refactor(agent-kit): pass CAS store through AgentContext

Expose the store created during context build on AgentContext so agents
reuse the same in-memory cache instead of opening a second store.

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/mock-agent.ts

@@ -1,11 +1,7 @@
 #!/usr/bin/env bun
 // Mock agent for smoke testing
 import { bootstrap, type JSONSchema, putSchema } from "@uncaged/json-cas";
-import {
-  createAgent,
-  createAgentStore,
-  resolveStorageRoot,
-} from "../packages/uwf-agent-kit/src/index.js";
+import { createAgent } from "../packages/uwf-agent-kit/src/index.js";
 
 const MOCK_RAW_OUTPUT_SCHEMA: JSONSchema = {
   title: "mock-raw-output",
@@ -21,7 +17,7 @@ const agent = createAgent({
   name: "mock",
   run: async (ctx) => {
     const output = `Mock output for role ${ctx.role}: task was "${ctx.prompt}"`;
-    const { store } = await createAgentStore(resolveStorageRoot());
+    const { store } = ctx;
     await bootstrap(store);
     const schemaHash = await putSchema(store, MOCK_RAW_OUTPUT_SCHEMA);
     const detailHash = await store.put(schemaHash, { text: output });