Cap dev-runner output buffering

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/__tests__/dev-runner-output.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, it } from "vitest";
+import { createCapturedOutputBuffer } from "../../../scripts/dev-runner-output.mjs";
+
+describe("createCapturedOutputBuffer", () => {
+  it("keeps small output unchanged", () => {
+    const capture = createCapturedOutputBuffer(32);
+    capture.append("hello");
+    capture.append(" world");
+
+    expect(capture.finish()).toEqual({
+      text: "hello world",
+      totalBytes: 11,
+      truncated: false,
+    });
+  });
+
+  it("retains only the bounded tail when output grows large", () => {
+    const capture = createCapturedOutputBuffer(8);
+    capture.append("abcd");
+    capture.append(Buffer.from("efgh"));
+    capture.append("ijkl");
+
+    const result = capture.finish();
+    expect(result.truncated).toBe(true);
+    expect(result.totalBytes).toBe(12);
+    expect(result.text).toContain("total 12 bytes");
+    expect(result.text.endsWith("efghijkl")).toBe(true);
+  });
+});