SQLite's LOWER() folds ASCII only -- lower('Édith') is 'Édith' unchanged --
so the EF-sourced facet fields UNDER-matched any stored value whose prefix
carries an uppercase non-ASCII character. An under-match is unrecoverable:
no later stage can reintroduce a row SQL never returned.
Adds a SECOND, ADDITIVE query taken only when the provider is SQLite and q
contains a non-ASCII character: raw Dapper SQL folding through etv_upper(),
a SqliteConnection.CreateFunction scalar implementing ToUpperInvariant.
Every other case -- all-ASCII q, and MySQL for all q -- runs the existing
EF query byte-identically.
MySQL needed no change and gets none: verified on MySQL 8.4 that its LOWER()
is Unicode-aware and its ci collation makes the predicate OVER-match, which
the existing ordinal filter already discards.
The fold is ToUpperInvariant because OrdinalIgnoreCase equality is a strict
SUBSET of invariant-uppercase equality, so the SQL stage yields a superset of
the final filter's matches and can never under-match. Note OrdinalIgnoreCase
is NOT "invariant-upper then ordinal": ToUpperInvariant('ſ') is 'S', yet
"ſweet".StartsWith("S", OrdinalIgnoreCase) is false. Tests pin that.
No migration, no model change; both provider snapshots are untouched.
Refs #668
Decisions-Edit: yes
timothy
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