fix: disable Gunicorn in telemetry tests to fix multi-process telemetry collection

Telemetry tests use an OTLP collector that expects single-process
telemetry spans. Gunicorn's multi-process architecture spawns multiple
workers, each with separate telemetry instrumentation, preventing the
test collector from capturing all spans.

This commit adds LLAMA_STACK_DISABLE_GUNICORN environment variable
support and sets it in telemetry test configuration to ensure
single-process Uvicorn is used during tests while maintaining
production multi-process behavior.

Fixes failing tests:
- test_streaming_chunk_count
- test_telemetry_format_completeness

src/llama_stack/cli/stack/run.py

@@ -169,11 +169,17 @@ class StackRun(Subcommand):
         # Another approach would be to ignore SIGINT entirely - let uvicorn handle it through its own
         # signal handling but this is quite intrusive and not worth the effort.
         try:
-            if sys.platform in ("linux", "darwin"):
+            # Check if Gunicorn should be disabled (for testing or debugging)
+            disable_gunicorn = os.getenv("LLAMA_STACK_DISABLE_GUNICORN", "false").lower() == "true"
+
+            if not disable_gunicorn and sys.platform in ("linux", "darwin"):
                 # On Unix-like systems, use Gunicorn with Uvicorn workers for production-grade performance
                 self._run_with_gunicorn(host, port, uvicorn_config)
             else:
                 # On other systems (e.g., Windows), fall back to Uvicorn directly
+                # Also used when LLAMA_STACK_DISABLE_GUNICORN=true (for tests)
+                if disable_gunicorn:
+                    logger.info("Gunicorn disabled via LLAMA_STACK_DISABLE_GUNICORN environment variable")
                 uvicorn.run("llama_stack.core.server.server:create_app", **uvicorn_config)  # type: ignore[arg-type]
         except (KeyboardInterrupt, SystemExit):
             logger.info("Received interrupt signal, shutting down gracefully...")

tests/integration/telemetry/conftest.py

@@ -30,6 +30,7 @@ def telemetry_test_collector():
             "OTEL_EXPORTER_OTLP_PROTOCOL": "http/protobuf",
             "OTEL_BSP_SCHEDULE_DELAY": "200",
             "OTEL_BSP_EXPORT_TIMEOUT": "2000",
+            "LLAMA_STACK_DISABLE_GUNICORN": "true",  # Disable multi-process for telemetry collection
         }
 
         previous_env = {key: os.environ.get(key) for key in env_overrides}