Fix optional dependency error classification

[id774]

Summary

• Automatic.require_optional now classifies a LoadError as a missing optional dependency only when its path matches the exact feature it was asked to require, converting that case to the new Automatic::OptionalDependencyError (a LoadError subtype).
• A LoadError raised from inside that feature's own load (a different, unrelated missing file) is re-raised unconverted, as the original exception.
• Automatic::CLI#run_recipe and the subcommand dispatch path now rescue Automatic::OptionalDependencyError specifically instead of LoadError in general, so an unrelated LoadError propagates instead of being reported as the one-line operator diagnostic.
• AutomaticSpec.plugin_available? (spec/spec_helper.rb) now rescues only Automatic::OptionalDependencyError to skip a plugin spec; any other LoadError from a plugin's own load now fails the spec instead of being silently skipped.

Reason

Previously, Automatic.require_optional caught every LoadError raised while requiring a feature, including one raised from a nested require deep inside that feature's own load path. That collapsed two different failures into one message: "the optional gem is not installed." This meant a genuinely broken plugin, dependency, or installation could be misreported as an operator-fixable missing-gem situation by the CLI, and could be silently skipped (false green) by the plugin spec helper, rather than surfacing as a real failure.

Compatibility

• Automatic.require_optional's argument interface (feature, needed_by:, gem_name:) is unchanged.
• The user-facing message for a genuinely missing optional dependency (gem name, needed_by, gem install guidance, source-checkout bundle guidance, original load failure) is unchanged.
• Automatic::OptionalDependencyError is a LoadError subtype, so any existing caller rescuing LoadError still catches it.
• No dependency, VERSION, or public CLI interface change.

Tests

• bundle exec rspec spec/lib/automatic_spec.rb — 17 examples, 0 failures.
• bundle exec rspec spec/lib/automatic/cli_spec.rb — 25 examples, 0 failures.
• bundle exec rspec spec/lib/automatic_spec_helper_spec.rb (new regression spec for AutomaticSpec.plugin_available?) — 3 examples, 0 failures.
• bundle exec rake spec — 373 examples, 0 failures.
• gem build automatic.gemspec — succeeded.
• bundle exec ruby -Ilib -e "require 'automatic'" — succeeded.
• bundle exec bin/automatic --version and --help — succeeded.

Version History

Recorded as one independent release item under the existing unreleased v26.09 section of doc/VERSIONS:

Distinguish missing optional dependencies from unrelated load failures so CLI diagnostics and plugin-spec skips do not hide broken loads.

VERSION remains 26.09; no version bump.

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https://claude.ai/code/session_01H8NygEHhT3zGMnBmQF2F6Q

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