Type-mismatched comparisons and `= NULL` / `!= NULL` in a
WHERE expression now yield WARNING diagnostics — the command
still parses and runs (the ADR-0026 §7 permissive posture is
unchanged), but the validity indicator can flag it before
submission.
Computed post-walk from the built command's `Expr` against
the table's column types: a Compare / Between / In with a
column operand and a non-null literal whose type the column
cannot hold, or a Compare with `=` / `!=` against NULL. New
catalog keys `diagnostic.type_mismatch` / `diagnostic.eq_null`.
This is ADR-0026's deferred step 5, folded into ADR-0027's
diagnostics-severity model as the user requested.
claude@clouddev1
73c74701c2