fix(adapter-utils): treat Retry-After: 0 as retry-immediately

Greptile flagged `parsed > 0` as a P1 (Retry-After: 0 falls back to
exponential backoff). The mechanism they described — `new Date("0")`
returning Invalid Date in Node 20+ — does not reproduce: V8 parses
`"0"` as year-2000 in local TZ on Node 20.20.2 and 22.22.1, so the
date branch coincidentally returns 0 ms via `Math.max(0, past - now)`.

The current code is therefore *accidentally correct* on Node 20+ in
2026, but relies on implementation-defined Date parsing per ES spec
and would break under a future V8 change or a system clock set before
year 2000. Switching `parsed > 0` to `parsed >= 0` makes the intent
explicit, matches RFC 7231 §7.1.3 ("0" = "you may retry at once"),
and skips the date branch entirely on the common case.

Also pins the behavior with two test changes:
- Strengthen the existing onRetry test to assert `delayMs: 0`.
- New explicit test: Retry-After: 0 with baseDelayMs/maxDelayMs set
  to 60s — passes only if delayMs is actually 0, not exponential.

packages/adapter-utils/src/server-utils.test.ts

@@ -2687,6 +2687,8 @@ describe("buildPaperclipEnv", () => {
       const env = buildPaperclipEnv({ id: "agent-1", companyId: "company-1" });
       expect(env.PAPERCLIP_API_URL).toBe("http://localhost:3200");
     });
+  });
+});
 
 describe("fetchWithRetry", () => {
   let originalFetch: typeof fetch;
@@ -2784,11 +2786,33 @@ describe("fetchWithRetry", () => {
         attempt: 1,
         maxRetries: 3,
         status: 429,
+        delayMs: 0,
         retryAfterHeader: "0",
       }),
     );
   });
 
+  it("treats Retry-After: 0 as 'retry immediately' (delayMs: 0)", async () => {
+    const fetchMock = vi
+      .fn()
+      .mockResolvedValueOnce(makeResponse(429, { "retry-after": "0" }))
+      .mockResolvedValueOnce(makeResponse(200));
+    globalThis.fetch = fetchMock as unknown as typeof fetch;
+
+    const onRetry = vi.fn();
+
+    const res = await fetchWithRetry(
+      "https://example.test",
+      {},
+      { baseDelayMs: 60_000, maxDelayMs: 60_000, onRetry },
+    );
+
+    expect(res.status).toBe(200);
+    expect(onRetry).toHaveBeenCalledWith(
+      expect.objectContaining({ delayMs: 0, retryAfterHeader: "0" }),
+    );
+  });
+
   it("treats custom retryableStatuses as retryable (e.g. 403)", async () => {
     const fetchMock = vi
       .fn()

packages/adapter-utils/src/server-utils.ts

@@ -3620,7 +3620,7 @@ export async function fetchWithRetry(
 
     if (retryAfter) {
       const parsed = Number(retryAfter);
-      if (!Number.isNaN(parsed) && parsed > 0) {
+      if (!Number.isNaN(parsed) && parsed >= 0) {
         delayMs = parsed * 1000;
       } else {
         const date = new Date(retryAfter).getTime();