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-crypto-web/src/memory-storage.ts

@@ -1,4 +1,8 @@
-import type { StorageProvider, IdentityKeyPair, SignedPreKey, OneTimePreKey, SessionState, RetiredIdentity, PersistedStreamState, PeerVerification } from '@shade/core';
+import type {
+  StorageProvider, IdentityKeyPair, SignedPreKey, OneTimePreKey,
+  SessionState, RetiredIdentity, PersistedStreamState, PeerVerification,
+  BroadcastChannelRecord, BroadcastMemberRecord,
+} from '@shade/core';
 import { constantTimeEqual } from '@shade/core';
 
 /**
@@ -167,4 +171,62 @@ export class MemoryStorage implements StorageProvider {
       }
     }
   }
+
+  // ─── Broadcast channels (V4.6) ────────────────────────────
+
+  private broadcastChannels = new Map<string, BroadcastChannelRecord>();
+  private broadcastMembers = new Map<string, Map<string, BroadcastMemberRecord>>();
+
+  async saveBroadcastChannel(channel: BroadcastChannelRecord): Promise<void> {
+    this.broadcastChannels.set(channel.channelId, cloneChannel(channel));
+  }
+
+  async getBroadcastChannel(channelId: string): Promise<BroadcastChannelRecord | null> {
+    const v = this.broadcastChannels.get(channelId);
+    return v ? cloneChannel(v) : null;
+  }
+
+  async listBroadcastChannels(): Promise<BroadcastChannelRecord[]> {
+    return [...this.broadcastChannels.values()].map(cloneChannel);
+  }
+
+  async removeBroadcastChannel(channelId: string): Promise<void> {
+    this.broadcastChannels.delete(channelId);
+    this.broadcastMembers.delete(channelId);
+  }
+
+  async saveBroadcastMember(member: BroadcastMemberRecord): Promise<void> {
+    let inner = this.broadcastMembers.get(member.channelId);
+    if (!inner) {
+      inner = new Map();
+      this.broadcastMembers.set(member.channelId, inner);
+    }
+    inner.set(member.peerAddress, { ...member });
+  }
+
+  async getBroadcastMembers(channelId: string): Promise<BroadcastMemberRecord[]> {
+    const inner = this.broadcastMembers.get(channelId);
+    return inner ? [...inner.values()].map((m) => ({ ...m })) : [];
+  }
+
+  async removeBroadcastMember(channelId: string, peerAddress: string): Promise<void> {
+    this.broadcastMembers.get(channelId)?.delete(peerAddress);
+  }
+}
+
+function cloneChannel(c: BroadcastChannelRecord): BroadcastChannelRecord {
+  const out: BroadcastChannelRecord = {
+    channelId: c.channelId,
+    ownerRole: c.ownerRole,
+    ownerAddress: c.ownerAddress,
+    generation: c.generation,
+    chainKey: new Uint8Array(c.chainKey),
+    iteration: c.iteration,
+    signingPublicKey: new Uint8Array(c.signingPublicKey),
+    createdAt: c.createdAt,
+    updatedAt: c.updatedAt,
+  };
+  if (c.label !== undefined) out.label = c.label;
+  if (c.signingPrivateKey !== undefined) out.signingPrivateKey = new Uint8Array(c.signingPrivateKey);
+  return out;
 }