ALTER TABLE <T> ADD [CONSTRAINT <name>] (CHECK | UNIQUE | FOREIGN KEY)
and DROP CONSTRAINT <name>. ADD = table-CHECK + composite UNIQUE + FK
(ADD PRIMARY KEY and a named UNIQUE refused — composite UNIQUE is
anonymous in our model). Each ADD reuses a low-level path with a dry-run
guard (table-CHECK/UNIQUE rebuild; FK -> add_relationship, bare
REFERENCES -> parent single PK). DROP CONSTRAINT resolves the name to a
named table-CHECK then a child-side FK, else refuses. One undo step each.
Named table-CHECKs round-trip: a nullable `name` column on
__rdbms_playground_table_checks (rebuild-only arrival; a named add on a
pre-4g project is refused with a "rebuild first" hint) plus a project.yaml
check_constraints {expr, name} extension (bare-string form still reads).
The internal-__rdbms_* guard was folded into do_add_constraint /
do_add_relationship, completing that guard class.
Grammar: the action Choice keeps one branch per verb (add/drop/rename/
alter) with an inner Choice fanning out on the distinct second keyword,
since the walker's Choice does not backtrack between same-led branches.
Tests: 7 Tier-1 parse + 2 yaml round-trip + 1 internal-guard + 9 Tier-3
e2e. Help/usage refreshed; ADR-0035 §13 4g + README + requirements.md in
lockstep.
claude@clouddev1
6ff97f6e20