fix(runtime): __name__ guard in a2a_mcp_server allows module-as-script and test imports

- Restructure main() to accept (transport, port) params so argparse
  moves into the __name__ guard block, not the function body.
- Replace the fragile __spec__.name check with a reliable basename
  comparison: os.path.basename(sys.argv[0]) == os.path.basename(__spec__.origin).
  Fires for `python a2a_mcp_server.py` and `python -m
  molecule_runtime.a2a_mcp_server`, but NOT for test imports where
  sys.argv[0] is the outer runner (pytest, python -c, etc.).
- Add missing `import uvicorn` inside _run_http_server() so the HTTP
  transport actually starts (was a pre-existing bug — uvicorn was used
  but never imported).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

molecule_runtime/a2a_mcp_server.py

@@ -406,6 +406,7 @@ async def _handle_http_mcp(request) -> dict | None:
 async def _run_http_server(port: int):
     """Run MCP server over HTTP/SSE — compatible with Hermes MCP-native agents."""
     try:
+        import uvicorn
         from starlette.applications import Starlette
         from starlette.routing import Route
         from starlette.responses import JSONResponse, Response
@@ -480,8 +481,25 @@ async def _run_http_server(port: int):
     await server.serve()
 
 
-async def main():  # pragma: no cover
-    """Entry point — select transport from CLI args or default to stdio."""
+async def main(transport: str = "stdio", port: int = 9100):  # pragma: no cover
+    """Run the MCP server with the given transport and port."""
+    if transport == "http":
+        await _run_http_server(port)
+    else:
+        await _handle_stdio()
+
+
+if __name__ == "__main__" or (
+    __spec__ is not None
+    and _os.path.basename(sys.argv[0]) == _os.path.basename(__spec__.origin)
+):
+    # Fires for:
+    #   python a2a_mcp_server.py       → __name__ == "__main__"
+    #   python -m molecule_runtime.a2a_mcp_server  → sys.argv[0] = module path
+    # Does NOT fire for:
+    #   import molecule_runtime.a2a_mcp_server  (pytest or otherwise)
+    #       → sys.argv[0] is the outer runner (pytest, python -c, etc.)
+    #       → os.path.basename(sys.argv[0]) != os.path.basename(__spec__.origin)
     parser = argparse.ArgumentParser(description="A2A MCP Server")
     parser.add_argument(
         "--transport",
@@ -496,12 +514,4 @@ async def main():  # pragma: no cover
         help="TCP port for HTTP transport (default 9100)",
     )
     args = parser.parse_args()
-
-    if args.transport == "http":
-        await _run_http_server(args.port)
-    else:
-        await _handle_stdio()
-
-
-if __name__ == "__main__":  # pragma: no cover
-    asyncio.run(main())
+    asyncio.run(main(transport=args.transport, port=args.port))