docs(578): scope the bound to LOGICAL ROWS — physical work is not bounded, and I claimed it was

Comment- and docs-only. Verified: the diff for both .cs files contains no non-comment line.

HIGH (claim). "LIMIT n reads exactly n index entries and n rows" is false, and the bounded-physical-
work reading it implied is false with it. Two mechanisms, both retracted explicitly in the record
rather than quietly reworded:

- MySQL purge lag. Deleted clustered-index records survive until purge runs and a range scan still
  traverses them, so returning 2,000 VISIBLE rows can touch far more index records. Deletion history
  therefore STILL affects physical work — precisely what attempt 4's failure was supposed to have
  made irrelevant. Attempt 5 removes the LOGICAL dependence on Id distribution; it does not make
  physical work independent of deletion history.
- Unbounded row width. Artists/AlbumArtists are unrestricted TEXT/longtext and both SQLite and InnoDB
  spill to overflow pages, so a row count implies neither a byte count nor a page-read count.

The guarantee is now stated as exactly what it is: at most 20,000 LOGICAL rows returned/materialized,
and at most 10 round trips (11 for artist). The 392 KiB measurement is labelled one data point on one
library whose credits average ~20 B/row, with an instruction to re-measure rather than extrapolate
for long credit lists or MySQL over a network. Also noted: the query-shape test pins the SQL STRING —
it cannot pin a plan, MVCC visibility work or payload I/O, and on MySQL using the index to satisfy
ORDER BY is an optimizer choice, not a semantic guarantee.

Precision fix, and the reviewer is right that the sloppy version misleads: "any predicate defeats
LIMIT" is wrong, since the query's own cursor is a predicate. The distinction is a SEEKABLE PREDICATE
ON THE ORDERING KEY (positions the scan, never discards a row) versus a RESIDUAL predicate (discards
rows the engine already produced, so LIMIT bounds survivors and says nothing about how many were
produced). Restated in the handler, the record and api-conventions.

MEDIUM. docs/decisions.md still advertised "a superset LIKE pre-filter that may over-match but never
under-match" for list-valued columns. That is the documented entry point for convention lookups, so a
maintainer starting there was told to preserve exactly what round 4 deleted, in direct contradiction
of the linked active record. Fixed.

LOW. Two test comments read as current: "however many non-matching rows" (false past the ceiling —
now bounded and cross-referenced to the test that pins that boundary) and the ampersand case
"widens to the bare anchor" (no prefix predicate exists; kept because it is the input shape that
broke the old scheme, now labelled as such).

Fifth consecutive round of stale text, so this sweep was done by grepping the subject across handler,
tests, record, decisions.md, api-conventions.md and the endpoint description: LIKE, ESCAPE,
pre-filter, superset, over-match, under-match, anchor, keyspace, window, candidate, row cap, index
entries, 392, and every deleted constant name. Every surviving hit is now either current-and-correct
or explicitly framed as history.

docs/decisions.md

@@ -215,4 +215,4 @@ another doc or an old issue comment should land here and then follow the link.
 - 2026-07-25 — Rule-builder group nesting is bounded-arbitrary depth (`MAX_GROUP_DEPTH`), not one level (#436) — [`spa.rulebuilder-nesting`](decisions/records/spa/rulebuilder-nesting.md)
 - 2026-07-25 — The rationale-edit marker is a git trailer, not a substring anywhere in the commit range (#609) — [`ci.decisions-edit-trailer`](decisions/records/ci/decisions-edit-trailer.md)
 - 2026-07-25 — UI-E2E: headless Playwright flows in the existing `functional-e2e` job, browser baked into the CI image (#445) — [`ci.ui-e2e-harness`](decisions/records/ci/ui-e2e-harness.md)
-- 2026-07-26 — Facet-value typeahead restated: every artist source covered; list-valued columns via a superset LIKE pre-filter that may over-match but never under-match (#578) — [`api.search-field-values-sources`](decisions/records/api/search-field-values-sources.md)
+- 2026-07-26 — Facet-value typeahead restated: every artist source covered; the JSON-column source is paged by row position with no residual SQL predicate (#578) — [`api.search-field-values-sources`](decisions/records/api/search-field-values-sources.md)