fix(diagnostics): remove private issue refs in checks and add AST guard - #207

Merged — thank you, this is a clean piece of work.

Two things I want to name specifically. Scoping the guard to palinode/diagnostics/ at the directory boundary is exactly right: a repo-wide version can't work, because it would reject this same file's test_bare_number_is_rejected fixture, and you sidestepped that structurally rather than with an exclusion list. And you reused _issue_refs instead of writing a second definition of what counts as unfollowable — that distinction is deliberately single-sourced, so extending the guard without forking it is the right instinct.

You also updated the existing linked_issue == "#190" assertion in test_diagnostics_skeleton.py alongside the implementation, in its own clearly-named commit. Carrying the test surface with the change instead of leaving it to the reviewer is the part that made this reviewable in one pass.

One note for anyone reading this back: the guard covers docstrings as well as ordinary literals, since both are string constants to the AST. That's the behaviour we want — worth knowing so it isn't a surprise the first time a docstring trips it.

I'll add you to AUTHORS.md. If you'd like another issue, say so and I'll point you at one.

Thanks @Paul-Kyle! Appreciate the detailed review, feedback, and the add to AUTHORS.md.

I'd love to take on another issue #169 - please feel free to point me at one whenever convenient!
I've commented on #169 as well!