src/middleware/tool_call.rs

This file is your innermost middleware: it performs the registry lookup and runs the tool. There is no next here, because this is the end of your chain.

Key items

You build it with ToolCallMiddleware::new(registry), which stores an Arc<ToolRegistry> and registers under the name "tool_call".

Behavior notes

A registry miss becomes the soft error Tool not found: x. Available: ..., which is the exact shape UnknownToolMiddleware detects in order to append suggestions.

Panic containment wraps the call as AssertUnwindSafe(tool.call(...)).catch_unwind(), raced against your cancel signal. A panic becomes a soft error naming the tool and message, so your pipeline never hard-fails from a tool panic.

Cancellation observed here becomes the soft result "tool 'x' cancelled". In practice your engine’s biased cancel-vs-dispatch select usually wins first and surfaces the hard LoopError::Cancelled.

Deep dive: Middleware.