Make the INSERT row source a Choice between the VALUES clause and
Subgrammar(&sql_select::SQL_SELECT_COMPOUND). SQL_SELECT_COMPOUND
is itself a Choice that admits a leading WITH, so a WITH-prefixed
SELECT row source (R4) parses through it for free; the two
branches start on disjoint keywords (values vs select/with) so the
Choice never ambiguously commits. No worker change — do_sql_insert
already executes the validated SQL and re-persists, and the engine
handles insert-from-query.
Tests: grammar accept (plain / column-list+projection / WITH-
prefixed / trailing-semi) and reject (__rdbms_* on the SELECT's
FROM slot, incomplete select); integration parse-path lowering +
worker round-trip (rows land, CSV re-persisted) incl. R4 WITH end-
to-end; walker cross-cut that the Phase-2 unknown_column diagnostic
fires on the INSERT…SELECT projection; DA-gate test that a self-
sourced INSERT…SELECT runs as a plain insert (no cascade summary —
that is DELETE-only). Still behind the dev `sqlinsert` entry word
(shared `insert` is 3j). 1493 tests green, clippy clean.
claude@clouddev1
6ff9144c7a