chore: merge ODM bucket incarnation safeguards from main

docs/architecture/crate-boundaries.md

@@ -87,6 +87,12 @@ The guard requires the documents and section headings listed in its `require_sou
 
 ## On-Demand Migration Service
 
+Read-through, backfill and external pull orchestration belong in an application
+service under `rustfs/src/<service>/`. ECStore owns the storage primitives they
+need, including atomic commits, lifecycle locks and on-disk metadata. A service
+may use these primitives without moving its provider clients or scheduling
+policy into the engine.
+
 `rustfs/src/on_demand_migration/` owns source clients, pull scheduling, list
 merging, runtime state and backfill orchestration. Its `storage_api.rs` is the
 only ECStore facade boundary. Object write-back still enters the application's
@@ -101,6 +107,13 @@ deployment constraints in the admin use case before the incarnation-fenced
 metadata update. Backfill reads metadata from its store's instance context and
 preserves the checkpoint ETag compare-and-set, lease and tail-drained writes.
 
+An ODM runtime is bound to the bucket incarnation published with its metadata,
+not just its name. Source reads and write-back reject a different incarnation.
+Checkpoint writes hold the user bucket's lifecycle fence through their complete
+commit and read-back, even if their caller stops waiting; the storage commit
+also observes lock loss. Deleting and recreating a bucket must not let work for
+its previous incarnation repopulate objects or checkpoints.
+
 Observability owns its metric DTOs and accepts application snapshot callbacks;
 it does not depend on the ODM runtime. The application registers both bucket
 and backfill snapshots during startup, before metadata and metric collection.