feat: surface stale-CODEOWNERS diff as info output instead of inline error

[dkisselev]

Summary

Follow-up to #107. That PR appended the stale-file diff to the CODEOWNERS out of date validation error itself. Two consequences:

1. The actionable line gets buried. A long diff renders directly under the headline, pushing Run \…` to update the CODEOWNERS file` (and any other validation categories) far up the CI log.
2. The wrapping gem raises the whole diff. The code_ownership Ruby gem raises the returned message, so the entire diff lands inside the stack trace.

This PR keeps the diff but moves it out of the error and into RunResult.info_messages.

How it works

main.rs::maybe_print_errors already prints info_messages before the validation errors and still process::exit(1). So:

• the diff prints first, as informational stdout;
• the terse, actionable headline prints last, at the bottom of the log where people look;
• exit code is unchanged (still 1).

Before (#107)

CODEOWNERS out of date. Run `bin/codeownership validate` to update the CODEOWNERS file
The following changes are required (- current, + expected):
-# Outdated content to trigger validation error
... <potentially hundreds of diff lines> ...

After

The following changes are required (- current, + expected):
-# Outdated content to trigger validation error
... <diff> ...

CODEOWNERS out of date. Run `bin/codeownership validate` to update the CODEOWNERS file

Implementation

• Error::messages() no longer emits the diff for CodeownershipFileIsStale (back to vec![]).
• New Errors::info_messages() extracts the diff(s) as informational strings.
• Runner::validate_all populates RunResult.info_messages from it alongside the (now terse) validation_errors.
• The diff field on the error variant is retained, just sourced differently.

Tests

• Updated the three exact-match integration tests (executable_name_config_test.rs, invalid_project_test.rs) for the new ordering — diff block first, headline after.
• Existing codeowners_diff unit tests are unchanged.

All tests, clippy --all-targets --all-features -D warnings, and fmt --check pass (enforced by the pre-commit hook).

Note

This does not fully shrink what the gem raises: both info_messages and validation_errors go to stdout, so if the gem captures all of stdout the diff is still in the captured text. It does fix log ordering/readability. Genuinely shrinking the raised error would require routing the diff to stderr (a separate channel) — happy to take that direction instead if preferred.

🤖 Generated with Claude Code