feat: TUI usa SIGHUP para hot-reload de agente individual

restartAgent() ahora escribe run/reload.txt con el agentID y envía
SIGHUP al launcher en lugar de matar y reiniciar el proceso completo.
Si el launcher no está corriendo, conserva el comportamiento anterior
(stop + start completo).

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

shell/tui/adapter.go

@@ -4,8 +4,10 @@ package tui
 
 import (
 	"fmt"
+	"os"
 	"os/exec"
 	"strings"
+	"syscall"
 	"time"
 
 	tea "github.com/charmbracelet/bubbletea"
@@ -140,13 +142,28 @@ func (a *Adapter) disableAgent(id string) tea.Cmd {
 
 func (a *Adapter) restartAgent(id string) tea.Cmd {
 	return func() tea.Msg {
-		_ = a.mgr.StopUnified()
-		time.Sleep(500 * time.Millisecond)
-		err := a.mgr.StartUnified()
-		if err == nil {
+		pid := a.mgr.UnifiedPID()
+		if pid <= 0 {
+			// Launcher not running — fall back to full restart.
+			_ = a.mgr.StopUnified()
 			time.Sleep(500 * time.Millisecond)
+			err := a.mgr.StartUnified()
+			if err == nil {
+				time.Sleep(500 * time.Millisecond)
+			}
+			return puretui.MsgActionDone{AgentID: id, Action: "Restart", Err: err}
 		}
-		return puretui.MsgActionDone{AgentID: id, Action: "Restart", Err: err}
+
+		// Launcher is running — write target and send SIGHUP for hot-reload.
+		if id != "" {
+			_ = os.WriteFile("run/reload.txt", []byte(id), 0o644)
+		}
+		err := syscall.Kill(pid, syscall.SIGHUP)
+		if err != nil {
+			return puretui.MsgActionDone{AgentID: id, Action: "Restart", Err: err}
+		}
+		time.Sleep(1 * time.Second)
+		return puretui.MsgActionDone{AgentID: id, Action: "Restart", Err: nil}
 	}
 }