Pin three untested guards: download timer, URL fragment, short APP1 (closes #89)

The download idle deadline's timer is unref'd so it never holds the
process open, and a test checks no timer is left after a download
completes or fails. A test covers the rejection of "#" in a request
path. The EXIF scan compares the Exif header only when the APP1 length
is at least 8, so it never reads the next segment's bytes.

Model: opus-5-5

test/api/client.test.ts

@@ -474,6 +474,16 @@ describe("ApiClient request URLs", () => {
         );
         expect(calls).toHaveLength(0);
     });
+
+    it("rejects a path that carries a fragment", async () => {
+        const { fetch, calls } = recordingFetch();
+        const client = new ApiClient({ fetch });
+
+        await expect(client.getJSON("/diff#top")).rejects.toThrow(
+            /must not contain "\?" or "#"/,
+        );
+        expect(calls).toHaveLength(0);
+    });
 });
 
 describe("ApiError", () => {
@@ -980,6 +990,52 @@ describe("ApiClient timeouts", () => {
         }
         expect(joined).toEqual(payload);
     });
+
+    it("leaves no timer pending after a download completes or fails", async () => {
+        vi.useFakeTimers();
+        try {
+            const { fetch } = scriptedFetch(
+                streamResponse(new Uint8Array([1, 2, 3])),
+                textResponse("gone", 404),
+            );
+            const client = new ApiClient({
+                fetch,
+                retry: { ...noWait, attempts: 1 },
+            });
+
+            expect(await readAll(await client.getFileStream(1))).toBe(3);
+            expect(vi.getTimerCount()).toBe(0);
+
+            await expect(client.getFileStream(2)).rejects.toBeInstanceOf(
+                ApiError,
+            );
+            expect(vi.getTimerCount()).toBe(0);
+        } finally {
+            vi.useRealTimers();
+        }
+    });
+
+    it("never lets the download timer keep the process alive", async () => {
+        const spy = vi.spyOn(globalThis, "setTimeout");
+        try {
+            const { fetch } = scriptedFetch(
+                streamResponse(new Uint8Array([1])),
+            );
+            const client = new ApiClient({
+                fetch,
+                downloadTimeoutMs: 12_345,
+                retry: noWait,
+            });
+
+            const stream = await client.getFileStream(1);
+            const i = spy.mock.calls.findIndex((call) => call[1] === 12_345);
+            const timer = spy.mock.results[i]!.value as NodeJS.Timeout;
+            expect(timer.hasRef()).toBe(false);
+            await stream.cancel();
+        } finally {
+            spy.mockRestore();
+        }
+    });
 });
 
 describe("ApiClient error typing", () => {