fix(core): add retry with backoff for post-push sync race condition (#9335)

When git push completes, the webhook fires immediately but GCS upload
may still be in progress. This causes KeyError when trying to read
commit objects that haven't been uploaded yet.

Add retry with exponential backoff (1s, 2s, 4s) to handle this race.

🐾 Generated with [Letta Code](https://letta.com)

Co-authored-by: Letta <noreply@letta.com>

letta/server/rest_api/routers/v1/git_http.py

@@ -471,15 +471,27 @@ async def _sync_after_push(actor_id: str, agent_id: str) -> None:
     from letta.services.block_manager_git import GitEnabledBlockManager
 
     if isinstance(_server_instance.block_manager, GitEnabledBlockManager):
-        try:
-            files = await _server_instance.memory_repo_manager.git.get_files(
-                agent_id=agent_id,
-                org_id=org_id,
-                ref="HEAD",
-            )
-        except Exception:
-            logger.exception("Failed to read repo files from storage for post-push block sync (agent=%s)", agent_id)
-            files = {}
+        # Retry with backoff to handle race condition where GCS upload is still in progress
+        # after git-receive-pack returns. The webhook fires immediately but commit objects
+        # may not be fully uploaded yet.
+        files = {}
+        max_retries = 3
+        for attempt in range(max_retries):
+            try:
+                files = await _server_instance.memory_repo_manager.git.get_files(
+                    agent_id=agent_id,
+                    org_id=org_id,
+                    ref="HEAD",
+                )
+                logger.info("get_files returned %d files (attempt %d)", len(files), attempt + 1)
+                break
+            except Exception as e:
+                if attempt < max_retries - 1:
+                    wait_time = 2**attempt  # 1s, 2s, 4s
+                    logger.warning("Failed to read repo files (attempt %d/%d), retrying in %ds: %s", attempt + 1, max_retries, wait_time, e)
+                    await asyncio.sleep(wait_time)
+                else:
+                    logger.exception("Failed to read repo files after %d retries (agent=%s)", max_retries, agent_id)
 
         expected_labels = set()
         synced = 0