The body is lean: it states the project-specific rules (imports, prohibited crates) and immediately gives executable code snippets without explaining what an error or Result type is, assuming Claude's competence; every section earns its place.

Provides fully executable, copy-paste-ready Rust snippets (Report::new, change_context, attach, attach_with) plus concrete DO/DON'T rules and a decision table pointing to the right crate per location.

The Quick Start Guide sequences decisions by task (defining -> propagating -> documenting) with 'Use when' guidance, and the decision table gives an explicit routing rule plus a cross-skill link for the HashQL exception; this is effectively a single-action routing skill so the simple-skill note applies.

The SKILL.md is a concise overview that splits detailed content into three one-level-deep, well-signaled references (defining-errors.md, propagating-errors.md, documenting-errors.md), all of which exist in ./references/ with matching content; navigation is easy and references are not nested.

Lists multiple concrete actions including 'defining custom errors', 'propagating errors with change_context', 'adding context with attach', 'implementing Error trait', and 'documenting error conditions', matching the 'multiple specific concrete actions' anchor.

Clearly answers 'what' (HASH error handling patterns using error-stack crate) and 'when' via an explicit 'Use when working with...' clause enumerating specific triggers, satisfying the what-AND-when anchor.

Covers natural user-facing terms like 'Result types', 'Report types', 'error-stack', 'change_context', 'attach', and 'Error trait' that a developer would naturally say, with good coverage of the domain's vocabulary.

The niche is narrow and well-bounded (HASH-specific error-stack usage) with distinct trigger terms unlikely to conflict with other skills; the HashQL exception is handled in the body.