feat(05-01): add messages table to schema

- Add messages table with sender/recipient pattern for agent-user communication
- Support message types: question, info, error, response
- Add requiresResponse flag and status tracking (pending, read, responded)
- Include parentMessageId for threading responses to original questions
- Add relations for sender/recipient agents and message threading

src/db/schema.ts

@@ -197,3 +197,54 @@ export const agentsRelations = relations(agents, ({ one }) => ({
 
 export type Agent = InferSelectModel<typeof agents>;
 export type NewAgent = InferInsertModel<typeof agents>;
+
+// ============================================================================
+// MESSAGES
+// ============================================================================
+
+export const messages = sqliteTable('messages', {
+  id: text('id').primaryKey(),
+  senderType: text('sender_type', { enum: ['agent', 'user'] }).notNull(),
+  senderId: text('sender_id').references(() => agents.id, { onDelete: 'set null' }), // Agent ID if senderType='agent', null for user
+  recipientType: text('recipient_type', { enum: ['agent', 'user'] }).notNull(),
+  recipientId: text('recipient_id').references(() => agents.id, { onDelete: 'set null' }), // Agent ID if recipientType='agent', null for user
+  type: text('type', { enum: ['question', 'info', 'error', 'response'] })
+    .notNull()
+    .default('info'),
+  content: text('content').notNull(),
+  requiresResponse: integer('requires_response', { mode: 'boolean' })
+    .notNull()
+    .default(false),
+  status: text('status', { enum: ['pending', 'read', 'responded'] })
+    .notNull()
+    .default('pending'),
+  parentMessageId: text('parent_message_id').references((): ReturnType<typeof text> => messages.id, { onDelete: 'set null' }), // Links response to original question
+  createdAt: integer('created_at', { mode: 'timestamp' }).notNull(),
+  updatedAt: integer('updated_at', { mode: 'timestamp' }).notNull(),
+});
+
+export const messagesRelations = relations(messages, ({ one, many }) => ({
+  // Sender agent (optional - null for user senders)
+  senderAgent: one(agents, {
+    fields: [messages.senderId],
+    references: [agents.id],
+    relationName: 'senderAgent',
+  }),
+  // Recipient agent (optional - null for user recipients)
+  recipientAgent: one(agents, {
+    fields: [messages.recipientId],
+    references: [agents.id],
+    relationName: 'recipientAgent',
+  }),
+  // Parent message (for threading responses)
+  parentMessage: one(messages, {
+    fields: [messages.parentMessageId],
+    references: [messages.id],
+    relationName: 'parentMessage',
+  }),
+  // Child messages (replies to this message)
+  childMessages: many(messages, { relationName: 'parentMessage' }),
+}));
+
+export type Message = InferSelectModel<typeof messages>;
+export type NewMessage = InferInsertModel<typeof messages>;