fix(cluster): stop cluster-apply crash-loops from the recovery-sidecar trap (#284)

* fix(cluster): stop cluster-apply crash-loops from the recovery-sidecar trap

A `cluster apply` carrying a schema change against a graph that has
non-main branches, or an unsupported "needs backfill" migration, armed a
recovery sidecar *before* calling the engine, then left it behind when the
engine rejected the apply pre-movement. The server refuses to boot while
any sidecar is pending, and re-running apply re-armed a fresh sidecar — an
unescapable crash loop. None of the engine rejections are bugs; the trap
is in the apply/serve choreography.

Three coordinated changes:

1. Preview before arming the sidecar. `cluster apply` now runs
   `preview_schema_apply_with_options` before `write_recovery_sidecar`, so
   parser/planner rejections (non-main branches, unsupported plan) fail
   loudly without leaving recovery work behind. The post-preview engine
   error path now deletes the sidecar when the live schema still matches
   the recorded digest (nothing moved), and keeps it only on real
   mid-movement failure — both branches covered by new engine-failpoint
   tests (cluster failpoints now enable omnigraph/failpoints).

2. Per-graph quarantine at serve time instead of whole-cluster refusal.
   A graph-attributed pending sidecar, an unopenable graph root, a query
   parse failure, or an unresolvable embedding provider now quarantines
   just that graph (logged loudly at every boot layer) while healthy
   graphs serve; `/graphs` lists only ready graphs and quarantined routes
   404. Cluster-global problems (missing/unreadable state, malformed or
   unattributable sidecars, shared-catalog or cluster-policy errors, zero
   healthy graphs) stay fail-fast. `--require-all-graphs` /
   OMNIGRAPH_REQUIRE_ALL_GRAPHS=1 restores all-or-nothing boot.

3. Backfill embedding-provider profile metadata on apply. Mirrors the
   existing policy-binding backfill: a pre-5A ledger missing
   `embedding_profile` is now detected as a metadata-only change and
   backfilled by a no-op apply, instead of bricking serve with
   `embedding_provider_profile_missing` forever.

Tests: trap (no sidecar after a rejected apply), both digest-cleanup
branches, per-graph quarantine (cluster + server), embedding backfill.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs: resilient cluster boot + recovery-sidecar trap fix

Amend RFC-005 D4 readiness posture (cluster-global fail-fast vs graph-local
quarantine; deviation #5 for --require-all-graphs), add the v0.7.0 release
note, and update the user cluster/server/deployment docs and the
OMNIGRAPH_REQUIRE_ALL_GRAPHS env var.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(cluster): surface sidecar-cleanup failures; document severity promotion

Address Greptile review on PR #284:

- The pre-movement sidecar cleanup fast-path discarded `delete_object`'s
  result, so a transient delete failure left the graph quarantined with no
  signal. Add `try_delete_object` (Result-returning) and emit a
  `recovery_sidecar_cleanup_failed` warning diagnostic on failure; the
  fire-and-forget `delete_object` now delegates to it.
- Document why the serve-time loop promotes every `list_recovery_sidecars`
  diagnostic to a cluster-fatal error (the listing only emits genuine
  read/parse/version failures, as warnings, whose blast radius serving
  cannot prove) and note the promote-by-code path if that ever changes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docker/entrypoint.sh

@@ -17,7 +17,12 @@ if [ -n "${OMNIGRAPH_CLUSTER:-}" ]; then
     echo "OMNIGRAPH_CLUSTER is an exclusive boot source; unset OMNIGRAPH_TARGET_URI/OMNIGRAPH_CONFIG/OMNIGRAPH_TARGET" >&2
     exit 64
   fi
-  exec "$SERVER_BIN" --cluster "${OMNIGRAPH_CLUSTER}" --bind "${bind}"
+  set -- --cluster "${OMNIGRAPH_CLUSTER}" --bind "${bind}"
+  case "${OMNIGRAPH_REQUIRE_ALL_GRAPHS:-}" in
+    ""|0|false|FALSE) ;;
+    *) set -- "$@" --require-all-graphs ;;
+  esac
+  exec "$SERVER_BIN" "$@"
 fi
 
 # URI comes from the env var (the positional arg wins over any config
@@ -46,6 +51,8 @@ omnigraph-server container startup requires one of:
 
 Optional:
   - OMNIGRAPH_BIND (default: 0.0.0.0:8080)
+  - OMNIGRAPH_REQUIRE_ALL_GRAPHS (cluster mode: fail startup unless every
+    applied graph is healthy)
   - OMNIGRAPH_TARGET (used with OMNIGRAPH_CONFIG)
   - OMNIGRAPH_CONFIG (may also accompany OMNIGRAPH_TARGET_URI to add a
     policy file; the URI still comes from OMNIGRAPH_TARGET_URI)