write-spec - write a Gherkin .feature file

A Gherkin .feature file describes a feature's behaviour in a structured, human-readable format executable by a BDD test runner (Cucumber, SpecFlow, Behave, pytest-bdd, godog, etc.). It captures:

• What the feature does, from the user's perspective.
• Who uses it and why.
• Concrete scenarios with Given / When / Then steps.
• Edge cases and error paths, not just the happy path.

A good spec doubles as documentation and test plan. A bad spec reads like documentation and tests nothing - usually because scenarios are vague ("user does the thing" rather than "user enters '12345' and clicks 'Submit'").

This skill discovers the repo's conventions, discusses the feature with the user to draw out scenarios, then writes the .feature file in proper Gherkin.