Add on-receive packet analyzer for canonical copy. Closes #97.

app/repository/raw_packets.py

@@ -121,6 +121,18 @@ class RawPacketRepository:
             return None
         return row["message_id"]
 
+    @staticmethod
+    async def get_by_id(packet_id: int) -> tuple[int, bytes, int, int | None] | None:
+        """Return a raw packet row as (id, data, timestamp, message_id)."""
+        cursor = await db.conn.execute(
+            "SELECT id, data, timestamp, message_id FROM raw_packets WHERE id = ?",
+            (packet_id,),
+        )
+        row = await cursor.fetchone()
+        if not row:
+            return None
+        return (row["id"], bytes(row["data"]), row["timestamp"], row["message_id"])
+
     @staticmethod
     async def prune_old_undecrypted(max_age_days: int) -> int:
         """Delete undecrypted packets older than max_age_days. Returns count deleted."""