Add bounce mailbox processing

src/govoplan_mail/backend/sending/imap.py

@@ -180,6 +180,29 @@ class ImapMailboxMessageResult:
     message: ImapMailboxMessageDetail
 
 
+@dataclass(frozen=True, slots=True)
+class ImapRawMessageResult:
+    host: str
+    port: int
+    security: str
+    folder: str
+    uid: str
+    flags: list[str]
+    size_bytes: int
+    raw: bytes
+
+
+@dataclass(frozen=True, slots=True)
+class ImapUidListResult:
+    host: str
+    port: int
+    security: str
+    folder: str
+    uids: list[str]
+    uidvalidity: str | None
+    cursor_reset: bool = False
+
+
 @dataclass(frozen=True, slots=True)
 class ImapAppendResult:
     host: str
@@ -1079,6 +1102,126 @@ def get_imap_message(*, imap_config: ImapConfig, folder: str, uid: str) -> ImapM
             _log_imap_cleanup_failure("reading message", cleanup_exc)
 
 
+def get_imap_raw_message(
+    *,
+    imap_config: ImapConfig,
+    folder: str,
+    uid: str,
+) -> ImapRawMessageResult:
+    """Fetch bounded raw MIME without changing mailbox flags."""
+
+    host, port = _require_imap_config(imap_config)
+    folder = (folder or "INBOX").strip() or "INBOX"
+    uid = str(uid).strip()
+    if not uid:
+        raise ImapConfigurationError("Message UID is required")
+    if is_mock_imap_host(imap_config.host):
+        record = get_record(uid, include_raw=True)
+        if not record or not _mock_folder_matches(record, folder):
+            raise ImapAppendError(
+                f"Mock mailbox message {uid!r} was not found in folder {folder!r}",
+                temporary=False,
+            )
+        raw = _mock_raw_bytes(record)
+        return ImapRawMessageResult(
+            host=host,
+            port=port,
+            security=imap_config.security.value,
+            folder=folder,
+            uid=uid,
+            flags=["\\Seen"] if record.get("kind") == "imap_append" else [],
+            size_bytes=len(raw),
+            raw=raw,
+        )
+
+    client = _open_imap(imap_config)
+    try:
+        _select_readonly(client, folder)
+        fetched_uid, flags, size_bytes, raw = _fetch_message_by_uid(client, uid)
+        return ImapRawMessageResult(
+            host=host,
+            port=port,
+            security=imap_config.security.value,
+            folder=folder,
+            uid=fetched_uid,
+            flags=flags,
+            size_bytes=size_bytes if size_bytes is not None else len(raw),
+            raw=raw,
+        )
+    finally:
+        try:
+            client.logout()
+        except Exception as cleanup_exc:
+            _log_imap_cleanup_failure("reading raw message", cleanup_exc)
+
+
+def list_imap_uids_since(
+    *,
+    imap_config: ImapConfig,
+    folder: str,
+    highest_uid: int = 0,
+    expected_uidvalidity: str | None = None,
+    limit: int = 100,
+) -> ImapUidListResult:
+    """Return new UIDs oldest-first so a bounded watcher cannot skip a burst."""
+
+    host, port = _require_imap_config(imap_config)
+    folder = (folder or "INBOX").strip() or "INBOX"
+    bounded_limit = max(1, min(int(limit), 1_000))
+    if is_mock_imap_host(imap_config.host):
+        records = [
+            record
+            for record in list_records(limit=5_000)
+            if _mock_folder_matches(record, folder)
+        ]
+        cursor_reset = bool(
+            expected_uidvalidity and expected_uidvalidity != "mock-v1"
+        )
+        effective_highest = 0 if cursor_reset else highest_uid
+        numeric = sorted(
+            int(value)
+            for record in records
+            for value in (str(record.get("id") or ""),)
+            if value.isdigit() and int(value) > effective_highest
+        )
+        return ImapUidListResult(
+            host=host,
+            port=port,
+            security=imap_config.security.value,
+            folder=folder,
+            uids=[str(value) for value in numeric[:bounded_limit]],
+            uidvalidity="mock-v1",
+            cursor_reset=cursor_reset,
+        )
+
+    client = _open_imap(imap_config)
+    try:
+        _total, uidvalidity = _select_readonly(client, folder)
+        cursor_reset = bool(
+            expected_uidvalidity and uidvalidity != expected_uidvalidity
+        )
+        effective_highest = 0 if cursor_reset else highest_uid
+        numeric = sorted(
+            int(uid)
+            for uid in _search_all_uids(client)
+            if uid.isdigit() and int(uid) > effective_highest
+        )
+        return ImapUidListResult(
+            host=host,
+            port=port,
+            security=imap_config.security.value,
+            folder=folder,
+            uids=[str(value) for value in numeric[:bounded_limit]],
+            uidvalidity=uidvalidity,
+            cursor_reset=cursor_reset,
+        )
+    finally:
+        try:
+            client.logout()
+        except Exception as cleanup_exc:
+            _log_imap_cleanup_failure("listing watcher UIDs", cleanup_exc)
+
+
 def append_message_to_sent(
     message_bytes: bytes,
     *,