diff --git a/extension/src/shared/types.ts b/extension/src/shared/types.ts
index 7893e38..a845d52 100644
--- a/extension/src/shared/types.ts
+++ b/extension/src/shared/types.ts
@@ -196,11 +196,21 @@ export type HistoryRetention =
   | { kind: 'last_n'; value: number }
   | { kind: 'days'; value: number };
 
+/// Optional per-level caps on attachment plaintext sizes.
+/// All fields optional; if undefined that level is uncapped.
+/// γ₁ enforces; γ₂ ships the configuration UI.
+export interface AttachmentCaps {
+  per_attachment_max_bytes?: number;
+  per_item_max_bytes?: number;
+  per_vault_soft_max_bytes?: number;
+  per_vault_hard_max_bytes?: number;
+}
+
 export interface VaultSettings {
   trash_retention: TrashRetention;
   field_history_retention: HistoryRetention;
   generator_defaults: GeneratorRequest;
-  attachment_caps: unknown;                 // opaque — γ tightens
+  attachment_caps: AttachmentCaps;
   autofill_origin_acks: Record<string, number>;
 }