feat: enhance agent management with support for multiple instances and update UI accordingly

shell/process/manager.go

@@ -29,8 +29,9 @@ type AgentInfo struct {
 // AgentStatus combines agent metadata with runtime state.
 type AgentStatus struct {
 	AgentInfo
-	Running bool
-	PID     int
+	Running   bool
+	PID       int
+	Instances int
 }
 
 // ProcessStats holds resource usage for a running process.
@@ -82,9 +83,17 @@ func (m *Manager) Scan() ([]AgentInfo, error) {
 
 // Status returns the runtime status for a single agent.
 func (m *Manager) Status(info AgentInfo) AgentStatus {
-	pid := m.resolveRunningPID(info.ID)
-	running := pid > 0
-	return AgentStatus{AgentInfo: info, Running: running, PID: pid}
+	pids := m.findProcessPIDs(info.ID)
+	primary := 0
+	if len(pids) > 0 {
+		primary = pids[0]
+	}
+	return AgentStatus{
+		AgentInfo: info,
+		Running:   len(pids) > 0,
+		PID:       primary,
+		Instances: len(pids),
+	}
 }
 
 // StatusAll returns status for every discovered agent.
@@ -101,13 +110,8 @@ func (m *Manager) StatusAll() ([]AgentStatus, error) {
 }
 
 // Start launches an agent process in the background.
+// Multiple instances of the same agent are allowed.
 func (m *Manager) Start(info AgentInfo) error {
-	// Check for orphan instances
-	if existing := m.findProcessPIDs(info.ID); len(existing) > 0 {
-		return fmt.Errorf("agent %q already has %d running instance(s) (PIDs: %v) — stop them first",
-			info.ID, len(existing), existing)
-	}
-
 	if err := os.MkdirAll(m.runDir, 0o755); err != nil {
 		return fmt.Errorf("create run dir: %w", err)
 	}
@@ -233,7 +237,11 @@ func (m *Manager) Stats(id string) (ProcessStats, error) {
 	if pid == 0 {
 		return ProcessStats{}, fmt.Errorf("agent %q is not running", id)
 	}
+	return m.statsForPID(pid, id), nil
+}
 
+// statsForPID gathers resource usage for a specific PID.
+func (m *Manager) statsForPID(pid int, id string) ProcessStats {
 	s := ProcessStats{PID: pid}
 
 	// Uptime from /proc/<pid>/stat
@@ -278,7 +286,7 @@ func (m *Manager) Stats(id string) (ProcessStats, error) {
 		s.LogBytes = info.Size()
 	}
 
-	return s, nil
+	return s
 }
 
 // LogTail returns the last N lines of an agent's log.