sfs v0.1: mountable synced file system for AI agents

- sfs mnt/umnt/sync/status/log/remote/whoami CLI (cobra)
- per-device append-only journals + content-addressed blob store
- deterministic lamport-ordered merge, LWW with conflict-copy preservation
- cloud-agnostic backends: S3, GCS, file:// (S3-compatible via AWS_ENDPOINT_URL)
- offline-first: real files on disk, journal locally, push on reconnect
- background sync daemon per mount with change tracking (device/author/time)
- macOS + Linux; Homebrew formula + goreleaser release pipeline

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

internal/config/config.go

@@ -0,0 +1,166 @@
+// Package config manages sfs's global state under the sfs home directory
+// (default ~/.sfs, overridable with $SFS_HOME): the device identity and the
+// registry of mounted folders.
+package config
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"encoding/json"
+	"os"
+	"os/exec"
+	"os/user"
+	"path/filepath"
+	"strings"
+)
+
+// Home returns the sfs home directory ($SFS_HOME or ~/.sfs).
+func Home() (string, error) {
+	if h := os.Getenv("SFS_HOME"); h != "" {
+		return h, nil
+	}
+	uh, err := os.UserHomeDir()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(uh, ".sfs"), nil
+}
+
+// Device identifies this machine and its operator in journals.
+type Device struct {
+	ID     string `json:"id"`
+	Name   string `json:"name"`
+	Author string `json:"author"`
+}
+
+// LoadDevice loads the device identity, creating one on first use.
+func LoadDevice() (Device, error) {
+	home, err := Home()
+	if err != nil {
+		return Device{}, err
+	}
+	p := filepath.Join(home, "device.json")
+	if data, err := os.ReadFile(p); err == nil {
+		var d Device
+		if err := json.Unmarshal(data, &d); err == nil && d.ID != "" {
+			return d, nil
+		}
+	}
+	d := Device{ID: randID(), Name: hostname(), Author: detectAuthor()}
+	if err := os.MkdirAll(home, 0o755); err != nil {
+		return Device{}, err
+	}
+	if err := writeJSON(p, d); err != nil {
+		return Device{}, err
+	}
+	return d, nil
+}
+
+func randID() string {
+	b := make([]byte, 6)
+	if _, err := rand.Read(b); err != nil {
+		return "device000000"
+	}
+	return hex.EncodeToString(b)
+}
+
+func hostname() string {
+	h, _ := os.Hostname()
+	h = strings.TrimSuffix(h, ".local")
+	if h == "" {
+		h = "device"
+	}
+	return h
+}
+
+func detectAuthor() string {
+	if out, err := exec.Command("git", "config", "--get", "user.email").Output(); err == nil {
+		if s := strings.TrimSpace(string(out)); s != "" {
+			return s
+		}
+	}
+	u := os.Getenv("USER")
+	if u == "" {
+		if cu, err := user.Current(); err == nil {
+			u = cu.Username
+		}
+	}
+	if u == "" {
+		u = "unknown"
+	}
+	return u + "@" + hostname()
+}
+
+// MountInfo describes one mounted folder.
+type MountInfo struct {
+	Volume string `json:"volume"`
+	Remote string `json:"remote,omitempty"`
+}
+
+func mountsPath() (string, error) {
+	home, err := Home()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(home, "mounts.json"), nil
+}
+
+// LoadMounts returns the abs-folder → mount registry.
+func LoadMounts() (map[string]MountInfo, error) {
+	p, err := mountsPath()
+	if err != nil {
+		return nil, err
+	}
+	out := map[string]MountInfo{}
+	data, err := os.ReadFile(p)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return out, nil
+		}
+		return nil, err
+	}
+	if err := json.Unmarshal(data, &out); err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func SaveMounts(m map[string]MountInfo) error {
+	p, err := mountsPath()
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+		return err
+	}
+	return writeJSON(p, m)
+}
+
+// VolumeDir returns (and creates parents for) the local store dir of a volume.
+func VolumeDir(volume string) (string, error) {
+	home, err := Home()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(home, "volumes", volume), nil
+}
+
+func writeJSON(path string, v any) error {
+	data, err := json.MarshalIndent(v, "", "  ")
+	if err != nil {
+		return err
+	}
+	tmp, err := os.CreateTemp(filepath.Dir(path), ".sfs-tmp-*")
+	if err != nil {
+		return err
+	}
+	defer os.Remove(tmp.Name())
+	if _, err := tmp.Write(data); err != nil {
+		tmp.Close()
+		return err
+	}
+	if err := tmp.Close(); err != nil {
+		return err
+	}
+	return os.Rename(tmp.Name(), path)
+}