`session_device` takes a `proto` so the harness can build a peer that
advertises the previous version, which is the only way to keep the
standing compatibility rule honest — the current version and the one
before it must interoperate, and until now the suite could only test the
newest code against itself.
⚠️ The capability signature is remade over the number actually claimed.
A bundle that advertises one version and signs another is rejected by
`provenVersion` and falls back to v1, so leaving the original signature
would let a compatibility test pass while exercising a pairing nobody
ships.
The override lives in the driver rather than in `registrationWire`: the
engine should publish what it implements, not what a test wants.
`session_reload` gained `as_version` for the same reason — reproducing a
session stored by an older build, which is a state no amount of running
the new code can otherwise produce.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
