The `CUSTOM_LEVELS`-only lookup raised `KeyError` for built-in
log levels such as 'INFO'. Resolve other registered names through
`logging.getLevelNamesMapping()` only when the custom lookup
misses, without eagerly evaluating the fallback on custom hits.
Deats,
- keep custom precedence, case-insensitive names and `NOTSET=0`;
- preserve integer inputs and unknown-name `KeyError` behavior;
- keep logger-local and global `isEnabledFor()` disable controls;
- advertise integer inputs on the adapter's `at_least_level()`;
- add 62 raw/adapted regressions with explicit threshold examples
and fixture docs distinguishing instance and global log state.
The logging suite passed all 70 cases; the original Piker consumer
probe passed 8/8 with its string-level feed guard retained.
Prompt-IO: ai/prompt-io/20261011T053737Z_a966928d_prompt_io.md
(this patch was generated in some part by `opencode` using
`gpt-6.1-sol` (`openai`))
Gud Boi