* docs: state that MinIO-encrypted objects are not readable by RustFS
Operators evaluating a MinIO migration had no warning that objects MinIO
wrote with SSE-S3, SSE-KMS, or SSE-C cannot be read back. The container
formats interoperate, so the limitation is easy to discover only after
the data has moved.
Document the limitation where a migration decision is actually made:
- minio-file-format-compat.md gains Part C, covering which object classes
transfer, the three seams that block each SSE mode with file:line
evidence, the reverse direction, and the current workarounds. It also
records that the `rio-v2` MinIO sealed-key parser does not close the
gap: the feature is absent from released artifacts, and the managed-SSE
detection gate is not feature-gated and returns before the parser runs.
- kms-backend-security.md gains an operator-facing warning next to the
backend comparison table, since configuring the static backend with
MinIO's key material looks like it should work and does not.
- s3-compatibility-matrix.md scopes its SSE row to RustFS's own
round-trip.
The read path treats an undetected MinIO-encrypted object as unencrypted
rather than failing, so all three notes tell operators to verify migrated
objects by content instead of by status code.
Refs rustfs/backlog#1638.
* docs: correct the failure mode for MinIO-encrypted objects
The read path does fail closed; the earlier text claimed ciphertext was
served as plaintext. MinIO's internal headers mark the object encrypted,
so the reader refuses when no material resolves. What is actually wrong
is the diagnosis: the refusal surfaces as a 500 InternalError.
