Merge branch 'main' into ragnorc/omnigraph-mcp-crate

Folds in v0.7.1 (release #290 + optimize/write-path/internal-table-compaction
fixes #288/#291/#297) under the MCP branch.

Conflict resolutions (5 files):
- crates/omnigraph-server/Cargo.toml: take main's 0.7.1 path-dep constraints;
  keep our omnigraph-mcp dep (bumped to 0.7.1) + http dep.
- crates/omnigraph-server/src/handlers.rs: keep our server_list_queries
  doc-comment (exposed @mcp(expose) subset, invoke_query-gated) — it supersedes
  main's pre-@mcp(expose) text, since this branch adds the per-query expose flag.
- docs/user/operations/server.md: keep our GET /queries description
  (invoke_query gate + @mcp(expose) exposure) over main's read-gated/list-all text.
- docs/dev/index.md: keep both in-flight RFC rows; renumber this branch's tenancy
  RFC 013 -> 014 (rfc-014-tenancy-cells.md) since main now owns RFC-013
  (rfc-013-write-path-latency.md). Title + index link updated; link-check green.
- openapi.json: regenerated from merged source (OMNIGRAPH_UPDATE_OPENAPI=1) — now
  info.version 0.7.1 with our invoke_query/@mcp schema.

Coherence: omnigraph-mcp bumped 0.7.0 -> 0.7.1 to match the workspace; Cargo.lock
updated. cargo build --workspace green; server/mcp/api-types/compiler suites green
(schema_routes.rs reopen-after-apply flakes under parallel IO on a near-full disk,
passes single-threaded — a pre-existing main test, unchanged by the merge).

docs/dev/testing.md

@@ -27,6 +27,8 @@ The engine's `tests/` is the principal coverage surface; most graph-shaped behav
 | `forbidden_apis.rs` | Defense-in-depth source-walk guard: engine code (`exec/`, `db/omnigraph/`, `loader/`, `changes/`) must not reach around the sealed storage trait to Lance inline-commit APIs, nor open datasets directly (`Dataset::open` / `DatasetBuilder::from_uri`/`from_namespace`) — reads route through `Snapshot::open` and the held-handle cache; `// forbidden-api-allow: <reason>` sentinel exempts reviewed lines |
 | `lance_surface_guards.rs` | Pins the Lance API surfaces omnigraph depends on (named runtime + compile-only guards; see [lance.md](lance.md)) — the first smoke check on any Lance version bump; e.g. `compact_files_still_fails_on_blob_columns` turns red when the upstream blob-compaction fix lands |
 | `warm_read_cost.rs` | Cost-budget tests for the warm read path (query-latency work), measured at the object-store boundary with Lance `IOTracker` (the LanceDB IO-counted pattern): a warm same-branch read does 0 manifest opens, 0 commit-graph opens, 1 version probe, validates the schema once (Fix 1 / finding A / Fix 2 at commit-history depth); stale same-branch reads perform exactly 2 probes and refresh manifest-only; recreated non-main branches with the same Lance version refresh by incarnation; recreated branch-owned table handles are distinguished by table e_tag or refresh-time cache clearing; recreated traversal topology is protected by synthetic snapshot-id incarnation or refresh-time cache clearing; a warm *repeat* read does 0 table opens via the held-handle cache and a write re-opens only the changed table at its new version/e_tag (Fix 3/6A). See "Cost-budget tests" below |
+| `write_cost.rs` | Cost-budget tests for the WRITE path (RFC-013), the latency twin of `warm_read_cost.rs` on the **shared `helpers::cost` harness** (`measure`/`IoCounts`/`assert_flat`/`local_graph`). Runs on **local FS**; gates the **internal-table** term (`__manifest`/`_graph_commits` scans flat in commit-history depth — `internal_table_scans_are_flat_in_history`, now **green every-PR** since RFC-013 step 2 brought the internal tables into `optimize`; the test compacts at each depth before measuring) plus green every-PR guards (single-insert `data_writes` bounded, a per-write read-op ceiling that fails the moment a round-trip is added, and a `measure_with_staged` fitness assert that a keyed insert routes through `stage_merge_insert` once with no `stage_append`/vector-index build). The **data-table opener** term is S3-only — see `write_cost_s3.rs` and the backend-split note in "Cost-budget tests" below |
+| `helpers/cost.rs` | The shared cost-budget harness (not a test): `IoCounts`/`StagedCounts` (counts by table class), `measure`/`measure_with_staged` (the one place the `with_query_io_probes` + `MergeWriteProbes` task-local + `IOTracker` wiring lives), `assert_flat(curve, select, slack, what)`, and store-agnostic `local_graph`/`s3_graph` fixtures. `warm_read_cost.rs`, `write_cost.rs`, and `write_cost_s3.rs` all consume it so a cost test body is written once and reads in one vocabulary |
 | `lifecycle.rs` | Graph lifecycle, schema state |
 | `point_in_time.rs` | Snapshots, time travel (`snapshot_at_version`, `entity_at`) |
 | `changes.rs` | `diff_between` / `diff_commits` |
@@ -70,9 +72,10 @@ The engine's `tests/` is the principal coverage surface; most graph-shaped behav
 
 ## RustFS / S3 integration
 
-CI runs three S3-backed tests against a containerized RustFS server (`.github/workflows/ci.yml` → `rustfs_integration` job):
+CI runs these S3-backed tests against a containerized RustFS server (`.github/workflows/ci.yml` → `rustfs_integration` job):
 
 - `cargo test -p omnigraph-engine --test s3_storage`
+- `cargo test -p omnigraph-engine --test write_cost_s3` (RFC-013 step 3a's data-table opener cost gate — flat across commit depth on S3; the term local FS can't reproduce)
 - `cargo test -p omnigraph-server --test s3` (single-graph serving + config-free `--cluster s3://` boot)
 - `cargo test -p omnigraph-cluster --test s3_cluster` (full control-plane lifecycle on the bucket)
 - `cargo test -p omnigraph-cli --test system_local local_cli_s3_end_to_end_init_load_read_flow`
@@ -127,7 +130,7 @@ When you pick up any change, walk through this:
 6. **For substrate-touching changes** (Lance behavior), reach for `failpoints` or fixture-driven scenarios, not stubbed-out mocks.
 7. **For server / API changes**, confirm the OpenAPI regeneration happens in `openapi.rs` and that the diff lands in `openapi.json`.
 8. **Verify your change makes an existing test fail before it makes the new one pass.** If you can break the code without breaking a test, your coverage gap is the problem to fix first.
-9. **Bound hot-path cost at history depth.** If the change touches a read or open path, add or extend a test that asserts a *bounded* cost (e.g. a warm same-branch read performs zero `Dataset::open`, or a fixed object-op count) against a fixture with realistic *commit-history depth*, not just realistic row counts. Cost that scales with history is invisible on a shallow fixture and only bites in production. See "Cost-budget tests" below.
+9. **Bound hot-path cost at history depth.** If the change touches a read, **write**, or open path, add or extend a test that asserts a *bounded* cost (e.g. a warm same-branch read performs zero `Dataset::open`, or a per-write read-op count flat across commit depth) against a fixture with realistic *commit-history depth*, not just realistic row counts. Reuse the shared `helpers::cost` harness (`measure`/`IoCounts`/`assert_flat`) — don't hand-roll `IOTracker` wiring. Cost that scales with history is invisible on a shallow fixture and only bites in production. See "Cost-budget tests" below.
 
 ## Cost-budget tests: bound hot-path cost at history depth
 
@@ -135,6 +138,7 @@ Correctness bugs fail loudly in tests; cost-scaling bugs pass every test and deg
 
 - **Assert a cost budget, not just a result.** For a read/open path, assert the number of `Dataset::open` calls (or object-store ops) a warm query performs, and that it does not grow with commit count. The reference is LanceDB's IO-counted tests, which assert a cached read costs 0-1 IO and carry a named regression test against "a list call on every subsequent query."
 - **Test at history depth.** Build a fixture with many *commits* (not many rows) and assert warm-read cost is flat across depths. A shallow fixture cannot catch an O(commits) cost.
+- **Use the shared harness, and gate each term on the backend where it manifests.** `helpers::cost` (`measure`/`IoCounts`/`assert_flat`/`local_graph`/`s3_graph`) is the one place the `IOTracker`/task-local plumbing lives — consume it, don't duplicate it. The write path has *two distinct* depth terms that split cleanly across backends, and conflating them is a real trap (the local data-table read count grows with depth too, but for a different reason — the merge-insert/RI scan reading O(depth) *fragments*, reduced by compaction, not by the opener): (1) the **internal-table** scan term (`__manifest`/`_graph_commits` fragment scans) reproduces on **any** backend including local FS, so `write_cost.rs` gates it on local every-PR; (2) the **data-table opener** term (latest-version resolution) is a per-object-store-RPC phenomenon — local-FS resolves latest with one cheap `read_dir` regardless of the opener used, so the namespace-vs-direct difference is **invisible on local** and only shows on a real object store (per-version GETs), gated by the bucket-gated `write_cost_s3.rs`. Same harness, different fixture; each term asserted where it actually appears.
 - This is the testing companion to invariant 15 in [docs/dev/invariants.md](invariants.md) (hot-path cost is bounded by work, not history).
 
 When in doubt, re-read [docs/dev/invariants.md](invariants.md) — quality gates apply to every change.