WIP: Refactor agent package - not compiling

- Renamed AppMessage to AgentMessage throughout
- New agent-loop.ts with AgentLoopContext, AgentLoopConfig
- Removed transport abstraction, Agent now takes streamFn directly
- Extracted streamProxy to proxy.ts utility
- Removed agent-loop from pi-ai (now in agent package)
- Updated consumers (coding-agent, mom) for AgentMessage rename
- Tests updated but some consumers still need migration

Known issues:
- AgentTool, AgentToolResult not exported from pi-ai
- Attachment not exported from pi-agent-core
- ProviderTransport removed but still referenced
- messageTransformer -> convertToLlm migration incomplete
- CustomMessages declaration merging not working properly

packages/agent/test/utils/calculate.ts

@@ -0,0 +1,32 @@
+import { type Static, Type } from "@sinclair/typebox";
+import type { AgentTool, AgentToolResult } from "../../src/types.js";
+
+export interface CalculateResult extends AgentToolResult<undefined> {
+	content: Array<{ type: "text"; text: string }>;
+	details: undefined;
+}
+
+export function calculate(expression: string): CalculateResult {
+	try {
+		const result = new Function(`return ${expression}`)();
+		return { content: [{ type: "text", text: `${expression} = ${result}` }], details: undefined };
+	} catch (e: any) {
+		throw new Error(e.message || String(e));
+	}
+}
+
+const calculateSchema = Type.Object({
+	expression: Type.String({ description: "The mathematical expression to evaluate" }),
+});
+
+type CalculateParams = Static<typeof calculateSchema>;
+
+export const calculateTool: AgentTool<typeof calculateSchema, undefined> = {
+	label: "Calculator",
+	name: "calculate",
+	description: "Evaluate mathematical expressions",
+	parameters: calculateSchema,
+	execute: async (_toolCallId: string, args: CalculateParams) => {
+		return calculate(args.expression);
+	},
+};