fix: add HTTP readiness check to wait_for_server and remove dead code (#1777)

The flaky SSE tests (test_sse_client_basic_connection_mounted_app,
test_request_context_isolation) fail intermittently because
wait_for_server() only checks TCP port connectivity. On slow CI
machines, the port may accept connections before the ASGI app is
fully initialized, causing SSE requests to fail.

- Add a two-stage readiness check to wait_for_server(): first TCP
  connect, then an actual HTTP request to verify the app is handling
  requests (any HTTP response, even 404, confirms readiness)
- Remove unreachable dead code after blocking server.run() calls in
  run_server() and run_mounted_server()
- Remove unused `time` import from test_sse.py

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: BabyChrist666

tests/shared/test_sse.py

@@ -1,7 +1,6 @@
 import json
 import multiprocessing
 import socket
-import time
 from collections.abc import AsyncGenerator, Generator
 from typing import Any
 from unittest.mock import AsyncMock, MagicMock, Mock, patch
@@ -134,11 +133,6 @@ def run_server(server_port: int) -> None:  # pragma: no cover
     print(f"starting server on {server_port}")
     server.run()
 
-    # Give server time to start
-    while not server.started:
-        print("waiting for server to start")
-        time.sleep(0.5)
-
 
 @pytest.fixture()
 def server(server_port: int) -> Generator[None, None, None]:
@@ -313,11 +307,6 @@ def run_mounted_server(server_port: int) -> None:  # pragma: no cover
     print(f"starting server on {server_port}")
     server.run()
 
-    # Give server time to start
-    while not server.started:
-        print("waiting for server to start")
-        time.sleep(0.5)
-
 
 @pytest.fixture()
 def mounted_server(server_port: int) -> Generator[None, None, None]:

tests/test_helpers.py

@@ -2,30 +2,54 @@
 
 import socket
 import time
+import urllib.error
+import urllib.request
 
 
 def wait_for_server(port: int, timeout: float = 20.0) -> None:
     """Wait for server to be ready to accept connections.
 
-    Polls the server port until it accepts connections or timeout is reached.
-    This eliminates race conditions without arbitrary sleeps.
+    First polls until the TCP port accepts connections, then verifies the
+    HTTP server is actually ready to handle requests. This two-stage check
+    prevents race conditions where the port is open but the ASGI app hasn't
+    finished initializing.
 
     Args:
         port: The port number to check
-        timeout: Maximum time to wait in seconds (default 5.0)
+        timeout: Maximum time to wait in seconds (default 20.0)
 
     Raises:
         TimeoutError: If server doesn't start within the timeout period
     """
     start_time = time.time()
+
+    # Stage 1: Wait for TCP port to accept connections
     while time.time() - start_time < timeout:
         try:
             with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
                 s.settimeout(0.1)
                 s.connect(("127.0.0.1", port))
-                # Server is ready
-                return
+                break  # Port is open, move to stage 2
         except (ConnectionRefusedError, OSError):
-            # Server not ready yet, retry quickly
             time.sleep(0.01)
-    raise TimeoutError(f"Server on port {port} did not start within {timeout} seconds")  # pragma: no cover
+    else:
+        raise TimeoutError(f"Server on port {port} did not start within {timeout} seconds")  # pragma: no cover
+
+    # Stage 2: Verify HTTP server is ready by making a request.
+    # A non-existent path returns 404/405 if the app is ready, or
+    # raises an error if the ASGI app hasn't finished initializing.
+    while time.time() - start_time < timeout:
+        try:
+            req = urllib.request.Request(
+                f"http://127.0.0.1:{port}/healthz",
+                method="GET",
+            )
+            with urllib.request.urlopen(req, timeout=1):
+                return  # Any successful response means server is ready
+        except urllib.error.HTTPError:
+            # 404/405/etc means the server IS handling requests
+            return
+        except (urllib.error.URLError, ConnectionError, OSError):
+            # Server not ready for HTTP yet
+            time.sleep(0.05)
+    raise TimeoutError(f"Server on port {port} did not become HTTP-ready within {timeout} seconds")  # pragma: no cover