Function select_tool 

pub fn select_tool(
    output: &str,
    tools: &[ToolDefinition],
) -> Result<ToolCall, ToolCallError>

Parse raw model output and extract the first tool call.

The parser looks for the <tool_call>…</tool_call> pattern emitted by the model and validates:

1. That a name field is present.
2. That the name appears in tools (when tools is non-empty).
3. That the arguments value, if present, is a valid JSON object.

On success the returned ToolCall carries a freshly generated ID.

Errors

• ToolCallError::NoToolCallFound — no <tool_call> tag found.
• ToolCallError::UnknownTool — name not in tools registry.
• ToolCallError::MalformedArguments — argument payload is not valid JSON.