Spec audit pass — survey AGENTS.md "In scope" against the
existing fixture set, identify shapes that are documented as
supported but not pinned end-to-end, and add minimal apply +
verify_no_drift fixtures for each. All new fixtures pass on
the current main with no behaviour change.

24 apply fixtures (all `verify_no_drift: true` — strongest
form: pins generated SQL string, MySQL accepting it, AND
catalog round-tripping back without spurious diff):

  Index shapes:
  - add_index_desc.yml — `KEY (col DESC)` round-trip.
  - add_index_invisible.yml — `KEY ... INVISIBLE` round-trip.
  - add_index_with_prefix_length.yml — `KEY (col(N))` on
    VARCHAR.
  - add_index_on_blob_with_prefix_length.yml — same on BLOB
    (where MySQL *requires* the prefix length).
  - add_multi_column_unique_index.yml — column ordering
    preserved through `STATISTICS.SEQ_IN_INDEX`.
  - add_fulltext_index.yml — `CREATE FULLTEXT INDEX` shape
    (one of the 4 CREATE INDEX variants `appendAlterHints`
    handles).
  - modify_index_columns.yml — index column-list change must
    DROP+CREATE in that order.

  Column shapes:
  - add_column_on_update_current_timestamp.yml — `ON UPDATE
    CURRENT_TIMESTAMP`.
  - add_column_default_current_timestamp_only.yml — `DEFAULT
    CURRENT_TIMESTAMP` without ON UPDATE.
  - add_column_with_comment.yml — column-level COMMENT.
  - add_generated_column_stored.yml — `GENERATED ALWAYS AS
    (...) STORED`.
  - add_enum_column.yml — basic ENUM column round-trip
    (element-list diff is a known TODO; this only pins the
    CREATE shape).
  - add_json_column.yml — JSON column round-trip.
  - add_decimal_column.yml — `DECIMAL(M, D)` precision/scale.

  Foreign key shapes:
  - add_fk_on_delete_cascade.yml — explicit ON DELETE
    CASCADE.
  - add_fk_on_update_cascade.yml — explicit ON UPDATE
    CASCADE.
  - add_self_referential_fk.yml — same-table FK
    (employee.manager_id → employee.id).
  - add_multi_column_fk.yml — composite FK column list
    ordering through `KEY_COLUMN_USAGE.ORDINAL_POSITION`.
  - cross_table_fk_ripple_on_column_rename.yml — parent-side
    column rename re-writes child-side FK RefCols
    (`rewriteCrossTableFKRefCols`) so the child FK doesn't
    diff as DROP+ADD.

  Constraint shapes:
  - change_primary_key.yml — single-column → composite PK
    (DROP PRIMARY KEY then ADD PRIMARY KEY ordering).

  View shapes:
  - modify_view_body.yml — view body change emits
    `CREATE OR REPLACE VIEW` and converges.
  - create_view_with_column_aliases.yml — view's explicit
    column-alias list `(uid, uname)`.

  Combined operations:
  - add_column_and_dependent_index.yml — ADD COLUMN + CREATE
    INDEX in same plan; CREATE INDEX must come after ADD
    COLUMN.
  - add_column_with_alter_hints_instant.yml — `--alter-
    algorithm=INSTANT` on a column-level ALTER (trailing-
    comma splice path, complement to the partition-op
    leading-position splice path).

2 plan fixtures (filter coverage):

  - exclude_filter.yml — `--exclude=<table>` companion to
    the existing `include_filter.yml` (only-exact-name case
    was pinned, the exclude direction wasn't).
  - include_filter_glob.yml — `--include=tmp_*` glob
    pattern (existing `include_filter.yml` only used an
    exact name).

Two probes during the audit surfaced known untracked spec
gaps where the round-trip doesn't actually converge today
(CHECK constraint `NOT ENFORCED` and `TIMESTAMP NULL
DEFAULT NULL`). Per the "no spec changes" scope of this
branch I removed those fixtures; they're worth a separate
follow-up to either fix the diff layer or document the
limitation.

Likewise table-level `COMMENT='…'` changes aren't tracked
by the diff today — fixture removed, would need a separate
spec discussion.

`make lint` clean, full `go test -p 1 ./...` green, all 26
new fixtures pass.

Grammar: "apply once" → "applies once".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

- TODO: rewrite the CHECK NOT ENFORCED entry to point at the real
  gap (catalog/tables.go hard-codes Enforced=true) — model and diff
  layers already plumb the flag.
- TODO: rewrite the table-level COMMENT entry to point at the diff
  layer (Engine/Comment intentionally not diffed) — model and
  catalog already plumb the field.
- testdata/apply/add_json_column.yml: COLUMN_TYPE, not DATA_TYPE,
  matches what catalog/tables.go loadColumns actually selects.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>