fix(optimize): skip blob-bearing tables to avoid Lance compaction crash (#138)

* test(optimize): pin Lance blob-column compaction failure as a surface guard

Lance compact_files mis-decodes blob-v2 columns under its forced BlobHandling::AllBinary read ("more fields in the schema than provided column indices"), failing even a pristine uniform-V2_2 multi-fragment blob table; reads use descriptor handling and are unaffected.

Guard 10 reproduces this and is self-retiring: it turns red on the Lance bump that fixes the bug, forcing LANCE_SUPPORTS_BLOB_COMPACTION to flip.

* fix(optimize): skip blob-bearing tables instead of crashing compaction

omnigraph optimize aborted the whole sweep when any node/edge table had a Blob property: Lance compact_files cannot decode blob-v2 columns under AllBinary (the column-index error pinned by the surface guard). Skip blob-bearing tables behind a LANCE_SUPPORTS_BLOB_COMPACTION gate and report them via TableOptimizeStats.skipped / SkipReason (surfaced in the CLI and a tracing::warn) instead of erroring, which also isolates the failure so the other tables still compact.

Reads/writes are unaffected; only fragment/space reclamation on blob tables is deferred until the upstream Lance fix. Adds a maintenance.rs regression test (validated red with the column-index symptom before the fix, green after), a concise v0.6.1 release note, and updates docs (maintenance, cli-reference, AGENTS capability matrix, invariants Known Gaps, lance.md audit, constants).

* refactor(optimize): make TableOptimizeStats and SkipReason non_exhaustive

Both are returned result types, never built by callers, so #[non_exhaustive] makes this the last field/variant addition that can break downstream literal construction and keeps future ones non-breaking (review feedback on the public-field addition). The v0.6.1 Compatibility Notes call out the source-level change.

Also drops the now-stale "RED today / GREEN after the fix lands" narration in the optimize_skips_blob_table_and_reports_skip test (historical regression context now that the fix is in this branch), and folds in the expanded v0.6.1 release note.

* chore(release): bump workspace to v0.6.1

Coherent version bump to accompany the v0.6.1 release note: all five crate manifests + path-dependency constraints, Cargo.lock, the AGENTS.md surveyed-version line, and openapi.json info.version move 0.6.0 -> 0.6.1. Matches the established release pattern (#118 landed the v0.6.0 note + bump together) and resolves the Codex/Devin review flag that a v0.6.1 note without a bump leaves CARGO_PKG_VERSION reporting 0.6.0 and mixed package versions.

docs/dev/invariants.md

@@ -130,6 +130,15 @@ them explicit.
 - **Deletes and vector indexes:** `delete_where` and vector index creation still
   advance Lance HEAD inline because the required public Lance APIs are missing.
   Keep D2 and recovery coverage in place until those residuals are removed.
+- **Blob-column compaction:** Lance `compact_files` mis-decodes blob-v2 columns
+  under its forced `BlobHandling::AllBinary` read ("more fields in the schema
+  than provided column indices"), so `optimize` skips any table with a `Blob`
+  property — reporting `SkipReason::BlobColumnsUnsupportedByLance` (loud, not a
+  silent drop) behind the `LANCE_SUPPORTS_BLOB_COMPACTION` gate. Reads and writes
+  are unaffected; only space/fragment reclamation on blob tables is deferred.
+  Remove the skip when the upstream Lance fix lands — the
+  `lance_surface_guards.rs::compact_files_still_fails_on_blob_columns` guard
+  turns red on that bump to force it.
 - **Planner capability/stat surfaces:** cost-aware planning, complete
   capability advertisement, and explain-with-cost are roadmap. Do not describe
   them as implemented.

docs/dev/lance.md

@@ -176,7 +176,8 @@ Migration from Lance 4.0.0 → 6.0.1 landed in this cycle (DataFusion 52 → 53,
 - **Lance #6666 still open** (`build_index_metadata_from_segments` public): vector-index two-phase blocked; inline `create_vector_index` residual retained.
 - **Lance #6877 still open** (`MergeInsertBuilder` dup-rowid): PR #109's `SourceDedupeBehavior::FirstSeen` + `check_batch_unique_by_keys` precondition stay load-bearing.
 - **`Dataset::force_delete_branch`** (`branches().delete(name, force=true)`, dataset.rs:524) tolerates a missing branch-*contents* ref (vs plain `delete_branch`'s `RefNotFound`), but on the local store still errors `NotFound` if the branch `tree/` directory is fully absent (`remove_dir_all`'s NotFound is not caught for Lance's native error variant, refs.rs:526-549). Both variants still refuse a branch with referencing descendants (`RefConflict`). `TableStore::force_delete_branch` wraps this to be fully idempotent (tolerates already-absent). The single-authority branch-delete redesign uses it for orphan reclamation (eager best-effort reclaim + cleanup reconciler). Pinned by `lance_surface_guards.rs::force_delete_branch_semantics`. Branch delete is "flip the ref atomically, then `remove_dir_all(tree/{branch})`"; branch-exclusive data lives under `tree/{branch}/` so a drop reclaims it immediately without touching `main`.
+- **Lance blob-v2 `compact_files` bug** (no public issue found as of 2026-06): `compact_files` disables binary-copy for blob datasets and forces `BlobHandling::AllBinary` on the read side; the v2.1+ structural decoder then mis-counts column infos for the blob-v2 struct and fails with `Invalid user input: there were more fields in the schema than provided column indices / infos` (`lance-encoding/src/decoder.rs::ColumnInfoIter::expect_next`). This fails even a pristine uniform-V2_2 multi-fragment blob table; vector/list/scalar/ragged columns and mixed file versions all compact fine. Reads/queries use descriptor handling (`BlobHandling::default()`) and are unaffected. `optimize` skips blob-bearing tables behind `LANCE_SUPPORTS_BLOB_COMPACTION = false` (`db/omnigraph/optimize.rs`), reporting `SkipReason::BlobColumnsUnsupportedByLance`. Pinned by `lance_surface_guards.rs::compact_files_still_fails_on_blob_columns`, which turns red when the bug is fixed → flip the gate, remove the skip branch + the `maintenance.rs::optimize_skips_blob_table_and_reports_skip` skip assertions.
 
-Surface guards added: `crates/omnigraph/tests/lance_surface_guards.rs` (9 named guards; 4 runtime + 5 compile-only). Future Lance bumps re-run this file first as the smoke check. Two additional guards from the original plan deferred to follow-up (`manifest_cas_returns_row_level_contention_variant` needs full publisher-race harness; `table_version_metadata_byte_compatible_with_v4` needs `pub(crate)` reach extension).
+Surface guards added: `crates/omnigraph/tests/lance_surface_guards.rs` (10 named guards; 5 runtime + 5 compile-only). Future Lance bumps re-run this file first as the smoke check. Two additional guards from the original plan deferred to follow-up (`manifest_cas_returns_row_level_contention_variant` needs full publisher-race harness; `table_version_metadata_byte_compatible_with_v4` needs `pub(crate)` reach extension).
 
 Bump this date stanza on the next alignment pass.