feat: add Detach option for process group isolation

RunOptions.Detach creates the process in its own process group
(Setpgid) and uses context.Background() instead of the parent
context. Detached processes survive parent death.

Co-Authored-By: Virgil <virgil@lethean.io>

service.go

@@ -9,6 +9,7 @@ import (
 	"os/exec"
 	"sync"
 	"sync/atomic"
+	"syscall"
 	"time"
 
 	"forge.lthn.ai/core/go/pkg/core"
@@ -96,7 +97,12 @@ func (s *Service) Start(ctx context.Context, command string, args ...string) (*P
 func (s *Service) StartWithOptions(ctx context.Context, opts RunOptions) (*Process, error) {
 	id := fmt.Sprintf("proc-%d", s.idCounter.Add(1))
 
-	procCtx, cancel := context.WithCancel(ctx)
+	// Detached processes use Background context so they survive parent death
+	parentCtx := ctx
+	if opts.Detach {
+		parentCtx = context.Background()
+	}
+	procCtx, cancel := context.WithCancel(parentCtx)
 	cmd := exec.CommandContext(procCtx, opts.Command, opts.Args...)
 
 	if opts.Dir != "" {
@@ -106,6 +112,11 @@ func (s *Service) StartWithOptions(ctx context.Context, opts RunOptions) (*Proce
 		cmd.Env = append(cmd.Environ(), opts.Env...)
 	}
 
+	// Detached processes get their own process group
+	if opts.Detach {
+		cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+	}
+
 	// Set up pipes
 	stdout, err := cmd.StdoutPipe()
 	if err != nil {

types.go

@@ -73,6 +73,10 @@ type RunOptions struct {
 	// DisableCapture disables output buffering.
 	// By default, output is captured to a ring buffer.
 	DisableCapture bool
+	// Detach creates the process in its own process group (Setpgid).
+	// Detached processes survive parent death and context cancellation.
+	// The context is replaced with context.Background() when Detach is true.
+	Detach bool
 }
 
 // Info provides a snapshot of process state without internal fields.