fix(M2-005,M2-006): enforce user ownership at repo level for conversations and agents

ConversationsRepo: add userId parameter to findById, update, remove, findMessages,
and addMessage so every query filters by conversations.userId in the WHERE clause.
This prevents cross-user data access even if the controller layer were bypassed.

AgentsRepo: add optional ownerId parameter to update (enforced for user-owned agents,
omitted for admin system-agent path) and required ownerId to remove so the DELETE
WHERE clause always scopes to the requesting user's agents.

Controller call sites updated to pass userId/ownerId to the repo methods. The
resource-ownership unit test updated to reflect that findById now returns undefined
(not a foreign-user object) when ownership is checked at the DB layer.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/brain/src/agents.ts

@@ -1,4 +1,4 @@
-import { eq, or, type Db, agents } from '@mosaic/db';
+import { eq, and, or, type Db, agents } from '@mosaic/db';
 
 export type Agent = typeof agents.$inferSelect;
 export type NewAgent = typeof agents.$inferInsert;
@@ -27,6 +27,10 @@ export function createAgentsRepo(db: Db) {
       return db.select().from(agents).where(eq(agents.isSystem, true));
     },
 
+    /**
+     * Return only agents the user may access: their own agents plus all system agents.
+     * Never returns other users' private agents.
+     */
     async findAccessible(ownerId: string): Promise<Agent[]> {
       return db
         .select()
@@ -39,17 +43,44 @@ export function createAgentsRepo(db: Db) {
       return rows[0]!;
     },
 
-    async update(id: string, data: Partial<NewAgent>): Promise<Agent | undefined> {
+    /**
+     * Update an agent.
+     *
+     * For user-owned agents pass `ownerId` — the WHERE clause will enforce ownership so that
+     * one user cannot overwrite another user's agent.  For system agents the caller must
+     * omit `ownerId` (admin-only path) and the WHERE clause only matches on `id`.
+     *
+     * Returns undefined when no row was matched (not found or ownership mismatch).
+     */
+    async update(
+      id: string,
+      data: Partial<NewAgent>,
+      ownerId?: string,
+    ): Promise<Agent | undefined> {
+      const condition =
+        ownerId !== undefined
+          ? and(eq(agents.id, id), eq(agents.ownerId, ownerId))
+          : eq(agents.id, id);
+
       const rows = await db
         .update(agents)
         .set({ ...data, updatedAt: new Date() })
-        .where(eq(agents.id, id))
+        .where(condition)
         .returning();
       return rows[0];
     },
 
-    async remove(id: string): Promise<boolean> {
-      const rows = await db.delete(agents).where(eq(agents.id, id)).returning();
+    /**
+     * Delete a user-owned agent, scoped to the given owner.
+     * Will not match system agents even if the id is correct, because system agents have
+     * `ownerId = null` which cannot equal a real user id.
+     * Returns false when no row was matched (not found, wrong owner, or system agent).
+     */
+    async remove(id: string, ownerId: string): Promise<boolean> {
+      const rows = await db
+        .delete(agents)
+        .where(and(eq(agents.id, id), eq(agents.ownerId, ownerId)))
+        .returning();
       return rows.length > 0;
     },
   };

packages/brain/src/conversations.ts

@@ -1,4 +1,4 @@
-import { eq, asc, desc, type Db, conversations, messages } from '@mosaic/db';
+import { eq, and, asc, desc, type Db, conversations, messages } from '@mosaic/db';
 
 /** Maximum number of conversations returned per list query. */
 const MAX_CONVERSATIONS = 200;
@@ -21,8 +21,15 @@ export function createConversationsRepo(db: Db) {
         .limit(MAX_CONVERSATIONS);
     },
 
-    async findById(id: string): Promise<Conversation | undefined> {
-      const rows = await db.select().from(conversations).where(eq(conversations.id, id));
+    /**
+     * Find a conversation by ID, scoped to the given user.
+     * Returns undefined if the conversation does not exist or belongs to a different user.
+     */
+    async findById(id: string, userId: string): Promise<Conversation | undefined> {
+      const rows = await db
+        .select()
+        .from(conversations)
+        .where(and(eq(conversations.id, id), eq(conversations.userId, userId)));
       return rows[0];
     },
 
@@ -31,21 +38,47 @@ export function createConversationsRepo(db: Db) {
       return rows[0]!;
     },
 
-    async update(id: string, data: Partial<NewConversation>): Promise<Conversation | undefined> {
+    /**
+     * Update a conversation, scoped to the given user.
+     * Returns undefined if the conversation does not exist or belongs to a different user.
+     */
+    async update(
+      id: string,
+      userId: string,
+      data: Partial<NewConversation>,
+    ): Promise<Conversation | undefined> {
       const rows = await db
         .update(conversations)
         .set({ ...data, updatedAt: new Date() })
-        .where(eq(conversations.id, id))
+        .where(and(eq(conversations.id, id), eq(conversations.userId, userId)))
         .returning();
       return rows[0];
     },
 
-    async remove(id: string): Promise<boolean> {
-      const rows = await db.delete(conversations).where(eq(conversations.id, id)).returning();
+    /**
+     * Delete a conversation, scoped to the given user.
+     * Returns false if the conversation does not exist or belongs to a different user.
+     */
+    async remove(id: string, userId: string): Promise<boolean> {
+      const rows = await db
+        .delete(conversations)
+        .where(and(eq(conversations.id, id), eq(conversations.userId, userId)))
+        .returning();
       return rows.length > 0;
     },
 
-    async findMessages(conversationId: string): Promise<Message[]> {
+    /**
+     * Find messages for a conversation, scoped to the given user.
+     * Returns an empty array if the conversation does not exist or belongs to a different user.
+     */
+    async findMessages(conversationId: string, userId: string): Promise<Message[]> {
+      // Verify ownership of the parent conversation before returning messages.
+      const conv = await db
+        .select()
+        .from(conversations)
+        .where(and(eq(conversations.id, conversationId), eq(conversations.userId, userId)));
+      if (conv.length === 0) return [];
+
       return db
         .select()
         .from(messages)
@@ -54,7 +87,19 @@ export function createConversationsRepo(db: Db) {
         .limit(MAX_MESSAGES);
     },
 
-    async addMessage(data: NewMessage): Promise<Message> {
+    /**
+     * Add a message to a conversation, scoped to the given user.
+     * Verifies the parent conversation belongs to the user before inserting.
+     * Returns undefined if the conversation does not exist or belongs to a different user.
+     */
+    async addMessage(data: NewMessage, userId: string): Promise<Message | undefined> {
+      // Verify ownership of the parent conversation before inserting the message.
+      const conv = await db
+        .select()
+        .from(conversations)
+        .where(and(eq(conversations.id, data.conversationId), eq(conversations.userId, userId)));
+      if (conv.length === 0) return undefined;
+
       const rows = await db.insert(messages).values(data).returning();
       return rows[0]!;
     },