fix(coding-agent): support dynamic tool registration and tool prompt snippets closes #1720

packages/coding-agent/test/agent-session-dynamic-tools.test.ts

@@ -0,0 +1,75 @@
+import { existsSync, mkdirSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { getModel } from "@mariozechner/pi-ai";
+import { Type } from "@sinclair/typebox";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { DefaultResourceLoader } from "../src/core/resource-loader.js";
+import { createAgentSession } from "../src/core/sdk.js";
+import { SessionManager } from "../src/core/session-manager.js";
+import { SettingsManager } from "../src/core/settings-manager.js";
+
+describe("AgentSession dynamic tool registration", () => {
+	let tempDir: string;
+	let agentDir: string;
+
+	beforeEach(() => {
+		tempDir = join(tmpdir(), `pi-dynamic-tool-test-${Date.now()}-${Math.random().toString(36).slice(2)}`);
+		agentDir = join(tempDir, "agent");
+		mkdirSync(agentDir, { recursive: true });
+	});
+
+	afterEach(() => {
+		if (tempDir && existsSync(tempDir)) {
+			rmSync(tempDir, { recursive: true, force: true });
+		}
+	});
+
+	it("refreshes tool registry when tools are registered after initialization", async () => {
+		const settingsManager = SettingsManager.create(tempDir, agentDir);
+		const sessionManager = SessionManager.inMemory();
+
+		const resourceLoader = new DefaultResourceLoader({
+			cwd: tempDir,
+			agentDir,
+			settingsManager,
+			extensionFactories: [
+				(pi) => {
+					pi.on("session_start", () => {
+						pi.registerTool({
+							name: "dynamic_tool",
+							label: "Dynamic Tool",
+							description: "Tool registered from session_start",
+							promptSnippet: "Run dynamic test behavior",
+							parameters: Type.Object({}),
+							execute: async () => ({
+								content: [{ type: "text", text: "ok" }],
+								details: {},
+							}),
+						});
+					});
+				},
+			],
+		});
+		await resourceLoader.reload();
+
+		const { session } = await createAgentSession({
+			cwd: tempDir,
+			agentDir,
+			model: getModel("anthropic", "claude-sonnet-4-5")!,
+			settingsManager,
+			sessionManager,
+			resourceLoader,
+		});
+
+		expect(session.getAllTools().map((tool) => tool.name)).not.toContain("dynamic_tool");
+
+		await session.bindExtensions({});
+
+		expect(session.getAllTools().map((tool) => tool.name)).toContain("dynamic_tool");
+		expect(session.getActiveToolNames()).toContain("dynamic_tool");
+		expect(session.systemPrompt).toContain("- dynamic_tool: Run dynamic test behavior");
+
+		session.dispose();
+	});
+});

packages/coding-agent/test/extensions-runner.test.ts

@@ -60,6 +60,7 @@ describe("ExtensionRunner", () => {
 		getActiveTools: () => [],
 		getAllTools: () => [],
 		setActiveTools: () => {},
+		refreshTools: () => {},
 		getCommands: () => [],
 		setModel: async () => false,
 		getThinkingLevel: () => "off",

packages/coding-agent/test/system-prompt.test.ts

@@ -37,4 +37,19 @@ describe("buildSystemPrompt", () => {
 			expect(prompt).toContain("- write:");
 		});
 	});
+
+	describe("custom tool snippets", () => {
+		test("includes custom tools in available tools section", () => {
+			const prompt = buildSystemPrompt({
+				selectedTools: ["read", "dynamic_tool"],
+				toolSnippets: {
+					dynamic_tool: "Run dynamic test behavior",
+				},
+				contextFiles: [],
+				skills: [],
+			});
+
+			expect(prompt).toContain("- dynamic_tool: Run dynamic test behavior");
+		});
+	});
 });