diff --git a/internal/cli/secrets.go b/internal/cli/secrets.go
index f554e93..2f1a019 100644
--- a/internal/cli/secrets.go
+++ b/internal/cli/secrets.go
@@ -276,11 +276,118 @@ var secretsDeleteCmd = &cobra.Command{
 	},
 }
 
+var secretsRotateMasterDryRun bool
+
+var secretsRotateMasterCmd = &cobra.Command{
+	Use:   "rotate-master",
+	Short: "Generate a new master key + re-encrypt all namespace secrets (REQ-129, C-30)",
+	Long: `Generate a new master key, re-encrypt every namespace's .env.secrets
+under the new key, and re-seal the master key to OIDC. With --dry-run,
+reports the affected namespaces without writing. Atomic per-namespace;
+automatic rollback to the old key on any failure (C-30).`,
+	Args: cobra.NoArgs,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		mkPath := paths.MasterKeyPath()
+		oldKey, err := secrets.LoadMasterKey(mkPath)
+		if err != nil {
+			return fmt.Errorf("load current master key: %w", err)
+		}
+
+		// Find all namespaces with .env.secrets files.
+		root := paths.Root()
+		entries, err := os.ReadDir(root)
+		if err != nil {
+			return fmt.Errorf("read ORCA_HOME: %w", err)
+		}
+		var namespaces []string
+		for _, ent := range entries {
+			if !ent.IsDir() || ent.Name() == "cluster" {
+				continue
+			}
+			secPath := paths.NSSecrets(ent.Name())
+			if _, err := os.Stat(secPath); err == nil {
+				namespaces = append(namespaces, ent.Name())
+			}
+		}
+		if secretsRotateMasterDryRun {
+			fmt.Fprintf(cmd.OutOrStdout(), "dry-run: would re-encrypt %d namespace(s) under a new master key:\n", len(namespaces))
+			for _, ns := range namespaces {
+				fmt.Fprintf(cmd.OutOrStdout(), "  - %s\n", ns)
+			}
+			return nil
+		}
+
+		// Generate new master key.
+		newKey, err := secrets.GenerateMasterKey()
+		if err != nil {
+			return fmt.Errorf("generate new master key: %w", err)
+		}
+
+		// Re-encrypt each namespace. On any failure, rollback.
+		rolled := make(map[string][]string) // ns -> old encrypted (for rollback)
+		for _, ns := range namespaces {
+			_, lines, err := loadMasterAndNSSecrets(ns)
+			if err != nil {
+				// Rollback already-processed namespaces.
+				rollbackRotation(rolled, oldKey)
+				return fmt.Errorf("load secrets for ns %s: %w", ns, err)
+			}
+			// Save the old encrypted content for rollback.
+			secPath := paths.NSSecrets(ns)
+			oldEnc, _ := os.ReadFile(secPath)
+			rolled[ns] = []string{string(oldEnc)}
+
+			// Re-encrypt under the new key.
+			newNSKey, err := secrets.DeriveNamespaceKey(newKey, ns)
+			if err != nil {
+				rollbackRotation(rolled, oldKey)
+				return fmt.Errorf("derive new ns key for %s: %w", ns, err)
+			}
+			enc, err := secrets.EncryptEnvFile(newNSKey, lines)
+			if err != nil {
+				rollbackRotation(rolled, oldKey)
+				return fmt.Errorf("re-encrypt ns %s: %w", ns, err)
+			}
+			if err := writeAtomicFile(secPath, []byte(enc), 0o600); err != nil {
+				rollbackRotation(rolled, oldKey)
+				return fmt.Errorf("write ns %s: %w", ns, err)
+			}
+		}
+
+		// Save the new master key.
+		if err := secrets.SaveMasterKey(mkPath, newKey); err != nil {
+			rollbackRotation(rolled, oldKey)
+			return fmt.Errorf("save new master key (rolled back): %w", err)
+		}
+
+		slog.Info("secrets rotate-master", "namespaces", len(namespaces))
+		if jsonOutput {
+			return printJSON(map[string]any{"rotated": true, "namespaces": namespaces})
+		}
+		fmt.Fprintf(cmd.OutOrStdout(), "✓ Master key rotated; %d namespace(s) re-encrypted\n", len(namespaces))
+		return nil
+	},
+}
+
+// rollbackRotation restores old encrypted secrets for already-processed
+// namespaces (C-30: automatic rollback on failure).
+func rollbackRotation(rolled map[string][]string, oldKey []byte) {
+	mkPath := paths.MasterKeyPath()
+	_ = secrets.SaveMasterKey(mkPath, oldKey) // restore old key
+	for ns, oldEnc := range rolled {
+		if len(oldEnc) > 0 {
+			_ = writeAtomicFile(paths.NSSecrets(ns), []byte(oldEnc[0]), 0o600)
+		}
+	}
+}
+
 func init() {
 	secretsCmd.AddCommand(secretsSetCmd)
 	secretsCmd.AddCommand(secretsGetCmd)
 	secretsCmd.AddCommand(secretsListCmd)
 	secretsCmd.AddCommand(secretsRotateCmd)
 	secretsCmd.AddCommand(secretsDeleteCmd)
+	secretsRotateMasterCmd.Flags().BoolVar(&secretsRotateMasterDryRun, "dry-run", false, "report affected namespaces without writing (C-30)")
+	secretsCmd.AddCommand(secretsRotateMasterCmd)
 	rootCmd.AddCommand(secretsCmd)
 }