KnownProblemsIntegrityTest

Guards DefaultKnownProblemsProvider against becoming dead config.

A known problem suppresses a check for a named entity. If that entity is later renamed or removed from the stubs, the entry stops matching anything — but nothing fails, because a suppression that never fires looks exactly like a suppression that was not needed. The entry survives as documentation of a problem that no longer exists at an id that no longer exists, and the next reader trusts it.

A typo made when writing an entry is already caught: the failure it was meant to suppress simply stays red. This test covers the other direction — an entry that was correct when written and has since drifted.

Scope, stated plainly: this asserts the entity exists. It does not assert the suppression is still needed — an entry whose underlying divergence PHP has since fixed keeps passing here. Detecting that means re-running each affected check with the suppression lifted, which is a larger piece of work; see T-W4 in .claude/reviews/REVIEW-2026-08-04-deprecated-since.md.