refactor(agent): expose concrete harness

packages/agent/src/harness/agent-harness.ts

@@ -1,6 +1,6 @@
 import { randomUUID } from "node:crypto";
 import { readFileSync } from "node:fs";
-import type { ImageContent, Model } from "@mariozechner/pi-ai";
+import type { AssistantMessage, ImageContent, Model } from "@mariozechner/pi-ai";
 import { Agent } from "../agent.js";
 import type { AgentEvent, AgentMessage, AgentTool, ThinkingLevel } from "../types.js";
 import { collectEntriesForBranchSummary, generateBranchSummary } from "./compaction/branch-summarization.js";
@@ -8,7 +8,6 @@ import { compact, DEFAULT_COMPACTION_SETTINGS, prepareCompaction } from "./compa
 import { expandPromptTemplate } from "./prompt-templates.js";
 import type {
 	AbortResult,
-	AgentHarness,
 	AgentHarnessContext,
 	AgentHarnessConversationState,
 	AgentHarnessEvent,
@@ -50,7 +49,7 @@ function createUserMessage(text: string, images?: ImageContent[]): AgentMessage
 	return { role: "user", content, timestamp: Date.now() };
 }
 
-export class DefaultAgentHarness implements AgentHarness {
+export class AgentHarness {
 	readonly agent: Agent;
 	readonly env: ExecutionEnv;
 	readonly conversation: AgentHarnessConversationState;
@@ -284,8 +283,9 @@ export class DefaultAgentHarness implements AgentHarness {
 		}
 	}
 
-	async prompt(text: string, options?: { images?: ImageContent[] }): Promise<void> {
+	async prompt(text: string, options?: { images?: ImageContent[] }): Promise<AssistantMessage> {
 		if (!this.operation.idle) throw new Error("AgentHarness is busy");
+		const beforeLength = this.agent.state.messages.length;
 		this.operation.idle = false;
 		this.operation.liveOperationId = randomUUID();
 		const expanded = this.expandSkillCommand(expandPromptTemplate(text, this.promptTemplates));
@@ -310,15 +310,26 @@ export class DefaultAgentHarness implements AgentHarness {
 		if (beforeResult?.messages) messages = [...beforeResult.messages, ...messages];
 		if (beforeResult?.systemPrompt) this.agent.state.systemPrompt = beforeResult.systemPrompt;
 		await this.agent.prompt(messages);
+		let response: AssistantMessage | undefined;
+		const newMessages = this.agent.state.messages.slice(beforeLength);
+		for (let i = newMessages.length - 1; i >= 0; i--) {
+			const message = newMessages[i]!;
+			if (message.role === "assistant") {
+				response = message;
+				break;
+			}
+		}
+		if (!response) throw new Error("AgentHarness prompt completed without an assistant message");
+		return response;
 	}
 
-	async skill(name: string, args?: string): Promise<void> {
+	async skill(name: string, args?: string): Promise<AssistantMessage> {
 		const skill = this.skills.find((candidate) => candidate.name === name);
 		if (!skill) throw new Error(`Unknown skill: ${name}`);
 		let content = readFileSync(skill.filePath, "utf8");
 		content = content.replace(/^---\s*\n[\s\S]*?\n---\s*\n?/, "").trim();
 		const prompt = args ? `${content}\n\n${args}` : content;
-		await this.prompt(prompt);
+		return await this.prompt(prompt);
 	}
 
 	steer(message: AgentMessage): void {

packages/agent/src/harness/factory.ts

@@ -1,6 +1,6 @@
-import { DefaultAgentHarness } from "./agent-harness.js";
+import { AgentHarness } from "./agent-harness.js";
 import { Session } from "./session/session.js";
-import type { AgentHarness, AgentHarnessOptions, SessionMetadata, SessionStorage } from "./types.js";
+import type { AgentHarnessOptions, SessionMetadata, SessionStorage } from "./types.js";
 
 export function createSession<TMetadata extends SessionMetadata>(
 	storage: SessionStorage<TMetadata>,
@@ -9,5 +9,5 @@ export function createSession<TMetadata extends SessionMetadata>(
 }
 
 export function createAgentHarness(options: AgentHarnessOptions): AgentHarness {
-	return new DefaultAgentHarness(options);
+	return new AgentHarness(options);
 }

packages/agent/src/harness/types.ts

@@ -1,5 +1,5 @@
 import type { ImageContent, Model, TextContent } from "@mariozechner/pi-ai";
-import type { Agent, AgentEvent, AgentMessage, ThinkingLevel } from "../index.js";
+import type { AgentEvent, AgentMessage, ThinkingLevel } from "../index.js";
 import type { Session } from "./session/session.js";
 
 export type SourceScope = "user" | "project" | "temporary";
@@ -524,60 +524,10 @@ export interface AgentHarnessOptions {
 	promptTemplates?: PromptTemplate[];
 	skills?: Skill[];
 	requestAuth?: (model: Model<any>) => Promise<{ apiKey: string; headers?: Record<string, string> } | undefined>;
-	initialModel?: Model<any>;
+	initialModel: Model<any>;
 	initialThinkingLevel?: ThinkingLevel;
 	initialActiveToolNames?: string[];
 	initialSystemPromptInputs?: SystemPromptInputs;
 }
 
-export interface AgentHarness {
-	readonly agent: Agent;
-	readonly env: ExecutionEnv;
-	readonly conversation: AgentHarnessConversationState;
-	readonly operation: AgentHarnessOperationState;
-
-	prompt(text: string, options?: AgentHarnessPromptOptions): Promise<void>;
-	skill(name: string, args?: string): Promise<void>;
-
-	steer(message: AgentMessage): void;
-	followUp(message: AgentMessage): void;
-	nextTurn(message: AgentMessage): void;
-
-	appendMessage(message: AgentMessage): Promise<void>;
-
-	shell(
-		command: string,
-		options?: {
-			cwd?: string;
-			env?: Record<string, string>;
-			timeout?: number;
-			signal?: AbortSignal;
-			onStdout?: (chunk: string) => void;
-			onStderr?: (chunk: string) => void;
-		},
-	): Promise<{ stdout: string; stderr: string; exitCode: number }>;
-
-	compact(customInstructions?: string): Promise<CompactResult>;
-	navigateTree(
-		targetId: string,
-		options?: { summarize?: boolean; customInstructions?: string; replaceInstructions?: boolean; label?: string },
-	): Promise<NavigateTreeResult>;
-
-	setModel(model: Model<any>): Promise<void>;
-	setThinkingLevel(level: ThinkingLevel): Promise<void>;
-	setActiveTools(toolNames: string[]): Promise<void>;
-	setSystemPromptInputs(inputs: SystemPromptInputs): Promise<void>;
-
-	abort(): Promise<AbortResult>;
-	waitForIdle(): Promise<void>;
-
-	subscribe(listener: (event: AgentHarnessEvent, signal?: AbortSignal) => Promise<void> | void): () => void;
-
-	on<TType extends keyof AgentHarnessEventResultMap>(
-		type: TType,
-		handler: (
-			event: Extract<AgentHarnessEvent, { type: TType }>,
-			ctx: AgentHarnessContext,
-		) => Promise<AgentHarnessEventResultMap[TType]> | AgentHarnessEventResultMap[TType],
-	): () => void;
-}
+export type { AgentHarness } from "./agent-harness.js";

packages/agent/test/harness/factory.test.ts

@@ -1,3 +1,4 @@
+import { getModel } from "@mariozechner/pi-ai";
 import { describe, expect, it } from "vitest";
 import { NodeExecutionEnv } from "../../src/harness/execution-env.js";
 import { createAgentHarness, createSession } from "../../src/harness/factory.js";
@@ -16,7 +17,7 @@ describe("harness factories", () => {
 	it("creates agent harnesses", () => {
 		const session = createSession(new InMemorySessionStorage());
 		const env = new NodeExecutionEnv({ cwd: process.cwd() });
-		const harness = createAgentHarness({ env, session });
+		const harness = createAgentHarness({ env, session, initialModel: getModel("anthropic", "claude-sonnet-4-5") });
 		expect(harness.env).toBe(env);
 		expect(harness.conversation.session).toBe(session);
 	});

packages/agent/test/scratch/simple.ts

@@ -0,0 +1,13 @@
+import { getModel } from "@mariozechner/pi-ai";
+import { InMemorySessionStorage } from "../../src/harness/session/storage/memory.js";
+import { createAgentHarness, NodeExecutionEnv, Session } from "../../src/index.js";
+
+const session = new Session(new InMemorySessionStorage());
+const agent = createAgentHarness({
+	env: new NodeExecutionEnv({ cwd: process.cwd() }),
+	session,
+	initialModel: getModel("openai-codex", "gpt-5.5"),
+});
+
+const response = await agent.prompt("What is 2 + 2?");
+console.log(response);