---
name: fill
description: This skill should be used when the user explicitly wants a specific todo!() stub implemented for them. Use when the user says "fill in this todo", "implement this one for me", "you can write this part", "I'm delegating this stub", or points at a specific unimplemented function they want completed. Implements only the targeted stub — nothing else.
argument-hint: "[optional: identify which todo!() to fill]"
---

# Fill a `todo!()` Stub

The user is explicitly handing off a specific stub. Implement it correctly
and idiomatically.

## Rules

- Implement **only** the specific `todo!()` indicated — do not touch adjacent code
- Write idiomatic Rust: prefer iterators over manual loops where natural,
  use `?` for error propagation, avoid unnecessary clones
- Add a `// NOTE:` comment for any non-obvious decision
  (e.g. why `Arc` vs `Rc`, why a specific iterator adapter)
- If the implementation reveals a design issue upstream (e.g. the function
  signature makes the task harder than it should be), note it as a
  `// DESIGN NOTE:` comment rather than silently working around it
- Do NOT refactor surrounding code

## After Generating

Add a short explanation (as a chat response, not a code comment) describing
**what the implementation is doing and why** — treat it as a mini code review
of the code you just wrote, so the user learns from it rather than just
accepting it.

## Input
$ARGUMENTS — identify which `todo!()` to fill, or infer from context