Record potools optimization learnings

[dshkol]

Summary

• add an implemented recommendation record for the potools optimization review
• distinguish the initial Gemini 3.7 candidate from Michael Chirico's iterative refinements
• update the data.table guide to consider whole-vector algorithms when ordered groups make them appropriate
• cite Brodie Gaslam's article on ordered grouped algorithms and numerical precision

Upstream cross-reference

This records the outcome and learnings from MichaelChirico/potools#334, which is merged upstream:

MichaelChirico/potools#334

The record links the initial generated commit, Michael's follow-up benchmark, the merge event, and the implemented default-branch commit. It also states that no reusable benchmark harness was preserved and keeps the inconclusive data.table timing regression visible.

Why

The case shows that sorted or otherwise constrained data can admit a simpler whole-vector operation than a general table operation. The guidance keeps that lesson narrow: include sorting and setup in the benchmark, reuse group boundaries, and validate numerical precision and special values.

Validation

• skill validator: passed
• git diff --check main...HEAD: passed
• recommendation frontmatter parsed and verified