feat: add process management commands for daemon control

Add systemd-style subcommands for managing KVS instances:
- start <config>  - Daemonize and run in background
- stop <config>   - Gracefully stop daemon
- restart <config> - Restart daemon
- status [config] - Show status of all or specific instances

Key features:
- PID files stored in ~/.kvs/pids/ (global across all directories)
- Logs stored in ~/.kvs/logs/
- Config names support both 'node1' and 'node1.yaml' formats
- Backward compatible: 'kvs config.yaml' still runs in foreground
- Proper stale PID detection and cleanup

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

daemon/pid.go

@@ -0,0 +1,171 @@
+package daemon
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"syscall"
+)
+
+// getPIDDir returns the absolute path to the PID directory
+func getPIDDir() (string, error) {
+	homeDir, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("failed to get user home directory: %w", err)
+	}
+	return filepath.Join(homeDir, ".kvs", "pids"), nil
+}
+
+// getLogDir returns the absolute path to the log directory
+func getLogDir() (string, error) {
+	homeDir, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("failed to get user home directory: %w", err)
+	}
+	return filepath.Join(homeDir, ".kvs", "logs"), nil
+}
+
+// GetPIDFilePath returns the PID file path for a given config file
+func GetPIDFilePath(configPath string) string {
+	pidDir, err := getPIDDir()
+	if err != nil {
+		// Fallback to local directory
+		pidDir = ".kvs/pids"
+	}
+
+	// Extract basename without extension
+	basename := filepath.Base(configPath)
+	name := strings.TrimSuffix(basename, filepath.Ext(basename))
+
+	return filepath.Join(pidDir, name+".pid")
+}
+
+// EnsurePIDDir creates the PID directory if it doesn't exist
+func EnsurePIDDir() error {
+	pidDir, err := getPIDDir()
+	if err != nil {
+		return err
+	}
+	return os.MkdirAll(pidDir, 0755)
+}
+
+// WritePID writes the current process PID to a file
+func WritePID(configPath string) error {
+	if err := EnsurePIDDir(); err != nil {
+		return fmt.Errorf("failed to create PID directory: %w", err)
+	}
+
+	pidFile := GetPIDFilePath(configPath)
+	pid := os.Getpid()
+
+	return os.WriteFile(pidFile, []byte(fmt.Sprintf("%d\n", pid)), 0644)
+}
+
+// ReadPID reads the PID from a file and checks if the process is running
+func ReadPID(configPath string) (int, bool, error) {
+	pidFile := GetPIDFilePath(configPath)
+
+	data, err := os.ReadFile(pidFile)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return 0, false, nil
+		}
+		return 0, false, fmt.Errorf("failed to read PID file: %w", err)
+	}
+
+	pidStr := strings.TrimSpace(string(data))
+	pid, err := strconv.Atoi(pidStr)
+	if err != nil {
+		return 0, false, fmt.Errorf("invalid PID in file: %w", err)
+	}
+
+	// Check if process is actually running
+	process, err := os.FindProcess(pid)
+	if err != nil {
+		return pid, false, nil
+	}
+
+	// Send signal 0 to check if process exists
+	err = process.Signal(syscall.Signal(0))
+	if err != nil {
+		return pid, false, nil
+	}
+
+	return pid, true, nil
+}
+
+// RemovePID removes the PID file
+func RemovePID(configPath string) error {
+	pidFile := GetPIDFilePath(configPath)
+	err := os.Remove(pidFile)
+	if err != nil && !os.IsNotExist(err) {
+		return fmt.Errorf("failed to remove PID file: %w", err)
+	}
+	return nil
+}
+
+// ListRunningInstances returns a list of running KVS instances
+func ListRunningInstances() ([]InstanceInfo, error) {
+	var instances []InstanceInfo
+
+	pidDir, err := getPIDDir()
+	if err != nil {
+		return nil, err
+	}
+
+	// Check if PID directory exists
+	if _, err := os.Stat(pidDir); os.IsNotExist(err) {
+		return instances, nil
+	}
+
+	entries, err := os.ReadDir(pidDir)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read PID directory: %w", err)
+	}
+
+	for _, entry := range entries {
+		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".pid") {
+			continue
+		}
+
+		name := strings.TrimSuffix(entry.Name(), ".pid")
+		configPath := name + ".yaml" // Assume .yaml extension
+
+		pid, running, err := ReadPID(configPath)
+		if err != nil {
+			continue
+		}
+
+		instances = append(instances, InstanceInfo{
+			Name:    name,
+			PID:     pid,
+			Running: running,
+		})
+	}
+
+	return instances, nil
+}
+
+// InstanceInfo holds information about a KVS instance
+type InstanceInfo struct {
+	Name    string
+	PID     int
+	Running bool
+}
+
+// StopProcess stops a process by PID
+func StopProcess(pid int) error {
+	process, err := os.FindProcess(pid)
+	if err != nil {
+		return fmt.Errorf("failed to find process: %w", err)
+	}
+
+	// Try graceful shutdown first (SIGTERM)
+	if err := process.Signal(syscall.SIGTERM); err != nil {
+		return fmt.Errorf("failed to send SIGTERM: %w", err)
+	}
+
+	return nil
+}