`src/middleware/output_limit.rs` — `OutputLimitMiddleware`

A hard cap on how much text a tool may return to the model.

Key items

• OutputLimitMiddleware::new(max_chars) — explicit limit; new(0) disables the layer entirely (the zero-disables convention).

Behavior notes

• Character-based, never byte-based — truncation lands on char boundaries (multi-byte scripts are safe); the marker \n[truncated] is reserved inside the budget.
• Keeps the head of the text; exact-at-limit passes through unchanged (strictly-greater comparison).
• Multipart outputs share one budget across text parts, in order; images pass through untouched; the parts array is never resized.
• Error text is also subject to the cap; duration and resolved_tool_name preserved; never sets is_error.

Deep dive: Middleware.