feat(agent): implement multi-step agent loop with tool-calling support

[Jonnytoshen]

Overview

Upgrades the single-turn streamText call to a multi-step agent loop that lets the model call tools, inspect results, and continue reasoning — all within a single user turn.

Changes

New: src/tools/

Tool	Description
WeatherTool	Query weather by city name (mock data for now)
CalculatorTool	Evaluate math expressions

Both tools are re-exported via a barrel index.ts.

New: src/agent-loop.ts

Implements agentLoop(model, tools, messages, system):

• Iterates over fullStream events: text-delta, tool-call, tool-result
• Merges each step's messages back into the history so the model can reason over tool results
• Exits when no tool calls are made in a step; hard-capped at MAX_STEPS = 10 to prevent runaway loops

Modified: src/index.ts

• Replaces the inline streamText call with agentLoop()
• Registers WeatherTool and CalculatorTool in the tools map
• Updates the system prompt to reflect tool-use capability

Other

• src/version.ts: reads the version string from package.json, removing the hardcoded literal from the startup banner
• tsconfig.json: enables skipLibCheck to suppress type declaration errors introduced by the JSON module import

Testing

pnpm dev
# Try the following to verify tool calls:
# "What's the weather in Beijing today?"
# "What is 2 to the power of 10?"

Follow-up

• Connect WeatherTool to a real weather API
• Add unit tests for agentLoop step logic and tool execute functions
• Consider making MAX_STEPS configurable