Add an invariant test pinning docs/relay-connector-contract.md to the
Python source of truth so the doc (which the connector repo mirrors by
hand) cannot silently drift:
- CapabilityDescriptor §2 table ⟷ dataclass fields + required/optional
- SessionSource wire keys (to_dict output) ⟷ §3 documented fields
- per-platform discriminator columns exist as real SessionSource fields
- guard that is_bot stays off the wire until deliberately promoted
Writing the test surfaced a real gap: §3 only enumerated 5 discriminators
in its per-platform table while to_dict() emits 12 keys. Seven wire keys
the connector must populate (chat_name, chat_topic, user_id_alt,
chat_id_alt, parent_chat_id, message_id, user_name) were undocumented —
a connector author reading the doc would never know to set them. Added a
complete SessionSource wire-field table to §3. The connector's existing
contract.ts already carries all 12, so no connector change is needed; the
doc was the lagging artifact.
5feec8b4cf