Add authenticated remote MCP HTTP entrypoint (#10)

Add a bearer-protected streamable HTTP MCP ASGI entrypoint for production deployment.

Includes remote host/origin configuration, health checks, fallback token handling, documentation, and tests covering authentication behavior.

Verified with full local pytest suite and GitHub CI. Copilot review feedback addressed before merge.

tests/test_mcp_http.py

@@ -0,0 +1,69 @@
+"""Tests for the authenticated MCP HTTP entrypoint."""
+
+import os
+
+from starlette.responses import Response
+from starlette.testclient import TestClient
+
+os.environ.setdefault("SECRET_KEY", "test-secret-key-for-testing-only")
+os.environ.setdefault("AUTOMATION_TOKEN", "test-automation-token-for-testing")
+
+from musicround.mcp_http import BearerAuthMiddleware, build_app, mcp  # noqa: E402
+
+
+async def _dummy_app(scope, receive, send):
+    await Response(status_code=204)(scope, receive, send)
+
+
+def test_healthz_does_not_require_auth(monkeypatch):
+    monkeypatch.setenv("MCP_BEARER_TOKEN", "test-mcp-token")
+    client = TestClient(build_app())
+
+    response = client.get("/healthz")
+
+    assert response.status_code == 200
+    assert response.json() == {"ok": True}
+
+
+def test_mcp_requires_bearer_token(monkeypatch):
+    monkeypatch.setenv("MCP_BEARER_TOKEN", "test-mcp-token")
+    client = TestClient(BearerAuthMiddleware(_dummy_app))
+
+    missing = client.get("/mcp")
+    wrong = client.get("/mcp", headers={"Authorization": "Bearer wrong"})
+    accepted = client.get("/mcp", headers={"Authorization": "Bearer test-mcp-token"})
+
+    assert missing.status_code == 401
+    assert missing.headers["WWW-Authenticate"] == "Bearer"
+    assert wrong.status_code == 401
+    assert accepted.status_code != 401
+
+
+def test_mcp_falls_back_to_automation_token(monkeypatch):
+    monkeypatch.delenv("MCP_BEARER_TOKEN", raising=False)
+    monkeypatch.setenv("AUTOMATION_TOKEN", "automation-token")
+    client = TestClient(BearerAuthMiddleware(_dummy_app))
+
+    accepted = client.get("/mcp", headers={"Authorization": "Bearer automation-token"})
+
+    assert accepted.status_code == 204
+
+
+def test_mcp_reports_missing_bearer_configuration(monkeypatch):
+    monkeypatch.delenv("MCP_BEARER_TOKEN", raising=False)
+    monkeypatch.delenv("AUTOMATION_TOKEN", raising=False)
+    client = TestClient(BearerAuthMiddleware(_dummy_app))
+
+    response = client.get("/mcp", headers={"Authorization": "Bearer anything"})
+
+    assert response.status_code == 500
+
+
+def test_allowed_hosts_are_replaced_between_builds(monkeypatch):
+    monkeypatch.setenv("MCP_ALLOWED_HOSTS", "first.example")
+    build_app()
+    monkeypatch.setenv("MCP_ALLOWED_HOSTS", "second.example")
+    build_app()
+
+    assert "first.example" not in mcp.settings.transport_security.allowed_hosts
+    assert "second.example" in mcp.settings.transport_security.allowed_hosts