feat(builtin-agent): persist ReAct loop turns as session JSONL

Each turn (assistant response / tool result) is appended to a JSONL file
at ~/.uncaged/workflow/sessions/<sessionId>.jsonl during the loop.

On completion, the JSONL is read back, each turn is stored as a CAS node,
and the detail payload references them as a flat turns[] array in
chronological order. The session file is then deleted.

Benefits:
- Real-time observability: tail -f the JSONL to watch loop progress
- Crash recovery: partial JSONL survives process death
- Zero write contention: one file per session
- Detail stays a flat array for easy consumption by CLI/dashboard

Changes:
- New session.ts: initSessionDir, appendSessionTurn, readSessionTurns, removeSession
- loop.ts: append JSONL each turn instead of accumulating in-memory
- detail.ts: reads session JSONL → persists turns to CAS → stores detail
- agent.ts: passes storageRoot/sessionId to loop, cleans up session on completion
- types.ts: remove index from TurnPayload (order is implicit in JSONL/array)
- schemas.ts: sync with type changes

Ref: #433

packages/workflow-agent-builtin/src/agent.ts

@@ -7,17 +7,26 @@ import {
   resolveModel,
   resolveStorageRoot,
 } from "@uncaged/workflow-agent-kit";
-import { generateUlid } from "@uncaged/workflow-util";
+import { createLogger, generateUlid } from "@uncaged/workflow-util";
 
 import { storeBuiltinDetail } from "./detail.js";
 import type { ChatMessage } from "./llm/index.js";
 import { BUILTIN_CONTINUE_MAX_TURNS, BUILTIN_MAX_TURNS, runBuiltinLoop } from "./loop.js";
 import { buildBuiltinMessages } from "./prompt.js";
-import type { BuiltinSessionState } from "./types.js";
+import { initSessionDir, removeSession } from "./session.js";
 
-const sessions = new Map<string, BuiltinSessionState>();
+const log = createLogger({ sink: { kind: "stderr" } });
 
-function getSession(sessionId: string): BuiltinSessionState {
+type SessionRecord = {
+  sessionId: string;
+  model: string;
+  startedAtMs: number;
+  messages: ChatMessage[];
+};
+
+const sessions = new Map<string, SessionRecord>();
+
+function getSession(sessionId: string): SessionRecord {
   const session = sessions.get(sessionId);
   if (session === undefined) {
     throw new Error(`builtin session not found: ${sessionId}`);
@@ -36,7 +45,7 @@ async function runBuiltinWithMessages(
   storageRoot: string,
   provider: ReturnType<typeof resolveModel>,
   messages: ChatMessage[],
-  session: BuiltinSessionState,
+  session: SessionRecord,
   store: Store,
   maxTurns: number,
 ): Promise<AgentRunResult> {
@@ -45,22 +54,31 @@ async function runBuiltinWithMessages(
     messages,
     toolCtx: buildToolContext(storageRoot),
     maxTurns,
-    existingTurns: session.turns,
+    storageRoot,
+    sessionId: session.sessionId,
   });
 
   session.messages = loopResult.messages;
-  session.turns = loopResult.turns;
 
-  const { detailHash, output } = await storeBuiltinDetail(
+  if (loopResult.turnCount === 0) {
+    log("5RWTK9NB", "no turns produced, returning empty output");
+    await removeSession(storageRoot, session.sessionId);
+    return { output: "", detailHash: "", sessionId: session.sessionId };
+  }
+
+  // Read jsonl → persist turns to CAS → store detail
+  const { detailHash } = await storeBuiltinDetail(
     store,
+    storageRoot,
     session.sessionId,
     session.model,
     session.startedAtMs,
-    session.turns,
   );
 
-  const finalOutput = output !== "" ? output : loopResult.finalText;
+  // Clean up session jsonl
-  return { output: finalOutput, detailHash, sessionId: session.sessionId };
+  await removeSession(storageRoot, session.sessionId);
+
+  return { output: loopResult.finalText, detailHash, sessionId: session.sessionId };
 }
 
 async function runBuiltin(ctx: AgentContext): Promise<AgentRunResult> {
@@ -69,14 +87,14 @@ async function runBuiltin(ctx: AgentContext): Promise<AgentRunResult> {
   const provider = resolveModel(config, config.defaultModel);
 
   const sessionId = generateUlid(Date.now());
+  await initSessionDir(storageRoot);
   const messages = buildBuiltinMessages(ctx);
 
-  const session: BuiltinSessionState = {
+  const session: SessionRecord = {
     sessionId,
     model: provider.model,
     startedAtMs: Date.now(),
     messages,
-    turns: [],
   };
   sessions.set(sessionId, session);
 

packages/workflow-agent-builtin/src/detail.ts

@@ -1,72 +1,15 @@
 import { bootstrap, putSchema, type Store } from "@uncaged/json-cas";
 
 import { BUILTIN_DETAIL_SCHEMA, BUILTIN_TURN_SCHEMA } from "./schemas.js";
-import type {
+import { readSessionTurns } from "./session.js";
-  BuiltinDetailPayload,
+import type { BuiltinDetailPayload } from "./types.js";
-  BuiltinLoopTurn,
-  BuiltinToolCall,
-  BuiltinTurnPayload,
-  BuiltinTurnRole,
-} from "./types.js";
-
-function mapToolCalls(calls: NonNullable<BuiltinLoopTurn["toolCalls"]>): BuiltinToolCall[] {
-  return calls.map((call) => ({
-    name: call.name,
-    args: call.args,
-  }));
-}
-
-function loopTurnToAssistantPayload(turn: BuiltinLoopTurn, index: number): BuiltinTurnPayload {
-  return {
-    index,
-    role: "assistant",
-    content: turn.assistantContent ?? "",
-    toolCalls:
-      turn.toolCalls !== null && turn.toolCalls.length > 0 ? mapToolCalls(turn.toolCalls) : null,
-    reasoning: null,
-  };
-}
-
-function loopTurnToToolPayloads(turn: BuiltinLoopTurn, startIndex: number): BuiltinTurnPayload[] {
-  if (turn.toolResults === null || turn.toolResults.length === 0) {
-    return [];
-  }
-  const payloads: BuiltinTurnPayload[] = [];
-  let index = startIndex;
-  for (const result of turn.toolResults) {
-    payloads.push({
-      index,
-      role: "tool" as BuiltinTurnRole,
-      content: result.content,
-      toolCalls: null,
-      reasoning: null,
-    });
-    index += 1;
-  }
-  return payloads;
-}
-
-/** Last assistant message with non-empty text. */
-export function extractFinalAssistantText(turns: BuiltinLoopTurn[]): string {
-  for (let i = turns.length - 1; i >= 0; i--) {
-    const turn = turns[i];
-    if (turn === undefined) {
-      continue;
-    }
-    const text = turn.assistantContent;
-    if (text !== null && text.trim() !== "") {
-      return text;
-    }
-  }
-  return "";
-}
 
 type BuiltinSchemaHashes = {
   turn: string;
   detail: string;
 };
 
-async function registerBuiltinSchemas(store: Store): Promise<BuiltinSchemaHashes> {
+export async function registerBuiltinSchemas(store: Store): Promise<BuiltinSchemaHashes> {
   await bootstrap(store);
   const [turn, detail] = await Promise.all([
     putSchema(store, BUILTIN_TURN_SCHEMA),
@@ -75,30 +18,22 @@ async function registerBuiltinSchemas(store: Store): Promise<BuiltinSchemaHashes
   return { turn, detail };
 }
 
+/** Read session jsonl, persist each turn to CAS, return detail hash. */
 export async function storeBuiltinDetail(
   store: Store,
+  storageRoot: string,
   sessionId: string,
   model: string,
   startedAtMs: number,
-  turns: BuiltinLoopTurn[],
   nowMs: number = Date.now(),
-): Promise<{ detailHash: string; output: string }> {
+): Promise<{ detailHash: string; turnCount: number }> {
   const schemas = await registerBuiltinSchemas(store);
+  const turns = await readSessionTurns(storageRoot, sessionId);
+
   const turnHashes: string[] = [];
-  let turnIndex = 0;
+  for (const turn of turns) {
-
+    const hash = await store.put(schemas.turn, turn);
-  for (const loopTurn of turns) {
+    turnHashes.push(hash);
-    const assistant = loopTurnToAssistantPayload(loopTurn, turnIndex);
-    const assistantHash = await store.put(schemas.turn, assistant);
-    turnHashes.push(assistantHash);
-    turnIndex += 1;
-
-    const toolPayloads = loopTurnToToolPayloads(loopTurn, turnIndex);
-    for (const toolPayload of toolPayloads) {
-      const toolHash = await store.put(schemas.turn, toolPayload);
-      turnHashes.push(toolHash);
-      turnIndex += 1;
-    }
   }
 
   const duration = Math.max(0, nowMs - startedAtMs);
@@ -110,6 +45,5 @@ export async function storeBuiltinDetail(
     turns: turnHashes,
   };
   const detailHash = await store.put(schemas.detail, detail);
-  const output = extractFinalAssistantText(turns);
+  return { detailHash, turnCount: turnHashes.length };
-  return { detailHash, output };
 }

packages/workflow-agent-builtin/src/index.ts

@@ -1,14 +1,16 @@
 export { createBuiltinAgent } from "./agent.js";
-export { extractFinalAssistantText, storeBuiltinDetail } from "./detail.js";
+export { registerBuiltinSchemas, storeBuiltinDetail } from "./detail.js";
 export type { ChatMessage, LlmAssistantResponse, LlmToolCall } from "./llm/index.js";
 export { chatCompletionWithTools } from "./llm/index.js";
 export { BUILTIN_CONTINUE_MAX_TURNS, BUILTIN_MAX_TURNS, runBuiltinLoop } from "./loop.js";
 export { buildBuiltinMessages } from "./prompt.js";
+export { appendSessionTurn, initSessionDir, readSessionTurns, removeSession } from "./session.js";
 export type { BuiltinTool, ToolContext } from "./tools/index.js";
 export { executeBuiltinTool, getBuiltinTools } from "./tools/index.js";
 export type {
   BuiltinDetailPayload,
   BuiltinLoopTurn,
-  BuiltinSessionState,
+  BuiltinToolCallRecord,
+  BuiltinToolResultRecord,
   BuiltinTurnPayload,
 } from "./types.js";

packages/workflow-agent-builtin/src/loop.ts

@@ -2,13 +2,14 @@ import type { ResolvedLlmProvider } from "@uncaged/workflow-agent-kit";
 import { createLogger } from "@uncaged/workflow-util";
 
 import { type ChatMessage, chatCompletionWithTools, type LlmToolCall } from "./llm/index.js";
+import { appendSessionTurn } from "./session.js";
 import {
   builtinToolsToOpenAi,
   executeBuiltinTool,
   getBuiltinTools,
   type ToolContext,
 } from "./tools/index.js";
-import type { BuiltinLoopTurn, BuiltinToolCallRecord, BuiltinToolResultRecord } from "./types.js";
+import type { BuiltinToolCall, BuiltinTurnPayload } from "./types.js";
 
 const log = createLogger({ sink: { kind: "stderr" } });
 
@@ -20,31 +21,61 @@ export type RunBuiltinLoopOptions = {
   messages: ChatMessage[];
   toolCtx: ToolContext;
   maxTurns: number;
-  existingTurns: BuiltinLoopTurn[];
+  storageRoot: string;
+  sessionId: string;
 };
 
 export type RunBuiltinLoopResult = {
   finalText: string;
   messages: ChatMessage[];
-  turns: BuiltinLoopTurn[];
+  turnCount: number;
 };
 
-function mapToolCalls(calls: LlmToolCall[]): BuiltinToolCallRecord[] {
+function mapToolCallsForPayload(calls: LlmToolCall[]): BuiltinToolCall[] {
   return calls.map((call) => ({
-    id: call.id,
     name: call.name,
     args: call.arguments,
   }));
 }
 
+async function appendTurn(
+  storageRoot: string,
+  sessionId: string,
+  payload: BuiltinTurnPayload,
+): Promise<void> {
+  await appendSessionTurn(storageRoot, sessionId, payload);
+}
+
+async function executeTurnTools(
+  calls: Array<{ id: string; name: string; arguments: string }>,
+  toolCtx: ToolContext,
+  messages: ChatMessage[],
+  storageRoot: string,
+  sessionId: string,
+): Promise<number> {
+  let turnCount = 0;
+  for (const call of calls) {
+    const result = await executeBuiltinTool(call.name, call.arguments, toolCtx);
+    messages.push({ role: "tool", tool_call_id: call.id, content: result });
+    await appendTurn(storageRoot, sessionId, {
+      role: "tool",
+      content: result,
+      toolCalls: null,
+      reasoning: null,
+    });
+    turnCount += 1;
+  }
+  return turnCount;
+}
+
 /** Agent run loop: LLM ↔ tools until no tool_calls or maxTurns. */
 export async function runBuiltinLoop(
   options: RunBuiltinLoopOptions,
 ): Promise<RunBuiltinLoopResult> {
   const messages = [...options.messages];
-  const turns = [...options.existingTurns];
   const openAiTools = builtinToolsToOpenAi(getBuiltinTools());
   let finalText = "";
+  let turnCount = 0;
 
   for (let turn = 0; turn < options.maxTurns; turn++) {
     log("8K2M4N7P", `builtin loop turn ${turn + 1}/${options.maxTurns}`);
@@ -59,36 +90,33 @@ export async function runBuiltinLoop(
 
     if (response.toolCalls === null || response.toolCalls.length === 0) {
       finalText = response.content ?? "";
-      turns.push({
+      await appendTurn(options.storageRoot, options.sessionId, {
-        assistantContent: response.content,
+        role: "assistant",
+        content: response.content ?? "",
         toolCalls: null,
-        toolResults: null,
+        reasoning: null,
       });
+      turnCount += 1;
       break;
     }
 
-    const toolCallRecords = mapToolCalls(response.toolCalls);
+    // Assistant turn with tool calls
-    const toolResults: BuiltinToolResultRecord[] = [];
+    await appendTurn(options.storageRoot, options.sessionId, {
-
+      role: "assistant",
-    for (const call of response.toolCalls) {
+      content: response.content ?? "",
-      const result = await executeBuiltinTool(call.name, call.arguments, options.toolCtx);
+      toolCalls: mapToolCallsForPayload(response.toolCalls),
-      toolResults.push({
+      reasoning: null,
-        toolCallId: call.id,
-        name: call.name,
-        content: result,
-      });
-      messages.push({
-        role: "tool",
-        tool_call_id: call.id,
-        content: result,
-      });
-    }
-
-    turns.push({
-      assistantContent: response.content,
-      toolCalls: toolCallRecords,
-      toolResults,
     });
+    turnCount += 1;
+
+    // Execute tools
+    turnCount += await executeTurnTools(
+      response.toolCalls,
+      options.toolCtx,
+      messages,
+      options.storageRoot,
+      options.sessionId,
+    );
   }
 
   if (finalText === "" && messages.length > 0) {
@@ -106,5 +134,5 @@ export async function runBuiltinLoop(
     }
   }
 
-  return { finalText, messages, turns };
+  return { finalText, messages, turnCount };
 }

packages/workflow-agent-builtin/src/schemas.ts

@@ -13,9 +13,8 @@ const BUILTIN_TOOL_CALL_SCHEMA: JSONSchema = {
 export const BUILTIN_TURN_SCHEMA: JSONSchema = {
   title: "builtin-turn",
   type: "object",
-  required: ["index", "role", "content"],
+  required: ["role", "content"],
   properties: {
-    index: { type: "integer" },
     role: { type: "string", enum: ["assistant", "tool"] },
     content: { type: "string" },
     toolCalls: {

packages/workflow-agent-builtin/src/session.ts

@@ -0,0 +1,59 @@
+import { appendFile, mkdir, readFile, rm } from "node:fs/promises";
+import { join } from "node:path";
+
+import { createLogger } from "@uncaged/workflow-util";
+
+import type { BuiltinTurnPayload } from "./types.js";
+
+const log = createLogger({ sink: { kind: "stderr" } });
+
+function sessionsDir(storageRoot: string): string {
+  return join(storageRoot, "sessions");
+}
+
+function sessionFile(storageRoot: string, sessionId: string): string {
+  return join(sessionsDir(storageRoot), `${sessionId}.jsonl`);
+}
+
+/** Ensure sessions directory exists. */
+export async function initSessionDir(storageRoot: string): Promise<void> {
+  await mkdir(sessionsDir(storageRoot), { recursive: true });
+}
+
+/** Append a turn to the session jsonl file. */
+export async function appendSessionTurn(
+  storageRoot: string,
+  sessionId: string,
+  turn: BuiltinTurnPayload,
+): Promise<void> {
+  const line = `${JSON.stringify(turn)}\n`;
+  await appendFile(sessionFile(storageRoot, sessionId), line, "utf-8");
+  log("3XQVN8KR", `session ${sessionId} appended ${turn.role} turn`);
+}
+
+/** Read all turns from session jsonl. Returns empty array if file does not exist. */
+export async function readSessionTurns(
+  storageRoot: string,
+  sessionId: string,
+): Promise<BuiltinTurnPayload[]> {
+  try {
+    const content = await readFile(sessionFile(storageRoot, sessionId), "utf-8");
+    const lines = content
+      .trim()
+      .split("\n")
+      .filter((l) => l.length > 0);
+    return lines.map((l) => JSON.parse(l) as BuiltinTurnPayload);
+  } catch {
+    return [];
+  }
+}
+
+/** Remove session jsonl file (called after detail is persisted to step CAS). */
+export async function removeSession(storageRoot: string, sessionId: string): Promise<void> {
+  try {
+    await rm(sessionFile(storageRoot, sessionId));
+    log("7FWDP2MJ", `session ${sessionId} removed`);
+  } catch {
+    // already gone — fine
+  }
+}

packages/workflow-agent-builtin/src/types.ts

@@ -34,7 +34,6 @@ export type BuiltinToolCall = {
 };
 
 export type BuiltinTurnPayload = {
-  index: number;
   role: BuiltinTurnRole;
   content: string;
   toolCalls: BuiltinToolCall[] | null;