docs: close cross-surface residual wording, scope, and release posture

Makefile

@@ -251,14 +251,14 @@ coffeeshop-cross-surface-equivalence-report:
 	uv run -- python -m benchbox.core.equivalence.cross_surface --benchmark coffeeshop
 
 # Enforced gate: clickbench SQL<->DataFrame equivalence on a bounded DuckDB cell.
-# In GATES (datavault remains staged) and run in the blocking correctness-gate (pr.yml);
+# In GATES and run in the blocking correctness-gate (pr.yml);
 # exits non-zero on any unclassified divergence. Q18's order-less LIMIT is the one
 # classified exception (see _project/analysis/clickbench-cross-surface-divergences.md).
 clickbench-cross-surface-equivalence-report:
 	uv run -- python -m benchbox.core.equivalence.cross_surface --benchmark clickbench
 
 # Enforced gate: joinorder_synthetic SQL<->DataFrame equivalence on a bounded DuckDB
-# cell. In GATES (datavault remains staged) and run in the blocking correctness-gate
+# cell. In GATES and run in the blocking correctness-gate
 # (pr.yml); exits non-zero on any unclassified divergence (see
 # _project/analysis/joinorder-synthetic-cross-surface-divergences.md).
 joinorder-synthetic-cross-surface-equivalence-report:

_project/decisions/cross-surface-scope-and-release-posture-2026-09-27.md

@@ -0,0 +1,54 @@
+# Cross-surface scope boundary and release-branch posture
+
+Date: 2026-09-27
+
+Status: Accepted.
+
+## Scope boundary
+
+Cross-surface gates (`benchbox/core/equivalence/cross_surface.py`, `GATES`)
+cover benchmarks that ship both a SQL surface and a static `QueryRegistry`
+DataFrame surface. That is transcription and regression verification against
+DuckDB SQL references at a bounded equivalence scale: the two surfaces are
+authored from the same understanding by the same person, so the gate catches
+transcription drift, not shared conceptual errors, and its signal holds only
+at the gated scale (see the module docstring and
+`_project/analysis/cross-surface-oracle-independence.md` for per-benchmark
+provenance).
+
+Out of scope for the cross-surface gate, by construction:
+
+- Operation-pipeline benchmarks with no DataFrame query surface route to the
+  w2 fallback oracle (differential second-engine check or curated
+  expected-results subset), not to a cross-surface builder:
+  `write_primitives`, `metadata_primitives`, `transaction_primitives`,
+  `tpcdi` (see `_project/analysis/cross-surface-applicability.md`).
+- Dual-surface benchmarks that have a SQL surface plus a DataFrame query
+  registry but are not currently gated, per
+  `_project/analysis/cross-surface-applicability.md`: `joinorder` and
+  `nyctaxi` are not cheaply gateable (bounded-scale rejection, canonical
+  manifest fetch, or downloader-backed network fetch); `tpch_skew` and
+  `tsbs_devops` have unverified SQL-to-DataFrame ID mappings (zero verbatim
+  ID overlap, mapping must be confirmed independently, never guessed);
+  `tpcds_obt` has an abandoned correspondence (OBT-native Q1..Q17 versus
+  TPC-DS numbered SQL IDs, ruled out without renumbering one side). These
+  stay outside `GATES` until their named precondition is met; the
+  `joinorder_synthetic` CI-enforced gate covers scaled smoke-test data for
+  the JoinOrder family in the meantime.
+- `ai_primitives` and `vector_search` stay `supports_dataframe: false` in
+  `benchmark_registry.yaml` and are likewise single-surface benchmarks
+  needing a fallback oracle, not cross-surface members.
+
+Building the w2 fallback oracle itself is explicitly out of scope here; this
+record only routes the benchmarks to it so they are not silently unguarded.
+
+## Release-branch posture
+
+`test.yml` runs only the bounded `test-correctness-gate` on release-bound
+pull requests; the per-benchmark cross-surface suite runs in `pr.yml` on
+`develop`. Release PRs therefore rely on develop-time squash-merge
+enforcement: every change entering `develop` passes the blocking
+correctness-gate suite (including all `GATES` cross-surface reports) before
+it can ride a release. Adding the cross-surface suite to `test.yml` is a
+separate, explicitly approved CI change if it is ever wanted; until then,
+release coverage is by inheritance, not by omission.

benchbox/core/equivalence/builders/datavault.py

@@ -1,4 +1,4 @@
-"""Data Vault cross-surface gate builder (staged)."""
+"""Data Vault cross-surface gate builder."""
 
 from __future__ import annotations