[jmgirard]

Adds second oracle types for finer results in cairn/ORACLES.md, or records the parts still on one type.

• Five new tests: the final fit at a two-element eval_time equals the fit at its first element; a new weight on a left-out fold leaves its summary row unchanged; the desirability rule picks what its definitions pick; renormalized probability averages sum to one; a censored average over three repeats takes tune's median .pred_time.
• One assertion: the final fit's recorded first metric equals the set's first name.
• A source note for desirability2's help pages, registry rows and lines, and D-123.
• No package code change.

Candidate row: Give finer results a second oracle