OPT-06: within-solve basis-reuse hull classification

Descriptive Release measurements for one implementation and three small 2D fixtures. No speedup or general scaling claim is made.

Measured source commit: ef70e8c580a9556b0f5d96e49070d33221bf5b64
Evidence: 42 measured rows, 0 failed rows; report status remains descriptive because no separate limiter profile was collected.
Timing scope: steady_clock around reduce_hull or reduce_hull_basis_reuse only; point cloud setup, HiGHS LP workspace creation, and independent hull-equivalence verification excluded.

Median durations

Per-method summary

case_id	method	attempts	successes	median_ns	min_ns	max_ns	median_lp_calls	median_pivots	median_degenerate_pivots	median_bulk_candidates	median_bulk_removals
degenerate	baseline	7	7	633400	623800	656100	7	0	0	0	3
degenerate	basis-reuse	7	7	51200	48800	53600	0	4	0	4	2
interior-basis	baseline	7	7	471200	456100	664300	5	0	0	0	1
interior-basis	basis-reuse	7	7	44400	42800	51500	0	4	2	2	0
permuted	baseline	7	7	901200	890100	936700	10	0	0	0	6
permuted	basis-reuse	7	7	52200	49400	55500	0	4	0	7	2

Evidence and limits

Every timed pair is followed by untimed mutual LP-membership checks of both retained hulls against each other. The deterministic interior-basis fixture is covered by the unit test but excluded from timing because the LP baseline returned incomplete; raw failed attempts are preserved separately.

Hardware/compiler/build details and all raw rows are retained in records.json, trials.csv, summary.csv, raw stdout JSONL, raw stderr, and the sanitized build log. LP/pivot/bulk counters describe operations, not elapsed-time components.

The fixtures are intentionally small and do not model the fuel-consumption application or establish production workload scaling. Timed methods are alternated, but no tuned performance verdict is drawn; a dedicated limiter profile and broader workload family would be needed before claiming a winner.