Optimize API connection loop performance (#9184)

tests/integration/fixtures/api_reboot_timeout.yaml

@@ -0,0 +1,7 @@
+esphome:
+  name: api-reboot-test
+host:
+api:
+  reboot_timeout: 0.5s  # Very short timeout for fast testing
+logger:
+  level: DEBUG

tests/integration/test_api_reboot_timeout.py

@@ -0,0 +1,35 @@
+"""Test API server reboot timeout functionality."""
+
+import asyncio
+import re
+
+import pytest
+
+from .types import RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_api_reboot_timeout(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+) -> None:
+    """Test that the device reboots when no API clients connect within the timeout."""
+    loop = asyncio.get_running_loop()
+    reboot_future = loop.create_future()
+    reboot_pattern = re.compile(r"No clients; rebooting")
+
+    def check_output(line: str) -> None:
+        """Check output for reboot message."""
+        if not reboot_future.done() and reboot_pattern.search(line):
+            reboot_future.set_result(True)
+
+    # Run the device without connecting any API client
+    async with run_compiled(yaml_config, line_callback=check_output):
+        # Wait for reboot with timeout
+        # (0.5s reboot timeout + some margin for processing)
+        try:
+            await asyncio.wait_for(reboot_future, timeout=2.0)
+        except asyncio.TimeoutError:
+            pytest.fail("Device did not reboot within expected timeout")
+
+    # Test passes if we get here - reboot was detected