test(engine): pin Lance 7 immutable-PK behavior + sharpen native-namespace alignment notes (#240)

* test(engine): pin Lance 7 immutable-PK behavior + sharpen native-namespace alignment notes

Follow-up polish to the Lance 7.0.0 alignment (the immutable-PK migration fix
and the realigned native-namespace surface test). Two precision nits, no
behavior change:

1. Pin the upstream behavior we now depend on. Lance 7 makes the unenforced PK
   immutable once set (`lance::dataset::transaction`): re-applying the reserved
   `lance-schema:unenforced-primary-key` key — even with the same value — errors
   "cannot be changed once set". That is exactly what broke `migrate_v1_to_v2`'s
   crash-idempotency and forced its field-guard. Add
   `lance_surface_guards.rs::unenforced_primary_key_is_immutable_once_set` so a
   future Lance bump that relaxes immutability turns red, prompting re-evaluation
   of the migration guard. (Matches the "first smoke check on a Lance bump"
   discipline in docs/dev/lance.md.)

2. Clarify that the native `DirectoryNamespace` decoupling is contingent on
   omnigraph's legacy boolean PK key, not an unconditional v7 property: with the
   position key the native namespace would still read the manifest. omnigraph
   keeps the boolean key deliberately — Lance honors it permanently (maps to PK
   position 0) and one uniform on-disk format beats a new-vs-old split, since
   existing graphs can't be re-keyed under the same immutability rule. Updated
   the test comment and the lance.md stanza; also corrected the stale `is_empty()`
   description of the migration guard (it now matches on the specific PK field).

* test(engine): make the immutable-PK guard's red-bar diagnostic fire in every change-shape

Review follow-up: the guard's re-set assertion chained `.unwrap().await.unwrap_err()`,
which only surfaces the actionable "Lance no longer rejects re-setting the unenforced
PK" message when immutability is enforced on the async commit path and still returns an
error. Two other change-shapes would panic generically instead, defeating the guard's
purpose:

- if Lance moves the check to the sync validation stage, the first `.unwrap()` panics
  with a bare "unwrap() on Err";
- if Lance relaxes immutability so the re-set succeeds, `.unwrap_err()` panics with a
  bare "unwrap_err() on Ok".

Normalize the sync `.update()` result and the async `.await` into one `Result` and assert
on it, so the diagnostic fires whichever stage enforces (or relaxes) the rule.

docs/dev/lance.md

@@ -166,8 +166,8 @@ Migration from Lance 6.0.1 → 7.0.0 landed in this cycle. **Arrow stayed 58, Da
 - **BTREE range-query bound inclusiveness fixed** (PR #6796, issue #6792): `x <= hi AND x > lo` returned the wrong boundary row on 6.0.1. omnigraph today builds BTREE only on string `@key` columns (`id`/`src`/`dst`) and queries them by equality/IN, not range, so its *current* query patterns almost certainly never hit this bug — but the corrected boundary semantics are a contract we rely on the moment a BTREE-range path appears (BTREE-on-properties via the index-type tickets, or a range-on-key query). Pinned by `lance_surface_guards.rs::btree_range_query_boundary_is_correct` (reproduces #6792's 5-row + BTREE shape).
 - **`WriteParams::auto_cleanup` default flipped from on (every-20-commits) to `None`** (PR #6755). On 6.0.1 the on-by-default hook could GC versions the `__manifest` pins for snapshots/time-travel. omnigraph owns cleanup explicitly (`optimize.rs::cleanup_all_tables`). Two parts to the fix, because `auto_cleanup` is **create-time config only and has no effect on existing datasets** (Lance `write.rs` docs): (1) `auto_cleanup: None` at all 11 `WriteParams` sites so *new* datasets store no cleanup config; (2) — the load-bearing half — `skip_auto_cleanup: true` on every commit path, because graphs created **before** the bump still carry the on-config in their datasets, and Lance's hook fires off the *dataset's stored* config at commit time (`io/commit.rs`: `if !commit_config.skip_auto_cleanup`). So the staged commit path (`commit_staged` → `CommitBuilder::with_skip_auto_cleanup(true)`), the `__manifest` publisher (`MergeInsertBuilder::skip_auto_cleanup(true)`), and the direct `WriteParams` paths all skip the hook. Without this, an upgraded graph would still auto-cleanup and delete `__manifest`-pinned versions. Pinned by `lance_surface_guards.rs::skip_auto_cleanup_suppresses_version_gc` (negative control + with-skip survival).
 - **Lance #6658 SHIPPED in 7.0.0** (`DeleteBuilder::execute_uncommitted`, exposed via PR #6781) → MR-A (migrate `delete_where` to the staged two-phase API, retire the parse-time D2 rule) is now **unblocked**, tracked separately (dev-graph `iss-950`). The bump itself keeps `delete_where` inline; the `_compile_delete_result_field_shape` guard is left untouched until MR-A.
-- **The unenforced primary key is now immutable once set** (`lance::dataset::transaction`, ~L2472–2480: `if !primary_key_before.is_empty() && (writes_primary_key || primary_key_after != primary_key_before) → "the unenforced primary key is a reserved key and cannot be changed once set"`). omnigraph marks `__manifest.object_id` as the unenforced PK (`lance-schema:unenforced-primary-key`) for merge-insert row-level CAS — baked into `manifest_schema()` at init, and added by the `migrate_v1_to_v2` internal-schema migration for pre-v0.4.0 graphs. The migration relied on Lance 6's idempotent re-apply for crash-recovery (a crash after the field-set but before the stamp bump re-enters the migration with the PK already present); under v7 that re-apply errors, so a real v1 graph could never finish migrating. Fixed by guarding the set with `schema().unenforced_primary_key().is_empty()` (`db/manifest/migrations.rs`). Regression: `db::manifest::tests::test_publish_migrates_pre_stamp_manifest_to_current_version` (was red under v7).
-- **Native `DirectoryNamespace` no longer recognizes omnigraph's manifest-tracked tables** (`lance-namespace-impls` dir.rs ~L1310): `list/describe/create_table_version` route through `check_table_status`, which reports an omnigraph table absent → `TableNotFound`. omnigraph production never uses Lance's native namespace (its publisher writes `__manifest` directly via merge_insert; its own `namespace.rs` impls are custom), so this is test-only — the `test_directory_namespace_direct_publish_cannot_replace_native_omnigraph_write_path` surface guard was realigned to the v7 behavior (it now asserts the native namespace is fully decoupled, which only strengthens the guard's thesis).
+- **The unenforced primary key is now immutable once set** (`lance::dataset::transaction`, ~L2472–2480: `if !primary_key_before.is_empty() && (writes_primary_key || primary_key_after != primary_key_before) → "the unenforced primary key is a reserved key and cannot be changed once set"`). omnigraph marks `__manifest.object_id` as the unenforced PK (`lance-schema:unenforced-primary-key`) for merge-insert row-level CAS — baked into `manifest_schema()` at init, and added by the `migrate_v1_to_v2` internal-schema migration for pre-v0.4.0 graphs. The migration relied on Lance 6's idempotent re-apply for crash-recovery (a crash after the field-set but before the stamp bump re-enters the migration with the PK already present); under v7 that re-apply errors, so a real v1 graph could never finish migrating. Fixed by guarding the set on the manifest's unenforced-PK field (`db/manifest/migrations.rs::migrate_v1_to_v2`): `["object_id"]` → no-op, `[]` → set, any other PK field → loud refusal (the wrong CAS key, unchangeable under v7). Pinned by `lance_surface_guards.rs::unenforced_primary_key_is_immutable_once_set` (red if Lance relaxes immutability); regression: `db::manifest::tests::test_publish_migrates_pre_stamp_manifest_to_current_version` (was red under v7).
+- **Native `DirectoryNamespace` no longer recognizes omnigraph's manifest-tracked tables** (`lance-namespace-impls` dir.rs ~L1310): `list/describe/create_table_version` route through `check_table_status`, which reports an omnigraph table absent → `TableNotFound`. The decoupling is *contingent on omnigraph's legacy boolean PK key*, not an unconditional v7 property: v7's namespace eagerly adds the new `lance-schema:unenforced-primary-key:position` key to any `__manifest` lacking it; that write hits the immutable-PK rule above (the boolean key already set the PK), so `ensure_manifest_table_up_to_date` errors and the namespace silently falls back to directory listing. omnigraph keeps the boolean key deliberately — Lance honors it permanently (maps to PK position 0), and one uniform on-disk format beats a new-vs-old split (existing graphs can't be re-keyed to the position key under that same immutability rule). omnigraph production never uses Lance's native namespace (its publisher writes `__manifest` directly via merge_insert; its own `namespace.rs` impls are custom), so this is test-only — the `test_directory_namespace_direct_publish_cannot_replace_native_omnigraph_write_path` surface guard was realigned to the v7 behavior (it now asserts the native namespace is fully decoupled, which only strengthens the guard's thesis).
 - **Still NOT fixed in 7.0.0:** vector-index two-phase (Lance #6666 open) — `create_vector_index` inline residual retained; blob-column compaction — `compact_files_still_fails_on_blob_columns` guard still red on a fix, `optimize` still skips blob tables behind `LANCE_SUPPORTS_BLOB_COMPACTION`.
 - **No Lance API surface omnigraph uses changed at *compile* time** (the only compile break was object_store) — but **two runtime behaviors did** (the unenforced-PK immutability and the native-namespace `TableNotFound`, above), each caught by the full engine test suite rather than the build. `CleanupPolicy`, `WriteParams` (apart from the `auto_cleanup` default), `CompactionOptions`, the namespace models (resolved via `lance-namespace-reqwest-client` 0.7.7, unchanged across the bump), `Operation`, `ManifestLocation`, and `MergeInsertBuilder` shapes are all stable. Lesson: a clean build is not a clean alignment — run `cargo test --workspace` before declaring a Lance bump done.