feat: populate seq_id for ping messages (#8844)

* feat: populate seq_id for ping messages

* fix import

letta/server/rest_api/streaming_response.py

@@ -4,6 +4,7 @@
 
 import asyncio
 import json
+import re
 from collections.abc import AsyncIterator
 from datetime import datetime, timezone
 from uuid import uuid4
@@ -57,6 +58,7 @@ async def add_keepalive_to_stream(
     # A small maxsize prevents unbounded memory growth if the client is slow
     queue = asyncio.Queue(maxsize=1)
     stream_exhausted = False
+    last_seq_id = None
 
     async def stream_reader():
         """Read from the original stream and put items in the queue."""
@@ -81,13 +83,19 @@ async def add_keepalive_to_stream(
                     # Stream finished
                     break
                 elif msg_type == "data":
+                    # Track seq_id from chunks for ping messages
+                    if isinstance(data, str):
+                        seq_id_match = re.search(r'"seq_id":(\d+)', data)  # Look for "seq_id":<number> pattern in the SSE chunk
+                        if seq_id_match:
+                            last_seq_id = int(seq_id_match.group(1))
+
                     yield data
 
             except asyncio.TimeoutError:
                 # No data received within keepalive interval
                 if not stream_exhausted:
-                    # Send keepalive ping in the same format as [DONE]
-                    yield f"data: {LettaPing(id=f'ping-{uuid4()}', date=datetime.now(timezone.utc), run_id=run_id).model_dump_json()}\n\n"
+                    # Send keepalive ping with the last seq_id to allow clients to track progress
+                    yield f"data: {LettaPing(id=f'ping-{uuid4()}', date=datetime.now(timezone.utc), run_id=run_id, seq_id=last_seq_id).model_dump_json()}\n\n"
                 else:
                     # Stream is done but queue might be processing
                     # Check if there's anything left