docs(agents): streamline instruction routing (#6358)

.agents/skills/adversarial-validation/references/compatibility.md

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+# Compatibility Lens
+
+- Internal metadata uses `metadata_compat` helpers for dual RustFS/MinIO keys,
+  including mixed casing and removal of both twins.
+- Binary UUID metadata treats absent, empty, and nil as no value. Unversioned
+  remote tiers receive no `versionId`; versioned purge requests retain the real
+  version ID.
+- `xl.meta` changes preserve supported header/meta versions, recompute
+  signatures, decode legacy fixtures, and remain readable by old RustFS/MinIO.
+- Foreign/corrupt metadata validates parallel array lengths and missing fields;
+  it returns a decode error rather than indexing, panicking, or fabricating data.
+- Do not “correct” byte-for-byte MinIO ports without legacy fixture evidence.
+  Bitrot framing, shard math, distribution, and inline prefixes are contracts.
+- Client-visible metadata/events strip both internal prefixes
+  case-insensitively.
+- Proto fields are appended, never reused/renumbered; FlatBuffers tables extend
+  compatibly and absent new fields fail closed where authorization/quorum is
+  involved.
+- Replay real client request shapes and exact pagination boundaries for S3
+  handler changes.
+- Bucket metadata/IAM/config parsing remains compatible with pinned real MinIO
+  fixtures and encrypted migration data.
+- Compatibility shims use `RUSTFS_COMPAT_TODO(<task-id>)`, have a removal
+  condition, and default toward reading old data safely.