fix(forget): populate retention groups for manual runs

internal/restic/runner.go

@@ -322,7 +322,7 @@ type ForgetGroup struct {
 // any keep-* would delete every snapshot in the tagged set).
 // Returns the first error encountered, or nil when every group runs
 // to a clean exit.
-func (e Env) RunForget(ctx context.Context, groups []ForgetGroup, handle LineHandler) error {
+func (e Env) RunForget(ctx context.Context, groups []ForgetGroup, dryRun bool, handle LineHandler) error {
 	if len(groups) == 0 {
 		return fmt.Errorf("restic forget: refusing to run with no groups (would be a no-op)")
 	}
@@ -332,6 +332,9 @@ func (e Env) RunForget(ctx context.Context, groups []ForgetGroup, handle LineHan
 		}
 		args := []string{"forget", "--json", "--tag", g.Tag}
 		args = append(args, g.Policy.args()...)
+		if dryRun {
+			args = append(args, "--dry-run")
+		}
 		cmd := e.resticCmd(ctx, args...)
 		if err := runWithPump(cmd, handle); err != nil {
 			return err

internal/restic/runner_test.go

@@ -60,6 +60,26 @@ func TestRunPruneInvokesPrune(t *testing.T) {
 	t.Fatalf("expected 'prune' in captured output; got: %v", *lines)
 }
 
+func TestRunForgetDryRunArgument(t *testing.T) {
+	bin := setupScriptBin(t, `echo "$@"`)
+	env := Env{Bin: bin}
+	lines, h := captureLines()
+	keepLast := 1
+	groups := []ForgetGroup{{
+		Tag:    "documents",
+		Policy: ForgetPolicy{KeepLast: &keepLast},
+	}}
+	if err := env.RunForget(context.Background(), groups, true, h); err != nil {
+		t.Fatalf("RunForget: %v", err)
+	}
+	for _, line := range *lines {
+		if strings.Contains(line, "forget --json --tag documents --keep-last 1 --dry-run") {
+			return
+		}
+	}
+	t.Fatalf("expected forget invocation with --dry-run; got: %v", *lines)
+}
+
 // --- B2: RunCheck ---
 
 func TestRunCheckLockSniff(t *testing.T) {