release(v4.6.0): broadcast channels — Signal sender-keys for one-to-many fan-out

Lands the broadcast-channel primitive Prism asked for in
Docs/shade-feature-request-sender-keys.md. The crypto in
@shade/core/sender-keys.ts was already in place; this release wires
it up as a first-class app-facing API, adds the persistence schema
across all six storage backends (memory, sqlite, indexeddb +
encrypted variants), introduces wire type 0x21 in @shade/proto,
and ships Prism's three acceptance tests verbatim.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/shade-core/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@shade/core",
-  "version": "4.5.0",
+  "version": "4.6.0",
   "type": "module",
   "main": "src/index.ts",
   "types": "src/index.ts",

packages/shade-core/src/storage.ts

@@ -46,6 +46,50 @@ export interface PersistedStreamState {
  */
 export type PeerVerificationSource = 'user' | 'transitive' | 'tofu-after-warning';
 
+/**
+ * Persisted broadcast-channel state (V4.6). Holds the sender-key chain that
+ * lets the channel owner encrypt a single ciphertext and fan it out to all
+ * paired members.
+ *
+ * - `ownerRole === 'sender'`: this device created the channel; the record
+ *   carries the full chain (chainKey + iteration + signing keypair).
+ * - `ownerRole === 'receiver'`: this device joined a channel that
+ *   `ownerAddress` owns; we hold a tracking copy of the chain (chainKey +
+ *   iteration + signing public key only — no private signing key).
+ *
+ * `generation` is bumped each time `removeMember` rotates the chain. Stale
+ * broadcasts at lower generations are silently dropped on receive.
+ */
+export interface BroadcastChannelRecord {
+  /** Opaque, stable across restarts. UUID-style. */
+  channelId: string;
+  ownerRole: 'sender' | 'receiver';
+  /** The address that owns the channel (i.e. the only sender). */
+  ownerAddress: string;
+  label?: string;
+  /** Sender-key generation — bumped on rotation. Starts at 0. */
+  generation: number;
+  /** Current chain key (32 bytes). */
+  chainKey: Uint8Array;
+  /** Counter advanced by `senderKeyEncrypt` / `senderKeyDecrypt`. */
+  iteration: number;
+  /** Owner's Ed25519 signing public key (32 bytes). */
+  signingPublicKey: Uint8Array;
+  /** Owner's Ed25519 signing private key. Present iff `ownerRole === 'sender'`. */
+  signingPrivateKey?: Uint8Array;
+  createdAt: number;
+  updatedAt: number;
+}
+
+/** Membership row for a broadcast channel (sender-side only). */
+export interface BroadcastMemberRecord {
+  channelId: string;
+  peerAddress: string;
+  joinedAt: number;
+  /** When this peer was revoked. `null` while still active. */
+  removedAt: number | null;
+}
+
 /**
  * Persistent record that a peer's safety number was verified at a point
  * in time. `identityVersion` is the local counter for that peer's identity:
@@ -188,4 +232,35 @@ export interface StorageProvider {
 
   /** Prune stream-state rows in `'finished' | 'aborted'` status older than `olderThan`. */
   pruneStreamStates?(olderThan: number): Promise<void>;
+
+  // ─── Broadcast channels (V4.6) — optional ─────────────────
+
+  /**
+   * Persist or replace the broadcast-channel record. Idempotent upsert on
+   * `channelId`. Backends that don't implement broadcast-channel support
+   * may omit this; the SDK throws a clear error when the app tries to
+   * call `createBroadcastChannel` on such a backend.
+   */
+  saveBroadcastChannel?(channel: BroadcastChannelRecord): Promise<void>;
+
+  /** Look up a broadcast channel by id. */
+  getBroadcastChannel?(channelId: string): Promise<BroadcastChannelRecord | null>;
+
+  /** Enumerate all broadcast channels persisted on this device. */
+  listBroadcastChannels?(): Promise<BroadcastChannelRecord[]>;
+
+  /** Drop a broadcast channel and all its membership rows. */
+  removeBroadcastChannel?(channelId: string): Promise<void>;
+
+  /** Persist or replace a broadcast-membership row (sender-side only). */
+  saveBroadcastMember?(member: BroadcastMemberRecord): Promise<void>;
+
+  /**
+   * List membership rows for a channel. Includes revoked members (with
+   * `removedAt !== null`); callers filter as needed.
+   */
+  getBroadcastMembers?(channelId: string): Promise<BroadcastMemberRecord[]>;
+
+  /** Hard-delete a single membership row. */
+  removeBroadcastMember?(channelId: string, peerAddress: string): Promise<void>;
 }