feat: implement mcp frontend

examples/config.py

@@ -13,6 +13,7 @@ from beaver_gateway.agents.claude import ClaudeAgent
 from beaver_gateway.agents.raycast import RaycastAgent, RemoteTool, UserPreferences
 from beaver_gateway.core.registry import Gateway
 from beaver_gateway.frontends.anthropic import AnthropicMessagesFrontend
+from beaver_gateway.frontends.mcp_server import McpServerFrontend
 from beaver_gateway.mcp.types import McpServer
 
 
@@ -94,14 +95,41 @@ gateway = Gateway(
         # Phase 2.1 — bundle of plain Python callables exposed as one
         # FastMCP namespace. The internal aggregator mounts it under
         # ``/mcp/time`` on ``127.0.0.1:INTERNAL_MCP_PORT``; Phase 2.2's
-        # ClaudeCode adapter will forward that URL into
-        # ``BackendOptions.mcp_servers``.
+        # ClaudeCode adapter forwards that URL into
+        # ``BackendOptions.mcp_servers``. Phase 3's ``McpServerFrontend``
+        # reverse-proxies the same internal URL out to external clients.
         McpServer.python_tool(name="time", tools=[current_time]),
+        # Phase 3 — illustrates the ``lenient`` flag. Real-world stdio MCPs
+        # sometimes print "Processing..." or other chatter to stdout before
+        # their actual JSON-RPC frames; the default mcp client forwards
+        # those parse failures downstream as warnings (visible in
+        # Cursor/Cline). With ``lenient=True`` we silently drop non-JSON
+        # lines, so downstream UIs see clean JSON-RPC only. The command
+        # below is just a placeholder — replace with whatever stdio MCP
+        # you actually want gateway to ingest (e.g. an obsidian-mcp).
+        #
+        # Commented out by default: example users won't have the binary
+        # installed and an unreachable command makes ``docker compose up``
+        # surface a confusing "command not found" line at first request.
+        # Uncomment after pointing ``command`` at a real stdio MCP.
+        #
+        # McpServer.stdio(
+        #     name="obsidian",
+        #     command=["uvx", "mcp-obsidian"],
+        #     env={"OBSIDIAN_API_KEY": "..."},
+        #     lenient=True,
+        # ),
     ],
     frontends=[
         # Phase 1.4 — expose the agents as `model=<name>` on an
         # Anthropic-compatible Messages endpoint. Auth comes from
         # `BOOTSTRAP_TOKENS` in the env (`name1:value1,name2:value2`).
         AnthropicMessagesFrontend(host="0.0.0.0", port=8000),
+        # Phase 3 — re-exposes every declared `McpServer` outside the
+        # gateway with bearer auth + audit log. Per-namespace endpoints
+        # at `/mcp/<name>/`; flat bundle at `/mcp/all/`. Discovery page
+        # (HTML, auth-gated) at `/` with copy-pastable Cursor / Claude
+        # Desktop snippets. Auth re-uses `BOOTSTRAP_TOKENS`.
+        McpServerFrontend(host="0.0.0.0", port=8001),
     ],
 )