mcp,tools,main: shut down MCP servers on agent switch

Client gains a Close() method that closes stdin (giving the subprocess
a clean EOF) then kills and reaps the process. Executor.Close() calls
Close() on all registered clients. agentEnv now carries the mcpExec so
the /agent command can close the outgoing executor before building the
new one.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

main.go

@@ -204,6 +204,7 @@ type model struct {
 	backendName string // e.g. "ollama", "openrouter", "openai"
 	agentName   string // active agent config name, e.g. "default"
 	agentsDir   string // path to ~/.config/ollie/agents/
+	mcpExec     *tools.Executor   // current agent's MCP executor; closed on agent switch
 	builtinExec *execpkg.Executor
 	confirmPtr  *agent.ConfirmFn // indirection so startAgent can set it per-run
 	ctxOverhead int // fixed per-request char overhead (system prompt + tool schemas)
@@ -243,6 +244,7 @@ type timeoutMsg struct{}
 
 // agentEnv holds the runtime state derived from an agent config file.
 type agentEnv struct {
+	mcpExec      *tools.Executor  // kept so it can be closed on agent switch
 	tools        []backend.Tool
 	exec         agent.ToolExecutor
 	confirm      *agent.ConfirmFn // pointer filled in by startAgent per-run
@@ -339,6 +341,7 @@ func buildAgentEnv(cfg *config.Config, builtinExec *execpkg.Executor) agentEnv {
 	}
 
 	return agentEnv{
+		mcpExec:      mcpExec,
 		tools:        allTools,
 		exec:         execFn,
 		confirm:      confirmPtr,
@@ -445,6 +448,7 @@ func main() {
 		backendName: backendName,
 		agentName:   agentName,
 		agentsDir:   agentsDir,
+		mcpExec:     env.mcpExec,
 		builtinExec: builtinExec,
 		confirmPtr:  env.confirm,
 		ctxOverhead: env.ctxOverhead,
@@ -856,7 +860,11 @@ func (m *model) handleCommand(input string) bool {
 			m.display = append(m.display, fmt.Sprintf("Error: agent %q: %v", name, err))
 			return true
 		}
+		if m.mcpExec != nil {
+			m.mcpExec.Close()
+		}
 		env := buildAgentEnv(cfg, m.builtinExec)
+		m.mcpExec = env.mcpExec
 		m.hooks = env.hooks
 		m.loopcfg.SystemPrompt = env.systemPrompt
 		m.loopcfg.Tools = env.tools

mcp/client.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"os/exec"
 	"sync"
 )
 
@@ -32,9 +33,11 @@ func (e *RPCError) Error() string {
 // of a subprocess).
 type Client struct {
 	mu     sync.Mutex
+	wc     io.WriteCloser
 	w      io.Writer
 	sc     *bufio.Scanner
 	nextID int
+	cmd    *exec.Cmd
 }
 
 // NewClient creates a Client from a reader and writer.
@@ -42,6 +45,26 @@ func NewClient(r io.Reader, w io.Writer) *Client {
 	return &Client{w: w, sc: bufio.NewScanner(r)}
 }
 
+// newClientWithProcess creates a Client that owns the given subprocess.
+// Close() will shut it down.
+func newClientWithProcess(r io.Reader, wc io.WriteCloser, cmd *exec.Cmd) *Client {
+	return &Client{wc: wc, w: wc, sc: bufio.NewScanner(r), cmd: cmd}
+}
+
+// Close shuts down the underlying subprocess: closes its stdin so it receives
+// EOF, then kills the process if it is still running.
+func (c *Client) Close() error {
+	var err error
+	if c.wc != nil {
+		err = c.wc.Close()
+	}
+	if c.cmd != nil && c.cmd.Process != nil {
+		c.cmd.Process.Kill()
+		c.cmd.Wait() // reap the process; ignore errors
+	}
+	return err
+}
+
 // Call sends a JSON-RPC request and returns the result.
 func (c *Client) Call(method string, params interface{}) (json.RawMessage, error) {
 	c.mu.Lock()

mcp/transport.go

@@ -37,7 +37,7 @@ func (t *STDIOTransport) Connect() (*Client, error) {
 		return nil, err
 	}
 
-	client := NewClient(stdout, stdin)
+	client := newClientWithProcess(stdout, stdin, cmd)
 
 	// MCP initialization handshake.
 	if _, err := client.Call("initialize", map[string]interface{}{

tools/executor.go

@@ -29,6 +29,13 @@ func (e *Executor) AddServer(name string, client *mcp.Client) {
 	e.servers[name] = client
 }
 
+// Close shuts down all connected MCP servers.
+func (e *Executor) Close() {
+	for _, client := range e.servers {
+		client.Close()
+	}
+}
+
 // ListTools returns all tools advertised by all connected servers.
 func (e *Executor) ListTools() ([]ToolInfo, error) {
 	var all []ToolInfo