feat: Add persistent chat sessions for iterative phase/task refinement

Introduces a chat loop where users send instructions to an agent that
applies changes (create/update/delete phases, tasks, pages) and stays
alive for follow-up messages. Includes schema + migration, repository
layer, chat prompt, file-io action field extension, output handler chat
mode, revert support for deletes, tRPC procedures, events, frontend
slide-over UI with inline changeset display and revert, and docs.

apps/server/db/schema.ts

@@ -264,7 +264,7 @@ export const agents = sqliteTable('agents', {
   })
     .notNull()
     .default('idle'),
-  mode: text('mode', { enum: ['execute', 'discuss', 'plan', 'detail', 'refine'] })
+  mode: text('mode', { enum: ['execute', 'discuss', 'plan', 'detail', 'refine', 'chat'] })
     .notNull()
     .default('execute'),
   pid: integer('pid'),
@@ -308,7 +308,7 @@ export const changeSets = sqliteTable('change_sets', {
   initiativeId: text('initiative_id')
     .notNull()
     .references(() => initiatives.id, { onDelete: 'cascade' }),
-  mode: text('mode', { enum: ['plan', 'detail', 'refine'] }).notNull(),
+  mode: text('mode', { enum: ['plan', 'detail', 'refine', 'chat'] }).notNull(),
   summary: text('summary'),
   status: text('status', { enum: ['applied', 'reverted'] })
     .notNull()
@@ -536,3 +536,71 @@ export const conversations = sqliteTable('conversations', {
 
 export type Conversation = InferSelectModel<typeof conversations>;
 export type NewConversation = InferInsertModel<typeof conversations>;
+
+// ============================================================================
+// CHAT SESSIONS
+// ============================================================================
+
+export const chatSessions = sqliteTable('chat_sessions', {
+  id: text('id').primaryKey(),
+  targetType: text('target_type', { enum: ['phase', 'task'] }).notNull(),
+  targetId: text('target_id').notNull(),
+  initiativeId: text('initiative_id')
+    .notNull()
+    .references(() => initiatives.id, { onDelete: 'cascade' }),
+  agentId: text('agent_id').references(() => agents.id, { onDelete: 'set null' }),
+  status: text('status', { enum: ['active', 'closed'] })
+    .notNull()
+    .default('active'),
+  createdAt: integer('created_at', { mode: 'timestamp' }).notNull(),
+  updatedAt: integer('updated_at', { mode: 'timestamp' }).notNull(),
+}, (table) => [
+  index('chat_sessions_target_idx').on(table.targetType, table.targetId),
+  index('chat_sessions_initiative_id_idx').on(table.initiativeId),
+]);
+
+export const chatSessionsRelations = relations(chatSessions, ({ one, many }) => ({
+  initiative: one(initiatives, {
+    fields: [chatSessions.initiativeId],
+    references: [initiatives.id],
+  }),
+  agent: one(agents, {
+    fields: [chatSessions.agentId],
+    references: [agents.id],
+  }),
+  messages: many(chatMessages),
+}));
+
+export type ChatSession = InferSelectModel<typeof chatSessions>;
+export type NewChatSession = InferInsertModel<typeof chatSessions>;
+
+// ============================================================================
+// CHAT MESSAGES
+// ============================================================================
+
+export const chatMessages = sqliteTable('chat_messages', {
+  id: text('id').primaryKey(),
+  chatSessionId: text('chat_session_id')
+    .notNull()
+    .references(() => chatSessions.id, { onDelete: 'cascade' }),
+  role: text('role', { enum: ['user', 'assistant', 'system'] }).notNull(),
+  content: text('content').notNull(),
+  changeSetId: text('change_set_id').references(() => changeSets.id, { onDelete: 'set null' }),
+  createdAt: integer('created_at', { mode: 'timestamp' }).notNull(),
+}, (table) => [
+  index('chat_messages_session_id_idx').on(table.chatSessionId),
+]);
+
+export const chatMessagesRelations = relations(chatMessages, ({ one }) => ({
+  chatSession: one(chatSessions, {
+    fields: [chatMessages.chatSessionId],
+    references: [chatSessions.id],
+  }),
+  changeSet: one(changeSets, {
+    fields: [chatMessages.changeSetId],
+    references: [changeSets.id],
+  }),
+}));
+
+export type ChatMessage = InferSelectModel<typeof chatMessages>;
+export type NewChatMessage = InferInsertModel<typeof chatMessages>;