fix: fall back to WHOIS when a bootstrap fetch aborts on its own

Any AbortError from the bootstrap fetch was rethrown, so a customFetch's own
timeout ended the whole lookup as "aborted" (documented as "your own signal
fired") with no WHOIS fallback; the same error during the RDAP domain fetch
already fell back. Caller aborts and deadlines are still rethrown.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/index.attempts.test.ts

@@ -342,3 +342,21 @@ describe("timeouts, deadline and abort", () => {
     expect(vi.mocked(whoisQuery)).not.toHaveBeenCalled();
   });
 });
+
+describe("bootstrap AbortError not caused by the caller", () => {
+  it("falls back to WHOIS instead of failing as aborted", async () => {
+    vi.mocked(whoisQuery).mockResolvedValue({
+      serverQueried: "whois.verisign-grs.com",
+      text: whoisText,
+    });
+    const customFetch: FetchLike = vi.fn(async () => {
+      throw new DOMException("customFetch timed out", "AbortError");
+    });
+    const res = await lookup("example.com", {
+      customFetch,
+      whoisHints: { com: "whois.verisign-grs.com" },
+    });
+    expect(res.ok, res.error).toBe(true);
+    expect(res.record?.source).toBe("whois");
+  });
+});

src/rdap/bootstrap.ts

@@ -76,12 +76,12 @@ async function loadBootstrapData(
           },
         ),
       );
-    } catch (err: unknown) {
+    } catch {
       // Preserve caller cancellation behavior - rethrow if explicitly aborted (or deadline hit)
       if (options?.signal?.aborted) throwIfAborted(options.signal);
-      if (err instanceof Error && err.name === "AbortError") throw err;
       // Network, timeout, or JSON parse errors - return empty array to fall back to WHOIS
-      // (the failure is recorded in ctx.attempts)
+      // (the failure is recorded in ctx.attempts). An AbortError the caller didn't cause (a
+      // customFetch's own timeout) is one of these.
       return undefined;
     }
   }