src/middleware/unknown_tool.rs

This file turns your bare “tool not found” errors into teachable moments, so the model reads "Tool not found: redd_file. Available: ... Did you mean 'read_file'?" and corrects itself.

Key items

You install it with UnknownToolMiddleware::new(registry), which ships a 0.4 threshold, or with with_threshold(0.0..=1.0) when you want a stricter match.

similarity(a, b) -> f64 is your public static scorer. It measures an LCS-based ratio, then adds a prefix bonus, and it returns the score to you.

Behavior notes

Detection is deliberately specific. Your middleware acts only on a single text part that is is_error and contains both “not found” and “tool”, so “file not found” never triggers it.

The suggestion lookup reads the post-dispatch ctx.tool_name, which stays correct even behind renaming middleware, and a test pins that.

Ties break lexicographically, so your suggestions stay deterministic and order-independent. Trust that ordering when you compare two runs.

Names your model was never shown are pre-answered by the engine and never dispatched, so they never reach this layer. Read the suggestion text as advice, not as a guarantee that the tool exists.

Deep dive: Middleware.