Add on_register callback and bump to 0.18.0

[ngan]

What

Adds a new on_register callback that fires when a fixture is registered (declared), before any caching:

config.on_register do |event, scope|
  # event: FixtureKit::Event (the declared fixture)
  # scope: the declaring context — for RSpec, the example group that called `fixture`
end

• New :register event in Callbacks::EVENTS, exposed via Configuration#on_register.
• Fired from Runner#register (the single registration entry point both the RSpec and Minitest adapters go through) as run(:register, Event.new(fixture), scope).
• The scope rides alongside the Event as a second argument, mirroring how duration accompanies the Event for on_cache_saved/on_cache_mounted. Event itself is unchanged.
• Bumps the version to 0.18.0 (additive, backward compatible).
• Documents the callback in docs/reference.md.

Why the scope is a separate argument (not read off the fixture)

The declaring scope is not derivable from the Fixture:

• A named fixture stores only its name string as identifier, not a scope.
• Named fixtures are shared across scopes — one Fixture instance can be declared in many groups — so fixture → scope isn't even a function (see the existing spec/unit/fixture_registry_spec.rb "reuses the same named fixture instance across different scopes").
• definition.path for a named fixture points at the fixture definition file (spec/fixture_kit/<name>.rb), not the declaring spec.

The scope is only known at the register(name, scope) call site, which is where the hook fires.

Motivation

Lets tooling map a fixture declaration back to its originating spec file (scope.metadata[:file_path] for RSpec) at load time, without scanning RSpec.world or monkeypatching the DSL. First consumer: the Buildkite RSpec formatter, to flag which spec-file folds use FixtureKit.

Tests

• configuration_spec — on_register registers/runs callbacks with the event and scope.
• fixture_runner_spec — register fires on_register with the fixture Event and declaring scope.
• Full suite green: 185 examples, 0 failures.

🤖 Generated with Claude Code

https://claude.ai/code/session_01L6ts71bokStreee58rP3or