diff --git a/packages/core/src/agent/agent-session.ts b/packages/core/src/agent/agent-session.ts
index 8531c7d0..5448736d 100644
--- a/packages/core/src/agent/agent-session.ts
+++ b/packages/core/src/agent/agent-session.ts
@@ -15,6 +15,7 @@ import {
   createLsTool,
   createWriteTruthFileTool,
 } from "./agent-tools.js";
+import { createBookContextTransform } from "./context-transform.js";
 
 // ---------------------------------------------------------------------------
 // Types
@@ -245,6 +246,7 @@ export async function runAgentSession(
           createLsTool(projectRoot),
         ],
       },
+      transformContext: createBookContextTransform(bookId, projectRoot),
       streamFn: streamSimple,
       getApiKey: (provider: string) => {
         if (config.apiKey) return config.apiKey;
diff --git a/packages/core/src/agent/index.ts b/packages/core/src/agent/index.ts
index 406eca66..860c69d5 100644
--- a/packages/core/src/agent/index.ts
+++ b/packages/core/src/agent/index.ts
@@ -11,3 +11,4 @@ export {
   createLsTool,
 } from "./agent-tools.js";
 export { runAgentSession, evictAgentCache, type AgentSessionConfig, type AgentSessionResult } from "./agent-session.js";
+export { createBookContextTransform } from "./context-transform.js";