RQL 2.0 conformance: divergence tracking

[kriszyp]

Tracking epic for converging Harper's REST query parsing/execution toward the RQL 2.0 specification (spec PR: HarperFast/rql#4). The spec is implementation-independent; this epic is Harper's divergence ledger — each row is either a bug (sub-issue), a feature gap (sub-issue), or a permitted representational difference (no action; Harper conforms via an adapter per spec §8).

Divergences (as of harper main, 2026-09)

#	Divergence	Class	Action
1	Simple queries (no structural chars) skip parsing; conditions surface as raw name/value pairs (dual shape)	permitted	adapter maps to canonical model
2	Chains attach as chainedConditions; nameless legs (a=ge=1&=5) inherit the previous comparator	representational + quirk	adapter; nameless legs are a syntax error in 2.0 — deprecate
3	Strict/coercive modeled as distinct comparators (equals/not_equal vs eq/ne)	permitted	adapter normalizes to value-literal modes (§5.2)
4	between is a first-class comparator	permitted	spec Appendix B alias; desugars to element-scoped ge+le
5	Sort is a linked list; select is a polymorphic array with marker props	permitted	adapter
6	(4) on a non-list comparator is the literal string "(4)"	tolerance	keep; producers must not rely on it
7	prop[]=v repeated array params	tolerance	spec Appendix B host accommodation
8	Parse errors deferred into the pipeline (parseError)	permitted	§6.1 allows deferred mode
9	group-by(...) accepted at parse and falls through into sort (missing break)	bug	fix in flight (dispatch harper-groupby-fallthrough); 2.0 parse-rejects reserved call names
10	Chained legs' values never type-coerced on the REST path → mixed-type ranges, silent superset/empty results	bug	#2433
11	Indexed elements attributes return one result per matching element (duplicates)	bug	#2434
12	contains matches numbers via decimal-string coercion	divergence	spec §5.1.1: string comparators match only strings; decide keep-as-divergence vs align
13	No not(...) group/scope negation	feature gap	sub-issue below
14	Element conditions (`prop[=ge=10	=le=2]`) and scoped sub-queries per §5.3 surface	partial

Pinning tests for rows 2/10/11/12 landed in #2437. The RQL reference parser + conformance suite (surface string → canonical AST) live on the spec branch; a differential corpus harness is queued (rql-conformance-corpus-diff).

[kriszyp]

Spec home for this ledger: the RQL 2.0 draft is now open as HarperFast/rql#86 (HarperFast/rql#86) — Appendix D links back to this epic, and Appendix E maps the PostgREST filter dialect onto the same canonical model.