Adds `anchor_presence_check_is_scoped_to_jsonc_blocks` to
`design_schema_drift.rs`. The test pins the property in two
directions: an anchor mentioned only in prose must report ABSENT
under the scoped helper; an anchor inside a ```jsonc``` block must
report PRESENT; the live `design/contracts/data-model.md` must
remain PRESENT (anti-over-narrowing guard).
The helper `anchor_in_jsonc_block` does not yet exist — this test
compile-blocks the entire `design_schema_drift` file, which is the
intended contract pressure: the GREEN side must introduce the
helper for any drift test to run.
Pre-rolesplit the audit framed this as "anchors live in Decision 11
instead of §Data model"; the role-split iter (176821c) made
`data-model.md` its own file, but the per-match scope was never
narrowed — `.contains()` still cannot tell jsonc-block anchors
(load-bearing) from prose anchors (incidental). This RED pins the
remaining surface.
refs #10
Brummel
c8c30d5682