feat: add MCP server endpoint for dynamic tool discovery and invocation

[syn-zhu]

Summary

Adds a Streamable HTTP MCP server endpoint to the kmcp controller, enabling agents to dynamically discover, introspect, and invoke tools on any MCPServer in the cluster at runtime. This mirrors the pattern already established by kagent-controller's A2A MCP endpoint (list_agents / invoke_agent) but for MCP server interactions.

Closes #122

New tools exposed at :8083/mcp

Tool	Purpose
list_mcp_servers	List MCPServer CRs (name, namespace, status, port, transport type)
list_tools	Connect to a specific MCPServer and return its tool catalog
call_tool	Invoke a specific tool on a specific MCPServer and return the result

Changes

• pkg/mcp/handler.go — MCP handler implementing the three tools with session caching and automatic reconnection on stale sessions
• pkg/mcp/server.go — HTTP server wrapper implementing manager.Runnable for controller-runtime lifecycle integration
• pkg/app/app.go — --mcp-bind-address flag (default :8083, set to 0 to disable) and MCP server wiring
• go.mod — Added github.com/modelcontextprotocol/go-sdk v1.2.0 (same version as kagent)
• Helm chart — MCP server values, deployment port, mcp-service.yaml (ClusterIP)

Tests

• pkg/mcp/handler_test.go — 16 unit tests covering:
  • list_mcp_servers: empty cluster, multi-namespace listing, namespace filtering, mixed ready/not-ready, default port
  • list_tools validation: invalid ref format, server not found
  • call_tool validation: missing tool name, invalid ref, server not found
  • getMCPServer helper: valid lookup, invalid format, non-existent
  • mcpServerURL derivation: stdio/http transport, custom path, default port
• pkg/mcp/server_test.go — 2 tests covering server start/shutdown lifecycle and construction

Test plan

• go build ./... — compiles cleanly
• go vet ./... — no issues
• go test ./pkg/mcp/... — all 18 tests pass
• helm template test helm/kmcp/ — renders correctly with MCP port, args, and service
• E2E: Deploy to cluster, port-forward to MCP service, verify list_mcp_servers / list_tools / call_tool work

🤖 Generated with Claude Code

[EItanya]

Hey there, I really love this idea, but I think we should put this in kagent. kmcp only deals with the MCPServer CRD and is really mostly about deployment. If we do this in kagent then we can also do this for the Services and RemoteMCPServers. What do you think?

[syn-zhu]

Hey there, I really love this idea, but I think we should put this in kagent. kmcp only deals with the MCPServer CRD and is really mostly about deployment. If we do this in kagent then we can also do this for the Services and RemoteMCPServers. What do you think?

Lemme take a look, just need to remind myself; the kagent controller already knows about RemoteMCPServers? If so then yeah, i think that makes sense