[mgravell]

Implements the three findings from the v4 group-surface overload audit (now checked in as notes/api-surface/overload-audit.md, with an implementation postscript).

1. SortedSets: one method per operation, the axis is data

A SortedSetRange operand in the Expiration mould - ByRank(start, stop), ByScore(min, max, exclude), ByValue(min, max, exclude), with default meaning the whole set by rank - and five methods where there were eleven:

await db.SortedSets.RangeAsync(key, SortedSetRange.ByScore(1, 10), Order.Descending);
await db.SortedSets.RangeWithScoresAsync(key, SortedSetRange.ByRank(0, 9));
await db.SortedSets.RangeAndStoreAsync(src, dst, SortedSetRange.ByValue("a", "j"), take: 3);
await db.SortedSets.RemoveRangeAsync(key, SortedSetRange.ByScore(max: 0));
await db.SortedSets.RangeLengthAsync(key, SortedSetRange.ByValue("a", "j"));

LengthAsync slims to bare ZCARD (ZCOUNT/ZLEXCOUNT live under RangeLengthAsync), and the SortedSetOrder axis enum disappears from RangeAndStoreAsync. The per-axis methods demote to internal - the wire spelling, bound-swapping and the legacy IDatabase adapter all stay put.

Where the server has no command for a cell, the dispatcher throws rather than quietly answering a different question: WITHSCORES over a lexical range (every member of such a set shares one score - the audit originally mis-called this cell "arbitrarily missing"), LIMIT over a rank range, and a count of a rank range. A by-rank exclusivity, which the old surface rejected at runtime, is now unrepresentable: ByRank has no exclude parameter.

Two things the operand store path gains over the legacy shape: open (-/+) lexical bounds, and descending bound-swapping done for you (with REV the server wants high-then-low, exclusivity travelling with its bound - the same normalization the reads have always applied).

2. Keys.RestoreAsync takes an Expiration

RESTORE has ABSTTL, so the operand that already spells relative/absolute/none is the right one. Relative renders as the positional millisecond ttl; absolute adds the ABSTTL trailer; KEEPTTL/PERSIST/ENX are rejected (a restored key has no expiry to keep). The TimeSpan.MaxValue-means-none wart survives only in the internal sibling that serves the legacy surface.

3. GeoCenter folds the geo search pairs 4 → 2

SearchAsync and SearchAndStoreAsync each differed only in how the centre was spelled (member vs longitude/latitude). GeoCenter is that choice as data, implicit from RedisValue/string/GeoPosition - not from a (double, double) tuple, which the full-suite run caught: SanityChecks.ValueTupleNotReferenced pins that this library never references System.ValueTuple (net461 only gets it from an extra package). A default centre is rejected rather than silently searching (0, 0).

En route

RangeByScoreCore and CombineCore accepted a CancellationToken from their public callers and dropped it before SendAsync; both now forward it. Geo's SearchCore (and possibly others) have the same drop - left alone here, worth a sweep of its own.

Tests

Wire tests rewritten against the operand surface with identical byte expectations, plus new coverage: rank-axis dispatch, descending stores, the refusal matrix, RESTORE's three expiry spellings, and the default-GeoCenter rejection. Full net10.0 suite: 7532 passed / 167 skipped; the only failures are the 8 known-environmental SortedSetScanLarge ones (dev-server btree ZSCAN duplicates, fixed in the server 8.12 branch). Docs (Groups.md, LegacyApi.md mapping tables) updated.