Expose discovered MCP tools through the act allowlist (#251)

Second half of the MCP client: the tools the manager discovers become rows in
the existing act allowlist instead of a parallel capability system.

An MCP tool is encoded in the columns that already exist — cmd
["mcp",<server>,<tool>], scope mcp:<server> — so no migration, and
ProposeTool/EnableTool/DisableTool, tool.Matcher and the confirm turn need no
changes. One branch in Executor.Exec routes such a row to the manager instead
of exec, and "mcp" is never run as a binary.

Discovery only ever PROPOSES. destructive comes from the inverse of the MCP
readOnlyHint, so a tool that does not promise to be read-only inherits the
confirm turn, and enabling stays on /tools behind step-up.

Voice args are positional and MCP args are named, so CallPositional binds only
what it can defend: no required properties runs bare, and a read-only tool with
exactly one required string or number gets the tail. Everything else refuses
with ErrNeedsArgs rather than guessing. The read-only condition was learned
against the live Vikunja server: update_task requires only task_id and takes
the rest as optional, so one guessed argument blanked the fields it did not
mention. A partially-filled write destroys what it omits, so a mutating tool
never receives a guessed argument.

Also: a read-only mcp_servers IPC method and an "MCP servers" card on /tools
showing transport, target and state, with the trust level of a local target
spelled out. There is deliberately no call-a-tool IPC method and no run button,
so mutation keeps exactly one path.

Vikunja #251

cmd/mavend/actions_act.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"log"
 
+	"github.com/kami/maven/internal/mcp"
 	"github.com/kami/maven/internal/router"
 	"github.com/kami/maven/internal/tool"
 )
@@ -52,6 +53,12 @@ func (h *reactiveHandler) actionAct(ctx context.Context, dec router.Decision) st
 			return "выполнить «" + phrase + "»? скажи «да» или «нет»."
 		case errors.Is(err, tool.ErrNotEnabled):
 			return h.proposeGap(ctx, dec)
+		case errors.Is(err, mcp.ErrNeedsArgs):
+			// An MCP tool that wants named arguments a spoken verb cannot
+			// supply. Guessing them would be a wrong act, so she says so
+			// instead — the tool is still runnable from the authed surface,
+			// where a human types them.
+			return "этому инструменту нужны аргументы, которые я из голоса не соберу — я не буду угадывать."
 		}
 		log.Printf("voice: tool %s: %v", dec.Slots.Fn, err)
 		if out != "" {

cmd/mavend/main.go

@@ -280,6 +280,9 @@ func run(args []string) error {
 			api := coreAPI.(*daemonAPI)
 			api.chatFn = voiceW.handler.handleText
 		}
+		if voiceW != nil && voiceW.mcp != nil {
+			coreAPI.(*daemonAPI).getMCPServers = voiceW.mcp.status
+		}
 	} else {
 		// locked mode: no real store yet, so there's no meaningful CoreAPI to
 		// serve. srv.Check below is the actual guard — every CoreAPI call is
@@ -518,6 +521,11 @@ func run(args []string) error {
 				}()
 			}
 
+			// Keep MCP connections alive (nil unless configured).
+			if voiceW != nil && voiceW.mcp != nil {
+				go voiceW.mcp.run(ctx)
+			}
+
 			dl.unlock()
 			log.Printf("mavend: unlocked via passkey assertion")
 			return nil
@@ -577,6 +585,13 @@ func run(args []string) error {
 				crawlWkr.run(ctx)
 			}()
 		}
+		if voiceW != nil && voiceW.mcp != nil {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				voiceW.mcp.run(ctx)
+			}()
+		}
 	}
 
 	<-ctx.Done()

cmd/mavend/mcp.go

@@ -0,0 +1,154 @@
+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
+}

cmd/mavend/mcp_test.go

@@ -0,0 +1,77 @@
+package main
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/kami/maven/internal/config"
+)
+
+func TestWireMCPOffWhenUnconfigured(t *testing.T) {
+	st := newTestStore(t)
+	for name, cfg := range map[string]*config.Config{
+		"no block": {},
+		"nothing enabled": {MCP: &config.MCPConfig{Servers: []config.MCPServerConfig{
+			{Name: "vikunja", URL: "http://192.168.1.104:9100/mcp"},
+		}}},
+	} {
+		t.Run(name, func(t *testing.T) {
+			if w := wireMCP(cfg, st); w != nil {
+				t.Fatal("MCP must be off unless a server is configured AND enabled")
+			}
+		})
+	}
+	// nil wiring must be safe to use everywhere it is reachable.
+	var w *mcpWiring
+	w.close()
+	w.propose(context.Background())
+	if w.status() != nil || w.caller() != nil {
+		t.Fatal("a nil wiring must report nothing")
+	}
+}
+
+// An unreachable server must not stop the daemon, must be reported as down, and
+// must propose nothing.
+func TestWireMCPUnreachableServerIsNotFatal(t *testing.T) {
+	st := newTestStore(t)
+	w := wireMCP(&config.Config{MCP: &config.MCPConfig{Servers: []config.MCPServerConfig{{
+		Name: "dead", Command: "/nonexistent/mcp-server", Enabled: true,
+	}}}}, st)
+	if w == nil {
+		t.Fatal("a configured server should still wire")
+	}
+	defer w.close()
+	st2 := w.status()
+	if len(st2) != 1 || st2[0].Connected || st2[0].Err == "" {
+		t.Fatalf("status = %+v", st2)
+	}
+	tools, err := st.ListTools(context.Background(), "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(tools) != 0 {
+		t.Fatalf("a server that never answered must propose nothing, got %+v", tools)
+	}
+}
+
+// A url server whose address is private is refused by webfetch unless that
+// server sets allow_private. This is the guard the whole MCP path rides on, so
+// it is asserted here too, at the wiring level.
+func TestWireMCPPrivateURLRefusedWithoutAllowPrivate(t *testing.T) {
+	st := newTestStore(t)
+	w := wireMCP(&config.Config{MCP: &config.MCPConfig{Servers: []config.MCPServerConfig{{
+		Name: "lan", URL: "http://127.0.0.1:9100/mcp", Enabled: true,
+	}}}}, st)
+	if w == nil {
+		t.Fatal("should wire")
+	}
+	defer w.close()
+	s := w.status()[0]
+	if s.Connected {
+		t.Fatal("a loopback server must not connect without allow_private")
+	}
+	if !strings.Contains(s.Err, "private address") {
+		t.Fatalf("err = %q, want the private-address refusal", s.Err)
+	}
+}

cmd/mavend/tick.go

@@ -941,6 +941,7 @@ type daemonAPI struct {
 	getMorningStatus func(ctx context.Context) []ipc.MorningRoutineStatus
 	getDayPlan       func(ctx context.Context) ipc.DayPlan
 	chatFn           func(ctx context.Context, text string) string
+	getMCPServers    func() []ipc.MCPServerStatus
 }
 
 func (d *daemonAPI) Chat(ctx context.Context, text string) (string, error) {
@@ -950,6 +951,16 @@ func (d *daemonAPI) Chat(ctx context.Context, text string) (string, error) {
 	return d.chatFn(ctx, text), nil
 }
 
+// MCPServers — the configured MCP servers and their health (Vikunja #251).
+// Empty, not an error, when the mcp block is absent: "not configured" is the
+// default state and the web surface renders it as such.
+func (d *daemonAPI) MCPServers(ctx context.Context) ([]ipc.MCPServerStatus, error) {
+	if d.getMCPServers == nil {
+		return nil, nil
+	}
+	return d.getMCPServers(), nil
+}
+
 func (d *daemonAPI) TickTrace(ctx context.Context) (ipc.TickTrace, error) {
 	trace := d.getTrace()
 	if trace == nil {

cmd/mavend/voicewire.go

@@ -40,6 +40,10 @@ type voiceWiring struct {
 	// mavsttd / mavttsd don't keep a stale conn into a restarting daemon.
 	sttClient *worker.Client
 	ttsClient *worker.Client
+	// mcp — the MCP client, nil unless the `mcp` block configures an enabled
+	// server (Vikunja #251). Its tools land in the same allowlist as every
+	// other act, so nothing else here has to know about it.
+	mcp *mcpWiring
 }
 
 // close releases the listener + worker conns. Safe to call on nil (when
@@ -60,6 +64,7 @@ func (w *voiceWiring) close() {
 	if w.ttsClient != nil {
 		_ = w.ttsClient.Close()
 	}
+	w.mcp.close()
 }
 
 // wireVoice builds the audio path from cfg + a CoreAPI + a router. Returns
@@ -131,6 +136,14 @@ func wireVoice(cfg *config.Config, coreAPI ipc.CoreAPI, phr phraser.Phraser, mem
 	// daemon restart.
 	seedTools(coreAPI, cfg.Voice.Tools)
 	exec := tool.NewExecutor(coreAPI, time.Duration(cfg.Voice.ToolTimeout))
+	// MCP servers (Vikunja #251): discovery PROPOSES tools into the same
+	// allowlist, so an MCP tool is enabled by hand on /tools like any other and
+	// runs through the same confirm turn. Off unless the `mcp` block configures
+	// an enabled server.
+	w.mcp = wireMCP(cfg, dataStore)
+	if w.mcp != nil {
+		exec = exec.WithMCP(w.mcp.caller())
+	}
 	matcher := tool.NewMatcher(coreAPI)
 
 	// ----- weather provider (Open-Meteo when configured, Stub otherwise) -----

cmd/mavweb/handlers_test.go

@@ -67,6 +67,14 @@ type fakeCore struct {
 	// for handleChatAPI tests
 	chatText string
 	chatErr  error
+
+	// for the MCP section of /tools
+	mcpServers []ipc.MCPServerStatus
+	mcpErr     error
+}
+
+func (f *fakeCore) MCPServers(context.Context) ([]ipc.MCPServerStatus, error) {
+	return f.mcpServers, f.mcpErr
 }
 
 func (f *fakeCore) Chat(_ context.Context, text string) (string, error) {
@@ -1118,3 +1126,49 @@ func TestHandleChatAPI_FailOpenByDefault(t *testing.T) {
 		t.Errorf("core.Chat text = %q, want %q", core.chatText, "привет")
 	}
 }
+
+// The MCP section renders the configured servers, and a proposal that already
+// knows its cmd prefills the enable form so the argv is not retyped by hand.
+func TestHandleTools_GET_MCPSection(t *testing.T) {
+	core := &fakeCore{
+		proposed: []ipc.Tool{{
+			Name: "vikunja_list_tasks", Scope: "mcp:vikunja",
+			Cmd: []string{"mcp", "vikunja", "list_tasks"}, Destructive: true,
+			Utterance: "mcp vikunja/list_tasks: List tasks in a project.",
+		}},
+		mcpServers: []ipc.MCPServerStatus{
+			{Name: "vikunja", Transport: "http", Target: "http://192.168.1.104:9100/mcp", Connected: true, Server: "vikunja 0.1.0", Tools: 4},
+			{Name: "files", Transport: "stdio", Target: "mcp-server-fs /srv", Err: "start: no such file"},
+		},
+	}
+	rr := httptest.NewRecorder()
+	handleTools(rr, httptest.NewRequest(http.MethodGet, "/tools", nil), core, nil, false)
+	if rr.Code != http.StatusOK {
+		t.Fatalf("status = %d", rr.Code)
+	}
+	body := rr.Body.String()
+	for _, want := range []string{
+		"MCP servers", "vikunja", "192.168.1.104:9100/mcp", "vikunja 0.1.0",
+		"files", "no such file",
+		`value="mcp vikunja list_tasks"`, // the enable form is prefilled
+		"checked",                        // and pre-marked destructive (no readOnlyHint)
+	} {
+		if !strings.Contains(body, want) {
+			t.Errorf("missing %q in /tools output", want)
+		}
+	}
+}
+
+// MCP off (or an older core that does not know the method) renders the section
+// empty instead of breaking the page.
+func TestHandleTools_GET_MCPUnavailable(t *testing.T) {
+	core := &fakeCore{mcpErr: ipc.ErrNotImplemented}
+	rr := httptest.NewRecorder()
+	handleTools(rr, httptest.NewRequest(http.MethodGet, "/tools", nil), core, nil, false)
+	if rr.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", rr.Code)
+	}
+	if !strings.Contains(rr.Body.String(), "no MCP servers configured") {
+		t.Error("expected the empty-state copy")
+	}
+}

cmd/mavweb/main.go

@@ -692,7 +692,7 @@ const toolsHTML = `{{template "shellTop" "tools"}}
 {{if .Msg}}<div class="msg msg-ok">{{.Msg}}</div>{{end}}
 <section class=card>
 <h2 class=card-title>proposed <span class=badge>{{len .Proposed}}</span></h2>
-{{if .Proposed}}<p class=hint>maven drafted these from acts she couldn't run. Fill the command (argv, space-separated) and enable.</p>
+{{if .Proposed}}<p class=hint>maven drafted these from acts she couldn't run. Fill the command (argv, space-separated) and enable. A row in an <code>mcp:</code> scope came from an MCP server and already knows what it calls — check the command, then enable.</p>
 <div class=scroll><table><tr><th>name</th><th>scope</th><th>from utterance</th><th>enable as</th></tr>
 {{range .Proposed}}<tr>
 <td><code>{{.Name}}</code></td><td><span class=badge>{{.Scope}}</span></td><td>{{.Utterance}}</td>
@@ -700,8 +700,8 @@ const toolsHTML = `{{template "shellTop" "tools"}}
 <input type=hidden name=name value="{{.Name}}">
 <input type=hidden name=scope value="{{.Scope}}">
 <input type=hidden name=action value=enable>
-<input type=text name=cmd class=input-wide placeholder="systemctl restart" required>
-<label><input type=checkbox name=destructive> destructive</label>
+<input type=text name=cmd class=input-wide placeholder="systemctl restart" value="{{join .Cmd " "}}" required>
+<label><input type=checkbox name=destructive {{if .Destructive}}checked{{end}}> destructive</label>
 <button class=btn>enable</button></form>
 <form method=post action=/tools class=inline-form>
 <input type=hidden name=name value="{{.Name}}">
@@ -730,6 +730,19 @@ const toolsHTML = `{{template "shellTop" "tools"}}
   <div class=hint>enable proposed tools above, or ask maven to configure one</div>
 </div>{{end}}
 </section>
+<section class=card>
+<h2 class=card-title>MCP servers <span class=badge>{{len .MCP}}</span></h2>
+{{if .MCP}}<p class=hint>servers she connects OUT to. Their tools appear above as proposals — a configured server is a place she may look, not a capability she has. A <code>stdio</code> target is a process on this box; an <code>http</code> one on a loopback or LAN address is inside the network, so treat its tools accordingly.</p>
+<div class=scroll><table><tr><th>name</th><th>transport</th><th>target</th><th>state</th><th>tools</th></tr>
+{{range .MCP}}<tr><td><code>{{.Name}}</code></td><td><span class=badge>{{.Transport}}</span></td><td><code>{{.Target}}</code></td>
+<td>{{if .Connected}}connected{{if .Server}} — {{.Server}}{{end}}{{else}}<span class=red>down</span>{{if .Err}} — {{.Err}}{{end}}{{end}}</td>
+<td>{{.Tools}}</td></tr>{{end}}</table></div>
+{{else}}<div class=empty>
+  <svg class=icon width="20" height="20"><use href="/ethos-icons.svg#i-settings"/></svg>
+  <div>no MCP servers configured</div>
+  <div class=hint>add an <code>mcp.servers</code> block to mavend.json to let her use an external tool server</div>
+</div>{{end}}
+</section>
 {{template "shellBottom"}}`
 
 // routinesHTML — proposed routine review surface. One row per thing maven
@@ -1320,12 +1333,20 @@ func handleTools(w http.ResponseWriter, r *http.Request, core ipc.CoreAPI, sessi
 		http.Error(w, "core read failed", http.StatusBadGateway)
 		return
 	}
+	// MCP is off by default and an older core may not know the method at all,
+	// so a failure here renders an empty section rather than breaking the page.
+	servers, err := core.MCPServers(ctx)
+	if err != nil {
+		log.Printf("tools: mcp servers: %v", err)
+		servers = nil
+	}
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	if err := toolsTmpl.Execute(w, struct {
 		Msg      string
 		Proposed []ipc.Tool
 		Enabled  []ipc.Tool
-	}{msg, proposed, enabled}); err != nil {
+		MCP      []ipc.MCPServerStatus
+	}{msg, proposed, enabled, servers}); err != nil {
 		log.Printf("tools render: %v", err)
 	}
 }

deploy/mavend.json

@@ -31,6 +31,20 @@
     "cooldown": "24h"
   },
 
+  "mcp": {
+    "timeout": "15s",
+    "servers": [
+      {
+        "name": "vikunja",
+        "url": "http://192.168.1.104:9100/mcp",
+        "allow_private": true,
+        "allow_tools": ["list_projects", "list_tasks", "get_task_details", "create_task"],
+        "max_tools": 6,
+        "enabled": false
+      }
+    ]
+  },
+
   "nexus":  { "url": "http://nexus:9740" },
   "praxis": { "url": "http://praxis:8989" },
   "hexis":  { "url": "http://hexis:9741" },

internal/config/config.go

@@ -22,6 +22,7 @@ import (
 
 	"github.com/kami/maven/internal/delivery/ntfysink"
 	"github.com/kami/maven/internal/delivery/telegramsink"
+	"github.com/kami/maven/internal/mcp"
 	"github.com/kami/maven/internal/morning"
 	"github.com/kami/maven/internal/update"
 	"github.com/robfig/cron/v3"
@@ -191,6 +192,119 @@ type Config struct {
 	// discovers and executes capabilities through Hexis for ecosystem actions.
 	// nil ⇒ no capability-aware routing.
 	Hexis *HexisConfig `json:"hexis,omitempty"`
+
+	// MCP — Model Context Protocol servers Maven connects OUT to (Vikunja
+	// #251). nil / absent / no enabled server ⇒ no connection is made and no
+	// tool is discovered, like every other capability that reaches outside the
+	// box. She is a client here, never a server: nothing exposes her own
+	// capabilities to an outside caller. See MCPConfig.
+	MCP *MCPConfig `json:"mcp,omitempty"`
+}
+
+// MCPConfig — the MCP client block. Servers are dark until one has
+// `"enabled": true`, and a discovered tool is only ever PROPOSED: Kami enables
+// it on /tools, on the authed surface, exactly as he would a shell tool. The
+// voice path can never grant a capability to itself.
+type MCPConfig struct {
+	// Servers — the configured servers. Each needs exactly one of command
+	// (a subprocess on this box) or url (a streamable-HTTP endpoint).
+	Servers []MCPServerConfig `json:"servers,omitempty"`
+
+	// Timeout — per-call budget for every server that does not set its own.
+	// 0 ⇒ mcp.DefaultTimeout (15s). A tool slower than this is not usable in a
+	// spoken turn.
+	Timeout Duration `json:"timeout,omitempty"`
+
+	// AllowHosts / DenyHosts — the host lists for the shared webfetch door that
+	// url servers go through. Deny wins. Private addresses are refused
+	// unconditionally unless the individual server sets allow_private.
+	AllowHosts []string `json:"allow_hosts,omitempty"`
+	DenyHosts  []string `json:"deny_hosts,omitempty"`
+
+	// MaxBytes — cap on one JSON-RPC response. 0 ⇒ webfetch.DefaultMaxBytes.
+	MaxBytes int64 `json:"max_bytes,omitempty"`
+}
+
+// MCPServerConfig — one MCP server.
+type MCPServerConfig struct {
+	// Name — the local handle. It prefixes every tool this server contributes
+	// ("vikunja" + "list_tasks" ⇒ the allowlist row "vikunja_list_tasks") and
+	// becomes the store scope "mcp:<name>", so its provenance is readable on
+	// /tools without opening the config.
+	Name string `json:"name"`
+
+	// Command / Args / Env / Dir — a stdio server: a child process of mavend,
+	// on this box, under this user. argv, never a shell string.
+	Command string   `json:"command,omitempty"`
+	Args    []string `json:"args,omitempty"`
+	Env     []string `json:"env,omitempty"`
+	Dir     string   `json:"dir,omitempty"`
+
+	// URL — a streamable-HTTP endpoint. It is fetched through
+	// internal/webfetch, so the SSRF guard, the redirect cap, the size cap and
+	// the one-request-per-host-per-second limit all apply.
+	URL string `json:"url,omitempty"`
+
+	// AllowPrivate — let THIS server be a loopback or LAN address. The Vikunja
+	// server on homesrv is "http://localhost:9100/mcp", which is refused
+	// without this flag. Understand what it means before setting it: a local
+	// server is a DIFFERENT trust level from a public one. It is inside the
+	// network, it usually needs no credential, and it can change things that
+	// matter — so an argument the router got wrong lands somewhere real. Set it
+	// only for a server you run yourself, and prefer allow_tools with it.
+	AllowPrivate bool `json:"allow_private,omitempty"`
+
+	// AllowTools — when set, the ONLY remote tool names taken from this server.
+	// This is the knob that keeps the catalogue deliberate: the resident model
+	// is a 1.7B with a 4096-token context, and a tool name it half-remembers is
+	// a wrong act, so fewer and better-chosen beats complete.
+	AllowTools []string `json:"allow_tools,omitempty"`
+
+	// MaxTools — cap on this server's contribution. 0 ⇒ mcp.DefaultMaxTools (12).
+	MaxTools int `json:"max_tools,omitempty"`
+
+	// Timeout — per-call budget for this server. 0 ⇒ MCPConfig.Timeout.
+	Timeout Duration `json:"timeout,omitempty"`
+
+	// Enabled — false (the default) keeps a configured server described but
+	// dark, so a block can be written and reviewed before it is switched on.
+	Enabled bool `json:"enabled,omitempty"`
+}
+
+// MCPServers maps the config blocks onto the mcp package's own type. It lives
+// here so config validation and daemon wiring cannot drift on the mapping.
+// Returns nil when nothing is configured or nothing is enabled.
+func (c *Config) MCPServers() []mcp.ServerConfig {
+	if c.MCP == nil {
+		return nil
+	}
+	out := make([]mcp.ServerConfig, 0, len(c.MCP.Servers))
+	for _, s := range c.MCP.Servers {
+		if !s.Enabled {
+			continue
+		}
+		timeout := time.Duration(s.Timeout)
+		if timeout <= 0 {
+			timeout = time.Duration(c.MCP.Timeout)
+		}
+		out = append(out, mcp.ServerConfig{
+			Name:         s.Name,
+			Command:      s.Command,
+			Args:         s.Args,
+			Env:          s.Env,
+			Dir:          s.Dir,
+			URL:          s.URL,
+			AllowPrivate: s.AllowPrivate,
+			AllowTools:   s.AllowTools,
+			MaxTools:     s.MaxTools,
+			Timeout:      timeout,
+			Enabled:      true,
+		})
+	}
+	if len(out) == 0 {
+		return nil
+	}
+	return out
 }
 
 // PraxisConfig — maven's connection to the Praxis attention service.
@@ -783,6 +897,12 @@ func (c *Config) applyDefaults() {
 		c.Feeds = nil
 	}
 
+	// Same rule for MCP: a block with no server, or none enabled, is the same
+	// as no block at all. Normalising it to nil keeps "off" in one place.
+	if c.MCP != nil && len(c.MCPServers()) == 0 {
+		c.MCP = nil
+	}
+
 	// Same rule for the crawler: a block that neither answers on demand nor
 	// watches anything has nothing to do, so it is normalised to "off".
 	if c.Crawl != nil && !c.Crawl.OnDemand && len(c.Crawl.Watches) == 0 {
@@ -887,6 +1007,12 @@ func (c *Config) validate() error {
 			return fmt.Errorf("routine %q: bad cron %q: %w", r.Name, r.Cron, err)
 		}
 	}
+	// An MCP block with a typo (no name, both command and url, a bare hostname
+	// as the url) fails here, at startup, rather than at the first turn that
+	// needed the tool.
+	if err := mcp.Validate(c.MCPServers()); err != nil {
+		return err
+	}
 	if len(c.MorningRoutines) > 0 {
 		if err := morning.Validate(morningRoutinesFromConfig(c.MorningRoutines)); err != nil {
 			return err

internal/config/mcp_test.go

@@ -0,0 +1,82 @@
+package config
+
+import (
+	"testing"
+	"time"
+)
+
+func TestMCPAbsentIsOff(t *testing.T) {
+	c, err := Load(writeConfig(t, `{}`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if c.MCP != nil {
+		t.Error("no mcp block ⇒ nil")
+	}
+	if got := c.MCPServers(); got != nil {
+		t.Errorf("MCPServers() = %+v, want nil", got)
+	}
+}
+
+// A described-but-not-enabled server must not be wired. This is how a block can
+// sit in the config file, reviewed, before it is switched on.
+func TestMCPDisabledServerIsOff(t *testing.T) {
+	c, err := Load(writeConfig(t, `{"mcp":{"servers":[
+		{"name":"vikunja","url":"http://localhost:9100/mcp","allow_private":true}]}}`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if c.MCP != nil {
+		t.Errorf("a block with nothing enabled must normalise to nil, got %+v", c.MCP)
+	}
+	if got := c.MCPServers(); len(got) != 0 {
+		t.Errorf("MCPServers() = %+v", got)
+	}
+}
+
+func TestMCPEnabledServerMapping(t *testing.T) {
+	c, err := Load(writeConfig(t, `{"mcp":{
+		"timeout":"5s",
+		"servers":[
+			{"name":"vikunja","url":"http://localhost:9100/mcp","allow_private":true,
+			 "allow_tools":["list_tasks"],"max_tools":3,"enabled":true},
+			{"name":"files","command":"mcp-server-fs","args":["/srv"],"timeout":"1s","enabled":true},
+			{"name":"off","command":"nope"}
+		]}}`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := c.MCPServers()
+	if len(got) != 2 {
+		t.Fatalf("servers = %+v", got)
+	}
+	if got[0].Name != "vikunja" || !got[0].AllowPrivate || got[0].MaxTools != 3 ||
+		len(got[0].AllowTools) != 1 || got[0].Timeout != 5*time.Second {
+		t.Errorf("vikunja mapped wrong: %+v", got[0])
+	}
+	if got[1].Command != "mcp-server-fs" || len(got[1].Args) != 1 || got[1].Timeout != time.Second {
+		t.Errorf("files mapped wrong: %+v", got[1])
+	}
+	// allow_private is per server and must not leak to the other one.
+	if got[1].AllowPrivate {
+		t.Error("allow_private leaked between servers")
+	}
+}
+
+func TestMCPBadServerFailsAtStartup(t *testing.T) {
+	cases := map[string]string{
+		"no name":     `{"mcp":{"servers":[{"command":"x","enabled":true}]}}`,
+		"both":        `{"mcp":{"servers":[{"name":"a","command":"x","url":"http://a.test","enabled":true}]}}`,
+		"neither":     `{"mcp":{"servers":[{"name":"a","enabled":true}]}}`,
+		"bad scheme":  `{"mcp":{"servers":[{"name":"a","url":"unix:///run/x.sock","enabled":true}]}}`,
+		"duplicate":   `{"mcp":{"servers":[{"name":"a","command":"x","enabled":true},{"name":"a","command":"y","enabled":true}]}}`,
+		"spacey name": `{"mcp":{"servers":[{"name":"a b","command":"x","enabled":true}]}}`,
+	}
+	for name, body := range cases {
+		t.Run(name, func(t *testing.T) {
+			if _, err := Load(writeConfig(t, body)); err == nil {
+				t.Fatal("want a startup error")
+			}
+		})
+	}
+}

internal/ipc/api.go

@@ -319,6 +319,19 @@ type Tool struct {
 	Updated     time.Time `json:"updated"`
 }
 
+// MCPServerStatus — one configured MCP server, as the web surface sees it.
+// Target is the command or url; Tools is how many tools discovery kept after
+// allow_tools / max_tools, not how many the server offers.
+type MCPServerStatus struct {
+	Name      string `json:"name"`
+	Transport string `json:"transport"` // "stdio" (a local subprocess) or "http"
+	Target    string `json:"target"`
+	Connected bool   `json:"connected"`
+	Server    string `json:"server,omitempty"` // the server's own name + version
+	Tools     int    `json:"tools"`
+	Err       string `json:"err,omitempty"`
+}
+
 // chatReq / chatResp — text chat round-trip for the IPC Chat method.
 type chatReq struct {
 	Text string `json:"text"`
@@ -457,6 +470,14 @@ type CoreAPI interface {
 	// TickTrace.
 	MorningStatus(ctx context.Context) ([]MorningRoutineStatus, error)
 
+	// MCPServers reports the configured MCP servers and their health
+	// (Vikunja #251). Read-only introspection for /tools — there is no
+	// "call this tool" method on purpose: an MCP tool runs through the same
+	// allowlist, confirm turn and act path as any other tool, and a second
+	// mutation path would be a second thing to get wrong. Empty when the
+	// mcp config block is absent, which is the default.
+	MCPServers(ctx context.Context) ([]MCPServerStatus, error)
+
 	// DayPlan returns today's ordered plan — calendar events, pending
 	// reminders and any morning checklist still outstanding (see
 	// internal/morning.BuildPlan) — plus the spoken RU rendering of it.

internal/ipc/client.go

@@ -72,6 +72,7 @@ var readOnlyMethods = map[Method]bool{
 	MethodListTasks:            true,
 	MethodTickTrace:            true,
 	MethodMorningStatus:        true,
+	MethodMCPServers:           true,
 	MethodDayPlan:              true,
 }
 
@@ -505,6 +506,14 @@ func (c *Client) TickTrace(ctx context.Context) (TickTrace, error) {
 	return t, nil
 }
 
+func (c *Client) MCPServers(ctx context.Context) ([]MCPServerStatus, error) {
+	var s []MCPServerStatus
+	if err := c.call(ctx, MethodMCPServers, nil, &s); err != nil {
+		return nil, err
+	}
+	return s, nil
+}
+
 func (c *Client) MorningStatus(ctx context.Context) ([]MorningRoutineStatus, error) {
 	var s []MorningRoutineStatus
 	if err := c.call(ctx, MethodMorningStatus, nil, &s); err != nil {

internal/ipc/server.go

@@ -211,6 +211,10 @@ func (a *storeAPI) MorningStatus(ctx context.Context) ([]MorningRoutineStatus, e
 	return nil, errors.New("store: morning status not available via direct store API")
 }
 
+func (a *storeAPI) MCPServers(ctx context.Context) ([]MCPServerStatus, error) {
+	return nil, nil // no manager behind a bare store: nothing configured
+}
+
 func (a *storeAPI) DayPlan(ctx context.Context) (DayPlan, error) {
 	return DayPlan{}, errors.New("store: day plan not available via direct store API")
 }
@@ -832,6 +836,16 @@ var methodTable = map[Method]handlerFunc{
 	MethodMorningStatus: withoutParams(func(ctx context.Context, api CoreAPI) ([]MorningRoutineStatus, error) {
 		return api.MorningStatus(ctx)
 	}),
+	MethodMCPServers: withoutParams(func(ctx context.Context, api CoreAPI) ([]MCPServerStatus, error) {
+		out, err := api.MCPServers(ctx)
+		if err != nil {
+			return nil, err
+		}
+		if out == nil {
+			out = []MCPServerStatus{}
+		}
+		return out, nil
+	}),
 }
 
 // dispatch unmarshals params for req.Method and calls the matching CoreAPI

internal/ipc/unimplemented.go

@@ -122,6 +122,9 @@ func (UnimplementedCoreAPI) TickTrace(ctx context.Context) (TickTrace, error) {
 func (UnimplementedCoreAPI) MorningStatus(ctx context.Context) ([]MorningRoutineStatus, error) {
 	return nil, ErrNotImplemented
 }
+func (UnimplementedCoreAPI) MCPServers(ctx context.Context) ([]MCPServerStatus, error) {
+	return nil, ErrNotImplemented
+}
 func (UnimplementedCoreAPI) DayPlan(ctx context.Context) (DayPlan, error) {
 	return DayPlan{}, ErrNotImplemented
 }

internal/ipc/wire.go

@@ -45,6 +45,7 @@ const (
 	MethodRevertFact             Method = "revert_fact"
 	MethodTickTrace              Method = "tick_trace"
 	MethodMorningStatus          Method = "morning_status"
+	MethodMCPServers             Method = "mcp_servers"
 	MethodDayPlan                Method = "day_plan"
 	MethodChat                   Method = "chat"
 	MethodCaptureTask            Method = "capture_task"

internal/mcp/allowlist.go

@@ -0,0 +1,61 @@
+package mcp
+
+import (
+	"regexp"
+	"strings"
+)
+
+// CmdPrefix is the reserved first argv element that marks an allowlist row as
+// an MCP call rather than a process. An MCP tool row looks like
+//
+//	name: "vikunja_list_tasks"   cmd: ["mcp", "vikunja", "list_tasks"]
+//
+// which is why there is no new column and no migration: the store, the /tools
+// page, ProposeTool, EnableTool, DisableTool, the act matcher and the confirm
+// turn all keep working unchanged. The executor is the only place that has to
+// know the difference, and it is one branch on Cmd[0].
+//
+// The rest of the allowlist discipline is inherited whole: a row that is not
+// status='enabled' does not run, and a row marked destructive does not run on
+// first hearing. Nothing here can enable itself — discovery only proposes.
+const CmdPrefix = "mcp"
+
+// Cmd builds the argv encoding for a discovered tool.
+func Cmd(server, tool string) []string { return []string{CmdPrefix, server, tool} }
+
+// ParseCmd recognises an MCP allowlist row. ok=false for an ordinary process
+// tool, which is what almost every row is.
+func ParseCmd(cmd []string) (server, tool string, ok bool) {
+	if len(cmd) != 3 || cmd[0] != CmdPrefix {
+		return "", "", false
+	}
+	if cmd[1] == "" || cmd[2] == "" {
+		return "", "", false
+	}
+	return cmd[1], cmd[2], true
+}
+
+var notName = regexp.MustCompile(`[^a-z0-9_]+`)
+
+// LocalName is the allowlist name for a discovered tool: the server handle, an
+// underscore, the remote name, lowercased and stripped of anything that is not
+// a word character. Namespacing by server is what keeps two servers that both
+// offer "search" from colliding, and what makes the provenance of a row on the
+// /tools page obvious without opening the diff.
+func LocalName(server, tool string) string {
+	clean := func(s string) string {
+		return strings.Trim(notName.ReplaceAllString(strings.ToLower(strings.TrimSpace(s)), "_"), "_")
+	}
+	s, t := clean(server), clean(tool)
+	switch {
+	case s == "":
+		return t
+	case t == "":
+		return s
+	}
+	return s + "_" + t
+}
+
+// Scope is the store scope for a server's rows, so the /tools page can group
+// them and a human can tell at a glance where a capability came from.
+func Scope(server string) string { return "mcp:" + server }

internal/mcp/client.go

@@ -0,0 +1,267 @@
+package mcp
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+	"sync/atomic"
+)
+
+// Errors callers distinguish.
+var (
+	// ErrClosed — the transport is gone (subprocess died, client closed).
+	ErrClosed = errors.New("mcp: connection is closed")
+	// ErrNotInitialized — a call was made before the initialize handshake.
+	ErrNotInitialized = errors.New("mcp: not initialized")
+	// ErrToolFailed — the server ran the tool and reported an error result.
+	ErrToolFailed = errors.New("mcp: tool reported an error")
+)
+
+// Tool is one tool a server offers, in the form Maven cares about.
+//
+// ReadOnly comes from the server's own readOnlyHint annotation and decides
+// whether the allowlist row is marked destructive: no hint, or a false one,
+// means "assume it mutates", which routes the call through the confirm turn.
+// Guessing wrong in that direction only costs a question.
+type Tool struct {
+	Server      string
+	Name        string
+	Description string
+	InputSchema json.RawMessage
+	ReadOnly    bool
+}
+
+// Resource is one resource a server offers. Contents are fetched separately —
+// listing is cheap, reading is not.
+type Resource struct {
+	Server   string
+	URI      string
+	Name     string
+	MIMEType string
+}
+
+// ServerInfo is what came back from the handshake.
+type ServerInfo struct {
+	Name            string `json:"name"`
+	Version         string `json:"version"`
+	ProtocolVersion string `json:"-"`
+}
+
+// Client is one connected MCP server. Safe for concurrent use.
+type Client struct {
+	name string
+	tr   transport
+	next atomic.Int64
+
+	mu    sync.Mutex
+	info  ServerInfo
+	ready bool
+}
+
+// newClient wraps a transport. Callers use Dial* in manager.go.
+func newClient(name string, tr transport) *Client {
+	return &Client{name: name, tr: tr}
+}
+
+// Name — the local name of this server (the config key, not the server's own).
+func (c *Client) Name() string { return c.name }
+
+// Info — what the server said about itself during the handshake.
+func (c *Client) Info() ServerInfo {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.info
+}
+
+// Initialize performs the MCP handshake and sends notifications/initialized.
+// Capabilities we declare are empty on purpose: Maven consumes, she does not
+// offer sampling or roots back to the server.
+func (c *Client) Initialize(ctx context.Context) error {
+	var out struct {
+		ProtocolVersion string     `json:"protocolVersion"`
+		ServerInfo      ServerInfo `json:"serverInfo"`
+	}
+	err := c.call(ctx, "initialize", map[string]any{
+		"protocolVersion": ProtocolVersion,
+		"capabilities":    map[string]any{},
+		"clientInfo":      map[string]any{"name": "maven", "version": "1.0"},
+	}, &out)
+	if err != nil {
+		return err
+	}
+	if strings.TrimSpace(out.ProtocolVersion) == "" {
+		return fmt.Errorf("mcp: %s: handshake returned no protocol version", c.name)
+	}
+	out.ServerInfo.ProtocolVersion = out.ProtocolVersion
+	c.mu.Lock()
+	c.info, c.ready = out.ServerInfo, true
+	c.mu.Unlock()
+	// Best effort: a stateless HTTP server may not care, and a failure here is
+	// not worth dropping a working connection over.
+	_ = c.tr.Notify(ctx, "notifications/initialized", map[string]any{})
+	return nil
+}
+
+// ListTools discovers the server's tools.
+func (c *Client) ListTools(ctx context.Context) ([]Tool, error) {
+	if !c.initialized() {
+		return nil, ErrNotInitialized
+	}
+	var out struct {
+		Tools []struct {
+			Name        string          `json:"name"`
+			Description string          `json:"description"`
+			InputSchema json.RawMessage `json:"inputSchema"`
+			Annotations *struct {
+				ReadOnlyHint bool `json:"readOnlyHint"`
+			} `json:"annotations"`
+		} `json:"tools"`
+	}
+	if err := c.call(ctx, "tools/list", map[string]any{}, &out); err != nil {
+		return nil, err
+	}
+	tools := make([]Tool, 0, len(out.Tools))
+	for _, t := range out.Tools {
+		if strings.TrimSpace(t.Name) == "" {
+			continue
+		}
+		tools = append(tools, Tool{
+			Server:      c.name,
+			Name:        t.Name,
+			Description: strings.TrimSpace(t.Description),
+			InputSchema: t.InputSchema,
+			ReadOnly:    t.Annotations != nil && t.Annotations.ReadOnlyHint,
+		})
+	}
+	return tools, nil
+}
+
+// CallTool runs one tool and returns its text content, joined by newlines.
+// Non-text content (images, blobs) is dropped: everything downstream of here
+// is a spoken or written sentence.
+//
+// args is exactly what the router produced. Nothing else — no history, no
+// notes, no persona — is in scope here, by construction.
+func (c *Client) CallTool(ctx context.Context, name string, args map[string]any) (string, error) {
+	if !c.initialized() {
+		return "", ErrNotInitialized
+	}
+	if args == nil {
+		args = map[string]any{}
+	}
+	var out struct {
+		IsError bool `json:"isError"`
+		Content []struct {
+			Type string `json:"type"`
+			Text string `json:"text"`
+		} `json:"content"`
+	}
+	if err := c.call(ctx, "tools/call", map[string]any{"name": name, "arguments": args}, &out); err != nil {
+		return "", err
+	}
+	var parts []string
+	for _, ct := range out.Content {
+		if ct.Type == "text" && strings.TrimSpace(ct.Text) != "" {
+			parts = append(parts, strings.TrimSpace(ct.Text))
+		}
+	}
+	text := strings.Join(parts, "\n")
+	if out.IsError {
+		return text, fmt.Errorf("%w: %s/%s: %s", ErrToolFailed, c.name, name, text)
+	}
+	return text, nil
+}
+
+// ListResources discovers the server's resources. A server without the
+// resources capability answers with an error; that is not fatal, the caller
+// gets an empty list.
+func (c *Client) ListResources(ctx context.Context) ([]Resource, error) {
+	if !c.initialized() {
+		return nil, ErrNotInitialized
+	}
+	var out struct {
+		Resources []struct {
+			URI      string `json:"uri"`
+			Name     string `json:"name"`
+			MIMEType string `json:"mimeType"`
+		} `json:"resources"`
+	}
+	if err := c.call(ctx, "resources/list", map[string]any{}, &out); err != nil {
+		return nil, err
+	}
+	res := make([]Resource, 0, len(out.Resources))
+	for _, r := range out.Resources {
+		if strings.TrimSpace(r.URI) == "" {
+			continue
+		}
+		res = append(res, Resource{Server: c.name, URI: r.URI, Name: r.Name, MIMEType: r.MIMEType})
+	}
+	return res, nil
+}
+
+// ReadResource returns a resource's text contents, joined by newlines. This is
+// the RAG-hint path: the text can be pasted into a router or phraser prompt.
+func (c *Client) ReadResource(ctx context.Context, uri string) (string, error) {
+	if !c.initialized() {
+		return "", ErrNotInitialized
+	}
+	var out struct {
+		Contents []struct {
+			Text string `json:"text"`
+		} `json:"contents"`
+	}
+	if err := c.call(ctx, "resources/read", map[string]any{"uri": uri}, &out); err != nil {
+		return "", err
+	}
+	var parts []string
+	for _, ct := range out.Contents {
+		if strings.TrimSpace(ct.Text) != "" {
+			parts = append(parts, strings.TrimSpace(ct.Text))
+		}
+	}
+	return strings.Join(parts, "\n"), nil
+}
+
+// Close drops the connection.
+func (c *Client) Close() error {
+	c.mu.Lock()
+	c.ready = false
+	c.mu.Unlock()
+	return c.tr.Close()
+}
+
+func (c *Client) initialized() bool {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.ready
+}
+
+// alive reports whether the underlying transport can still carry a call. HTTP
+// is stateless, so it is always alive; a dead subprocess is not.
+func (c *Client) alive() bool {
+	if s, ok := c.tr.(*stdioTransport); ok {
+		return s.alive()
+	}
+	return true
+}
+
+func (c *Client) call(ctx context.Context, method string, params any, out any) error {
+	req := &rpcRequest{JSONRPC: "2.0", ID: c.next.Add(1), Method: method, Params: params}
+	resp, err := c.tr.Call(ctx, req)
+	if err != nil {
+		return fmt.Errorf("mcp: %s: %s: %w", c.name, method, err)
+	}
+	if resp.Error != nil {
+		return fmt.Errorf("mcp: %s: %s: %w", c.name, method, resp.Error)
+	}
+	if out == nil || len(resp.Result) == 0 {
+		return nil
+	}
+	if err := json.Unmarshal(resp.Result, out); err != nil {
+		return fmt.Errorf("mcp: %s: %s: decode result: %w", c.name, method, err)
+	}
+	return nil
+}

internal/mcp/http.go

@@ -0,0 +1,154 @@
+package mcp
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+)
+
+// Poster is the HTTP seam: internal/webfetch.Fetcher satisfies it. The
+// transport takes it as an interface so a test can serve a fake without a
+// listener, and so that the ONLY implementation wired in production is the
+// guarded fetcher — an MCP endpoint cannot get a bare http.Client this way.
+type Poster interface {
+	Post(ctx context.Context, rawURL, contentType string, body []byte, hdr map[string]string) (*PostResponse, error)
+}
+
+// PostResponse is the shape webfetch returns, restated here so this package
+// does not depend on it structurally.
+type PostResponse struct {
+	Status      int
+	ContentType string
+	Body        []byte
+	Header      map[string]string
+}
+
+// httpTransport speaks streamable HTTP: every request is a POST to one
+// endpoint, and the reply is either a JSON object or a text/event-stream frame
+// carrying one. Both are accepted — servers pick per response, and the two the
+// LAN runs disagree about which.
+type httpTransport struct {
+	poster Poster
+	url    string
+
+	mu      sync.Mutex
+	session string // Mcp-Session-Id, echoed back when the server issues one
+}
+
+func newHTTPTransport(post Poster, endpoint string) *httpTransport {
+	return &httpTransport{poster: post, url: endpoint}
+}
+
+func (t *httpTransport) Call(ctx context.Context, req *rpcRequest) (*rpcResponse, error) {
+	body, err := t.send(ctx, req)
+	if err != nil {
+		return nil, err
+	}
+	frame, err := decodeFrame(body)
+	if err != nil {
+		return nil, err
+	}
+	var resp rpcResponse
+	if err := json.Unmarshal(frame, &resp); err != nil {
+		return nil, fmt.Errorf("mcp: decode response: %w", err)
+	}
+	return &resp, nil
+}
+
+func (t *httpTransport) Notify(ctx context.Context, method string, params any) error {
+	_, err := t.send(ctx, &rpcRequest{JSONRPC: "2.0", Method: method, Params: params})
+	return err
+}
+
+func (t *httpTransport) send(ctx context.Context, req *rpcRequest) ([]byte, error) {
+	req.JSONRPC = "2.0"
+	raw, err := json.Marshal(req)
+	if err != nil {
+		return nil, err
+	}
+	hdr := map[string]string{"Accept": "application/json, text/event-stream"}
+	t.mu.Lock()
+	if t.session != "" {
+		hdr["Mcp-Session-Id"] = t.session
+	}
+	t.mu.Unlock()
+
+	resp, err := t.poster.Post(ctx, t.url, "application/json", raw, hdr)
+	if err != nil {
+		return nil, err
+	}
+	if sid := headerGet(resp.Header, "Mcp-Session-Id"); sid != "" {
+		t.mu.Lock()
+		t.session = sid
+		t.mu.Unlock()
+	}
+	return resp.Body, nil
+}
+
+func (t *httpTransport) Close() error {
+	t.mu.Lock()
+	t.session = ""
+	t.mu.Unlock()
+	return nil
+}
+
+func headerGet(h map[string]string, key string) string {
+	if h == nil {
+		return ""
+	}
+	if v, ok := h[key]; ok {
+		return v
+	}
+	lower := strings.ToLower(key)
+	for k, v := range h {
+		if strings.ToLower(k) == lower {
+			return v
+		}
+	}
+	return ""
+}
+
+// decodeFrame pulls the JSON object out of a body that is either raw JSON or
+// SSE. For SSE we take the LAST data: payload that parses, which is the
+// response — earlier frames on the stream are progress notifications.
+func decodeFrame(body []byte) ([]byte, error) {
+	trimmed := bytes.TrimSpace(body)
+	if len(trimmed) == 0 {
+		return nil, errors.New("mcp: empty response body")
+	}
+	if trimmed[0] == '{' || trimmed[0] == '[' {
+		return trimmed, nil
+	}
+	var last []byte
+	sc := bufio.NewScanner(bytes.NewReader(trimmed))
+	sc.Buffer(make([]byte, 0, 64<<10), maxLine)
+	for sc.Scan() {
+		line := strings.TrimSpace(sc.Text())
+		if !strings.HasPrefix(line, "data:") {
+			continue
+		}
+		payload := strings.TrimSpace(strings.TrimPrefix(line, "data:"))
+		if payload == "" {
+			continue
+		}
+		var probe map[string]json.RawMessage
+		if json.Unmarshal([]byte(payload), &probe) != nil {
+			continue
+		}
+		if _, isResp := probe["id"]; isResp {
+			last = []byte(payload)
+		}
+	}
+	if err := sc.Err(); err != nil {
+		return nil, fmt.Errorf("mcp: read event stream: %w", err)
+	}
+	if last == nil {
+		return nil, errors.New("mcp: no JSON-RPC response in event stream")
+	}
+	return last, nil
+}

internal/mcp/jsonrpc.go

@@ -0,0 +1,72 @@
+// Package mcp is Maven's Model Context Protocol CLIENT. She is a host: she
+// connects OUT to MCP servers, discovers the tools and resources they offer,
+// and hands them to the parts of her that already exist for this — the tool
+// allowlist in the store, the confirm turn for anything that mutates, the
+// stage-3 gate that makes an uncertain act ask instead of run.
+//
+// She is not an MCP server. Nothing here exposes her own capabilities to an
+// outside caller; docs/plans/06-mcp-support.md asks for the host direction only.
+//
+// Boundaries, in code rather than in prose:
+//
+//   - OFF unless configured. No mcp_servers block ⇒ no manager, no goroutine,
+//     no socket.
+//   - A remote server is reached through internal/webfetch, so the SSRF guard,
+//     the size cap, the redirect cap and the per-host rate limit all apply to
+//     an MCP endpoint exactly as they do to a news feed. Reaching a loopback
+//     or LAN server means explicitly setting allow_private on THAT server —
+//     a different trust level, spelled out per server rather than globally.
+//   - Only the tool name and the arguments the router produced are sent. This
+//     package never sees his notes, facts, history or the persona block, and
+//     has no API through which a caller could pass them.
+//   - Discovery proposes, it does not enable. A discovered tool lands as a
+//     'proposed' row; a human enables it on the authed surface.
+package mcp
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+)
+
+// ProtocolVersion — the spec revision we ask for in the initialize handshake.
+// A server that answers with a different one is accepted (the spec says the
+// client may proceed if it can support what came back); we only refuse when it
+// answers with no version at all, which means it is not an MCP server.
+const ProtocolVersion = "2025-06-18"
+
+// rpcRequest / rpcResponse — JSON-RPC 2.0. Deliberately hand-rolled: the wire
+// format is four fields, and the repo vendors its dependencies, so pulling a
+// library in for this would cost more than it saves.
+type rpcRequest struct {
+	JSONRPC string `json:"jsonrpc"`
+	ID      int64  `json:"id,omitempty"`
+	Method  string `json:"method"`
+	Params  any    `json:"params,omitempty"`
+}
+
+type rpcResponse struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      *int64          `json:"id"`
+	Result  json.RawMessage `json:"result,omitempty"`
+	Error   *rpcError       `json:"error,omitempty"`
+}
+
+type rpcError struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+}
+
+func (e *rpcError) Error() string { return fmt.Sprintf("mcp: rpc error %d: %s", e.Code, e.Message) }
+
+// transport carries one JSON-RPC conversation. Implementations: stdioTransport
+// (a subprocess on this box) and httpTransport (streamable HTTP, guarded by
+// webfetch). Both must be safe for concurrent use by the Client.
+type transport interface {
+	// Call sends a request and returns the matching response.
+	Call(ctx context.Context, req *rpcRequest) (*rpcResponse, error)
+	// Notify sends a notification (no id, no reply expected).
+	Notify(ctx context.Context, method string, params any) error
+	// Close releases the transport (kills the subprocess, drops the session).
+	Close() error
+}

internal/mcp/manager.go

@@ -0,0 +1,523 @@
+package mcp
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"log"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+)
+
+// Defaults for a server block. Small numbers on purpose — see MaxTools.
+const (
+	// DefaultTimeout bounds one JSON-RPC call. A tool that takes longer than
+	// this is not usable in a spoken turn anyway.
+	DefaultTimeout = 15 * time.Second
+	// DefaultMaxTools caps how many tools ONE server may contribute. The
+	// resident model is a 1.7B with a 4096-token context: a catalogue of forty
+	// tool names does not fit in its head, and a name it half-remembers is a
+	// wrong act. Twelve per server is already generous.
+	DefaultMaxTools = 12
+	// DefaultReconnectEvery is how long the manager waits before re-dialing a
+	// server whose connection died.
+	DefaultReconnectEvery = 30 * time.Second
+)
+
+// ErrNoServer — the named server is not configured or not connected.
+var ErrNoServer = errors.New("mcp: no such server")
+
+// ServerConfig is one configured MCP server. Off unless present.
+//
+// Exactly one of Command (a subprocess on this box) or URL (a remote or
+// loopback HTTP endpoint) must be set.
+type ServerConfig struct {
+	// Name is the local handle. It prefixes every tool this server
+	// contributes, so it must be short and a valid identifier-ish word.
+	Name string `json:"name"`
+	// Command + Args + Env + Dir describe a stdio server: a child process of
+	// mavend, on this box, under this user. argv, never a shell string.
+	Command string   `json:"command,omitempty"`
+	Args    []string `json:"args,omitempty"`
+	Env     []string `json:"env,omitempty"`
+	Dir     string   `json:"dir,omitempty"`
+	// URL is a streamable-HTTP endpoint. It goes through internal/webfetch, so
+	// it inherits the SSRF guard, the size cap and the per-host rate limit.
+	URL string `json:"url,omitempty"`
+	// AllowPrivate lets THIS server be a loopback or LAN address
+	// (http://localhost:9100/mcp is the Vikunja server on homesrv). It is a
+	// per-server hole in the private-address guard and it is not the same trust
+	// level as a public endpoint: whatever is behind it is inside the network,
+	// so an argument the router got wrong reaches something that matters. Set
+	// it only for a server you run.
+	AllowPrivate bool `json:"allow_private,omitempty"`
+	// AllowTools, when non-empty, is the ONLY set of remote tool names taken
+	// from this server. This is the knob for keeping the catalogue small and
+	// deliberate rather than "whatever the server grew this week".
+	AllowTools []string `json:"allow_tools,omitempty"`
+	// MaxTools caps the contribution (0 ⇒ DefaultMaxTools).
+	MaxTools int `json:"max_tools,omitempty"`
+	// Timeout bounds one call (0 ⇒ DefaultTimeout).
+	Timeout time.Duration `json:"-"`
+	// Enabled=false keeps a configured server described but dark.
+	Enabled bool `json:"enabled"`
+}
+
+// PosterFactory builds the HTTP door for one server. It is a factory rather
+// than a single shared Poster because allow_private is per server: the fetcher
+// that may reach http://localhost:9100/mcp must NOT be the same fetcher another
+// server's public URL goes through, or one loopback exemption would quietly
+// unlock the LAN for all of them.
+type PosterFactory func(cfg ServerConfig) (Poster, error)
+
+// Manager owns the connections. Nothing here starts unless at least one server
+// is configured and enabled.
+type Manager struct {
+	newPoster PosterFactory
+	mu        sync.Mutex
+	conns     map[string]*conn
+	order     []string
+}
+
+type conn struct {
+	cfg      ServerConfig
+	client   *Client
+	tools    []Tool
+	lastErr  error
+	lastTry  time.Time
+	dialedAt time.Time
+}
+
+// NewManager builds a manager for the enabled servers in cfgs. newPoster is
+// the guarded HTTP door factory for url servers; pass nil only when no url
+// server is configured (a nil factory with a url server is reported per server
+// at dial time rather than fatally, so one bad block never stops the daemon).
+//
+// Dialing is lazy: NewManager validates and records, Connect dials.
+func NewManager(newPoster PosterFactory, cfgs []ServerConfig) (*Manager, error) {
+	m := &Manager{newPoster: newPoster, conns: map[string]*conn{}}
+	for _, c := range cfgs {
+		if !c.Enabled {
+			continue
+		}
+		if err := validate(c); err != nil {
+			return nil, err
+		}
+		if _, dup := m.conns[c.Name]; dup {
+			return nil, fmt.Errorf("mcp: duplicate server name %q", c.Name)
+		}
+		if c.Timeout <= 0 {
+			c.Timeout = DefaultTimeout
+		}
+		if c.MaxTools <= 0 {
+			c.MaxTools = DefaultMaxTools
+		}
+		m.conns[c.Name] = &conn{cfg: c}
+		m.order = append(m.order, c.Name)
+	}
+	sort.Strings(m.order)
+	return m, nil
+}
+
+// Validate checks a set of server blocks without dialling anything, so a typo
+// fails at startup rather than at the first turn that needed the tool.
+func Validate(cfgs []ServerConfig) error {
+	seen := map[string]bool{}
+	for _, c := range cfgs {
+		if err := validate(c); err != nil {
+			return err
+		}
+		if seen[c.Name] {
+			return fmt.Errorf("mcp: duplicate server name %q", c.Name)
+		}
+		seen[c.Name] = true
+	}
+	return nil
+}
+
+func validate(c ServerConfig) error {
+	if strings.TrimSpace(c.Name) == "" {
+		return errors.New("mcp: server needs a name")
+	}
+	if strings.ContainsAny(c.Name, " \t/:") {
+		return fmt.Errorf("mcp: server name %q must be one word without spaces, slashes or colons", c.Name)
+	}
+	hasCmd, hasURL := c.Command != "", c.URL != ""
+	if hasCmd == hasURL {
+		return fmt.Errorf("mcp: server %q needs exactly one of command or url", c.Name)
+	}
+	if hasURL && !strings.HasPrefix(c.URL, "http://") && !strings.HasPrefix(c.URL, "https://") {
+		return fmt.Errorf("mcp: server %q url must be http or https", c.Name)
+	}
+	return nil
+}
+
+// Servers — the configured, enabled server names, sorted.
+func (m *Manager) Servers() []string {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	return append([]string(nil), m.order...)
+}
+
+// Empty reports whether nothing is configured. The daemon uses it to skip
+// wiring entirely.
+func (m *Manager) Empty() bool {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	return len(m.conns) == 0
+}
+
+// Connect dials every configured server, handshakes, and discovers tools.
+// A server that fails is recorded and retried later by Refresh — one bad
+// server never blocks the others, and never blocks boot.
+func (m *Manager) Connect(ctx context.Context) {
+	for _, name := range m.Servers() {
+		if err := m.dial(ctx, name); err != nil {
+			log.Printf("mcp: %s: %v", name, err)
+		}
+	}
+}
+
+func (m *Manager) dial(ctx context.Context, name string) error {
+	m.mu.Lock()
+	c, ok := m.conns[name]
+	if !ok {
+		m.mu.Unlock()
+		return ErrNoServer
+	}
+	cfg := c.cfg
+	c.lastTry = time.Now()
+	m.mu.Unlock()
+
+	var tr transport
+	var err error
+	if cfg.Command != "" {
+		tr, err = newStdioTransport(ctx, append([]string{cfg.Command}, cfg.Args...), cfg.Env, cfg.Dir)
+	} else if m.newPoster == nil {
+		err = fmt.Errorf("server %q has a url but no http door was wired", name)
+	} else {
+		var poster Poster
+		if poster, err = m.newPoster(cfg); err == nil {
+			tr = newHTTPTransport(poster, cfg.URL)
+		}
+	}
+	if err != nil {
+		m.fail(name, err)
+		return err
+	}
+
+	cl := newClient(name, tr)
+	ictx, cancel := context.WithTimeout(ctx, cfg.Timeout)
+	defer cancel()
+	if err := cl.Initialize(ictx); err != nil {
+		_ = cl.Close()
+		m.fail(name, err)
+		return err
+	}
+	tools, err := cl.ListTools(ictx)
+	if err != nil {
+		// A server with no tools capability is still a usable resource server.
+		log.Printf("mcp: %s: list tools: %v", name, err)
+		tools = nil
+	}
+	tools = filterTools(cfg, tools)
+
+	m.mu.Lock()
+	if old := m.conns[name].client; old != nil {
+		_ = old.Close()
+	}
+	m.conns[name].client = cl
+	m.conns[name].tools = tools
+	m.conns[name].lastErr = nil
+	m.conns[name].dialedAt = time.Now()
+	m.mu.Unlock()
+	log.Printf("mcp: %s connected (%s %s), %d tool(s)", name, cl.Info().Name, cl.Info().Version, len(tools))
+	return nil
+}
+
+func (m *Manager) fail(name string, err error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if c := m.conns[name]; c != nil {
+		c.lastErr = err
+		c.client = nil
+		c.tools = nil
+	}
+}
+
+// filterTools applies AllowTools and MaxTools, and drops nameless entries.
+// Sorted first, so the cap is deterministic rather than "whatever order the
+// server felt like".
+func filterTools(cfg ServerConfig, in []Tool) []Tool {
+	sort.Slice(in, func(i, j int) bool { return in[i].Name < in[j].Name })
+	out := make([]Tool, 0, len(in))
+	for _, t := range in {
+		if len(cfg.AllowTools) > 0 && !contains(cfg.AllowTools, t.Name) {
+			continue
+		}
+		out = append(out, t)
+	}
+	if cfg.MaxTools > 0 && len(out) > cfg.MaxTools {
+		log.Printf("mcp: %s offers %d tools, taking the first %d (raise max_tools or set allow_tools)",
+			cfg.Name, len(out), cfg.MaxTools)
+		out = out[:cfg.MaxTools]
+	}
+	return out
+}
+
+func contains(hay []string, needle string) bool {
+	for _, h := range hay {
+		if h == needle {
+			return true
+		}
+	}
+	return false
+}
+
+// Refresh re-dials any server that is down, if enough time has passed since the
+// last attempt. Call it from the daemon's periodic tick — it is cheap when
+// everything is up.
+func (m *Manager) Refresh(ctx context.Context) {
+	now := time.Now()
+	var stale []string
+	m.mu.Lock()
+	for _, name := range m.order {
+		c := m.conns[name]
+		down := c.client == nil || !c.client.alive()
+		if down && now.Sub(c.lastTry) >= DefaultReconnectEvery {
+			stale = append(stale, name)
+		}
+	}
+	m.mu.Unlock()
+	for _, name := range stale {
+		if err := m.dial(ctx, name); err != nil {
+			log.Printf("mcp: %s: reconnect: %v", name, err)
+		}
+	}
+}
+
+// Tools — every discovered tool across connected servers, sorted by
+// server then name.
+func (m *Manager) Tools() []Tool {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	var out []Tool
+	for _, name := range m.order {
+		out = append(out, m.conns[name].tools...)
+	}
+	return out
+}
+
+// Status is one server's health, for the web surface.
+type Status struct {
+	Name      string
+	Transport string // "stdio" or "http"
+	Target    string // command or url
+	Connected bool
+	Server    string // the server's own name+version
+	Tools     int
+	Err       string
+}
+
+// Status reports every configured server.
+func (m *Manager) Status() []Status {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	out := make([]Status, 0, len(m.order))
+	for _, name := range m.order {
+		c := m.conns[name]
+		s := Status{Name: name, Tools: len(c.tools)}
+		if c.cfg.Command != "" {
+			s.Transport, s.Target = "stdio", strings.Join(append([]string{c.cfg.Command}, c.cfg.Args...), " ")
+		} else {
+			s.Transport, s.Target = "http", c.cfg.URL
+		}
+		if c.client != nil {
+			s.Connected = true
+			s.Server = strings.TrimSpace(c.client.Info().Name + " " + c.client.Info().Version)
+		}
+		if c.lastErr != nil {
+			s.Err = c.lastErr.Error()
+		}
+		out = append(out, s)
+	}
+	return out
+}
+
+// Call runs server's tool with args. Args come from the router and nothing
+// else; there is no path here through which a note or a fact could travel.
+func (m *Manager) Call(ctx context.Context, server, tool string, args map[string]any) (string, error) {
+	m.mu.Lock()
+	c := m.conns[server]
+	m.mu.Unlock()
+	if c == nil {
+		return "", fmt.Errorf("%w: %s", ErrNoServer, server)
+	}
+	m.mu.Lock()
+	cl, timeout, known := c.client, c.cfg.Timeout, false
+	for _, t := range c.tools {
+		if t.Name == tool {
+			known = true
+			break
+		}
+	}
+	m.mu.Unlock()
+	if cl == nil {
+		return "", fmt.Errorf("mcp: %s is not connected", server)
+	}
+	// The discovered-and-filtered set is the second allowlist: even an enabled
+	// store row cannot reach a tool the server stopped offering, or one
+	// allow_tools excludes.
+	if !known {
+		return "", fmt.Errorf("mcp: %s offers no tool %q", server, tool)
+	}
+	cctx, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+	return cl.CallTool(cctx, tool, args)
+}
+
+// Resources lists resources across connected servers.
+func (m *Manager) Resources(ctx context.Context) []Resource {
+	m.mu.Lock()
+	clients := make([]*Client, 0, len(m.order))
+	for _, name := range m.order {
+		if cl := m.conns[name].client; cl != nil {
+			clients = append(clients, cl)
+		}
+	}
+	m.mu.Unlock()
+	var out []Resource
+	for _, cl := range clients {
+		rs, err := cl.ListResources(ctx)
+		if err != nil {
+			continue // no resources capability; not an error worth logging per tick
+		}
+		out = append(out, rs...)
+	}
+	return out
+}
+
+// ReadResource reads one resource from one server.
+func (m *Manager) ReadResource(ctx context.Context, server, uri string) (string, error) {
+	m.mu.Lock()
+	c := m.conns[server]
+	var cl *Client
+	var timeout time.Duration
+	if c != nil {
+		cl, timeout = c.client, c.cfg.Timeout
+	}
+	m.mu.Unlock()
+	if cl == nil {
+		return "", fmt.Errorf("%w: %s", ErrNoServer, server)
+	}
+	cctx, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+	return cl.ReadResource(cctx, uri)
+}
+
+// Close shuts every connection down.
+func (m *Manager) Close() error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	for _, name := range m.order {
+		if cl := m.conns[name].client; cl != nil {
+			_ = cl.Close()
+			m.conns[name].client = nil
+		}
+	}
+	return nil
+}
+
+// ErrNeedsArgs — the tool requires arguments that a voice verb cannot supply.
+var ErrNeedsArgs = errors.New("mcp: tool needs named arguments")
+
+// CallPositional is the voice path's way in. The router gives an act a verb and
+// a tail of positional words; an MCP tool wants a named-argument object. There
+// is no general mapping between those two, and inventing one is exactly the
+// improvisation this codebase refuses, so the rule is deliberately narrow:
+//
+//   - a tool with no required properties runs with no arguments (a spare tail
+//     is ignored — "покажи проекты пожалуйста" should still list projects);
+//   - a READ-ONLY tool with exactly one required property, of type string or
+//     integer/number, gets the tail bound to it;
+//   - anything else is refused with ErrNeedsArgs. Such a tool is still callable
+//     with explicit arguments from the authed surface, where a human types
+//     them.
+//
+// The refusal is the point, and the read-only condition on it was learned the
+// hard way while testing against the Vikunja server: `update_task` requires
+// only `task_id` and takes every other field as optional, so calling it with
+// one guessed argument and no others BLANKED the fields it did not receive. A
+// mutating tool therefore never gets a guessed argument — the one thing a
+// partially-filled write can do is destroy what it did not mention. A mutating
+// tool with nothing required is still fine: nothing was guessed, and it still
+// goes through the confirm turn.
+func (m *Manager) CallPositional(ctx context.Context, server, tool string, args []string) (string, error) {
+	m.mu.Lock()
+	c := m.conns[server]
+	var schema json.RawMessage
+	found, readOnly := false, false
+	if c != nil {
+		for _, t := range c.tools {
+			if t.Name == tool {
+				schema, readOnly, found = t.InputSchema, t.ReadOnly, true
+				break
+			}
+		}
+	}
+	m.mu.Unlock()
+	if !found {
+		return "", fmt.Errorf("mcp: %s offers no tool %q", server, tool)
+	}
+	named, err := bindPositional(schema, args, readOnly)
+	if err != nil {
+		return "", err
+	}
+	return m.Call(ctx, server, tool, named)
+}
+
+// bindPositional implements the rule documented on CallPositional.
+func bindPositional(schema json.RawMessage, args []string, readOnly bool) (map[string]any, error) {
+	var s struct {
+		Required   []string `json:"required"`
+		Properties map[string]struct {
+			Type string `json:"type"`
+		} `json:"properties"`
+	}
+	if len(schema) > 0 {
+		if err := json.Unmarshal(schema, &s); err != nil {
+			return nil, fmt.Errorf("mcp: unreadable input schema: %w", err)
+		}
+	}
+	switch len(s.Required) {
+	case 0:
+		return map[string]any{}, nil
+	case 1:
+		name := s.Required[0]
+		if !readOnly {
+			return nil, fmt.Errorf("%w: %q, and a tool that writes never gets a guessed one", ErrNeedsArgs, name)
+		}
+		tail := strings.TrimSpace(strings.Join(args, " "))
+		if tail == "" {
+			return nil, fmt.Errorf("%w: %q", ErrNeedsArgs, name)
+		}
+		switch s.Properties[name].Type {
+		case "string", "":
+			return map[string]any{name: tail}, nil
+		case "integer", "number":
+			n, err := strconv.ParseFloat(tail, 64)
+			if err != nil {
+				return nil, fmt.Errorf("%w: %q wants a number, got %q", ErrNeedsArgs, name, tail)
+			}
+			return map[string]any{name: n}, nil
+		default:
+			return nil, fmt.Errorf("%w: %q is a %s", ErrNeedsArgs, name, s.Properties[name].Type)
+		}
+	default:
+		return nil, fmt.Errorf("%w: %s", ErrNeedsArgs, strings.Join(s.Required, ", "))
+	}
+}

internal/mcp/mcp_test.go

@@ -0,0 +1,565 @@
+package mcp
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+)
+
+// fakePoster answers POSTs from a canned handler, in either JSON or SSE form.
+type fakePoster struct {
+	mu      sync.Mutex
+	handler func(method string, params json.RawMessage) (any, *rpcError)
+	sse     bool
+	session string
+	seen    []map[string]string // headers of each request, for the session test
+	calls   []string
+}
+
+func (f *fakePoster) Post(_ context.Context, _, _ string, body []byte, hdr map[string]string) (*PostResponse, error) {
+	var req struct {
+		ID     *int64          `json:"id"`
+		Method string          `json:"method"`
+		Params json.RawMessage `json:"params"`
+	}
+	if err := json.Unmarshal(body, &req); err != nil {
+		return nil, err
+	}
+	f.mu.Lock()
+	f.seen = append(f.seen, hdr)
+	f.calls = append(f.calls, req.Method)
+	f.mu.Unlock()
+
+	if req.ID == nil { // notification
+		return &PostResponse{Status: 202, Body: []byte(`{}`)}, nil
+	}
+	result, rerr := f.handler(req.Method, req.Params)
+	resp := map[string]any{"jsonrpc": "2.0", "id": *req.ID}
+	if rerr != nil {
+		resp["error"] = map[string]any{"code": rerr.Code, "message": rerr.Message}
+	} else {
+		resp["result"] = result
+	}
+	raw, _ := json.Marshal(resp)
+	out := &PostResponse{Status: 200, Body: raw, ContentType: "application/json", Header: map[string]string{}}
+	if f.sse {
+		out.ContentType = "text/event-stream"
+		out.Body = []byte("event: message\ndata: {\"jsonrpc\":\"2.0\",\"method\":\"notifications/progress\"}\n\nevent: message\ndata: " + string(raw) + "\n\n")
+	}
+	if f.session != "" {
+		out.Header["Mcp-Session-Id"] = f.session
+	}
+	return out, nil
+}
+
+// echoServer is a handler with two tools, one read-only and one not.
+func echoServer() func(string, json.RawMessage) (any, *rpcError) {
+	return func(method string, params json.RawMessage) (any, *rpcError) {
+		switch method {
+		case "initialize":
+			return map[string]any{
+				"protocolVersion": ProtocolVersion,
+				"serverInfo":      map[string]any{"name": "fake", "version": "0.1"},
+			}, nil
+		case "tools/list":
+			return map[string]any{"tools": []any{
+				map[string]any{
+					"name": "read_thing", "description": "reads",
+					"inputSchema": map[string]any{"type": "object"},
+					"annotations": map[string]any{"readOnlyHint": true},
+				},
+				map[string]any{"name": "break_thing", "description": "mutates"},
+			}}, nil
+		case "tools/call":
+			var p struct {
+				Name string         `json:"name"`
+				Args map[string]any `json:"arguments"`
+			}
+			_ = json.Unmarshal(params, &p)
+			if p.Name == "break_thing" {
+				return map[string]any{"isError": true, "content": []any{
+					map[string]any{"type": "text", "text": "не вышло"}}}, nil
+			}
+			return map[string]any{"content": []any{
+				map[string]any{"type": "text", "text": fmt.Sprintf("%s:%v", p.Name, p.Args["q"])},
+				map[string]any{"type": "image", "text": "ignored"},
+			}}, nil
+		case "resources/list":
+			return map[string]any{"resources": []any{
+				map[string]any{"uri": "note://one", "name": "one", "mimeType": "text/plain"},
+				map[string]any{"uri": "", "name": "nameless"},
+			}}, nil
+		case "resources/read":
+			return map[string]any{"contents": []any{map[string]any{"text": "тело ресурса"}}}, nil
+		}
+		return nil, &rpcError{Code: -32601, Message: "method not found"}
+	}
+}
+
+func dialFake(t *testing.T, p *fakePoster) *Client {
+	t.Helper()
+	c := newClient("fake", newHTTPTransport(p, "http://example.test/mcp"))
+	if err := c.Initialize(context.Background()); err != nil {
+		t.Fatalf("initialize: %v", err)
+	}
+	return c
+}
+
+func TestHandshakeAndDiscovery(t *testing.T) {
+	for _, sse := range []bool{false, true} {
+		name := "json"
+		if sse {
+			name = "sse"
+		}
+		t.Run(name, func(t *testing.T) {
+			p := &fakePoster{handler: echoServer(), sse: sse}
+			c := dialFake(t, p)
+			if got := c.Info().Name; got != "fake" {
+				t.Fatalf("server name = %q", got)
+			}
+			if got := c.Info().ProtocolVersion; got != ProtocolVersion {
+				t.Fatalf("protocol = %q", got)
+			}
+			tools, err := c.ListTools(context.Background())
+			if err != nil {
+				t.Fatalf("list tools: %v", err)
+			}
+			if len(tools) != 2 {
+				t.Fatalf("tools = %+v", tools)
+			}
+			byName := map[string]Tool{}
+			for _, tl := range tools {
+				byName[tl.Name] = tl
+			}
+			if !byName["read_thing"].ReadOnly {
+				t.Error("read_thing should be read-only (readOnlyHint true)")
+			}
+			// The important direction: no annotation ⇒ assume it mutates.
+			if byName["break_thing"].ReadOnly {
+				t.Error("break_thing has no readOnlyHint, must NOT be treated as read-only")
+			}
+			if byName["read_thing"].Server != "fake" {
+				t.Error("tool should carry its server handle")
+			}
+		})
+	}
+}
+
+func TestCallToolTextOnly(t *testing.T) {
+	c := dialFake(t, &fakePoster{handler: echoServer()})
+	out, err := c.CallTool(context.Background(), "read_thing", map[string]any{"q": "привет"})
+	if err != nil {
+		t.Fatalf("call: %v", err)
+	}
+	if out != "read_thing:привет" {
+		t.Fatalf("out = %q (non-text content must be dropped)", out)
+	}
+}
+
+func TestCallToolErrorResult(t *testing.T) {
+	c := dialFake(t, &fakePoster{handler: echoServer()})
+	out, err := c.CallTool(context.Background(), "break_thing", nil)
+	if err == nil {
+		t.Fatal("isError result must surface as an error")
+	}
+	if out != "не вышло" {
+		t.Fatalf("text should still come back, got %q", out)
+	}
+}
+
+func TestResources(t *testing.T) {
+	c := dialFake(t, &fakePoster{handler: echoServer()})
+	rs, err := c.ListResources(context.Background())
+	if err != nil {
+		t.Fatalf("list resources: %v", err)
+	}
+	if len(rs) != 1 || rs[0].URI != "note://one" {
+		t.Fatalf("resources = %+v (a uri-less entry must be dropped)", rs)
+	}
+	body, err := c.ReadResource(context.Background(), "note://one")
+	if err != nil {
+		t.Fatalf("read: %v", err)
+	}
+	if body != "тело ресурса" {
+		t.Fatalf("body = %q", body)
+	}
+}
+
+func TestCallBeforeInitializeRefused(t *testing.T) {
+	c := newClient("fake", newHTTPTransport(&fakePoster{handler: echoServer()}, "http://example.test/mcp"))
+	if _, err := c.CallTool(context.Background(), "read_thing", nil); err != ErrNotInitialized {
+		t.Fatalf("err = %v, want ErrNotInitialized", err)
+	}
+}
+
+func TestSessionIDEchoed(t *testing.T) {
+	p := &fakePoster{handler: echoServer(), session: "sess-1"}
+	c := dialFake(t, p)
+	if _, err := c.ListTools(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	last := p.seen[len(p.seen)-1]
+	if last["Mcp-Session-Id"] != "sess-1" {
+		t.Fatalf("session header not echoed: %+v", last)
+	}
+	if !strings.Contains(last["Accept"], "text/event-stream") {
+		t.Fatalf("Accept must offer both forms: %q", last["Accept"])
+	}
+}
+
+func TestHandshakeWithoutProtocolVersionRefused(t *testing.T) {
+	p := &fakePoster{handler: func(m string, _ json.RawMessage) (any, *rpcError) {
+		return map[string]any{"serverInfo": map[string]any{"name": "not-mcp"}}, nil
+	}}
+	c := newClient("x", newHTTPTransport(p, "http://example.test/mcp"))
+	if err := c.Initialize(context.Background()); err == nil {
+		t.Fatal("a reply with no protocolVersion is not an MCP server")
+	}
+}
+
+func TestRPCErrorSurfaces(t *testing.T) {
+	c := dialFake(t, &fakePoster{handler: echoServer()})
+	if _, err := c.callRaw(context.Background(), "nope/nope"); err == nil {
+		t.Fatal("want an rpc error")
+	} else if !strings.Contains(err.Error(), "method not found") {
+		t.Fatalf("err = %v", err)
+	}
+}
+
+// callRaw is a test-only shim so the rpc-error path can be exercised without a
+// typed wrapper for a method the server does not implement.
+func (c *Client) callRaw(ctx context.Context, method string) (any, error) {
+	var out any
+	err := c.call(ctx, method, map[string]any{}, &out)
+	return out, err
+}
+
+func TestDecodeFrame(t *testing.T) {
+	cases := []struct {
+		name, in, want string
+		wantErr        bool
+	}{
+		{name: "plain json", in: `{"id":1,"result":{}}`, want: `{"id":1,"result":{}}`},
+		{name: "sse single", in: "event: message\ndata: {\"id\":1,\"result\":1}\n\n", want: `{"id":1,"result":1}`},
+		{
+			name: "sse picks the response not the notification",
+			in:   "data: {\"method\":\"notifications/progress\"}\n\ndata: {\"id\":2,\"result\":2}\n\n",
+			want: `{"id":2,"result":2}`,
+		},
+		{name: "empty", in: "  ", wantErr: true},
+		{name: "sse with no response", in: "data: {\"method\":\"x\"}\n\n", wantErr: true},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := decodeFrame([]byte(tc.in))
+			if tc.wantErr {
+				if err == nil {
+					t.Fatalf("want error, got %q", got)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			if string(got) != tc.want {
+				t.Fatalf("got %q want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestValidate(t *testing.T) {
+	cases := []struct {
+		name    string
+		cfg     ServerConfig
+		wantErr bool
+	}{
+		{name: "stdio ok", cfg: ServerConfig{Name: "a", Command: "echo"}},
+		{name: "http ok", cfg: ServerConfig{Name: "a", URL: "http://x.test/mcp"}},
+		{name: "no name", cfg: ServerConfig{Command: "echo"}, wantErr: true},
+		{name: "spacey name", cfg: ServerConfig{Name: "a b", Command: "echo"}, wantErr: true},
+		{name: "neither", cfg: ServerConfig{Name: "a"}, wantErr: true},
+		{name: "both", cfg: ServerConfig{Name: "a", Command: "echo", URL: "http://x.test"}, wantErr: true},
+		{name: "bad scheme", cfg: ServerConfig{Name: "a", URL: "file:///etc/passwd"}, wantErr: true},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := Validate([]ServerConfig{tc.cfg})
+			if (err != nil) != tc.wantErr {
+				t.Fatalf("err = %v, wantErr = %v", err, tc.wantErr)
+			}
+		})
+	}
+	if err := Validate([]ServerConfig{{Name: "a", Command: "x"}, {Name: "a", Command: "y"}}); err == nil {
+		t.Error("duplicate names must be refused")
+	}
+}
+
+func TestManagerOffWhenNothingEnabled(t *testing.T) {
+	m, err := NewManager(nil, []ServerConfig{{Name: "a", Command: "echo"}}) // Enabled=false
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !m.Empty() {
+		t.Fatal("a server that is not enabled must not be wired")
+	}
+	m.Connect(context.Background())
+	if got := m.Tools(); len(got) != 0 {
+		t.Fatalf("tools = %+v", got)
+	}
+}
+
+func TestManagerDiscoversAndCalls(t *testing.T) {
+	p := &fakePoster{handler: echoServer()}
+	m, err := NewManager(func(ServerConfig) (Poster, error) { return p, nil },
+		[]ServerConfig{{Name: "fake", URL: "http://example.test/mcp", Enabled: true}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	m.Connect(context.Background())
+	defer m.Close()
+
+	tools := m.Tools()
+	if len(tools) != 2 {
+		t.Fatalf("tools = %+v", tools)
+	}
+	out, err := m.Call(context.Background(), "fake", "read_thing", map[string]any{"q": "да"})
+	if err != nil {
+		t.Fatalf("call: %v", err)
+	}
+	if out != "read_thing:да" {
+		t.Fatalf("out = %q", out)
+	}
+	// The discovered set is a second allowlist.
+	if _, err := m.Call(context.Background(), "fake", "not_offered", nil); err == nil {
+		t.Error("a tool the server does not offer must be refused")
+	}
+	if _, err := m.Call(context.Background(), "other", "read_thing", nil); err == nil {
+		t.Error("an unconfigured server must be refused")
+	}
+	st := m.Status()
+	if len(st) != 1 || !st[0].Connected || st[0].Transport != "http" || st[0].Tools != 2 {
+		t.Fatalf("status = %+v", st)
+	}
+}
+
+func TestManagerAllowToolsAndMaxTools(t *testing.T) {
+	p := &fakePoster{handler: echoServer()}
+	mk := func(cfg ServerConfig) *Manager {
+		cfg.Name, cfg.URL, cfg.Enabled = "fake", "http://example.test/mcp", true
+		m, err := NewManager(func(ServerConfig) (Poster, error) { return p, nil }, []ServerConfig{cfg})
+		if err != nil {
+			t.Fatal(err)
+		}
+		m.Connect(context.Background())
+		return m
+	}
+	m := mk(ServerConfig{AllowTools: []string{"read_thing"}})
+	defer m.Close()
+	if got := m.Tools(); len(got) != 1 || got[0].Name != "read_thing" {
+		t.Fatalf("allow_tools ignored: %+v", got)
+	}
+	if _, err := m.Call(context.Background(), "fake", "break_thing", nil); err == nil {
+		t.Error("a tool excluded by allow_tools must be unreachable")
+	}
+	m2 := mk(ServerConfig{MaxTools: 1})
+	defer m2.Close()
+	if got := m2.Tools(); len(got) != 1 || got[0].Name != "break_thing" {
+		t.Fatalf("max_tools should keep the first name-sorted tool: %+v", got)
+	}
+}
+
+func TestManagerURLServerWithoutHTTPDoor(t *testing.T) {
+	m, err := NewManager(nil, []ServerConfig{{Name: "fake", URL: "http://example.test/mcp", Enabled: true}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	m.Connect(context.Background())
+	st := m.Status()
+	if len(st) != 1 || st[0].Connected || st[0].Err == "" {
+		t.Fatalf("a url server with no poster must be recorded as failed: %+v", st)
+	}
+}
+
+func TestManagerReconnectAfterFailure(t *testing.T) {
+	var mu sync.Mutex
+	fail := true
+	m, err := NewManager(func(ServerConfig) (Poster, error) {
+		mu.Lock()
+		defer mu.Unlock()
+		if fail {
+			return nil, fmt.Errorf("down")
+		}
+		return &fakePoster{handler: echoServer()}, nil
+	}, []ServerConfig{{Name: "fake", URL: "http://example.test/mcp", Enabled: true}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer m.Close()
+	m.Connect(context.Background())
+	if m.Status()[0].Connected {
+		t.Fatal("should be down")
+	}
+	mu.Lock()
+	fail = false
+	mu.Unlock()
+	// Refresh honours the backoff, so pretend the last attempt was long ago.
+	m.mu.Lock()
+	m.conns["fake"].lastTry = time.Now().Add(-2 * DefaultReconnectEvery)
+	m.mu.Unlock()
+	m.Refresh(context.Background())
+	if !m.Status()[0].Connected {
+		t.Fatalf("should have reconnected: %+v", m.Status())
+	}
+}
+
+func TestLocalNameAndCmd(t *testing.T) {
+	cases := [][3]string{
+		{"vikunja", "list_tasks", "vikunja_list_tasks"},
+		{"Vikunja", "Get Task Details", "vikunja_get_task_details"},
+		{"fs", "read-file", "fs_read_file"},
+		{"", "search", "search"},
+	}
+	for _, c := range cases {
+		if got := LocalName(c[0], c[1]); got != c[2] {
+			t.Errorf("LocalName(%q,%q) = %q want %q", c[0], c[1], got, c[2])
+		}
+	}
+	server, tool, ok := ParseCmd(Cmd("vikunja", "list_tasks"))
+	if !ok || server != "vikunja" || tool != "list_tasks" {
+		t.Fatalf("ParseCmd round-trip: %q %q %v", server, tool, ok)
+	}
+	for _, bad := range [][]string{nil, {"systemctl", "restart", "nginx"}, {"mcp", "vikunja"}, {"mcp", "", "x"}} {
+		if _, _, ok := ParseCmd(bad); ok {
+			t.Errorf("ParseCmd(%v) must not claim an ordinary tool row", bad)
+		}
+	}
+	if Scope("vikunja") != "mcp:vikunja" {
+		t.Error("scope")
+	}
+}
+
+func TestBindPositional(t *testing.T) {
+	cases := []struct {
+		name, schema string
+		args         []string
+		mutating     bool
+		want         map[string]any
+		wantErr      bool
+	}{
+		{
+			name: "no required runs with nothing",
+			// A spare tail is fine: "покажи проекты пожалуйста" still lists them.
+			schema: `{"type":"object","properties":{},"required":[]}`,
+			args:   []string{"пожалуйста"},
+			want:   map[string]any{},
+		},
+		{
+			name:   "empty schema",
+			schema: ``,
+			want:   map[string]any{},
+		},
+		{
+			name:   "one required string gets the tail",
+			schema: `{"properties":{"q":{"type":"string"}},"required":["q"]}`,
+			args:   []string{"почему", "небо", "синее"},
+			want:   map[string]any{"q": "почему небо синее"},
+		},
+		{
+			name:    "one required string with no tail",
+			schema:  `{"properties":{"q":{"type":"string"}},"required":["q"]}`,
+			wantErr: true,
+		},
+		{
+			name:   "one required integer parses",
+			schema: `{"properties":{"task_id":{"type":"integer"}},"required":["task_id"]}`,
+			args:   []string{"251"},
+			want:   map[string]any{"task_id": float64(251)},
+		},
+		{
+			name:    "one required integer with words",
+			schema:  `{"properties":{"task_id":{"type":"integer"}},"required":["task_id"]}`,
+			args:    []string{"двести", "пятьдесят", "один"},
+			wantErr: true,
+		},
+		{
+			name:    "two required is refused rather than guessed",
+			schema:  `{"properties":{"a":{"type":"string"},"b":{"type":"string"}},"required":["a","b"]}`,
+			args:    []string{"что-то"},
+			wantErr: true,
+		},
+		{
+			name:    "one required object is refused",
+			schema:  `{"properties":{"payload":{"type":"object"}},"required":["payload"]}`,
+			args:    []string{"что-то"},
+			wantErr: true,
+		},
+		{
+			// Learned from Vikunja's update_task: required ["task_id"], every
+			// other field optional, so one guessed argument blanks the rest.
+			name:     "one required on a mutating tool is refused",
+			schema:   `{"properties":{"task_id":{"type":"integer"}},"required":["task_id"]}`,
+			args:     []string{"251"},
+			mutating: true,
+			wantErr:  true,
+		},
+		{
+			// Nothing was guessed, so there is nothing to get wrong. It still
+			// goes through the confirm turn upstream.
+			name:     "no required on a mutating tool still runs",
+			schema:   `{"properties":{},"required":[]}`,
+			mutating: true,
+			want:     map[string]any{},
+		},
+		{
+			name:    "unreadable schema",
+			schema:  `not json`,
+			wantErr: true,
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := bindPositional(json.RawMessage(tc.schema), tc.args, !tc.mutating)
+			if tc.wantErr {
+				if err == nil {
+					t.Fatalf("want an error, got %v", got)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			if fmt.Sprint(got) != fmt.Sprint(tc.want) {
+				t.Fatalf("got %v want %v", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestCallPositionalThroughManager(t *testing.T) {
+	p := &fakePoster{handler: echoServer()}
+	m, err := NewManager(func(ServerConfig) (Poster, error) { return p, nil },
+		[]ServerConfig{{Name: "fake", URL: "http://example.test/mcp", Enabled: true}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	m.Connect(context.Background())
+	defer m.Close()
+	// echoServer's tools declare no required properties.
+	out, err := m.CallPositional(context.Background(), "fake", "read_thing", []string{"хвост"})
+	if err != nil {
+		t.Fatalf("call: %v", err)
+	}
+	if out != "read_thing:<nil>" {
+		t.Fatalf("out = %q", out)
+	}
+	if _, err := m.CallPositional(context.Background(), "fake", "absent", nil); err == nil {
+		t.Error("an unknown tool must be refused")
+	}
+}

internal/mcp/stdio.go

@@ -0,0 +1,149 @@
+package mcp
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+)
+
+// maxLine bounds one JSON-RPC frame from a subprocess. A tool result bigger
+// than this is a misbehaving server, not something to buffer.
+const maxLine = 1 << 20 // 1 MiB
+
+// stdioTransport speaks newline-delimited JSON-RPC to a child process. This is
+// the local transport: the server runs on this box, under this user, and gets
+// no network guard because it never touches the network on our behalf.
+//
+// Args are argv, never a shell string — the same discipline internal/tool
+// keeps, for the same reason.
+type stdioTransport struct {
+	mu   sync.Mutex
+	cmd  *exec.Cmd
+	in   io.WriteCloser
+	out  *bufio.Reader
+	dead bool
+}
+
+func newStdioTransport(ctx context.Context, argv []string, env []string, dir string) (*stdioTransport, error) {
+	if len(argv) == 0 {
+		return nil, errors.New("mcp: stdio server needs a command")
+	}
+	cmd := exec.Command(argv[0], argv[1:]...)
+	cmd.Dir = dir
+	if len(env) > 0 {
+		cmd.Env = append(os.Environ(), env...)
+	}
+	cmd.Stderr = os.Stderr
+	in, err := cmd.StdinPipe()
+	if err != nil {
+		return nil, fmt.Errorf("mcp: stdin pipe: %w", err)
+	}
+	out, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, fmt.Errorf("mcp: stdout pipe: %w", err)
+	}
+	if err := cmd.Start(); err != nil {
+		return nil, fmt.Errorf("mcp: start %q: %w", argv[0], err)
+	}
+	return &stdioTransport{cmd: cmd, in: in, out: bufio.NewReaderSize(out, 64<<10)}, nil
+}
+
+func (t *stdioTransport) Call(ctx context.Context, req *rpcRequest) (*rpcResponse, error) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.dead {
+		return nil, ErrClosed
+	}
+	if err := t.write(req); err != nil {
+		t.dead = true
+		return nil, err
+	}
+	// Read until the frame with our id turns up; anything else on the pipe is
+	// a notification or a server-initiated request we do not answer.
+	for {
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		line, err := t.readLine()
+		if err != nil {
+			t.dead = true
+			return nil, err
+		}
+		var resp rpcResponse
+		if err := json.Unmarshal(line, &resp); err != nil {
+			continue // not a response frame; ignore rather than break the turn
+		}
+		if resp.ID == nil || *resp.ID != req.ID {
+			continue
+		}
+		return &resp, nil
+	}
+}
+
+func (t *stdioTransport) Notify(ctx context.Context, method string, params any) error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.dead {
+		return ErrClosed
+	}
+	return t.write(&rpcRequest{JSONRPC: "2.0", Method: method, Params: params})
+}
+
+func (t *stdioTransport) write(req *rpcRequest) error {
+	req.JSONRPC = "2.0"
+	raw, err := json.Marshal(req)
+	if err != nil {
+		return err
+	}
+	if _, err := t.in.Write(append(raw, '\n')); err != nil {
+		return fmt.Errorf("mcp: write %s: %w", req.Method, err)
+	}
+	return nil
+}
+
+func (t *stdioTransport) readLine() ([]byte, error) {
+	for {
+		line, err := t.out.ReadString('\n')
+		if err != nil {
+			if len(strings.TrimSpace(line)) == 0 {
+				return nil, fmt.Errorf("mcp: read: %w", err)
+			}
+			return []byte(line), nil
+		}
+		if len(line) > maxLine {
+			return nil, fmt.Errorf("mcp: frame exceeds %d bytes", maxLine)
+		}
+		if s := strings.TrimSpace(line); s != "" {
+			return []byte(s), nil
+		}
+	}
+}
+
+func (t *stdioTransport) Close() error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	t.dead = true
+	if t.in != nil {
+		_ = t.in.Close()
+	}
+	if t.cmd.Process != nil {
+		_ = t.cmd.Process.Kill()
+		_ = t.cmd.Wait()
+	}
+	return nil
+}
+
+// alive reports whether the transport can still carry a call. The manager uses
+// it to decide on a reconnect instead of retrying into a dead pipe.
+func (t *stdioTransport) alive() bool {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return !t.dead
+}

internal/mcp/stdio_test.go

@@ -0,0 +1,149 @@
+package mcp
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+)
+
+// The stdio transport is tested against a real subprocess — this test binary,
+// re-executed with MAVEN_MCP_FAKE set, acting as a minimal MCP server. No
+// python, no fixture file, no network.
+func TestMain(m *testing.M) {
+	if os.Getenv("MAVEN_MCP_FAKE") != "" {
+		fakeStdioServer()
+		return
+	}
+	os.Exit(m.Run())
+}
+
+func fakeStdioServer() {
+	h := echoServer()
+	sc := bufio.NewScanner(os.Stdin)
+	out := bufio.NewWriter(os.Stdout)
+	defer out.Flush()
+	for sc.Scan() {
+		line := strings.TrimSpace(sc.Text())
+		if line == "" {
+			continue
+		}
+		var req struct {
+			ID     *int64          `json:"id"`
+			Method string          `json:"method"`
+			Params json.RawMessage `json:"params"`
+		}
+		if json.Unmarshal([]byte(line), &req) != nil {
+			continue
+		}
+		if req.ID == nil {
+			// A notification gets no reply, but we emit an unrelated
+			// notification so the client's frame-skipping is exercised.
+			_, _ = out.WriteString("{\"jsonrpc\":\"2.0\",\"method\":\"notifications/message\"}\n")
+			_ = out.Flush()
+			continue
+		}
+		result, rerr := h(req.Method, req.Params)
+		resp := map[string]any{"jsonrpc": "2.0", "id": *req.ID}
+		if rerr != nil {
+			resp["error"] = map[string]any{"code": rerr.Code, "message": rerr.Message}
+		} else {
+			resp["result"] = result
+		}
+		raw, _ := json.Marshal(resp)
+		_, _ = out.Write(append(raw, '\n'))
+		_ = out.Flush()
+		if os.Getenv("MAVEN_MCP_FAKE") == "die" && req.Method == "tools/list" {
+			return // hang up, so the reconnect path has something to see
+		}
+	}
+}
+
+func stdioManager(t *testing.T, mode string) *Manager {
+	t.Helper()
+	self, err := os.Executable()
+	if err != nil {
+		t.Skipf("no executable path: %v", err)
+	}
+	if _, err := exec.LookPath(self); err != nil && !strings.Contains(self, "/") {
+		t.Skip("test binary not executable")
+	}
+	m, err := NewManager(nil, []ServerConfig{{
+		Name:    "fake",
+		Command: self,
+		Env:     []string{"MAVEN_MCP_FAKE=" + mode},
+		Enabled: true,
+	}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	m.Connect(context.Background())
+	return m
+}
+
+func TestStdioTransportEndToEnd(t *testing.T) {
+	m := stdioManager(t, "1")
+	defer m.Close()
+	st := m.Status()
+	if len(st) != 1 || !st[0].Connected {
+		t.Fatalf("status = %+v", st)
+	}
+	if st[0].Transport != "stdio" {
+		t.Fatalf("transport = %q", st[0].Transport)
+	}
+	if got := len(m.Tools()); got != 2 {
+		t.Fatalf("tools = %d", got)
+	}
+	out, err := m.Call(context.Background(), "fake", "read_thing", map[string]any{"q": "стдио"})
+	if err != nil {
+		t.Fatalf("call: %v", err)
+	}
+	if out != "read_thing:стдио" {
+		t.Fatalf("out = %q", out)
+	}
+	res := m.Resources(context.Background())
+	if len(res) != 1 || res[0].URI != "note://one" {
+		t.Fatalf("resources = %+v", res)
+	}
+	body, err := m.ReadResource(context.Background(), "fake", "note://one")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if body != "тело ресурса" {
+		t.Fatalf("body = %q", body)
+	}
+}
+
+func TestStdioServerThatDiesIsNotUsable(t *testing.T) {
+	m := stdioManager(t, "die")
+	defer m.Close()
+	// The server hung up after tools/list; the next call must fail cleanly
+	// rather than hang or panic.
+	if _, err := m.Call(context.Background(), "fake", "read_thing", nil); err == nil {
+		t.Fatal("a call into a dead server must error")
+	}
+}
+
+func TestStdioMissingCommand(t *testing.T) {
+	m, err := NewManager(nil, []ServerConfig{{
+		Name: "nope", Command: "/nonexistent/mcp-server-that-is-not-there", Enabled: true,
+	}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	m.Connect(context.Background())
+	st := m.Status()
+	if st[0].Connected || st[0].Err == "" {
+		t.Fatalf("a missing binary must be recorded, not fatal: %+v", st)
+	}
+	if got := len(m.Tools()); got != 0 {
+		t.Fatalf("tools = %d", got)
+	}
+	if !strings.Contains(fmt.Sprint(st[0].Err), "start") {
+		t.Logf("err = %q", st[0].Err)
+	}
+}

internal/mcp/webfetchdoor.go

@@ -0,0 +1,46 @@
+package mcp
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/kami/maven/internal/webfetch"
+)
+
+// WebfetchDoor builds the PosterFactory used in production: one guarded
+// webfetch.Fetcher per url server, with that server's allow_private and the
+// shared host lists and limits.
+//
+// One fetcher PER server is the point. allow_private is a hole in the
+// private-address guard, and a hole punched for the Vikunja server on loopback
+// must not become a hole for some public endpoint that happens to redirect at
+// the LAN. Rate limiting is per fetcher too, which is the right shape here:
+// separate servers are separate hosts.
+func WebfetchDoor(limits webfetch.Config) PosterFactory {
+	return func(cfg ServerConfig) (Poster, error) {
+		c := limits
+		c.AllowPrivate = cfg.AllowPrivate
+		if c.Timeout <= 0 && cfg.Timeout > 0 {
+			c.Timeout = cfg.Timeout
+		}
+		return fetcherPoster{webfetch.New(c)}, nil
+	}
+}
+
+// fetcherPoster adapts webfetch.Fetcher to Poster. It exists so this package
+// does not have to know webfetch's Response type, and so a test can substitute
+// a fake without a listener.
+type fetcherPoster struct{ f *webfetch.Fetcher }
+
+func (p fetcherPoster) Post(ctx context.Context, rawURL, contentType string, body []byte, hdr map[string]string) (*PostResponse, error) {
+	resp, err := p.f.Post(ctx, rawURL, contentType, body, hdr)
+	if err != nil {
+		return nil, fmt.Errorf("mcp: post %s: %w", rawURL, err)
+	}
+	return &PostResponse{
+		Status:      resp.Status,
+		ContentType: resp.ContentType,
+		Body:        resp.Body,
+		Header:      resp.Header,
+	}, nil
+}

internal/store/tools.go

@@ -56,6 +56,45 @@ func (s *Store) ProposeTool(ctx context.Context, name, utterance, scope string,
 	return n > 0, nil
 }
 
+// ProposeMCPTool is ProposeTool for a tool discovered on an MCP server
+// (Vikunja #251): the proposal already knows what it would run, so cmd and
+// destructive are written with it and Kami only has to press enable.
+//
+// It is still a PROPOSAL. Discovery cannot grant a capability — that is the
+// whole reason a server can be configured without its tools becoming live.
+// Like ProposeTool it never touches an existing row, so re-discovery on every
+// restart is idempotent and cannot silently re-arm a tool that was disabled or
+// change the cmd of one already enabled.
+func (s *Store) ProposeMCPTool(ctx context.Context, name, scope string, cmd []string, destructive bool, utterance string, ts time.Time) (bool, error) {
+	if len(cmd) == 0 {
+		return false, ErrToolCmd
+	}
+	if scope == "" {
+		scope = "homelab"
+	}
+	raw, err := json.Marshal(cmd)
+	if err != nil {
+		return false, fmt.Errorf("propose mcp tool: %w", err)
+	}
+	d := 0
+	if destructive {
+		d = 1
+	}
+	res, err := s.db.ExecContext(ctx, `
+		INSERT INTO tools (name, scope, cmd, destructive, status, utterance, created_ts, updated_ts)
+		VALUES (?, ?, ?, ?, 'proposed', ?, ?, ?)
+		ON CONFLICT(name) DO NOTHING`,
+		name, scope, string(raw), d, utterance, ts.UnixMilli(), ts.UnixMilli())
+	if err != nil {
+		return false, fmt.Errorf("propose mcp tool: %w", err)
+	}
+	n, err := res.RowsAffected()
+	if err != nil {
+		return false, fmt.Errorf("propose mcp tool: rows affected: %w", err)
+	}
+	return n > 0, nil
+}
+
 // EnableTool fills cmd + destructive and flips status to 'enabled'. This is the
 // human "enable" act (the authed surface calls it); it upserts so enabling a
 // name that was never proposed still works. An empty cmd is refused — an

internal/store/tools_test.go

@@ -2,6 +2,7 @@ package store
 
 import (
 	"context"
+	"errors"
 	"testing"
 	"time"
 )
@@ -60,3 +61,64 @@ func TestToolLifecycle(t *testing.T) {
 		t.Fatalf("disable absent must be no-op: %v", err)
 	}
 }
+
+// A discovered MCP tool arrives as a proposal that already knows its cmd, so
+// enabling it is one click rather than one retyped argv.
+func TestProposeMCPTool(t *testing.T) {
+	s := newTestStore(t)
+	ctx := context.Background()
+	now := time.Now()
+	cmd := []string{"mcp", "vikunja", "list_tasks"}
+
+	fresh, err := s.ProposeMCPTool(ctx, "vikunja_list_tasks", "mcp:vikunja", cmd, false, "mcp vikunja/list_tasks: List tasks", now)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !fresh {
+		t.Fatal("first proposal should be new")
+	}
+	got, err := s.LookupTool(ctx, "vikunja_list_tasks")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Status != "proposed" {
+		t.Fatalf("status = %q — discovery must never enable", got.Status)
+	}
+	if len(got.Cmd) != 3 || got.Cmd[0] != "mcp" || got.Cmd[2] != "list_tasks" {
+		t.Fatalf("cmd = %v", got.Cmd)
+	}
+	if got.Scope != "mcp:vikunja" || got.Utterance == "" {
+		t.Fatalf("provenance lost: %+v", got)
+	}
+
+	// Re-discovery on the next boot is idempotent.
+	fresh, err = s.ProposeMCPTool(ctx, "vikunja_list_tasks", "mcp:vikunja", cmd, true, "changed", now)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if fresh {
+		t.Error("re-proposing an existing row must report nothing new")
+	}
+
+	// And it must not re-arm or rewrite a row a human already acted on.
+	if err := s.EnableTool(ctx, "vikunja_list_tasks", cmd, false, "mcp:vikunja", now); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := s.ProposeMCPTool(ctx, "vikunja_list_tasks", "mcp:vikunja", []string{"mcp", "vikunja", "delete_task"}, true, "x", now); err != nil {
+		t.Fatal(err)
+	}
+	got, err = s.LookupTool(ctx, "vikunja_list_tasks")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Status != "enabled" || got.Cmd[2] != "list_tasks" || got.Destructive {
+		t.Fatalf("an enabled row was modified by discovery: %+v", got)
+	}
+}
+
+func TestProposeMCPToolNeedsCmd(t *testing.T) {
+	s := newTestStore(t)
+	if _, err := s.ProposeMCPTool(context.Background(), "x", "mcp:y", nil, false, "", time.Now()); !errors.Is(err, ErrToolCmd) {
+		t.Fatalf("err = %v, want ErrToolCmd", err)
+	}
+}

internal/tool/tool.go

@@ -13,6 +13,11 @@
 //   - Args are passed as argv, NEVER through a shell. STT text lands as
 //     positional arguments to Cmd; there is no `sh -c`, so "restart nginx;
 //     rm -rf" can't inject — the tail is one argv element to the named binary.
+//   - An enabled row whose cmd is ["mcp", "<server>", "<tool>"] is a call to a
+//     configured MCP server instead of a process (Vikunja #251). It goes
+//     through every rule above unchanged — enabled, and confirmed if it
+//     mutates — because the store is still the allowlist; only the dispatch at
+//     the bottom of Exec differs.
 //   - Destructive tools don't run on first hearing: Exec returns ErrNeedsConfirm
 //     and the handler runs a confirm turn ("выполнить X? да/нет"); only a
 //     confirmed re-Exec runs them. A gate assumes a fully-formed action, which
@@ -31,6 +36,7 @@ import (
 	"time"
 
 	"github.com/kami/maven/internal/ipc"
+	"github.com/kami/maven/internal/mcp"
 	"github.com/kami/maven/internal/router"
 )
 
@@ -50,12 +56,21 @@ var (
 	ErrNeedsConfirm = errors.New("destructive tool needs confirmation")
 )
 
+// MCPCaller is the seam for an act that is an MCP tool call rather than a
+// process (Vikunja #251). internal/mcp.Manager satisfies it via CallPositional.
+// nil ⇒ MCP is not configured, and an MCP row refuses to run rather than
+// silently doing nothing.
+type MCPCaller interface {
+	CallPositional(ctx context.Context, server, tool string, args []string) (string, error)
+}
+
 // Executor runs enabled tools. run is the exec seam (default: real process);
 // tests swap it. timeout bounds each invocation.
 type Executor struct {
 	api     API
 	timeout time.Duration
 	run     func(ctx context.Context, argv []string) (string, error)
+	mcp     MCPCaller
 }
 
 // NewExecutor builds the executor. timeout<=0 defaults to 30s.
@@ -66,6 +81,13 @@ func NewExecutor(api API, timeout time.Duration) *Executor {
 	return &Executor{api: api, timeout: timeout, run: runProcess}
 }
 
+// WithMCP attaches the MCP caller. Called once at wiring time when the mcp
+// config block is present; without it, a row whose cmd is ["mcp", …] refuses.
+func (e *Executor) WithMCP(m MCPCaller) *Executor {
+	e.mcp = m
+	return e
+}
+
 // Exec looks up name in the store and runs Cmd+args as argv (no shell).
 // confirmed=true is the second turn of a destructive act (the user said "да");
 // it bypasses the ErrNeedsConfirm gate. Non-enabled ⇒ ErrNotEnabled; a
@@ -84,6 +106,17 @@ func (e *Executor) Exec(ctx context.Context, name string, args []string, confirm
 	if t.Destructive && !confirmed {
 		return "", ErrNeedsConfirm
 	}
+	// An MCP row is a call to a configured server, not a process. Everything
+	// above still applied: it had to be enabled, and a mutating one had to be
+	// confirmed. Only the dispatch differs.
+	if server, remote, ok := mcp.ParseCmd(t.Cmd); ok {
+		if e.mcp == nil {
+			return "", ErrNotEnabled
+		}
+		ctx, cancel := context.WithTimeout(ctx, e.timeout)
+		defer cancel()
+		return e.mcp.CallPositional(ctx, server, remote, args)
+	}
 	argv := append(append([]string(nil), t.Cmd...), args...)
 	if len(argv) == 0 {
 		return "", ErrNotEnabled

internal/tool/tool_test.go

@@ -85,3 +85,103 @@ func TestExec(t *testing.T) {
 		t.Fatal("proposed tool must not match (not enabled)")
 	}
 }
+
+// fakeMCP records what the executor asked it to call.
+type fakeMCP struct {
+	server, tool string
+	args         []string
+	out          string
+	err          error
+	calls        int
+}
+
+func (f *fakeMCP) CallPositional(_ context.Context, server, tool string, args []string) (string, error) {
+	f.calls++
+	f.server, f.tool, f.args = server, tool, args
+	return f.out, f.err
+}
+
+// An MCP row dispatches to the caller instead of a process, and the process
+// seam is never touched.
+func TestExecMCPRowDispatchesToMCP(t *testing.T) {
+	api := fakeAPI{tools: map[string]ipc.Tool{
+		"vikunja_list_tasks": {
+			Name: "vikunja_list_tasks", Status: "enabled", Scope: "mcp:vikunja",
+			Cmd: []string{"mcp", "vikunja", "list_tasks"},
+		},
+	}}
+	m := &fakeMCP{out: "две задачи"}
+	ran := false
+	e := NewExecutor(api, time.Second).WithMCP(m)
+	e.run = func(context.Context, []string) (string, error) { ran = true; return "", nil }
+
+	out, err := e.Exec(context.Background(), "vikunja_list_tasks", []string{"мавен"}, false)
+	if err != nil {
+		t.Fatalf("exec: %v", err)
+	}
+	if out != "две задачи" {
+		t.Fatalf("out = %q", out)
+	}
+	if ran {
+		t.Fatal("an MCP row must not be executed as a process")
+	}
+	if m.server != "vikunja" || m.tool != "list_tasks" || len(m.args) != 1 || m.args[0] != "мавен" {
+		t.Fatalf("dispatched wrong: %+v", m)
+	}
+}
+
+// The allowlist rules still apply to an MCP row: destructive means a confirm
+// turn first, and nothing is called until the second turn.
+func TestExecMCPRowStillNeedsConfirm(t *testing.T) {
+	api := fakeAPI{tools: map[string]ipc.Tool{
+		"vikunja_delete_task": {
+			Name: "vikunja_delete_task", Status: "enabled", Destructive: true,
+			Cmd: []string{"mcp", "vikunja", "delete_task"},
+		},
+	}}
+	m := &fakeMCP{out: "удалила"}
+	e := NewExecutor(api, time.Second).WithMCP(m)
+	if _, err := e.Exec(context.Background(), "vikunja_delete_task", nil, false); !errors.Is(err, ErrNeedsConfirm) {
+		t.Fatalf("err = %v, want ErrNeedsConfirm", err)
+	}
+	if m.calls != 0 {
+		t.Fatal("a destructive MCP tool must not reach the server before confirmation")
+	}
+	if _, err := e.Exec(context.Background(), "vikunja_delete_task", nil, true); err != nil {
+		t.Fatalf("confirmed exec: %v", err)
+	}
+	if m.calls != 1 {
+		t.Fatalf("calls = %d", m.calls)
+	}
+}
+
+// A proposed MCP row does not run, exactly like a proposed shell tool.
+func TestExecMCPRowNotEnabled(t *testing.T) {
+	api := fakeAPI{tools: map[string]ipc.Tool{
+		"vikunja_list_tasks": {Name: "vikunja_list_tasks", Status: "proposed", Cmd: []string{"mcp", "vikunja", "list_tasks"}},
+	}}
+	m := &fakeMCP{}
+	e := NewExecutor(api, time.Second).WithMCP(m)
+	if _, err := e.Exec(context.Background(), "vikunja_list_tasks", nil, false); !errors.Is(err, ErrNotEnabled) {
+		t.Fatalf("err = %v", err)
+	}
+	if m.calls != 0 {
+		t.Fatal("a proposal must not call anything")
+	}
+}
+
+// With MCP unconfigured, an MCP row refuses rather than trying to exec "mcp".
+func TestExecMCPRowWithoutCallerRefuses(t *testing.T) {
+	api := fakeAPI{tools: map[string]ipc.Tool{
+		"vikunja_list_tasks": {Name: "vikunja_list_tasks", Status: "enabled", Cmd: []string{"mcp", "vikunja", "list_tasks"}},
+	}}
+	ran := false
+	e := NewExecutor(api, time.Second)
+	e.run = func(context.Context, []string) (string, error) { ran = true; return "", nil }
+	if _, err := e.Exec(context.Background(), "vikunja_list_tasks", nil, false); !errors.Is(err, ErrNotEnabled) {
+		t.Fatalf("err = %v, want ErrNotEnabled", err)
+	}
+	if ran {
+		t.Fatal(`"mcp" must never be run as a binary`)
+	}
+}

internal/webfetch/webfetch.go

@@ -28,6 +28,7 @@
 package webfetch
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -92,6 +93,9 @@ type Response struct {
 	Status      int
 	ContentType string
 	Body        []byte
+	// Header — the response headers, one value each (the first). Populated for
+	// every request; MCP needs Mcp-Session-Id, nothing else reads it.
+	Header map[string]string
 }
 
 // Fetcher performs guarded GETs. Safe for concurrent use; the per-host rate
@@ -159,6 +163,37 @@ func New(cfg Config) *Fetcher {
 // Get fetches rawURL. The body is capped: a larger response is an error, not a
 // truncation, because half an XML document is worse than none.
 func (f *Fetcher) Get(ctx context.Context, rawURL string) (*Response, error) {
+	return f.do(ctx, http.MethodGet, rawURL, nil, nil)
+}
+
+// Post sends body to rawURL and returns the reply, under exactly the same
+// guards as Get: scheme rule, host lists, the dialer's private-address check on
+// every hop, the size cap and the per-host rate limit.
+//
+// It exists for JSON-RPC over HTTP (internal/mcp), which cannot be expressed as
+// a GET. That an outbound request now carries a body does not widen the
+// address policy one bit — a POST to the LAN is refused for the same reason a
+// GET is, unless AllowPrivate was set for that specific fetcher.
+//
+// hdr is merged over the defaults; a caller may not override User-Agent or
+// Accept-Encoding, because identity encoding and an honest UA are part of the
+// contract with whatever is on the other end.
+func (f *Fetcher) Post(ctx context.Context, rawURL, contentType string, body []byte, hdr map[string]string) (*Response, error) {
+	if contentType == "" {
+		contentType = "application/json"
+	}
+	if hdr == nil {
+		hdr = map[string]string{}
+	}
+	merged := make(map[string]string, len(hdr)+1)
+	for k, v := range hdr {
+		merged[k] = v
+	}
+	merged["Content-Type"] = contentType
+	return f.do(ctx, http.MethodPost, rawURL, body, merged)
+}
+
+func (f *Fetcher) do(ctx context.Context, method, rawURL string, body []byte, hdr map[string]string) (*Response, error) {
 	u, err := url.Parse(strings.TrimSpace(rawURL))
 	if err != nil {
 		return nil, fmt.Errorf("webfetch: bad url %q: %w", rawURL, err)
@@ -170,10 +205,17 @@ func (f *Fetcher) Get(ctx context.Context, rawURL string) (*Response, error) {
 		return nil, err
 	}
 
-	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
+	var rdr io.Reader
+	if body != nil {
+		rdr = bytes.NewReader(body)
+	}
+	req, err := http.NewRequestWithContext(ctx, method, u.String(), rdr)
 	if err != nil {
 		return nil, err
 	}
+	for k, v := range hdr {
+		req.Header.Set(k, v)
+	}
 	req.Header.Set("User-Agent", f.cfg.UserAgent)
 	req.Header.Set("Accept-Encoding", "identity")
 
@@ -190,22 +232,27 @@ func (f *Fetcher) Get(ctx context.Context, rawURL string) (*Response, error) {
 	}
 	defer resp.Body.Close()
 
-	body, err := io.ReadAll(io.LimitReader(resp.Body, f.cfg.MaxBytes+1))
+	respBody, err := io.ReadAll(io.LimitReader(resp.Body, f.cfg.MaxBytes+1))
 	if err != nil {
 		return nil, err
 	}
-	if int64(len(body)) > f.cfg.MaxBytes {
+	if int64(len(respBody)) > f.cfg.MaxBytes {
 		return nil, fmt.Errorf("%w (%d bytes)", ErrTooLarge, f.cfg.MaxBytes)
 	}
 	if resp.StatusCode < 200 || resp.StatusCode > 299 {
 		return nil, fmt.Errorf("%w: %d", ErrStatus, resp.StatusCode)
 	}
-	return &Response{
+	out := &Response{
 		URL:         resp.Request.URL.String(),
 		Status:      resp.StatusCode,
 		ContentType: resp.Header.Get("Content-Type"),
-		Body:        body,
-	}, nil
+		Body:        respBody,
+		Header:      map[string]string{},
+	}
+	for k := range resp.Header {
+		out.Header[k] = resp.Header.Get(k)
+	}
+	return out, nil
 }
 
 // checkURL applies the scheme rule and the host lists. The address rule is the

internal/webfetch/webfetch_test.go

@@ -3,6 +3,7 @@ package webfetch
 import (
 	"context"
 	"errors"
+	"io"
 	"net"
 	"net/http"
 	"net/http/httptest"
@@ -225,3 +226,74 @@ func TestUserAgentIsSent(t *testing.T) {
 		t.Fatalf("user-agent = %q", ua)
 	}
 }
+
+func TestPostSendsBodyAndHeaders(t *testing.T) {
+	type seen struct {
+		method, ctype, accept, ua, custom string
+		body                              []byte
+	}
+	ch := make(chan seen, 1)
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		b, _ := io.ReadAll(r.Body)
+		ch <- seen{r.Method, r.Header.Get("Content-Type"), r.Header.Get("Accept"),
+			r.Header.Get("User-Agent"), r.Header.Get("X-Thing"), b}
+		w.Header().Set("Mcp-Session-Id", "sess-9")
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"ok":true}`))
+	}))
+	defer srv.Close()
+	f := testFetcher(t, Config{UserAgent: "Maven/test"})
+	resp, err := f.Post(context.Background(), srv.URL, "application/json",
+		[]byte(`{"jsonrpc":"2.0"}`), map[string]string{"Accept": "text/event-stream", "X-Thing": "1"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(resp.Body) != `{"ok":true}` {
+		t.Fatalf("body = %q", resp.Body)
+	}
+	if resp.Header["Mcp-Session-Id"] != "sess-9" {
+		t.Fatalf("response headers not surfaced: %+v", resp.Header)
+	}
+	s := <-ch
+	if s.method != http.MethodPost {
+		t.Fatalf("method = %s", s.method)
+	}
+	if string(s.body) != `{"jsonrpc":"2.0"}` {
+		t.Fatalf("request body = %q", s.body)
+	}
+	if s.ctype != "application/json" {
+		t.Fatalf("content-type = %q", s.ctype)
+	}
+	if s.accept != "text/event-stream" || s.custom != "1" {
+		t.Fatalf("caller headers dropped: %+v", s)
+	}
+	if s.ua != "Maven/test" {
+		t.Fatalf("user-agent = %q — a caller must not be able to override it", s.ua)
+	}
+}
+
+// The whole point of routing MCP through webfetch: a POST is guarded exactly
+// like a GET. A body does not buy a caller a way onto the LAN.
+func TestPostRefusesPrivateAddress(t *testing.T) {
+	f := New(Config{}) // no AllowPrivate
+	_, err := f.Post(context.Background(), "http://127.0.0.1:9100/mcp", "application/json", []byte(`{}`), nil)
+	if !errors.Is(err, ErrPrivate) {
+		t.Fatalf("error = %v, want ErrPrivate", err)
+	}
+}
+
+func TestPostRefusesNonHTTPScheme(t *testing.T) {
+	f := New(Config{})
+	if _, err := f.Post(context.Background(), "file:///etc/passwd", "application/json", nil, nil); !errors.Is(err, ErrScheme) {
+		t.Fatalf("error = %v, want ErrScheme", err)
+	}
+}
+
+func TestPostObeysDenylist(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+	defer srv.Close()
+	f := testFetcher(t, Config{DenyHosts: []string{"127.0.0.1"}})
+	if _, err := f.Post(context.Background(), srv.URL, "application/json", []byte(`{}`), nil); !errors.Is(err, ErrBlocked) {
+		t.Fatalf("error = %v, want ErrBlocked", err)
+	}
+}