feat: add per-provider mutex and Target-aware implementations

- Add snack.Locker embed for per-provider mutex serialization
- Update all providers (pacman, apk, apt, dpkg) to use []Target
  with version pinning support (pkg=version syntax)
- Add lock/unlock to all mutating operations (Install, Remove, Purge,
  Upgrade, Update)
- Add snack.TargetNames helper and formatTargets per provider
- apt: add FromRepo (-t) and Reinstall support
- dpkg: use Target.Source for .deb file paths in Install

apt/apt.go

@@ -8,7 +8,9 @@ import (
 )
 
 // Apt implements the snack.Manager interface using apt-get and apt-cache.
-type Apt struct{}
+type Apt struct {
+	snack.Locker
+}
 
 // New returns a new Apt manager.
 func New() *Apt {
@@ -19,27 +21,37 @@ func New() *Apt {
 func (a *Apt) Name() string { return "apt" }
 
 // Install one or more packages.
-func (a *Apt) Install(ctx context.Context, pkgs []string, opts ...snack.Option) error {
+func (a *Apt) Install(ctx context.Context, pkgs []snack.Target, opts ...snack.Option) error {
+	a.Lock()
+	defer a.Unlock()
 	return install(ctx, pkgs, opts...)
 }
 
 // Remove one or more packages.
-func (a *Apt) Remove(ctx context.Context, pkgs []string, opts ...snack.Option) error {
+func (a *Apt) Remove(ctx context.Context, pkgs []snack.Target, opts ...snack.Option) error {
+	a.Lock()
+	defer a.Unlock()
 	return remove(ctx, pkgs, opts...)
 }
 
 // Purge one or more packages including config files.
-func (a *Apt) Purge(ctx context.Context, pkgs []string, opts ...snack.Option) error {
+func (a *Apt) Purge(ctx context.Context, pkgs []snack.Target, opts ...snack.Option) error {
+	a.Lock()
+	defer a.Unlock()
 	return purge(ctx, pkgs, opts...)
 }
 
 // Upgrade all installed packages.
 func (a *Apt) Upgrade(ctx context.Context, opts ...snack.Option) error {
+	a.Lock()
+	defer a.Unlock()
 	return upgrade(ctx, opts...)
 }
 
 // Update refreshes the package index.
 func (a *Apt) Update(ctx context.Context) error {
+	a.Lock()
+	defer a.Unlock()
 	return update(ctx)
 }
 

apt/apt_linux.go

@@ -17,7 +17,21 @@ func available() bool {
 	return err == nil
 }
 
-func buildArgs(command string, pkgs []string, opts ...snack.Option) []string {
+// formatTargets converts targets to apt CLI arguments.
+// apt uses "pkg=version" for version pinning.
+func formatTargets(targets []snack.Target) []string {
+	args := make([]string, 0, len(targets))
+	for _, t := range targets {
+		if t.Version != "" {
+			args = append(args, t.Name+"="+t.Version)
+		} else {
+			args = append(args, t.Name)
+		}
+	}
+	return args
+}
+
+func buildArgs(command string, pkgs []snack.Target, opts ...snack.Option) []string {
 	o := snack.ApplyOptions(opts...)
 	var args []string
 	if o.Sudo {
@@ -30,11 +44,17 @@ func buildArgs(command string, pkgs []string, opts ...snack.Option) []string {
 	if o.DryRun {
 		args = append(args, "--dry-run")
 	}
-	args = append(args, pkgs...)
+	if o.FromRepo != "" {
+		args = append(args, "-t", o.FromRepo)
+	}
+	if o.Reinstall && command == "install" {
+		args = append(args, "--reinstall")
+	}
+	args = append(args, formatTargets(pkgs)...)
 	return args
 }
 
-func runAptGet(ctx context.Context, command string, pkgs []string, opts ...snack.Option) error {
+func runAptGet(ctx context.Context, command string, pkgs []snack.Target, opts ...snack.Option) error {
 	args := buildArgs(command, pkgs, opts...)
 	var cmd *exec.Cmd
 	if args[0] == "sudo" {
@@ -57,15 +77,15 @@ func runAptGet(ctx context.Context, command string, pkgs []string, opts ...snack
 	return nil
 }
 
-func install(ctx context.Context, pkgs []string, opts ...snack.Option) error {
+func install(ctx context.Context, pkgs []snack.Target, opts ...snack.Option) error {
 	return runAptGet(ctx, "install", pkgs, opts...)
 }
 
-func remove(ctx context.Context, pkgs []string, opts ...snack.Option) error {
+func remove(ctx context.Context, pkgs []snack.Target, opts ...snack.Option) error {
 	return runAptGet(ctx, "remove", pkgs, opts...)
 }
 
-func purge(ctx context.Context, pkgs []string, opts ...snack.Option) error {
+func purge(ctx context.Context, pkgs []snack.Target, opts ...snack.Option) error {
 	return runAptGet(ctx, "purge", pkgs, opts...)
 }
 

apt/apt_other.go

@@ -10,15 +10,15 @@ import (
 
 func available() bool { return false }
 
-func install(_ context.Context, _ []string, _ ...snack.Option) error {
+func install(_ context.Context, _ []snack.Target, _ ...snack.Option) error {
 	return snack.ErrUnsupportedPlatform
 }
 
-func remove(_ context.Context, _ []string, _ ...snack.Option) error {
+func remove(_ context.Context, _ []snack.Target, _ ...snack.Option) error {
 	return snack.ErrUnsupportedPlatform
 }
 
-func purge(_ context.Context, _ []string, _ ...snack.Option) error {
+func purge(_ context.Context, _ []snack.Target, _ ...snack.Option) error {
 	return snack.ErrUnsupportedPlatform
 }