List Internal Readiness Checks Endpoint

Operator drill-down on the ARD-720 post-snapshot validation paper trail.

Returns one row per (attempt_id, check_name, subject) — the append-only evidence written by the engine-setup gate. Operators use this to answer "why is this connector in failed_validation" without needing SQL access.

Filters:

• attempt_id narrows to one engine-setup attempt (latest first by default — combine with the rollup view below to find the right id).
• check_name narrows to a single validator family, such as row_count, snapshot_completion, domain_presence, table_presence, column_shape, pk_presence, unique_identity_presence, fk_validity, fk_presence, policy_presence, infra_signal, or unlogged_table_skipped.
• only_failed shows just the rows that drove the failed_validation verdict — the operator's primary view when paged.

Note: policy_presence rows with observed.present=false are informational by default and can appear on a healthy connector, so do not combine that drill-down with only_failed=true unless the connector opted into strict replicated-policy gating.