feat(tool-youtube-transcript): YouTube transcription tool

New standard tool extension backed by a self-hosted transcriber service
(http://100.102.55.49:41090, Tailscale, no API key). One tool
youtube_transcript — fetches transcripts for YouTube videos. Returns
completed (full text + timestamped segments), queued/processing (position
+ ETA + .youtube_subtitles_pending retry convention), or failed (error).

Pure core: validateUrl + format* functions + truncateOutput. Injected
edge: TranscriptClient (injectable fetchFn, AbortSignal.any for
cancellation). concurrencySafe true, capabilities network. 30 tests.

Verified: tsc EXIT 0, 1152 vitest, biome clean (327 files). Boot smoke
clean.

1 files changed, 35 insertions, 0 deletions

diff --git a/packages/tool-youtube-transcript/src/validate.test.ts b/packages/tool-youtube-transcript/src/validate.test.ts
new file mode 100644
index 0000000..3181bb1
--- /dev/null
+++ b/packages/tool-youtube-transcript/src/validate.test.ts
@@ -0,0 +1,35 @@
+import { describe, expect, it } from "vitest";
+import { validateUrl } from "./validate.js";
+
+describe("validateUrl", () => {
+	it("accepts valid URL", () => {
+		const result = validateUrl({ url: "https://www.youtube.com/watch?v=abc123" });
+		expect(result).toBe("https://www.youtube.com/watch?v=abc123");
+	});
+
+	it("rejects missing url", () => {
+		const result = validateUrl({ query: "no url here" });
+		expect(typeof result).toBe("object");
+		if (typeof result === "object") {
+			expect(result.error).toContain("url");
+		}
+	});
+
+	it("rejects empty url", () => {
+		const empty = validateUrl({ url: "" });
+		expect(typeof empty).toBe("object");
+		if (typeof empty === "object") {
+			expect(empty.error).toContain("url");
+		}
+		const whitespace = validateUrl({ url: "   " });
+		expect(typeof whitespace).toBe("object");
+	});
+
+	it("rejects null/non-object args", () => {
+		expect(typeof validateUrl(null)).toBe("object");
+		expect(typeof validateUrl(undefined)).toBe("object");
+		expect(typeof validateUrl("string")).toBe("object");
+		expect(typeof validateUrl(42)).toBe("object");
+		expect(typeof validateUrl(true)).toBe("object");
+	});
+});