fix(hub): present a node-audience token in the handshake, not the hub session token

2026-09-25T15:24:16Z

A member authenticated to a node in the MNP handshake with its hub *session* token — scope=user, valid at the hub API for hours. A node operator is in the threat model, so this handed them a live hub credential for the member: enough to enumerate the member's other groups, act as them, and (before the previous commit closed it) take the account over. The node genuinely needs a hub-signed membership assertion, so the fix is to make that a separate credential that opens nothing at the hub API. Two audiences signed by the one hub key (meshbay_common/tokens.py): - HUB_API_AUD — session tokens (login, device-auth, node-auth, refresh), used for hub calls and signaling. decode_access_token now binds this audience, so an MNP token cannot be replayed against the hub API. - MNP_AUD — a short-lived token a member presents to a node and nothing else, from POST /v1/nodes/mnp-token. authorize_token now binds this audience, so a session token presented to a node is refused. This closes the disclosure. The node's own self-decode (hub_client.py) reads its node token with audience=HUB_API_AUD. The client fetches the MNP token inside transport.connect() (and on every reconnect) using the session token, so callers are unchanged and signaling keeps using the session token. No regression to a long session: the MNP token is checked once, at the handshake, before any proof — a film already playing is not re-authenticated, so a 15-minute token does not interrupt a 4-hour film; reconnects refetch a fresh one. Denylist and membership checks are unchanged (the MNP token carries sub/jti/groups). Tests: authorize_token refuses a session/no-audience token and accepts an MNP token; the hub API refuses an MNP token; POST /v1/nodes/mnp-token is minted only for a member's own session. Verified red-before/green-after; common, node and hub suites green (the pre-existing test_cli_golden failure is an argparse/pytest prog artifact unrelated to this change). Still to do before deploy (B2): bump the MNP version and client.minimum so a stale desktop client is told to update rather than getting a handshake refusal, update docs/MESHBAY_DESIGN.md and MESHBAY_NODE_PROTOCOL.md, and validate against a real node locally, then deploy hub+node+SPA atomically. Co-Authored-By: Claude Opus 4.8

meshbay.git/packages/meshbay-common/src/meshbay_common/tokens.py, branch main

fix(hub): present a node-audience token in the handshake, not the hub session token