Maven/cmd/mavend/mcp.go

package main

import (
	"context"
	"fmt"
	"log"
	"time"

	"github.com/kami/maven/internal/config"
	"github.com/kami/maven/internal/ipc"
	"github.com/kami/maven/internal/mcp"
	"github.com/kami/maven/internal/store"
	"github.com/kami/maven/internal/webfetch"
)

// mcpRefreshInterval — how often the manager re-dials a server that is down.
// The manager applies its own backoff on top, so this being short is cheap.
const mcpRefreshInterval = time.Minute

// mcpWiring — the MCP client, when the `mcp` block configures at least one
// enabled server. nil ⇒ nothing was configured, nothing is connected, and an
// allowlist row that happens to look like an MCP row refuses to run.
//
// It lives on the voice wiring because MCP tools ARE acts: they run through
// tool.Executor, the enabled allowlist and the confirm turn, which only exist
// on the voice/chat path. No voice surface ⇒ nothing that could call a tool.
type mcpWiring struct {
	mgr *mcp.Manager
	st  *store.Store
}

// wireMCP builds the manager, connects, and proposes what it found. It never
// fails the daemon: a server that is unreachable at boot is logged and retried,
// because Maven starting is not contingent on someone else's process.
func wireMCP(cfg *config.Config, st *store.Store) *mcpWiring {
	servers := cfg.MCPServers()
	if len(servers) == 0 {
		return nil
	}
	limits := webfetch.Config{}
	if cfg.MCP != nil {
		limits.AllowHosts = cfg.MCP.AllowHosts
		limits.DenyHosts = cfg.MCP.DenyHosts
		limits.MaxBytes = cfg.MCP.MaxBytes
		limits.Timeout = time.Duration(cfg.MCP.Timeout)
	}
	mgr, err := mcp.NewManager(mcp.WebfetchDoor(limits), servers)
	if err != nil {
		// Validation already ran in config.validate, so this is a programming
		// error rather than a config one. Still not fatal: MCP off is a working
		// Maven.
		log.Printf("mcp: not wired: %v", err)
		return nil
	}
	w := &mcpWiring{mgr: mgr, st: st}
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()
	mgr.Connect(ctx)
	w.propose(ctx)
	return w
}

// propose writes a 'proposed' allowlist row for every discovered tool. It does
// NOT enable anything: a configured server is a place Maven may look, not a
// capability she has. Kami enables what he wants on /tools, behind step-up,
// which is the same gate a shell tool goes through.
//
// Re-running on every boot is idempotent — ProposeMCPTool never touches an
// existing row, so a tool he disabled stays disabled and one he enabled keeps
// the cmd he enabled it with.
func (w *mcpWiring) propose(ctx context.Context) {
	if w == nil {
		return
	}
	now := time.Now()
	fresh := 0
	for _, t := range w.mgr.Tools() {
		name := mcp.LocalName(t.Server, t.Name)
		// No readOnlyHint ⇒ assume it mutates ⇒ the confirm turn. Being wrong
		// in this direction only costs a question.
		destructive := !t.ReadOnly
		provenance := fmt.Sprintf("mcp %s/%s", t.Server, t.Name)
		if t.Description != "" {
			provenance += ": " + t.Description
		}
		ok, err := w.st.ProposeMCPTool(ctx, name, mcp.Scope(t.Server),
			mcp.Cmd(t.Server, t.Name), destructive, provenance, now)
		if err != nil {
			log.Printf("mcp: propose %s: %v", name, err)
			continue
		}
		if ok {
			fresh++
		}
	}
	if fresh > 0 {
		log.Printf("mcp: %d new tool proposal(s) waiting on /tools", fresh)
	}
}

// run re-dials downed servers and picks up tools that appeared, until ctx is
// canceled.
func (w *mcpWiring) run(ctx context.Context) {
	if w == nil {
		return
	}
	t := time.NewTicker(mcpRefreshInterval)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-t.C:
			w.mgr.Refresh(ctx)
			w.propose(ctx)
		}
	}
}

// status maps the manager's view onto the wire type the web surface reads.
func (w *mcpWiring) status() []ipc.MCPServerStatus {
	if w == nil {
		return nil
	}
	in := w.mgr.Status()
	out := make([]ipc.MCPServerStatus, 0, len(in))
	for _, s := range in {
		out = append(out, ipc.MCPServerStatus{
			Name:      s.Name,
			Transport: s.Transport,
			Target:    s.Target,
			Connected: s.Connected,
			Server:    s.Server,
			Tools:     s.Tools,
			Err:       s.Err,
		})
	}
	return out
}

func (w *mcpWiring) close() {
	if w == nil {
		return
	}
	_ = w.mgr.Close()
}

// caller is the tool.MCPCaller the executor gets, or nil when MCP is off.
func (w *mcpWiring) caller() *mcp.Manager {
	if w == nil {
		return nil
	}
	return w.mgr
}