feat(oxlint): add agent output mode

[JoviDeCroock]

Summary

• add an oxlint agent formatter with one-line diagnostics and no summary
• include diagnostic help text inline when available
• keep the scope to explicit --format agent support only

This comes in handy when running oxlint from an agent so we can reduce the tokens used.

Tests

• INSTA_UPDATE=always cargo test -p oxlint output_formatter::test::test_output_formatter_diagnostic_formats -- --nocapture
• cargo test -p oxlint agent -- --nocapture
• cargo test -p website_linter --all-features
• cargo test -p website_formatter --all-features

AI disclosure

Reviewed and opened with assistance from an AI coding agent.

[camchenry]

Thanks for working on this! We have discussed this here: #20514.

I think we should rename the formatter to "agent" so that it's clear this is not intended for human eyes. Maybe we'll add a true minimal output in the future too. What do you think?

We can also skip the auto enable discussed in that issue for now too.

[JoviDeCroock]

I was planning on doing the auto-detection as a follow-up 😅 I did not initially see that issue will give that a read, thank you for surfacing it.

I applied your feedback, hope this works for you, thank you so much for getting to this so quickly!

[Sysix]

Note: this looks a lot like stylish format https://github.com/oxc-project/oxc/blob/main/apps/oxlint/src/snapshots/fixtures__cli__output_formatter_diagnostic_--format%3Dstylish%20test.js%40oxlint.snap

[camchenry]

I think that's ok personally, since this allows agent to be more flexible if we think of a way to reduce tokens in the future

[leaysgur]

For now, could you please narrow down the scope of this PR to just oxlint?

I think that will make it easier to proceed (, and since oxfmt is not interactive like linter, already outputs minimal information and the code itself seems to have room for improvement.)

[camchenry]

For now, could you please narrow down the scope of this PR to just oxlint?

I think that will make it easier to proceed (, and since oxfmt is not interactive like linter, already outputs minimal information and the code itself seems to have room for improvement.)

yeah, I think this makes sense. let's drop the --agent option now for too, as I think --format agent should be sufficient (plus, we'll hopefully auto-enable this for everyone at some point so you don't even need a --agent flag)