Implement the memory-store `scan` verb — a query-LESS, LIVE-only, globally
ordered top-N-by-recency read — and advertise `sortable_chunk_fields=
[{updated_at}]` at the Bifrost handshake. Advertising the cap is what lights
up Worldtree's #349 person-prime turn-1 durable-fact injection (Branch-A
`"updated_at" in caps.sort_fields_supported`); the fix is ZERO Worldtree
change — the running provider announcing the cap is the trigger.
scan is:
- LIVE-only server-side (INV-009): superseded/tombstoned excluded — a dead
fact can never inject; person-prime's `lifecycle_state=live` does not ride
the scan wire, so server-side is authoritative.
- Globally ordered before pagination (INV-010): the full scope-filtered live
set is ordered by (sort.field, direction) globally; missing value LAST,
chunk_id tiebreak. Backed by an expression index on
json_extract(record_json,'$.updated_at') to stay in the 500ms budget.
- Cursor = offset into the global order; emits a next cursor only when a
further match exists (no empty trailing page — matches the reference).
Sort is dispatch-gated: an unadvertised sort.field raises InvalidArguments,
never a silent unsorted fallback.
Contract amended: un-defers scan, adds the FN spec + INV-009/INV-010 +
sortable_chunk_fields to INV-006. TDD 7/7 green (scan_recency tracer,
live_only, scope_isolation, unadvertised_sort, person_prime_record_shape,
cursor pagination, parity_vs_reference vs InMemoryMemoryStore #195). Full
suite 638 green.
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