oh-my-pi/packages/coding-agent/test/issue-2750-subagent-runtime-fallback.test.ts

import { afterEach, describe, expect, it, vi } from "bun:test";
import type { Api, Model } from "@oh-my-pi/pi-ai";
import { buildModel } from "@oh-my-pi/pi-catalog/build";
import { Settings } from "@oh-my-pi/pi-coding-agent/config/settings";
import * as sdkModule from "@oh-my-pi/pi-coding-agent/sdk";
import type { AgentSession } from "@oh-my-pi/pi-coding-agent/session/agent-session";
import { runSubprocess } from "@oh-my-pi/pi-coding-agent/task/executor";
import type { AgentDefinition } from "@oh-my-pi/pi-coding-agent/task/types";

function model(provider: string, id: string): Model<Api> {
	return buildModel({
		provider,
		id,
		name: id,
		api: "openai-completions",
		baseUrl: `https://${provider}.example.test`,
		reasoning: false,
		input: ["text"],
		cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
		contextWindow: 128000,
		maxTokens: 8192,
	});
}

function createYieldingSession(): AgentSession {
	const listeners: Array<(event: { type: string; [key: string]: unknown }) => void> = [];
	const session = {
		agent: { state: { systemPrompt: ["test"] } },
		state: { messages: [] },
		extensionRunner: undefined,
		sessionManager: { appendSessionInit: () => {} },
		getActiveToolNames: () => ["yield"],
		setActiveToolsByName: async () => {},
		subscribe: (listener: (event: { type: string; [key: string]: unknown }) => void) => {
			listeners.push(listener);
			return () => {};
		},
		prompt: async () => {
			for (const listener of listeners) {
				listener({
					type: "retry_fallback_applied",
					from: "primary/bad-runtime-model",
					to: "fallback/working-model",
					role: "subagent:issue-2750",
				});
				listener({
					type: "tool_execution_end",
					toolCallId: "tool-yield",
					toolName: "yield",
					result: { content: [{ type: "text", text: "Result submitted." }], details: { status: "success" } },
					isError: false,
				});
			}
		},
		waitForIdle: async () => {},
		getLastAssistantMessage: () => undefined,
		abort: async () => {},
		dispose: async () => {},
	};
	return session as unknown as AgentSession;
}

describe("issue #2750: subagent runtime model fallback", () => {
	afterEach(() => {
		vi.restoreAllMocks();
	});

	it("passes ordered subagent candidates as a child retry fallback chain", async () => {
		const primary = model("primary", "bad-runtime-model");
		const fallback = model("fallback", "working-model");
		let childFallbackChains: Record<string, string[]> | undefined;
		vi.spyOn(sdkModule, "createAgentSession").mockImplementation(async options => {
			if (!options) throw new Error("Expected createAgentSession options");
			childFallbackChains = options.settings?.get("retry.fallbackChains") as Record<string, string[]> | undefined;
			return { session: createYieldingSession(), extensionsResult: {}, setToolUIContext: () => {} } as never;
		});

		const agent: AgentDefinition = { name: "task", description: "test", systemPrompt: "test", source: "bundled" };
		const result = await runSubprocess({
			cwd: "/tmp",
			agent,
			task: "work",
			index: 0,
			id: "issue-2750",
			modelOverride: ["primary/bad-runtime-model", "fallback/working-model"],
			settings: Settings.isolated(),
			modelRegistry: {
				refresh: async () => {},
				getAvailable: () => [primary, fallback],
				getApiKey: async () => "test-key",
			} as never,
			enableLsp: false,
		});

		let fallbackChain: string[] | undefined;
		for (const role in childFallbackChains) {
			const chain = childFallbackChains[role];
			if (chain?.includes("fallback/working-model")) {
				fallbackChain = chain;
			}
		}
		expect(fallbackChain).toEqual(["fallback/working-model"]);
		expect(result.modelOverride).toEqual(["primary/bad-runtime-model", "fallback/working-model"]);
		expect(result.resolvedModel).toBe("fallback/working-model");
	});
});