Improve HTTP server startup performance (#4729)

tests/server/http/test_startup_imports.py

@@ -0,0 +1,73 @@
+"""Fresh-interpreter import guards for the default HTTP server path."""
+
+from __future__ import annotations
+
+import subprocess
+import sys
+import textwrap
+
+import pytest
+
+
+@pytest.mark.subprocess_heavy
+def test_default_http_app_does_not_load_opt_in_integrations() -> None:
+    script = textwrap.dedent(
+        """
+        import sys
+
+        from fastmcp import FastMCP
+
+        server = FastMCP("HTTP import guard")
+
+        @server.tool
+        def echo(value: str) -> str:
+            return value
+
+        app = server.http_app(transport="http", stateless_http=True)
+        assert app is not None
+
+        forbidden = (
+            "fastmcp.server.event_store",
+            "griffe",
+            "jsonref",
+            "key_value",
+            "prefab_ui",
+        )
+        loaded = [
+            name
+            for name in sys.modules
+            if any(name == root or name.startswith(f"{root}.") for root in forbidden)
+        ]
+        assert not loaded, loaded
+        """
+    )
+
+    result = subprocess.run(
+        [sys.executable, "-c", script],
+        capture_output=True,
+        text=True,
+    )
+
+    assert result.returncode == 0, result.stderr
+
+
+@pytest.mark.subprocess_heavy
+def test_fastmcp_server_import_does_not_load_context() -> None:
+    script = textwrap.dedent(
+        """
+        import sys
+
+        from fastmcp import FastMCP
+
+        assert FastMCP is not None
+        assert "fastmcp.server.context" not in sys.modules
+        """
+    )
+
+    result = subprocess.run(
+        [sys.executable, "-c", script],
+        capture_output=True,
+        text=True,
+    )
+
+    assert result.returncode == 0, result.stderr