText({
+        role: "assistant",
+        phase: "final_answer",
+        content: [
+          { type: "text", text: "Legacy answer" },
+          {
+            type: "text",
+            text: "Actual final answer",
+            textSignature: JSON.stringify({ v: 1, id: "msg_final", phase: "final_answer" }),
+          },
+        ],
+      }),
+    ).toBe("Actual final answer");
+  });
+});