fix: split telegram reasoning and answer draft streams (#20774)

Merged via /review-pr -> /prepare-pr -> /merge-pr.

Prepared head SHA: 7458444144
Co-authored-by: obviyus <22031114+obviyus@users.noreply.github.com>
Co-authored-by: obviyus <22031114+obviyus@users.noreply.github.com>
Reviewed-by: @obviyus

src/telegram/reasoning-lane-coordinator.test.ts

@@ -0,0 +1,25 @@
+import { describe, expect, it } from "vitest";
+import { splitTelegramReasoningText } from "./reasoning-lane-coordinator.js";
+
+describe("splitTelegramReasoningText", () => {
+  it("splits real tagged reasoning and answer", () => {
+    expect(splitTelegramReasoningText("<think>example</think>Done")).toEqual({
+      reasoningText: "Reasoning:\n_example_",
+      answerText: "Done",
+    });
+  });
+
+  it("ignores literal think tags inside inline code", () => {
+    const text = "Use `<think>example</think>` literally.";
+    expect(splitTelegramReasoningText(text)).toEqual({
+      answerText: text,
+    });
+  });
+
+  it("ignores literal think tags inside fenced code", () => {
+    const text = "```xml\n<think>example</think>\n```";
+    expect(splitTelegramReasoningText(text)).toEqual({
+      answerText: text,
+    });
+  });
+});