fix: wait out processing until the certificate exists

A global stamp now polls status processing the same way as pending
and returns only the completed result. The debug trace for
Verae-Debug-Test records one receipt id.

tests/test_global_client.py

@@ -97,6 +97,38 @@ async def test_existing_digest_returns_first_certificate_without_status_poll():
     assert len(http.calls) == 1
 
 
+async def test_processing_status_polls_until_certificate():
+    class ProcessingHttp(FakeHttp):
+        def __init__(self):
+            super().__init__()
+            self.status_calls = 0
+
+        def request(self, method, url, payload, headers):
+            self.calls.append((method, url, payload, headers))
+            if url.endswith("/api/timestamp"):
+                return _Resp(202, {"jobId": "job-p"})
+            if url.endswith("/api/status/job-p"):
+                self.status_calls += 1
+                if self.status_calls < 3:
+                    return _Resp(200, {"id": "job-p", "status": "processing"})
+                return _Resp(
+                    200,
+                    {
+                        "id": "job-p",
+                        "status": "completed",
+                        "result": "QmDone",
+                        "metadata": {"timestamp": "2026-09-23T00:00:00Z", "blockHash": "0xabc"},
+                    },
+                )
+            return _Resp(404, {"error": "nope"})
+
+    http = ProcessingHttp()
+    rec = GlobalClient("https://api.veraetime.net", http=http).submit(SHA256_EMPTY)
+    assert rec.receipt_id == "QmDone"
+    assert rec.receipt_id != "job-p"
+    assert http.status_calls == 3
+
+
 async def test_existing_without_certificate_polls_job():
     class PendingExisting(FakeHttp):
         def request(self, method, url, payload, headers):