## What changed
- Add the `lru_plus_lexical_v1` selector, combining the 50 most recent skills
with weighted lexical matches through reciprocal rank fusion.
- Include the combined selector in the shadow-selection experiment and propagate
query and candidate truncation metadata from both inputs.
- Generalize the existing reciprocal-rank fusion helper to accept a rank
constant while preserving the existing lexical/character selector behavior.
## Testing
- Cover lexical-only selection, merging recent and matching skills, promotion
from agreement between both rankings, and weak overlaps.
- Extend the skills extension test to verify invocation metrics for the new
selector alongside `lru_v1`.
GitOrigin-RevId: 1b7b82bc97ea919c719cd05a009351b701019306
jif
3d7f9b4637