feat(M5-004,M5-005,M5-006,M5-007): session-conversation binding, session:info broadcast, agent creation from TUI, and session metrics (#321)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/gateway/src/agent/agent.service.ts

@@ -23,7 +23,7 @@ import { createFileTools } from './tools/file-tools.js';
 import { createGitTools } from './tools/git-tools.js';
 import { createShellTools } from './tools/shell-tools.js';
 import { createWebTools } from './tools/web-tools.js';
-import type { SessionInfoDto } from './session.dto.js';
+import type { SessionInfoDto, SessionMetrics } from './session.dto.js';
 import { SystemOverrideService } from '../preferences/system-override.service.js';
 import { PreferencesService } from '../preferences/preferences.service.js';
 import { SessionGCService } from '../gc/session-gc.service.js';
@@ -93,6 +93,12 @@ export interface AgentSession {
   allowedTools: string[] | null;
   /** User ID that owns this session, used for preference lookups. */
   userId?: string;
+  /** Agent config ID applied to this session, if any (M5-001). */
+  agentConfigId?: string;
+  /** Human-readable agent name applied to this session, if any (M5-001). */
+  agentName?: string;
+  /** M5-007: per-session metrics. */
+  metrics: SessionMetrics;
 }
 
 @Injectable()
@@ -184,11 +190,13 @@ export class AgentService implements OnModuleDestroy {
     sessionId: string,
     options?: AgentSessionOptions,
   ): Promise<AgentSession> {
-    // Merge DB agent config when agentConfigId is provided
+    // Merge DB agent config when agentConfigId is provided (M5-001)
     let mergedOptions = options;
+    let resolvedAgentName: string | undefined;
     if (options?.agentConfigId) {
       const agentConfig = await this.brain.agents.findById(options.agentConfigId);
       if (agentConfig) {
+        resolvedAgentName = agentConfig.name;
         mergedOptions = {
           provider: options.provider ?? agentConfig.provider,
           modelId: options.modelId ?? agentConfig.model,
@@ -197,6 +205,8 @@ export class AgentService implements OnModuleDestroy {
           sandboxDir: options.sandboxDir,
           isAdmin: options.isAdmin,
           agentConfigId: options.agentConfigId,
+          userId: options.userId,
+          conversationHistory: options.conversationHistory,
         };
         this.logger.log(
           `Merged agent config "${agentConfig.name}" (${agentConfig.id}) into session ${sessionId}`,
@@ -330,6 +340,14 @@ export class AgentService implements OnModuleDestroy {
       sandboxDir,
       allowedTools,
       userId: mergedOptions?.userId,
+      agentConfigId: mergedOptions?.agentConfigId,
+      agentName: resolvedAgentName,
+      metrics: {
+        tokens: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+        modelSwitches: 0,
+        messageCount: 0,
+        lastActivityAt: new Date().toISOString(),
+      },
     };
 
     this.sessions.set(sessionId, session);
@@ -458,10 +476,12 @@ export class AgentService implements OnModuleDestroy {
       id: s.id,
       provider: s.provider,
       modelId: s.modelId,
+      ...(s.agentName ? { agentName: s.agentName } : {}),
       createdAt: new Date(s.createdAt).toISOString(),
       promptCount: s.promptCount,
       channels: Array.from(s.channels),
       durationMs: now - s.createdAt,
+      metrics: { ...s.metrics },
     }));
   }
 
@@ -472,13 +492,93 @@ export class AgentService implements OnModuleDestroy {
       id: s.id,
       provider: s.provider,
       modelId: s.modelId,
+      ...(s.agentName ? { agentName: s.agentName } : {}),
       createdAt: new Date(s.createdAt).toISOString(),
       promptCount: s.promptCount,
       channels: Array.from(s.channels),
       durationMs: Date.now() - s.createdAt,
+      metrics: { ...s.metrics },
     };
   }
 
+  /**
+   * Record token usage for a session turn (M5-007).
+   * Accumulates tokens across the session lifetime.
+   */
+  recordTokenUsage(
+    sessionId: string,
+    tokens: { input: number; output: number; cacheRead: number; cacheWrite: number; total: number },
+  ): void {
+    const session = this.sessions.get(sessionId);
+    if (!session) return;
+    session.metrics.tokens.input += tokens.input;
+    session.metrics.tokens.output += tokens.output;
+    session.metrics.tokens.cacheRead += tokens.cacheRead;
+    session.metrics.tokens.cacheWrite += tokens.cacheWrite;
+    session.metrics.tokens.total += tokens.total;
+    session.metrics.lastActivityAt = new Date().toISOString();
+  }
+
+  /**
+   * Record a model switch event for a session (M5-007).
+   */
+  recordModelSwitch(sessionId: string): void {
+    const session = this.sessions.get(sessionId);
+    if (!session) return;
+    session.metrics.modelSwitches += 1;
+    session.metrics.lastActivityAt = new Date().toISOString();
+  }
+
+  /**
+   * Increment message count for a session (M5-007).
+   */
+  recordMessage(sessionId: string): void {
+    const session = this.sessions.get(sessionId);
+    if (!session) return;
+    session.metrics.messageCount += 1;
+    session.metrics.lastActivityAt = new Date().toISOString();
+  }
+
+  /**
+   * Update the model tracked on a live session (M5-002).
+   * This records the model change in the session metadata so subsequent
+   * session:info emissions reflect the new model.  The Pi session itself is
+   * not reconstructed — the model is used on the next createSession call for
+   * the same conversationId when the session is torn down or a new one is created.
+   */
+  updateSessionModel(sessionId: string, modelId: string): void {
+    const session = this.sessions.get(sessionId);
+    if (!session) return;
+    const prev = session.modelId;
+    session.modelId = modelId;
+    this.recordModelSwitch(sessionId);
+    this.logger.log(`Session ${sessionId}: model updated ${prev} → ${modelId} (M5-002)`);
+  }
+
+  /**
+   * Apply a new agent config to a live session mid-conversation (M5-003).
+   * Updates agentName, agentConfigId, and modelId on the session object.
+   * System prompt and tools take effect when the next session is created for
+   * this conversationId (they are baked in at session creation time).
+   */
+  applyAgentConfig(
+    sessionId: string,
+    agentConfigId: string,
+    agentName: string,
+    modelId?: string,
+  ): void {
+    const session = this.sessions.get(sessionId);
+    if (!session) return;
+    session.agentConfigId = agentConfigId;
+    session.agentName = agentName;
+    if (modelId) {
+      this.updateSessionModel(sessionId, modelId);
+    }
+    this.logger.log(
+      `Session ${sessionId}: agent switched to "${agentName}" (${agentConfigId}) (M5-003)`,
+    );
+  }
+
   addChannel(sessionId: string, channel: string): void {
     const session = this.sessions.get(sessionId);
     if (session) {

apps/gateway/src/agent/session.dto.ts

@@ -1,11 +1,32 @@
+/** Token usage metrics for a session (M5-007). */
+export interface SessionTokenMetrics {
+  input: number;
+  output: number;
+  cacheRead: number;
+  cacheWrite: number;
+  total: number;
+}
+
+/** Per-session metrics tracked throughout the session lifetime (M5-007). */
+export interface SessionMetrics {
+  tokens: SessionTokenMetrics;
+  modelSwitches: number;
+  messageCount: number;
+  lastActivityAt: string;
+}
+
 export interface SessionInfoDto {
   id: string;
   provider: string;
   modelId: string;
+  /** M5-005: human-readable agent name when an agent config is applied. */
+  agentName?: string;
   createdAt: string;
   promptCount: number;
   channels: string[];
   durationMs: number;
+  /** M5-007: per-session metrics (token usage, model switches, etc.) */
+  metrics: SessionMetrics;
 }
 
 export interface SessionListDto {

apps/gateway/src/chat/chat.gateway.ts

@@ -119,6 +119,17 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
         // When resuming an existing conversation, load prior messages to inject as context (M1-004)
         const conversationHistory = await this.loadConversationHistory(conversationId, userId);
 
+        // M5-004: Check if there's an existing sessionId bound to this conversation
+        let existingSessionId: string | undefined;
+        if (userId) {
+          existingSessionId = await this.getConversationSessionId(conversationId, userId);
+          if (existingSessionId) {
+            this.logger.log(
+              `Resuming existing sessionId=${existingSessionId} for conversation=${conversationId}`,
+            );
+          }
+        }
+
         // Determine provider/model via routing engine or per-session /model override (M4-012 / M4-007)
         let resolvedProvider = data.provider;
         let resolvedModelId = data.modelId;
@@ -153,7 +164,9 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
           }
         }
 
-        agentSession = await this.agentService.createSession(conversationId, {
+        // M5-004: Use existingSessionId as sessionId when available (session reuse)
+        const sessionIdToCreate = existingSessionId ?? conversationId;
+        agentSession = await this.agentService.createSession(sessionIdToCreate, {
           provider: resolvedProvider,
           modelId: resolvedModelId,
           agentConfigId: data.agentId,
@@ -180,10 +193,15 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
     }
 
     // Ensure conversation record exists in the DB before persisting messages
+    // M5-004: Also bind the sessionId to the conversation record
     if (userId) {
       await this.ensureConversation(conversationId, userId);
+      await this.bindSessionToConversation(conversationId, userId, conversationId);
     }
 
+    // M5-007: Count the user message
+    this.agentService.recordMessage(conversationId);
+
     // Persist the user message
     if (userId) {
       try {
@@ -234,6 +252,7 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
     this.agentService.addChannel(conversationId, `websocket:${client.id}`);
 
     // Send session info so the client knows the model/provider (M4-008: include routing decision)
+    // Include agentName when a named agent config is active (M5-001)
     {
       const agentSession = this.agentService.getSession(conversationId);
       if (agentSession) {
@@ -244,6 +263,7 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
           modelId: agentSession.modelId,
           thinkingLevel: piSession.thinkingLevel,
           availableThinkingLevels: piSession.getAvailableThinkingLevels(),
+          ...(agentSession.agentName ? { agentName: agentSession.agentName } : {}),
           ...(routingDecisionToStore ? { routingDecision: routingDecisionToStore } : {}),
         });
       }
@@ -301,6 +321,7 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
       modelId: session.modelId,
       thinkingLevel: session.piSession.thinkingLevel,
       availableThinkingLevels: session.piSession.getAvailableThinkingLevels(),
+      ...(session.agentName ? { agentName: session.agentName } : {}),
     });
   }
 
@@ -323,11 +344,23 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
    * Set a per-conversation model override (M4-007).
    * When set, the routing engine is bypassed and the specified model is used.
    * Pass null to clear the override and resume automatic routing.
+   * M5-005: Emits session:info to clients subscribed to this conversation when a model is set.
+   * M5-007: Records a model switch in session metrics.
    */
   setModelOverride(conversationId: string, modelName: string | null): void {
     if (modelName) {
       modelOverrides.set(conversationId, modelName);
       this.logger.log(`Model override set: conversation=${conversationId} model="${modelName}"`);
+
+      // M5-002: Update the live session's modelId so session:info reflects the new model immediately
+      this.agentService.updateSessionModel(conversationId, modelName);
+
+      // M5-005: Broadcast session:info to all clients subscribed to this conversation
+      const agentSession = this.agentService.getSession(conversationId);
+      if (agentSession) {
+        // Find all clients subscribed to this conversation and emit updated session:info
+        this.broadcastSessionInfo(conversationId);
+      }
     } else {
       modelOverrides.delete(conversationId);
       this.logger.log(`Model override cleared: conversation=${conversationId}`);
@@ -341,6 +374,39 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
     return modelOverrides.get(conversationId);
   }
 
+  /**
+   * M5-005: Broadcast session:info to all clients currently subscribed to a conversation.
+   * Called on model or agent switch to ensure the TUI TopBar updates immediately.
+   */
+  broadcastSessionInfo(
+    conversationId: string,
+    extra?: { agentName?: string; routingDecision?: RoutingDecisionInfo },
+  ): void {
+    const agentSession = this.agentService.getSession(conversationId);
+    if (!agentSession) return;
+
+    const piSession = agentSession.piSession;
+    const payload = {
+      conversationId,
+      provider: agentSession.provider,
+      modelId: agentSession.modelId,
+      thinkingLevel: piSession.thinkingLevel,
+      availableThinkingLevels: piSession.getAvailableThinkingLevels(),
+      ...(extra?.agentName ? { agentName: extra.agentName } : {}),
+      ...(extra?.routingDecision ? { routingDecision: extra.routingDecision } : {}),
+    };
+
+    // Emit to all clients currently subscribed to this conversation
+    for (const [clientId, session] of this.clientSessions) {
+      if (session.conversationId === conversationId) {
+        const socket = this.server.sockets.sockets.get(clientId);
+        if (socket?.connected) {
+          socket.emit('session:info', payload);
+        }
+      }
+    }
+  }
+
   /**
    * Ensure a conversation record exists in the DB.
    * Creates it if absent — safe to call concurrently since a duplicate insert
@@ -363,6 +429,45 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
     }
   }
 
+  /**
+   * M5-004: Bind the agent sessionId to the conversation record in the DB.
+   * Updates the sessionId column so future resumes can reuse the session.
+   */
+  private async bindSessionToConversation(
+    conversationId: string,
+    userId: string,
+    sessionId: string,
+  ): Promise<void> {
+    try {
+      await this.brain.conversations.update(conversationId, userId, { sessionId });
+    } catch (err) {
+      this.logger.error(
+        `Failed to bind sessionId=${sessionId} to conversation=${conversationId}`,
+        err instanceof Error ? err.stack : String(err),
+      );
+    }
+  }
+
+  /**
+   * M5-004: Retrieve the sessionId bound to a conversation, if any.
+   * Returns undefined when the conversation does not exist or has no bound session.
+   */
+  private async getConversationSessionId(
+    conversationId: string,
+    userId: string,
+  ): Promise<string | undefined> {
+    try {
+      const conv = await this.brain.conversations.findById(conversationId, userId);
+      return conv?.sessionId ?? undefined;
+    } catch (err) {
+      this.logger.error(
+        `Failed to get sessionId for conversation=${conversationId}`,
+        err instanceof Error ? err.stack : String(err),
+      );
+      return undefined;
+    }
+  }
+
   /**
    * Load prior conversation messages from DB for context injection on session resume (M1-004).
    * Returns an empty array when no history exists, the conversation is not owned by the user,
@@ -439,6 +544,17 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
           usage: usagePayload,
         });
 
+        // M5-007: Accumulate token usage in session metrics
+        if (stats?.tokens) {
+          this.agentService.recordTokenUsage(conversationId, {
+            input: stats.tokens.input ?? 0,
+            output: stats.tokens.output ?? 0,
+            cacheRead: stats.tokens.cacheRead ?? 0,
+            cacheWrite: stats.tokens.cacheWrite ?? 0,
+            total: stats.tokens.total ?? 0,
+          });
+        }
+
         // Persist the assistant message with metadata
         const cs = this.clientSessions.get(client.id);
         const userId = (client.data.user as { id: string } | undefined)?.id;

apps/gateway/src/commands/command-executor-p8012.spec.ts

@@ -19,6 +19,8 @@ const mockRegistry = {
 
 const mockAgentService = {
   getSession: vi.fn(() => undefined),
+  applyAgentConfig: vi.fn(),
+  updateSessionModel: vi.fn(),
 };
 
 const mockSystemOverride = {
@@ -38,6 +40,33 @@ const mockRedis = {
   del: vi.fn(),
 };
 
+const mockAgentConfig = {
+  id: 'my-agent-id',
+  name: 'my-agent-id',
+  model: 'claude-sonnet-4-6',
+  provider: 'anthropic',
+  systemPrompt: null,
+  allowedTools: null,
+  isSystem: false,
+  ownerId: 'user-123',
+  status: 'idle',
+  createdAt: new Date(),
+  updatedAt: new Date(),
+};
+
+const mockBrain = {
+  agents: {
+    // findByName resolves with the agent when name matches, undefined otherwise
+    findByName: vi.fn((name: string) =>
+      Promise.resolve(name === 'my-agent-id' ? mockAgentConfig : undefined),
+    ),
+    findById: vi.fn((id: string) =>
+      Promise.resolve(id === 'my-agent-id' ? mockAgentConfig : undefined),
+    ),
+    create: vi.fn(),
+  },
+};
+
 function buildService(): CommandExecutorService {
   return new CommandExecutorService(
     mockRegistry as never,
@@ -45,6 +74,7 @@ function buildService(): CommandExecutorService {
     mockSystemOverride as never,
     mockSessionGC as never,
     mockRedis as never,
+    mockBrain as never,
     null,
     null,
   );

apps/gateway/src/commands/command-executor.service.ts

@@ -1,6 +1,7 @@
 import { forwardRef, Inject, Injectable, Logger, Optional } from '@nestjs/common';
 import type { QueueHandle } from '@mosaic/queue';
 import type { SlashCommandPayload, SlashCommandResultPayload } from '@mosaic/types';
+import type { Brain } from '@mosaic/brain';
 import { AgentService } from '../agent/agent.service.js';
 import { ChatGateway } from '../chat/chat.gateway.js';
 import { SessionGCService } from '../gc/session-gc.service.js';
@@ -8,6 +9,7 @@ import { SystemOverrideService } from '../preferences/system-override.service.js
 import { ReloadService } from '../reload/reload.service.js';
 import { COMMANDS_REDIS } from './commands.tokens.js';
 import { CommandRegistryService } from './command-registry.service.js';
+import { BRAIN } from '../brain/brain.tokens.js';
 
 @Injectable()
 export class CommandExecutorService {
@@ -19,6 +21,7 @@ export class CommandExecutorService {
     @Inject(SystemOverrideService) private readonly systemOverride: SystemOverrideService,
     @Inject(SessionGCService) private readonly sessionGC: SessionGCService,
     @Inject(COMMANDS_REDIS) private readonly redis: QueueHandle['redis'],
+    @Inject(BRAIN) private readonly brain: Brain,
     @Optional()
     @Inject(forwardRef(() => ReloadService))
     private readonly reloadService: ReloadService | null,
@@ -87,7 +90,7 @@ export class CommandExecutorService {
           };
         }
         case 'agent':
-          return await this.handleAgent(args ?? null, conversationId);
+          return await this.handleAgent(args ?? null, conversationId, userId);
         case 'provider':
           return await this.handleProvider(args ?? null, userId, conversationId);
         case 'mission':
@@ -239,12 +242,14 @@ export class CommandExecutorService {
   private async handleAgent(
     args: string | null,
     conversationId: string,
+    userId: string,
   ): Promise<SlashCommandResultPayload> {
     if (!args) {
       return {
         command: 'agent',
         success: true,
-        message: 'Usage: /agent <agent-id> to switch, or /agent list to see available agents.',
+        message:
+          'Usage: /agent <agent-id> | /agent list | /agent new <name> to create a new agent.',
         conversationId,
       };
     }
@@ -258,14 +263,102 @@ export class CommandExecutorService {
       };
     }
 
-    // Switch agent — stub for now (full implementation in P8-015)
+    // M5-006: /agent new <name> — create a new agent config via brain.agents.create()
+    if (args.startsWith('new')) {
+      const namePart = args.slice(3).trim();
+      if (!namePart) {
+        return {
+          command: 'agent',
+          success: false,
+          message: 'Usage: /agent new <name> — provide a name for the new agent.',
+          conversationId,
+        };
+      }
+
+      try {
+        const defaultProvider = process.env['DEFAULT_PROVIDER'] ?? 'anthropic';
+        const defaultModel = process.env['DEFAULT_MODEL'] ?? 'claude-sonnet-4-5-20251001';
+
+        const newAgent = await this.brain.agents.create({
+          name: namePart,
+          provider: defaultProvider,
+          model: defaultModel,
+          status: 'idle',
+          ownerId: userId,
+          isSystem: false,
+        });
+
+        this.logger.log(`Created new agent "${newAgent.name}" (${newAgent.id}) for user ${userId}`);
+
         return {
           command: 'agent',
           success: true,
-      message: `Agent switch to "${args}" requested. Restart conversation to apply.`,
+          message: `Agent "${newAgent.name}" created with ID: ${newAgent.id}. Configure it via the web dashboard.`,
+          conversationId,
+          data: { agentId: newAgent.id, agentName: newAgent.name },
+        };
+      } catch (err) {
+        this.logger.error(`Failed to create agent: ${err}`);
+        return {
+          command: 'agent',
+          success: false,
+          message: `Failed to create agent: ${String(err)}`,
           conversationId,
         };
       }
+    }
+
+    // M5-003: Look up agent by name (or ID) and apply to session mid-conversation
+    const agentName = args.trim();
+    try {
+      // Try lookup by name first; fall back to ID-based lookup
+      let agentConfig = await this.brain.agents.findByName(agentName);
+      if (!agentConfig) {
+        // Try by ID (UUID-style input)
+        agentConfig = await this.brain.agents.findById(agentName);
+      }
+
+      if (!agentConfig) {
+        return {
+          command: 'agent',
+          success: false,
+          message: `Agent "${agentName}" not found. Use /agent list to see available agents.`,
+          conversationId,
+        };
+      }
+
+      // Apply the agent config to the live session and emit session:info (M5-003)
+      this.agentService.applyAgentConfig(
+        conversationId,
+        agentConfig.id,
+        agentConfig.name,
+        agentConfig.model ?? undefined,
+      );
+
+      // Broadcast updated session:info so TUI TopBar reflects new agent/model
+      this.chatGateway?.broadcastSessionInfo(conversationId, { agentName: agentConfig.name });
+
+      this.logger.log(
+        `Agent switched to "${agentConfig.name}" (${agentConfig.id}) for conversation ${conversationId} (M5-003)`,
+      );
+
+      return {
+        command: 'agent',
+        success: true,
+        message: `Switched to agent "${agentConfig.name}". System prompt and tools applied. Model: ${agentConfig.model ?? 'default'}.`,
+        conversationId,
+        data: { agentId: agentConfig.id, agentName: agentConfig.name, model: agentConfig.model },
+      };
+    } catch (err) {
+      this.logger.error(`Failed to switch agent "${agentName}": ${err}`);
+      return {
+        command: 'agent',
+        success: false,
+        message: `Failed to switch agent: ${String(err)}`,
+        conversationId,
+      };
+    }
+  }
 
   private async handleProvider(
     args: string | null,

apps/gateway/src/commands/commands.integration.spec.ts

@@ -39,6 +39,14 @@ const mockRedis = {
   keys: vi.fn().mockResolvedValue([]),
 };
 
+const mockBrain = {
+  agents: {
+    findByName: vi.fn().mockResolvedValue(undefined),
+    findById: vi.fn().mockResolvedValue(undefined),
+    create: vi.fn(),
+  },
+};
+
 // ─── Helpers ─────────────────────────────────────────────────────────────────
 
 function buildRegistry(): CommandRegistryService {
@@ -54,6 +62,7 @@ function buildExecutor(registry: CommandRegistryService): CommandExecutorService
     mockSystemOverride as never,
     mockSessionGC as never,
     mockRedis as never,
+    mockBrain as never,
     null, // reloadService (optional)
     null, // chatGateway (optional)
   );

packages/db/drizzle/0006_swift_shen.sql

@@ -0,0 +1 @@
+ALTER TABLE "conversations" ADD COLUMN "session_id" text;

packages/db/drizzle/meta/_journal.json

@@ -43,6 +43,13 @@
       "when": 1774225763410,
       "tag": "0005_minor_champions",
       "breakpoints": true
+    },
+    {
+      "idx": 6,
+      "version": "7",
+      "when": 1774227064500,
+      "tag": "0006_swift_shen",
+      "breakpoints": true
     }
   ]
 }

packages/db/src/schema.ts

@@ -319,6 +319,8 @@ export const conversations = pgTable(
       .references(() => users.id, { onDelete: 'cascade' }),
     projectId: uuid('project_id').references(() => projects.id, { onDelete: 'set null' }),
     agentId: uuid('agent_id').references(() => agents.id, { onDelete: 'set null' }),
+    /** M5-004: Agent session ID bound to this conversation. Nullable — set when a session is created. */
+    sessionId: text('session_id'),
     archived: boolean('archived').notNull().default(false),
     createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
     updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),