Fix IMAP lookup failures in reader

src/github_agent_bridge/reader.py

@@ -50,8 +50,19 @@ def fetch_once(self) -> int:
                 return 0
             uids = sorted(int(x) for x in data[0].split() if int(x) > last_uid)
             for uid in uids:
-                st, msgd = imap.uid("fetch", str(uid), "(RFC822)")
+                try:
+                    st, msgd = imap.uid("fetch", str(uid), "(RFC822)")
+                except imaplib.IMAP4.error as exc:
+                    self._record_fetch_failure(uid, f"IMAP4.error: {exc}")
+                    if self._is_lookup_failure(exc):
+                        self.queue.set_state("last_uid", str(uid))
+                        continue
+                    break
                 if st != "OK" or not msgd or not msgd[0]:
+                    self._record_fetch_failure(uid, f"{st}: {msgd!r}")
+                    if self._is_lookup_failure(msgd):
+                        self.queue.set_state("last_uid", str(uid))
+                        continue
                     break
                 msg = email.message_from_bytes(msgd[0][1])
                 from_addr = decode_header_value(msg.get("From", ""))
@@ -72,3 +83,10 @@ def fetch_once(self) -> int:
                 imap.logout()
             except Exception:
                 pass
+
+    def _record_fetch_failure(self, uid: int, detail: str) -> None:
+        self.queue.set_state("last_imap_fetch_error_uid", str(uid))
+        self.queue.set_state("last_imap_fetch_error", detail[:500])
+
+    def _is_lookup_failure(self, value: object) -> bool:
+        return "lookup failed" in str(value).lower()

tests/test_reader.py

@@ -0,0 +1,113 @@
+import imaplib
+
+from github_agent_bridge import reader
+
+
+class FakeQueue:
+    def __init__(self):
+        self.state = {}
+        self.enqueued = []
+
+    def get_state(self, key, default=""):
+        return self.state.get(key, default)
+
+    def set_state(self, key, value):
+        self.state[key] = value
+
+    def enqueue(self, notification, policy):
+        self.enqueued.append(notification)
+        return None, "enqueued"
+
+
+class FetchErrorImap:
+    logged_out = False
+
+    def __init__(self, host, port):
+        self.host = host
+        self.port = port
+
+    def login(self, username, password):
+        return "OK", []
+
+    def select(self, mailbox):
+        return "OK", []
+
+    def uid(self, command, *args):
+        if command == "search":
+            return "OK", [b"42"]
+        if command == "fetch":
+            raise imaplib.IMAP4.error(b"Lookup failed 423d73b8af312-310163d197dmb4381437a26")
+        raise AssertionError(command)
+
+    def logout(self):
+        type(self).logged_out = True
+
+
+class FetchNoImap(FetchErrorImap):
+    def uid(self, command, *args):
+        if command == "search":
+            return "OK", [b"43"]
+        if command == "fetch":
+            return "NO", [b"Lookup failed 423d73b8af312-310163d197dmb4381437a26"]
+        raise AssertionError(command)
+
+
+class FetchTemporaryNoImap(FetchErrorImap):
+    def uid(self, command, *args):
+        if command == "search":
+            return "OK", [b"44"]
+        if command == "fetch":
+            return "NO", [b"Temporary unavailable"]
+        raise AssertionError(command)
+
+
+def test_reader_records_and_skips_imap_fetch_lookup_error(monkeypatch):
+    queue = FakeQueue()
+    monkeypatch.setattr(reader.imaplib, "IMAP4_SSL", FetchErrorImap)
+
+    count = reader.ImapReader(
+        reader.ImapConfig("imap.example.com", 993, "bot@example.com", "secret"),
+        queue,
+        policy=object(),
+    ).fetch_once()
+
+    assert count == 0
+    assert queue.enqueued == []
+    assert queue.state["last_uid"] == "42"
+    assert queue.state["last_imap_fetch_error_uid"] == "42"
+    assert "Lookup failed" in queue.state["last_imap_fetch_error"]
+    assert FetchErrorImap.logged_out is True
+
+
+def test_reader_records_and_skips_failed_imap_fetch_status(monkeypatch):
+    queue = FakeQueue()
+    monkeypatch.setattr(reader.imaplib, "IMAP4_SSL", FetchNoImap)
+
+    count = reader.ImapReader(
+        reader.ImapConfig("imap.example.com", 993, "bot@example.com", "secret"),
+        queue,
+        policy=object(),
+    ).fetch_once()
+
+    assert count == 0
+    assert queue.enqueued == []
+    assert queue.state["last_uid"] == "43"
+    assert queue.state["last_imap_fetch_error_uid"] == "43"
+    assert queue.state["last_imap_fetch_error"].startswith("NO:")
+
+
+def test_reader_does_not_advance_last_uid_for_non_lookup_fetch_failure(monkeypatch):
+    queue = FakeQueue()
+    monkeypatch.setattr(reader.imaplib, "IMAP4_SSL", FetchTemporaryNoImap)
+
+    count = reader.ImapReader(
+        reader.ImapConfig("imap.example.com", 993, "bot@example.com", "secret"),
+        queue,
+        policy=object(),
+    ).fetch_once()
+
+    assert count == 0
+    assert queue.enqueued == []
+    assert "last_uid" not in queue.state
+    assert queue.state["last_imap_fetch_error_uid"] == "44"
+    assert "Temporary unavailable" in queue.state["last_imap_fetch_error"]