fix: matar process group completo de claude-code al cancelar

Cuando se cancela una invocación de claude-code, el proceso principal
moría pero sus hijos (subprocesos node, etc.) quedaban huérfanos
consumiendo recursos. Ahora se crea un process group (Setpgid) y se
mata el grupo entero con kill(-pgid, SIGKILL) tanto en Cancel como
después de Run(), asegurando limpieza completa.

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

shell/llm/claudecode.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"os/exec"
 	"strings"
+	"syscall"
 	"time"
 
 	"github.com/enmanuel/agents/internal/config"
@@ -80,6 +81,20 @@ func NewClaudeCodeComplete(cfg config.ClaudeCodeCfg, log *slog.Logger) coretypes
 		cmd.Env = filterEnv(os.Environ(), "ANTHROPIC_API_KEY")
 		cmd.Stdin = strings.NewReader(prompt)
 
+		// Create a new process group so we can kill claude + all its children.
+		cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+		// Override the default cancel behavior: kill the entire process group
+		// instead of just the main process, preventing orphaned child processes.
+		cmd.Cancel = func() error {
+			if cmd.Process != nil {
+				pgid := cmd.Process.Pid
+				log.Info("killing claude-code process group", "pgid", pgid)
+				// Negative PID = kill entire process group
+				return syscall.Kill(-pgid, syscall.SIGKILL)
+			}
+			return nil
+		}
+
 		var stdout, stderr bytes.Buffer
 		cmd.Stdout = &stdout
 		cmd.Stderr = &stderr
@@ -88,6 +103,12 @@ func NewClaudeCodeComplete(cfg config.ClaudeCodeCfg, log *slog.Logger) coretypes
 		err := cmd.Run()
 		elapsed := time.Since(start)
 
+		// Ensure the process group is fully dead after Run returns,
+		// even if cmd.Run() returned without triggering Cancel (normal exit).
+		if cmd.Process != nil {
+			_ = syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
+		}
+
 		log.Debug("claude_code_done",
 			"elapsed_ms", elapsed.Milliseconds(),
 			"stdout_len", stdout.Len(),