`_resolve_max_depth` is a process-wide `lru_cache`, so its once-per-value
warning survives across tests; any earlier in-process resolution of the same
invalid string turned `test_invalid_max_depth_warns_and_preserves_default_capture`'s
"exactly one warning" into 0 (probe: resolve 'nope' first, run the test ->
`assert 0 == 1`). An autouse fixture clears the cache around every test so the
assertions describe the plugin, not the order the tests ran in.
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