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/coding-agent/src/core/agent-session.ts

@@ -13,7 +13,14 @@
  * Modes use this class and add their own I/O layer on top.
  */
 
-import type { Agent, AgentEvent, AgentState, AppMessage, Attachment, ThinkingLevel } from "@mariozechner/pi-agent-core";
+import type {
+	Agent,
+	AgentEvent,
+	AgentMessage,
+	AgentState,
+	Attachment,
+	ThinkingLevel,
+} from "@mariozechner/pi-agent-core";
 import type { AssistantMessage, Message, Model, TextContent } from "@mariozechner/pi-ai";
 import { isContextOverflow, modelsAreEqual, supportsXhigh } from "@mariozechner/pi-ai";
 import { getAuthPath } from "../config.js";
@@ -403,7 +410,7 @@ export class AgentSession {
 	}
 
 	/** All messages including custom types like BashExecutionMessage */
-	get messages(): AppMessage[] {
+	get messages(): AgentMessage[] {
 		return this.agent.state.messages;
 	}