feat(journal): federation schema + per-user signing keypairs

social-federation tasks 2.1–2.5:

- users.public_key / users.private_key_encrypted (TEXT NULL): RSA 2048
  keypairs as JWK JSON; private key AES-256-GCM encrypted at rest with
  FEDERATION_KEY_ENCRYPTION_KEY.
- remote_actors table: cache of remote AP actors (display fields,
  inbox/outbox URLs, public key, software discovery field, poll cursor).
- activities.remote_origin_iri (UNIQUE) / remote_actor_iri / audience:
  provenance + audience tagging for rows ingested from remote outboxes.
  Replay-safe ingestion keys off the unique origin IRI.
- crypto.server.ts: generalized into createAesCipher(envVar, salt)
  factory; existing INTEGRATION_SECRET surface unchanged.
- federation-keys.server.ts: generate/ensure/load keypairs.
  RSASSA-PKCS1-v1_5 because that's what Mastodon interops on.
- backfill-user-keypairs pg-boss job: enqueued once per server startup
  when FEDERATION_ENABLED=true; only touches users with NULL keys, so
  re-runs are no-ops. New users get keys at registration (both passkey
  and magic-link paths), best-effort with the backfill as safety net.
- design.md: noted open question — activities.owner_id is NOT NULL but
  remote-ingested rows have no local owner; decide in task 7.2.

Schema is additive; zero behavior change while FEDERATION_ENABLED is
off. db:push verified clean against local Postgres.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/db/src/schema/journal.ts

@@ -44,6 +44,14 @@ export const users = journalSchema.table("users", {
   // content defaults; existing users were backfilled to `public` by an
   // earlier migration so behavior didn't change for them.
   profileVisibility: text("profile_visibility").$type<ProfileVisibility>().notNull().default("private"),
+  // Federation signing keypair (spec: social-federation). The public key
+  // is a JWK JSON string embedded in the actor object; the private key is
+  // a JWK encrypted at rest with FEDERATION_KEY_ENCRYPTION_KEY (see
+  // apps/journal app/lib/federation-keys.server.ts). NULL until generated —
+  // at registration for new users, or by the one-shot
+  // `backfill-user-keypairs` job for users predating federation.
+  publicKey: text("public_key"),
+  privateKeyEncrypted: text("private_key_encrypted"),
   termsAcceptedAt: timestamp("terms_accepted_at", { withTimezone: true }),
   termsVersion: text("terms_version"),
   createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
@@ -123,6 +131,16 @@ export const routeVersions = journalSchema.table("route_versions", {
   createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
 });
 
+/**
+ * Audience of an activity cached from a remote actor's outbox (spec:
+ * social-federation, "Audience-aware feed filtering"). Local activities
+ * are always 'public' here — their actual visibility lives in
+ * `visibility`; this column only matters for remote rows, where
+ * 'followers-only' content must reach only the local viewer whose
+ * accepted follow brought it in.
+ */
+export type Audience = "public" | "followers-only";
+
 export const activities = journalSchema.table("activities", {
   id: text("id").primaryKey(),
   ownerId: text("owner_id")
@@ -142,6 +160,14 @@ export const activities = journalSchema.table("activities", {
   participants: jsonb("participants").$type<string[]>(),
   visibility: text("visibility").$type<Visibility>().notNull().default("private"),
   synthetic: boolean("synthetic").notNull().default(false),
+  // Federation provenance (spec: social-federation). NULL for local
+  // activities. For rows ingested from a remote trails actor's outbox:
+  // `remoteOriginIri` is the activity's IRI on the origin instance
+  // (unique → replay-safe `ON CONFLICT DO NOTHING` ingestion), and
+  // `remoteActorIri` keys into `remote_actors`.
+  remoteOriginIri: text("remote_origin_iri").unique(),
+  remoteActorIri: text("remote_actor_iri"),
+  audience: text("audience").$type<Audience>().notNull().default("public"),
   createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
 }, (t) => ({
   // Hot paths: listActivities (sort by started_at) and listPublicActivitiesForOwner.
@@ -318,6 +344,26 @@ export const follows = journalSchema.table("follows", {
   followedUserIdx: index("follows_followed_user_idx").on(t.followedUserId),
 }));
 
+// Cache of remote ActivityPub actors we interact with (spec:
+// social-federation). One row per actor IRI: display fields for feed
+// cards, inbox/outbox URLs for delivery and polling, the public key for
+// inbound HTTP-Signature verification, and `software` (the discovery
+// field) for the trails-to-trails outbound check. Refreshed during
+// outbox polls so feed renders never re-fetch the actor document.
+export const remoteActors = journalSchema.table("remote_actors", {
+  actorIri: text("actor_iri").primaryKey(),
+  displayName: text("display_name"),
+  username: text("username"),
+  domain: text("domain"),
+  avatarUrl: text("avatar_url"),
+  inboxUrl: text("inbox_url"),
+  outboxUrl: text("outbox_url"),
+  publicKey: text("public_key"),
+  software: text("software"),
+  lastPolledAt: timestamp("last_polled_at", { withTimezone: true }),
+  createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
+});
+
 // Notifications. Each row is a single event the recipient should be
 // informed about. v1 types: follow_request_received, follow_request_approved,
 // follow_received, activity_published. The `payload` JSONB snapshots the