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/tools/ReadMusicTool.ts

@@ -12,22 +12,22 @@ import { FLUIDR3_INSTRUMENT_MAP } from '../../constants/generalMidiConstants';
  */
 export class ReadMusicTool extends BaseTool {
   readonly name = 'read_music';
-  readonly description = 'Read the music content from a specific track or all tracks, returning the content in ABC notation format.';
-  
+  readonly description = 'Read existing musical content from one or more tracks, returned as ABC notation. Use this to understand what notes already exist before making edits. Always call this before asking the user about their music. The output is bar-aligned and includes key/time signature headers.';
+
   readonly parameters: Record<string, ToolParameter> = {
     track_id: {
       type: 'string',
-      description: 'The track ID to read, or "all" to read all tracks. If not provided, reads the first available track.',
+      description: 'Which track to read. Pass a specific track ID, or "all" to read every track. If omitted, reads the first available track.',
       required: false
     },
     start_beat: {
       type: 'number',
-      description: 'Start beat position to read from (default: 0)',
+      description: 'Absolute beat position to start reading from. The actual output will be rounded down to the nearest bar boundary. Defaults to 0.',
       required: false
     },
     length: {
       type: 'number',
-      description: 'Length in beats to read (default: entire track/project)',
+      description: 'Number of beats to read. The actual output will be rounded up to the nearest bar boundary. If omitted, reads to the end of the track.',
       required: false
     }
   };