# Cross-version compatibility testing
Compatibility anchors for the canonical encoding live in two places:
1. **`golden/`** — the executable golden vectors (OBJECT_MODEL.md §12). They pin the
canonical bytes and identities of `encver=1` objects and are the primary
cross-version anchor: any implementation of the protocol must reproduce them
byte-for-byte.
2. **This directory** — reserved for **historical fixture archives**. When a future
protocol change (an `encver` or `schemever` bump) is made, a snapshot of the
previous golden set is archived here (e.g., `encver-1/`), and a compatibility test
is added that reads objects written under the old version with the new reader
according to the documented downgrade rules (OBJECT_MODEL.md §10.2).
Rules:
- Every archived snapshot is immutable and carries its own manifest in the
`gemel.golden.v1` format.
- A reader must pass the compatibility test for every archived version it claims to
support.
- Regeneration of historical snapshots is forbidden; they are historical records.