Consumer reads over the catalog: the collapse as SQL, then the metric card, checks and bands

[phas02]

What it buys

A reader attached to the catalog, with no engine door, gets the consumer-facing surfaces: the metric card (definition, unit, formula, standing rulings, as-of), the declared checks with their band, and the band points with their breach. The rest of the quality surface — profiles, coverage, the landing account, open questions, lineage, rivals — stays the docket's.

Gated: a stable tree and a test bed with a second reader attached to the catalog. Nothing here is built before both stand.

What stands

• crates/catalog/src/record.rs:183 — the record's relations are tables of the catalog's own database, glossql_<relation>; a reader reaches them by a second attach of that database, not through the lake's tables.
• crates/glossary/src/store.rs:1294 — collapsed_read: the collapse (newest per subject, aspect, actor kind; human over agent; a witness's detector where one stands) is Rust; crates/session/src/reads.rs:389 — verdicts runs the detectors for it.
• crates/session/reads/metric_surfaces.sql — the metric card's record row, in the engine's dialect.
• crates/glossary/src/store.rs:439 — check outcomes and band points are rows of measurements, JSON; crates/scripts/functions/metric_bands.sql calls the kernel at measure time and re-runs at re-measure; crates/scripts/functions/band_breach.sql and crates/scripts/functions/rate_tolerance.sql are the judgments, SQL over slots at read.
• crates/session/src/whatif.rs:63 — whatif_batch: a plan rewrite and a kernel call per read; nothing landed.
• crates/catalog/src/tables.rs:62 — the catalog creates the macro tables; a macro carries one implementation per dialect (ducklake_macro_impl.dialect); nothing writes them.
• crates/session/src/cube.rs:1231 — land_head_inner: a computed result landed under its key and replaced in one commit, the pattern a landed read would follow.

The change

Two roads, both through the collapse:

• The collapse as SQL: collapsed_read and the detector run expressed as one query the engine plans, equal to the Rust collapse on every fixture. The first unit, and the only one without the gate.
• Then, per surface, one of: a macro in the catalog with an implementation in the engine's dialect and one in the reader's, over the record's tables (two texts per rule, held equal by the test bed); or a landed read, one small table per dataset under the head mechanism, replaced when the measurements it reads move (one text, one landing per re-measure).
• Whatif and a forecast stay out: they call the kernel per read, and whether a business reader needs them realtime or cached is measured first.

Done when

• The collapse as SQL: the session suite holds it equal to the Rust collapse on the corpus fixtures, detectors included.
• With the gate open: the metric card, the checks and the band points read from a second reader attached to the catalog, equal to the engine's reads on the finance fixture.
• Whatif is unchanged.