Sibling parity sweeps: wrapper arity vs primitive, range vs one-element RangeSet, literal entry points #139

The claim-driven oracles hold each document's promise per type, so they find a bug where a promise is checked and miss it at the sibling site that makes the same promise implicitly. The changelog shows the pattern repeatedly: IsAdjacentTo (6.2.1) → IsStrictlyLeftOf / Except (7.0.0) → RangeSet.Except(TRange) (8.0.0); wrapper arities lagging their primitive set ("as DecimalSet does"); ==/!= untested on 18 of 20 set types until the Stryker run.

A differential sweep between two things that must agree needs no ground truth: whichever side disagrees is the bug.

Scope

Three sweeps in test/CodoMetis.ValueRanges.Conventions.Tests/, one [DynamicData] row per discovered type, each registered in test/oracles/oracles.json with a seed patch it is shown to catch:

1. Primitive set vs its wrapper arity over an identity wrapper (Int32Set vs Int32Set<Same<int>>): every public operation (Contains/Add/Remove/Union/Intersect/Except/IsSubsetOf/…, equality and the operators), Parse/TryParse (string and span), ToString, JSON write and read, TypeConverter — same value, or the same exception type on the same bad input. The input grid includes whitespace-padded quoted elements, duplicates, out-of-order, empty and the family's extremes.
2. A range vs the one-element RangeSet holding it: every binary operation over the shape matrix (the spec enumeration DomainParityOracleTests uses, plus bounds at the domain's extremes) — a set operation on one-element sets equals the set built from the range operation's result, and every predicate answers alike.
3. One literal through the five entry points: string Parse, span Parse, JSON, TypeConverter, IConfiguration binding — an equal value, or all refuse it.

A disagreement found goes through Candidates.Verdict into candidates.json with its own issue.

Done

• the sweeps pass, or every disagreement is a candidate with an issue
• a seed per sweep, and dotnet run tools/oracles.cs seeds is green
• docs/testing.md and docs/oracles.md describe the sweeps