recovery: document MR-847 ship across all reference docs (Phase 10)

Update the doc surface to reflect MR-847 having shipped end to end —
sidecar protocol, classifier, all-or-nothing decision tree, roll-forward
via ManifestBatchPublisher, roll-back via Dataset::restore with
fragment-set short-circuit, audit trail in
_graph_commit_recoveries.lance, OpenMode::{ReadWrite, ReadOnly}, and
the four migrated writers all carrying sidecars across Phase B → Phase C.

- docs/invariants.md §VI.23: change from "upheld at the writer-trait
  surface for inserts/updates/etc., per-table commit_staged → manifest
  publish window remains" to "upheld at the writer-trait surface AND
  across process boundaries". The MR-847 sweep closes the residual on
  the next Omnigraph::open. The "continuous in-process" property
  (no ExpectedVersionMismatch surfacing to subsequent writers between
  Phase B failure and process restart) is honest follow-up at MR-856.

- docs/runs.md: replace "Finalize → publisher residual" section with
  "Open-time recovery sweep (MR-847)" — describes the sidecar protocol
  lifecycle (Phases A-D), the sweep's classifier + decision dispatch,
  the audit trail, and the operator-facing query
  (omnigraph commit list --filter actor=omnigraph:recovery).

- AGENTS.md capability matrix "Atomic single-dataset commits" row:
  drop the "Layer (3) is not yet shipped — tracked in MR-847" caveat;
  describe the three layers as all shipping; reference MR-856 for the
  background-reconciler follow-up.

- docs/storage.md: add _graph_commit_recoveries.lance and
  __recovery/{ulid}.json to the on-disk layout (mermaid + prose).

- docs/branches-commits.md: new "Recovery audit trail (MR-847)"
  subsection describing the join from
  _graph_commits.lance:actor_id="omnigraph:recovery" to
  _graph_commit_recoveries.lance:graph_commit_id for operator
  post-mortem.

- docs/maintenance.md: note the MR-847 recovery floor on cleanup —
  --keep < 3 may garbage-collect Lance versions the recovery sweep
  needs as a rollback target. Default --keep 10 is safe.

- docs/testing.md: add tests/recovery.rs to the engine integration-test
  table; expand the failpoints.rs row to mention the four MR-847
  per-writer Phase B → recovery integration tests.

- .context/mr-847-design.md: prepend a "Status: DONE" stanza listing
  every commit hash + scope across phases 1-10.

AGENTS.md ↔ docs/ cross-link check passes (26 links, 26 docs).
Full workspace test sweep passes with --features failpoints (361 tests
across 20 binaries).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/maintenance.md

@@ -16,6 +16,7 @@
 - `CleanupPolicyOptions { keep_versions: Option<u32>, older_than: Option<Duration> }` — at least one is required.
 - Returns `[TableCleanupStats { table_key, bytes_removed, old_versions_removed }]`.
 - CLI guards with `--confirm`; without it, prints a preview line.
+- **MR-847 recovery floor:** `--keep < 3` may garbage-collect Lance versions that the open-time recovery sweep needs as a rollback target (the sweep restores to the manifest-pinned `expected_version`, which is HEAD-1 in the typical Phase B → Phase C drift case). Default `--keep 10` is safe.
 
 ## Tombstones