Queries executed via Databricks Connect v17 (Spark Connect / gRPC) on
serverless compute COMPLETE SUCCESSFULLY on the server side (Spark tasks
finish, results are produced), but the Spark Connect gRPC channel FAILS
TO DELIVER results back to the client application. The client receives
nothing, waits, and eventually cancels the query after its timeout.

This issue is 100% exclusive to Spark Connect. The Databricks SQL
Connector (poll-based HTTP) on the same data, same network, same user
has ZERO cancellations.

ENVIRONMENT:
------------
• databricks-connect version: 17 (latest)
• Client: External Python application via Databricks Connect
• Compute: Serverless (SERVERLESS_COMPUTE)
• Protocol: SPARK_CONNECT (gRPC / HTTP2)

EXACT FAILURE FLOW:
-------------------
1. Client app sends query via Databricks Connect (gRPC) → serverless
2. Serverless executes query — Spark tasks complete, results produced
3. *** Server FAILS to stream results back via gRPC ***
(result_fetch_duration_ms = 0 — result delivery never starts)
4. Client waits... receives nothing... hits app timeout
5. Client cancels query/session
6. Query recorded as CANCELED in query history