support custom tools (#2668)

packages/plugin/src/tool.ts

@@ -0,0 +1,20 @@
+import { z } from "zod/v4"
+
+export type ToolContext = {
+  sessionID: string
+  messageID: string
+  agent: string
+  abort: AbortSignal
+}
+
+export function tool<Args extends z.ZodRawShape>(
+  input: (zod: typeof z) => {
+    description: string
+    args: Args
+    execute: (args: z.infer<z.ZodObject<Args>>, ctx: ToolContext) => Promise<string>
+  },
+) {
+  return input(z)
+}
+
+export type ToolDefinition = ReturnType<typeof tool>