feat(plugins): attach tools to individual agent sessions

packages/plugin/src/boundaries.test.ts

@@ -92,7 +92,12 @@ function typeErrors(code: string): string[] {
 }
 describe("plugin SDK import boundaries", () => {
   it("publishes process capabilities without their Windows implementation helpers", () => {
-    expect(Object.keys(server).sort()).toEqual(["execCommand", "spawnProcess", "terminateProcess"]);
+    expect(Object.keys(server).sort()).toEqual([
+      "defineAgentTool",
+      "execCommand",
+      "spawnProcess",
+      "terminateProcess",
+    ]);
   });
 
   it("classifies every published entry", () => {
@@ -209,3 +214,35 @@ describe("plugin panel SDK boundary", () => {
     ).toEqual([]);
   });
 });
+
+describe("plugin agent tools SDK boundary", () => {
+  it("lets a session hook attach typed tools without exposing their transport", () => {
+    expect(
+      typeErrors(`
+      import { z } from "zod";
+      import { defineAgentTool, type PluginServerContext, type AgentToolResult, type AgentToolContext, type AgentToolDefinition } from "@getpaseo/plugin/server";
+      const tool: AgentToolDefinition = defineAgentTool({
+        name: "create_issue",
+        description: "Create an issue",
+        input: z.object({ title: z.string(), count: z.string().transform(Number) }),
+        async execute(input, { agent, paseo, signal }) {
+          const count: number = input.count;
+          // @ts-expect-error input is inferred from the schema
+          input.missing;
+          return { text: agent.id + input.title, structuredContent: { count } };
+        },
+      });
+      export default function contribute(server: PluginServerContext) {
+        server.before("agent.session_open", ({ request }) => {
+          const title: string | null = request.title;
+          // @ts-expect-error labels are read-only
+          request.labels.x = "changed";
+          if (request.labels.x !== "y") return;
+          return { ...request, tools: [...request.tools, tool] };
+        });
+        return () => {};
+      }
+    `),
+    ).toEqual([]);
+  });
+});

packages/plugin/src/server/agent-tools.ts

@@ -0,0 +1,39 @@
+import type { PaseoApi } from "@getpaseo/client";
+import type { z } from "zod";
+import type { PluginHookAgent } from "./lifecycle.js";
+
+export interface AgentToolContext {
+  agent: PluginHookAgent;
+  paseo: PaseoApi;
+  signal: AbortSignal;
+}
+
+export interface AgentToolResult {
+  text?: string;
+  structuredContent?: unknown;
+  isError?: boolean;
+}
+
+export interface AgentToolDefinition {
+  name: string;
+  title?: string;
+  description: string;
+  input: z.ZodType;
+  execute(input: unknown, context: AgentToolContext): AgentToolResult | Promise<AgentToolResult>;
+}
+
+export function defineAgentTool<Input extends z.ZodType>(tool: {
+  name: string;
+  title?: string;
+  description: string;
+  input: Input;
+  execute(
+    input: z.output<Input>,
+    context: AgentToolContext,
+  ): AgentToolResult | Promise<AgentToolResult>;
+}): AgentToolDefinition {
+  if (!/^[a-z][a-z0-9_]*$/.test(tool.name) || tool.name.length > 64) {
+    throw new Error(`Invalid agent tool name: ${tool.name}`);
+  }
+  return tool;
+}

packages/plugin/src/server/index.ts

@@ -24,3 +24,6 @@ export type {
 } from "./lifecycle.js";
 
 export { spawnProcess, execCommand, terminateProcess } from "./process.js";
+
+export { defineAgentTool } from "./agent-tools.js";
+export type { AgentToolDefinition, AgentToolResult, AgentToolContext } from "./agent-tools.js";

packages/plugin/src/server/lifecycle.ts

@@ -1,3 +1,4 @@
+import type { AgentToolDefinition } from "./agent-tools.js";
 import type {
   AgentPermissionRequest,
   AgentPermissionResponse,
@@ -36,6 +37,9 @@ export interface PluginSessionOpenRequest {
   cwd: string;
   reason: "create" | "resume" | "refresh" | "import";
   purpose: "interactive" | "history";
+  readonly title: string | null;
+  readonly labels: Readonly<Record<string, string>>;
+  tools: AgentToolDefinition[];
   env: Record<string, string>;
 }