Add session persistence and improve terminal ergonomics

src/agent.ts

@@ -94,6 +94,11 @@ export class Agent {
     return [...this.history];
   }
 
+  loadHistory(history: AgentMessage[]): void {
+    this.history.length = 0;
+    this.history.push(...history);
+  }
+
   reset(): void {
     this.history.length = 0;
   }

src/index.ts

@@ -5,15 +5,16 @@ import { Agent } from "./agent.js";
 import { CommandRegistry } from "./commands.js";
 import { EventBus } from "./events.js";
 import { loadExtensions } from "./extensions.js";
-import { ConsoleLogger } from "./logger.js";
+import { ConsoleLogger, ToggleLogger } from "./logger.js";
 import { OpenAIResponsesClient } from "./model/openai.js";
+import { SessionStore } from "./session.js";
 import { builtinTools } from "./tools/builtins.js";
 import { ToolRegistry } from "./tools/registry.js";
 
 const initialPrompt = process.argv.slice(2).join(" ").trim();
 
 const cwd = process.cwd();
-const logger = new ConsoleLogger();
+const logger = new ToggleLogger(new ConsoleLogger(), process.env.LOGS !== "off");
 const events = new EventBus();
 const registry = new ToolRegistry(events);
 const commands = new CommandRegistry(events);
@@ -21,6 +22,7 @@ const promptFragments = [
   process.env.SYSTEM_PROMPT ??
     "You are a helpful agent. Use tools when they are useful, and answer clearly."
 ];
+const sessionStore = new SessionStore(resolve(cwd, ".harness", "session.json"));
 
 for (const event of [
   "tool.registered",
@@ -66,17 +68,54 @@ await commands.register({
 await commands.register({
   name: "reset",
   description: "Clear the current conversation history.",
-  execute() {
+  async execute() {
     currentAgent?.reset();
+    loadedHistory = [];
+    await sessionStore.save([]);
     return "Conversation reset.";
   }
 });
 
 await commands.register({
   name: "history",
-  description: "Show how many conversation items are in memory.",
+  description: "Show current session details.",
   execute() {
-    return `Conversation items in memory: ${currentAgent?.getHistory().length ?? 0}`;
+    return [
+      `Conversation items in memory: ${currentAgent?.getHistory().length ?? loadedHistory.length}`,
+      `Session file: ${sessionStore.getPath()}`,
+      `Logs: ${logger.isEnabled() ? "on" : "off"}`
+    ].join("\n");
+  }
+});
+
+await commands.register({
+  name: "new",
+  description: "Start a new empty conversation.",
+  async execute() {
+    currentAgent?.reset();
+    loadedHistory = [];
+    await sessionStore.save([]);
+    return "Started a new conversation.";
+  }
+});
+
+await commands.register({
+  name: "save",
+  description: "Save the current conversation immediately.",
+  async execute() {
+    await sessionStore.save(currentAgent?.getHistory() ?? loadedHistory);
+    return `Session saved to ${sessionStore.getPath()}`;
+  }
+});
+
+await commands.register({
+  name: "logs",
+  description: "Toggle lifecycle logs on or off.",
+  execute(args) {
+    const next =
+      args === "on" ? true : args === "off" ? false : !logger.isEnabled();
+    logger.setEnabled(next);
+    return `Logs ${next ? "enabled" : "disabled"}.`;
   }
 });
 
@@ -84,16 +123,20 @@ await loadExtensions(resolve(cwd, "extensions"), registry, commands, events, cwd
 
 const systemPrompt = promptFragments.join("\n\n");
 let currentAgent: Agent | undefined;
+let loadedHistory = (await sessionStore.load())?.history ?? [];
 
 function getAgent(): Agent {
-  currentAgent ??= new Agent(
-    new OpenAIResponsesClient("gpt-5", systemPrompt, events),
-    registry,
-    {
-      cwd,
-      events
-    }
-  );
+  if (!currentAgent) {
+    currentAgent = new Agent(
+      new OpenAIResponsesClient("gpt-5", systemPrompt, events),
+      registry,
+      {
+        cwd,
+        events
+      }
+    );
+    currentAgent.loadHistory(loadedHistory);
+  }
 
   return currentAgent;
 }
@@ -134,6 +177,8 @@ async function handlePrompt(prompt: string, interactive = false): Promise<void>
 
   if (!interactive) {
     const answer = await getAgent().runTurn(prompt);
+    loadedHistory = getAgent().getHistory();
+    await sessionStore.save(loadedHistory);
     console.log(answer);
     return;
   }
@@ -143,13 +188,31 @@ async function handlePrompt(prompt: string, interactive = false): Promise<void>
 
   output.write("\x1b[36massistant>\x1b[0m ");
 
-  const answer = await getAgent().runTurn(prompt, {
-    onTextDelta(delta) {
-      wroteAssistantText = true;
-      streamedText += delta;
-      output.write(delta);
+  let answer: string;
+
+  try {
+    answer = await getAgent().runTurn(prompt, {
+      onTextDelta(delta) {
+        wroteAssistantText = true;
+        streamedText += delta;
+        output.write(delta);
+      }
+    });
+    loadedHistory = getAgent().getHistory();
+    await sessionStore.save(loadedHistory);
+  } catch (error) {
+    if (!wroteAssistantText) {
+      output.write(
+        error instanceof Error && error.message.includes("Missing credentials")
+          ? "Missing OPENAI_API_KEY. Set it before sending model prompts."
+          : error instanceof Error
+            ? error.message
+            : "Request failed."
+      );
     }
-  });
+    output.write("\n\n");
+    return;
+  }
 
   if (!wroteAssistantText) {
     output.write(answer);
@@ -168,15 +231,30 @@ if (initialPrompt) {
 const rl = createInterface({ input, output });
 
 console.log("Simple Agent Harness");
-console.log('Type a message, "/help" for commands, or "/exit" to quit.');
+console.log(
+  `Loaded ${loadedHistory.length} conversation items. Type "/help" for commands or "/exit" to quit.`
+);
+console.log('End a line with "\\" to continue onto the next line.');
 output.write("\x1b[32myou>\x1b[0m ");
 
+let multilineBuffer: string[] = [];
 for await (const prompt of rl) {
   if (prompt.trim() === "/exit") {
     break;
   }
 
-  await handlePrompt(prompt, true);
+  const continues = prompt.endsWith("\\");
+  const line = continues ? prompt.slice(0, -1) : prompt;
+  multilineBuffer.push(line);
+
+  if (continues) {
+    output.write("\x1b[33m...>\x1b[0m ");
+    continue;
+  }
+
+  const fullPrompt = multilineBuffer.join("\n");
+  multilineBuffer = [];
+  await handlePrompt(fullPrompt, true);
   output.write("\x1b[32myou>\x1b[0m ");
 }
 

src/logger.ts

@@ -17,3 +17,24 @@ export class ConsoleLogger implements Logger {
 export class NullLogger implements Logger {
   event(): void {}
 }
+
+export class ToggleLogger implements Logger {
+  constructor(
+    private readonly inner: Logger,
+    private enabled = true
+  ) {}
+
+  event(name: string, data?: LogData): void {
+    if (this.enabled) {
+      this.inner.event(name, data);
+    }
+  }
+
+  setEnabled(enabled: boolean): void {
+    this.enabled = enabled;
+  }
+
+  isEnabled(): boolean {
+    return this.enabled;
+  }
+}

src/session.ts

@@ -0,0 +1,40 @@
+import { mkdir, readFile, writeFile } from "node:fs/promises";
+import { dirname, resolve } from "node:path";
+import type { AgentMessage } from "./types.js";
+
+export type SessionSnapshot = {
+  history: AgentMessage[];
+  updatedAt: string;
+};
+
+export class SessionStore {
+  constructor(private readonly filePath: string) {}
+
+  async load(): Promise<SessionSnapshot | undefined> {
+    try {
+      return JSON.parse(await readFile(this.filePath, "utf8")) as SessionSnapshot;
+    } catch {
+      return undefined;
+    }
+  }
+
+  async save(history: AgentMessage[]): Promise<void> {
+    await mkdir(dirname(this.filePath), { recursive: true });
+    await writeFile(
+      this.filePath,
+      JSON.stringify(
+        {
+          history,
+          updatedAt: new Date().toISOString()
+        } satisfies SessionSnapshot,
+        null,
+        2
+      ),
+      "utf8"
+    );
+  }
+
+  getPath(): string {
+    return resolve(this.filePath);
+  }
+}