Merge branch 'main' into feat/ilm-legacy-recovery-execution

docs/architecture/s3-compatibility-matrix.md

@@ -55,6 +55,14 @@ Standard S3 areas that must not be described as complete:
 
 `excluded_tests.txt` holds tests that must not block the compatibility gate: vendor-specific or non-portable behavior, and intentionally unsupported product behavior such as ACL authorization.
 
+## Intentional Deviations From AWS S3
+
+Object keys are stored as file-system paths under each drive (`{drive}/{bucket}/{object}/xl.meta`), the same layout MinIO uses. The rules below exist to keep that layout unambiguous and are not compatibility gaps to close; clients that need the AWS behavior must adapt on their side.
+
+| Behavior | RustFS | AWS S3 | Why |
+|---|---|---|---|
+| Object key with a `.` or `..` path segment, or an empty segment (`//`), such as `a//b/./c/../d` | `400 InvalidArgument` (`check_object_args` in `crates/ecstore/src/bucket/utils.rs`, mirroring MinIO `IsValidObjectPrefix`) | Accepted as an opaque key | A `..` segment would resolve to a parent directory and `.`/`//` segments would alias other keys on disk; encoding them would change the MinIO-compatible on-disk format. |
+
 ## Update Rule
 
 When a feature starts passing, move its test entries from `unimplemented_tests.txt` to `implemented_tests.txt` and update the row here in the same PR. Do not change README wording beyond the supported coverage. Handler-level status (missing, stubbed, or diverging endpoints) is tracked in [minio-rustfs-router-compatibility.md](minio-rustfs-router-compatibility.md).

docs/operations/on-demand-migration.md

@@ -255,6 +255,8 @@ Source-backed responses report only what the source can vouch for: its ETag, its
 - The source ETag is always recorded in internal metadata regardless of the policy, so an audit or a later comparison can still see it.
 - `Last-Modified` of a pulled object is the local write time, not the source's. The source timestamp is preserved in metadata.
 
+A preserved source ETag does not describe the local part layout. Part reads and object attributes use the stored parts, and replication uses multipart transport when their logical boundaries are available. Legacy compressed or encrypted objects without a multipart ETag can lack those boundaries; they retain their existing streaming PUT path and its 5 GiB limit. Their replication target may therefore store a different part layout.
+
 ## Metadata mapping
 
 Copied to the local object: