Erase one scope for good, in CortexDB's dialect

memory-api's scoped erasure: { scope, audit_note? } (at most 256 chars; any other field is a 400). Unlike a forget, which by default only drops what was derived, an erasure deletes the scope's raw events, derived layers, blobs and index entries, and those of every scope below it, and releases their write keys. memory-api pins the scope under the caller's own root and runs the erasure with the caller's user-actor token, so a caller can erase only its own memory; the root itself is refused (use DELETE /memory). Synchronous and answered unwrapped: { erased, scope, scopes, erasure_ids }. A 502 ERASURE_INCOMPLETE is retriable. Not billed.