Tool trait, registry, and execution strategies for the behest agent runtime.

Key types

• [Tool] trait: the fundamental abstraction for callable capabilities
• [ToolRegistry]: thread-safe dynamic registration and dispatch
• [ToolExecutionStrategy]: controls serial vs parallel execution
• [FunctionTool]: closure-based tool with metadata
• [ToolOutput]: wrapped JSON output from tool execution

ToolExecutionStrategy

• Sequential: strict one-at-a-time execution
• Parallel: concurrent execution with a max concurrency cap
• Auto: intelligently groups read-only/concurrency-safe tools for parallel execution while serializing stateful tools