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/branches-commits.md

@@ -55,3 +55,9 @@ Filtered from `branch_list()` but visible to internals:
 
 - `__schema_apply_lock__` — serializes schema migrations.
 - `__run__<run-id>` — legacy from the pre-v0.4.0 Run state machine (removed in MR-771). The branch-name guard predicate `is_internal_run_branch` is kept as defense-in-depth so users cannot create a branch matching the legacy prefix; the filter will be removed once production legacy branches are swept (MR-770).
+
+## L2 — Recovery audit trail (MR-847)
+
+The four migrated writers (`MutationStaging::finalize`, `schema_apply`, `branch_merge`, `ensure_indices`) protect their multi-table commits with a sidecar at `__recovery/{ulid}.json` written before Phase B and deleted after Phase C. The next `Omnigraph::open` (gated on `OpenMode::ReadWrite`) runs the recovery sweep in `crates/omnigraph/src/db/manifest/recovery.rs`: classify per-table state, decide all-or-nothing per sidecar, roll forward / back, record an audit row.
+
+Audit rows live in `_graph_commit_recoveries.lance` (sibling to `_graph_commits.lance`) and reference the commit graph by `graph_commit_id`. The linked `_graph_commits.lance` row carries `actor_id="omnigraph:recovery"` (the system actor). To find recoveries for a specific original actor: `omnigraph commit list --filter actor=omnigraph:recovery`, then join to `_graph_commit_recoveries.lance` by `graph_commit_id` to read `recovery_for_actor`. Schema: see `crates/omnigraph/src/db/recovery_audit.rs`.