refactor: migrate agent system from XML tool calling to OpenAI SDK with native function calling

- Replace custom XML-based tool parsing (XMLToolExecutor) with OpenAI SDK's
  native tool_calls via `openai` npm package (dangerouslyAllowBrowser)
- Consolidate 4 LLM providers (OpenAI, Claude, Gemini, ClaudeOpenRouter)
  into a single OpenAI SDK-based LLMProvider compatible with any
  OpenAI-style API (OpenAI, OpenRouter, Ollama, vLLM)
- Move agentic tool execution loop from ChatBox into AgentCore
- Update Message type to support tool roles, tool_calls, and tool_call_id
- Update system prompt to remove XML formatting instructions (~45% smaller)
- Remove AttemptCompletionTool (replaced by stop_reason detection),
  ThinkTool, and ThinkingTool
- Polish tool descriptions for OpenAI function calling schema compliance
- Normalize base URLs by stripping /chat/completions suffix

src/agent/core/AgentState.ts

@@ -2,50 +2,73 @@
  * Manages the state of an agent conversation
  */
 
+/**
+ * Tool call info attached to assistant messages (OpenAI function calling format)
+ */
+export interface ToolCall {
+  id: string;
+  type: 'function';
+  function: {
+    name: string;
+    arguments: string; // JSON string of parameters
+  };
+}
+
 export interface Message {
   id: string;
-  role: 'user' | 'assistant';
-  content: string;
+  role: 'user' | 'assistant' | 'tool';
+  content: string | null;
   timestamp: number;
+  tool_calls?: ToolCall[];    // present on assistant messages when LLM invokes tools
+  tool_call_id?: string;      // present on tool-result messages, links back to ToolCall.id
 }
 
 export class AgentState {
   private messages: Message[] = [];
   private conversationId: string;
   private isWorkingOnTask: boolean = false;
-  
+
   constructor(conversationId?: string, isWorkingOnTask: boolean = false) {
     this.conversationId = conversationId || this.generateConversationId();
     this.isWorkingOnTask = isWorkingOnTask;
   }
-  
+
   /**
    * Add a message to the conversation
    */
-  addMessage(role: 'user' | 'assistant', content: string): string {
+  addMessage(
+    role: 'user' | 'assistant' | 'tool',
+    content: string | null,
+    options?: { tool_calls?: ToolCall[]; tool_call_id?: string }
+  ): string {
     const message: Message = {
       id: this.generateMessageId(),
       role,
       content,
-      timestamp: Date.now()
+      timestamp: Date.now(),
+      ...(options?.tool_calls ? { tool_calls: options.tool_calls } : {}),
+      ...(options?.tool_call_id ? { tool_call_id: options.tool_call_id } : {}),
     };
-    
+
     this.messages.push(message);
     return message.id;
   }
-  
+
   /**
    * Update the content of a message by ID
    */
-  updateMessage(messageId: string, content: string): boolean {
+  updateMessage(messageId: string, content: string | null, options?: { tool_calls?: ToolCall[] }): boolean {
     const messageIndex = this.messages.findIndex(msg => msg.id === messageId);
     if (messageIndex !== -1) {
       this.messages[messageIndex].content = content;
+      if (options?.tool_calls) {
+        this.messages[messageIndex].tool_calls = options.tool_calls;
+      }
       return true;
     }
     return false;
   }
-  
+
   /**
    * Remove a message by ID
    */
@@ -57,46 +80,46 @@ export class AgentState {
     }
     return false;
   }
-  
+
   /**
    * Remove the last N messages
    */
   removeLastMessages(count: number): void {
     this.messages.splice(-count, count);
   }
-  
+
   /**
    * Get all messages in the conversation
    */
   getMessages(): Message[] {
     return [...this.messages];
   }
-  
+
   /**
    * Get the conversation ID
    */
   getConversationId(): string {
     return this.conversationId;
   }
-  
+
   /**
    * Clear all messages
    */
   clearMessages(): void {
     this.messages = [];
   }
-  
+
   /**
    * Get the last N messages
    */
   getRecentMessages(count: number): Message[] {
     return this.messages.slice(-count);
   }
-  
+
   private generateConversationId(): string {
     return `conv_${Date.now()}_${Math.random().toString(36).substring(2, 15)}`;
   }
-  
+
   private generateMessageId(): string {
     return `msg_${Date.now()}_${Math.random().toString(36).substring(2, 15)}`;
   }
@@ -109,4 +132,4 @@ export class AgentState {
   setIsWorkingOnTask(isWorkingOnTask: boolean): void {
     this.isWorkingOnTask = isWorkingOnTask;
   }
-}
+}