fix: harden mcp channel bridge smoke

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

@@ -10,6 +10,14 @@ describe("shared/chat-message-content", () => {
     ).toBe("hello");
   });
 
+  it("returns plain string content", () => {
+    expect(
+      extractFirstTextBlock({
+        content: "hello from string content",
+      }),
+    ).toBe("hello from string content");
+  });
+
   it("preserves empty-string text in the first block", () => {
     expect(
       extractFirstTextBlock({

src/shared/chat-message-content.ts

@@ -3,6 +3,9 @@ export function extractFirstTextBlock(message: unknown): string | undefined {
     return undefined;
   }
   const content = (message as { content?: unknown }).content;
+  if (typeof content === "string") {
+    return content;
+  }
   if (!Array.isArray(content) || content.length === 0) {
     return undefined;
   }