fix: print the running tool once, not twice (#17)

src/__tests__/markdown.test.ts

@@ -116,6 +116,64 @@ describe("buildThreadMarkdown", () => {
     expect(markdown).not.toContain("Thinking");
   });
 
+  it("says what a running tool is doing exactly once, before any text arrives", () => {
+    // The reported bug, from a screenshot: the activity line and the answer
+    // placeholder both printed "Reading a page", one directly above the other.
+    const markdown = buildThreadMarkdown([
+      message({
+        role: "assistant",
+        isStreaming: true,
+        text: "",
+        activity: { label: "Reading a page", count: 1 },
+      }),
+    ]);
+
+    expect(markdown.match(/Reading a page/g)).toHaveLength(1);
+    // With nothing to read yet, the activity line is the stand-in, so the cursor
+    // rides on it rather than sitting on a line of its own.
+    expect(markdown).toContain(`_Reading a page…_ ${STREAMING_CURSOR}`);
+  });
+
+  it("keeps the activity line once the answer has started arriving", () => {
+    // The other half of the fix: a tool that starts mid-answer has to stay on
+    // screen, which is why the line is not just a stand-in for missing text.
+    const markdown = buildThreadMarkdown([
+      message({
+        role: "assistant",
+        isStreaming: true,
+        text: "Here is what I found.",
+        activity: { label: "Reading a page", count: 1 },
+      }),
+    ]);
+
+    expect(markdown).toContain("_Reading a page…_");
+    expect(markdown).toContain("Here is what I found.");
+    // And the cursor follows the answer, not the activity line.
+    expect(markdown).toContain(`Here is what I found. ${STREAMING_CURSOR}`);
+    expect(markdown).not.toContain(`_Reading a page…_ ${STREAMING_CURSOR}`);
+  });
+
+  it("names a repeat rather than leaving a bare count to be interpreted", () => {
+    const markdown = buildThreadMarkdown([
+      message({
+        role: "assistant",
+        isStreaming: true,
+        activity: { label: "Searching the web", count: 2 },
+      }),
+    ]);
+
+    expect(markdown).toContain("the same call again (2)");
+  });
+
+  it("drops the activity line when the message is no longer streaming", () => {
+    const markdown = buildThreadMarkdown([
+      message({ role: "assistant", text: "done", activity: { label: "Searching the web", count: 1 } }),
+    ]);
+
+    expect(markdown).not.toContain("Searching the web");
+    expect(markdown).not.toContain(STREAMING_CURSOR);
+  });
+
   it("shows a placeholder while an answer has no text yet", () => {
     expect(buildThreadMarkdown([message({ role: "assistant", isStreaming: true })])).toContain("Thinking");
     expect(buildThreadMarkdown([message({ role: "assistant" })])).toContain("No response");