hermes-agent/docs/relay-connector-contract.md

Relay ↔ Connector Contract (v1, EXPERIMENTAL)

Status: EXPERIMENTAL. This contract MAY CHANGE without a deprecation cycle until at least two real Class-1 platforms (Discord + Telegram) have validated it. Evolution during the experimental phase is additive-only, gated by contract_version. A breaking change updates both repos in lockstep.

This document is the formal interface between the Hermes gateway (Python, gateway/relay/) and the connector (Node/TypeScript, NousResearch/gateway-gateway). The connector implementer's first action is to read this file.

The gateway runs a generic RelayAdapter that dials out to the connector, receives a CapabilityDescriptor at handshake, then exchanges normalized MessageEvents (inbound) and actions (outbound) over a per-turn bidirectional WebSocket. The gateway never learns which concrete platform is fronting it; the connector owns all platform-specific socket/identity logic.

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1. Handshake

1. Gateway opens the transport (connect).
2. Gateway calls handshake(); connector returns a CapabilityDescriptor (section 2) describing the platform this adapter instance fronts.
3. Gateway configures the adapter from the descriptor (char limit, length unit, draft/edit/thread/markdown capabilities) and registers an inbound handler.
4. Connector then streams inbound events and accepts outbound actions.

contract_version (currently 1) is carried in the descriptor. The gateway ignores unknown descriptor fields (forward-compat) and fills missing optional fields from defaults.

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2. CapabilityDescriptor (handshake payload)

JSON object. Source of truth: gateway/relay/descriptor.py.

Field	Type	Required	Meaning
contract_version	int	yes	Contract version (additive-only within a version).
platform	string	yes	Platform name (e.g. "discord", "telegram").
label	string	yes	Human-readable label.
max_message_length	int	yes	Char limit; gateway exposes as MAX_MESSAGE_LENGTH. 0 → treat as 4096.
supports_draft_streaming	bool	yes	Native draft-streaming preview support.
supports_edit	bool	yes	Edit-based streaming possible; if false, consumer degrades to one-message-per-segment.
supports_threads	bool	yes	create_handoff_thread capability.
markdown_dialect	string	yes	"plain", "markdown_v2", "discord", … (drives supports_code_blocks).
len_unit	string	yes	"chars" (builtin len) or "utf16" (Telegram UTF-16 code units).
emoji	string	no	Display emoji (default 🔌).
platform_hint	string	no	System-prompt platform hint.
pii_safe	bool	no	Redact PII in session descriptions.

Most fields are a projection of the gateway's existing PlatformEntry; the runtime-only fields (len_unit, supports_*, markdown_dialect) come from the live platform adapter's capability methods.

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3. Inbound: MessageEvent envelope

The connector normalizes each platform wire event into a MessageEvent (gateway/platforms/base.py) and delivers it to the gateway. Inbound is delivered over the gateway's OUTBOUND /relay WebSocket (see the transport note below) — the connector pushes an inbound frame down the socket the gateway already dialed. The gateway keys the session via build_session_key() from the embedded SessionSource — so populating the right discriminators is the single highest-correctness responsibility of the connector.

Inbound transport (WS back-channel, not HTTP)

The gateway dials out to the connector's /relay WebSocket for the handshake + outbound actions (§4) + its own /stop egress (§5). Inbound rides the same socket in the other direction: the connector pushes an inbound frame (and interrupt_inbound for §5) down the gateway's outbound WS. There is no gateway-side inbound HTTP endpoint — a gateway need not (and, when hosted, cannot) expose any inbound port; everything flows over the connection it initiated.

Multi-instance routing. The connector instance that owns a platform's socket (and thus produces inbound events) is generally not the instance the gateway dialed its outbound WS into. The producing instance therefore publishes the event on the connector's internal relay bus (Redis pub/sub; RelayBus in src/core/relayBus.ts) keyed by tenant. Every connector instance subscribes and routes each message to its local sessions for that tenant (RelayServer.routeBusMessage); the single instance that actually holds the gateway's socket delivers it, and instances with no local session for the tenant no-op. Cross-instance delivery is thus an in-cluster Redis hop, not a public HTTP call.

Frames (connector → gateway, over the WS):

• {"type":"inbound", "event": <MessageEvent>, "bufferId"?}
• {"type":"interrupt_inbound", "session_key", "chat_id"} (§5)
• {"type":"passthrough_forward", "forward": <PassthroughForward>, "bufferId"?} (§5.1)

PassthroughForward is the wire form of a forwarded passthrough-plane request (Class-2/3 webhooks — Discord interactions, Twilio): {platform, botId, method, path, headers: [[k,v],…], bodyB64}. The body is base64-encoded so arbitrary bytes survive the newline-delimited-JSON transport; the gateway base64-decodes back to the exact bytes the connector forwarded (the connector already verified the provider signature and stripped any shared-identity credential at the edge — §6 — so the gateway re-processes a sanitized, token-free body and acts on it via the token-less follow_up path). See §3.1.

Trust. The WS upgrade is authenticated with the gateway's per-gateway secret (§6.1), so the channel is trusted end to end — inbound frames are not separately HMAC-signed (the authenticated socket subsumes the per-delivery origin proof the old HTTP path needed). The relay-bus hop is inside the connector trust domain (same as the lease/buffer/capability stores).

Earlier drafts of this contract delivered inbound over a signed HTTP POST to a gatewayEndpoint (HttpGatewayDelivery + a gateway-side inbound_receiver), HMAC-signed with a per-tenant delivery key. That required every gateway to expose a reachable inbound URL — impossible for hosted gateways, which have no public IP. The WS back-channel above replaces it; the per-tenant delivery key is retained at provision for forward-compat but is no longer used for inbound. The passthrough plane (Class-2/3 webhooks like Discord interactions / Twilio) historically still used gatewayEndpoint for its post-ACK forward; Phase 5 §5.1 moves that forward onto the WS too (the passthrough_forward frame above), so a hosted gateway needs zero public inbound surface and gatewayEndpoint is retired once the cutover lands.

3.1 Passthrough-plane forward (§5.1)

The passthrough plane answers the provider's latency-critical ACK at the connector EDGE (e.g. Discord's deferred interaction response within ~3s), then does a fire-and-forget forward of the real request to the gateway. That forward needs no response back (the provider was already satisfied), so it rides the same outbound WS as inbound via a passthrough_forward frame rather than an HTTP POST. The gateway processes the decoded request through its normal agent path (a Discord interaction is decoded to a MessageEvent and handled like a message; the reply egresses over the outbound / follow_up path). bufferId is present when the forward was buffered (Phase 5 §5.3 buffered-only flip) and the gateway acks it after durable handoff.

SessionSource fields (the wire surface)

Source of truth: SessionSource.to_dict() in gateway/session.py. These are every key the gateway accepts on the wire. platform, chat_id, chat_type, user_id, user_name, thread_id, chat_name, and chat_topic are always present (may be null); the rest are included only when set.

Field	Type	Always sent	Meaning
platform	string	yes	Platform name (matches the descriptor's platform).
chat_id	string	yes	Primary conversation id (channel/chat). Session-key discriminator.
chat_type	string	yes	dm / group / channel / thread / forum.
chat_name	string|null	yes	Human-readable chat name.
user_id	string|null	yes	Message author id. Session-key discriminator.
user_name	string|null	yes	Author display name.
thread_id	string|null	yes	Thread/forum-topic id when in a thread. Session-key discriminator.
chat_topic	string|null	yes	Channel topic/description (Discord, Slack).
user_id_alt	string	no	Platform-specific stable alt id (Signal UUID, Feishu union_id).
chat_id_alt	string	no	Alternate chat id (e.g. Signal group internal id).
guild_id	string	no	Discord guild / Slack workspace / Matrix server scope. REQUIRED for Discord server isolation. Session-key discriminator.
parent_chat_id	string	no	Parent channel when chat_id refers to a thread.
message_id	string	no	Id of the triggering message (for pin/reply/react).

is_bot (author-is-a-bot/webhook classification) exists on the gateway-side dataclass but is intentionally NOT on the wire in v1 — it is not part of to_dict(). Do not add it to the connector's SessionSource until it is first added here and to to_dict() (additive bump).

SessionSource discriminators per platform

Platform	chat_id	chat_type	user_id	thread_id	guild_id
Discord	channel id	dm/group/thread	author id	thread channel id (threads)	guild id (REQUIRED for server isolation)
Telegram	chat id	dm/group/forum	from id	forum topic id (forums)	—

Get Discord's guild_id wrong and two servers collide into one session. This is the #1 High-severity risk. The gateway's build_session_key() is the conformance oracle: for a given SessionSource, the connector's normalization must produce the same key the Python adapter would. (The Phase-1 stub tests assert known-input → known-key.)

Bot identity vs tenant (single-bot consolidation, Appendix A)

The envelope carries the originating bot identity as a field distinct from tenant. Tenant is resolved from the event's own discriminator (Discord guild_id, Telegram chat_id, webhook path/subdomain) — never from which token/socket/process delivered it. This keeps one shared bot able to front many tenants (Phase 6) without overloading an existing field.

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4. Outbound: action set

The gateway calls the transport with action dicts. Source of truth: gateway/relay/transport.py + gateway/relay/adapter.py.

op	Fields	Result
send	chat_id, content, reply_to?, metadata?	{success: bool, message_id?, error?}
edit	chat_id, message_id, content, metadata?	{success: bool, error?}
typing	chat_id	{success: bool}
follow_up	session_key, kind, content, metadata?	{success: bool, message_id?, error?}

get_chat_info(chat_id) is a separate proxied call returning at least {name, type}. Media actions follow the same envelope shape (deferred to a later contract revision; additive).

follow_up (A2 capability action). Some inbound payloads carry a credential that acts on the shared bot identity (e.g. a Discord interaction follow-up token). Per §6 the connector strips that at the edge and binds it in its capability vault keyed by the session; it never reaches the gateway. To use it, the gateway issues follow_up naming the session it is already in (session_key) plus the capability kind (e.g. discord.interaction_token) — never a token. The connector resolves the real value from its vault, enforces the tenant match (tenant B can never wield tenant A's capability), and egresses. success: false when the capability is absent/expired or the tenant doesn't match — the gateway has nothing to retry with, by design (a leaked gateway holds zero capability material). Source of truth: gateway/relay/transport.py (send_follow_up) + gateway/relay/adapter.py.

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5. Interrupt (/stop) routing

• Gateway → connector: send_interrupt(session_key, reason?) egresses a mid-turn /stop over the outbound WS. The connector MUST forward it to the gateway instance running that session_key (the routing invariant).
• Connector → gateway: an inbound interrupt for a session_key is delivered as an interrupt_inbound frame down the gateway's outbound WS (§3 transport note) — routed cross-instance via the relay bus to whichever instance holds the socket — and bridged by the adapter's on_interrupt(session_key, chat_id) into the existing per-session interrupt mechanism, cancelling exactly that turn (siblings untouched).

Both directions ride the gateway's outbound WS: the gateway→connector /stop egresses over it, and the connector→gateway interrupt rides the same inbound back-channel as a normalized event.

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6. Trust boundary & signed-body handling (A2)

The connector is the sole crypto/identity boundary. The gateway re-validates nothing.

Webhook signatures (Discord ed25519, Twilio HMAC, WeCom BizMsgCrypt) are computed over exact raw bytes, and some payloads are encrypted with a shared secret. The connector fronts a shared bot for many tenants and holds every tenant's platform secrets, so it:

• verifies / decrypts at the edge (the only place the secrets live),
• normalizes the payload into a tenant-scoped MessageEvent (§3),
• strips any shared-identity capability out of the payload and binds it in its capability vault, keyed by the session (see §4 follow_up),
• forwards only the sanitized MessageEvent — never the raw signed body.

The gateway therefore performs no platform signature/crypto verification on the relay path; it trusts the normalized event. This is an enforced invariant on the gateway side (tests/gateway/relay/test_relay_sheds_crypto.py: the relay package imports/calls no platform-crypto).

Why not "forward the signed body byte-for-byte so the gateway re-validates"? That earlier model is incoherent under an untrusted, disposable tenant gateway:

• Re-validating Twilio HMAC / WeCom crypto would require handing the gateway the shared signing secret — which is itself the leak, and on a shared bot it's a cross-tenant leak.
• WeCom payloads are encrypted with the shared secret; the connector must decrypt at the edge just to route, so forwarding ciphertext would again require giving the gateway the secret.
• A Discord interaction token lives inside the signed JSON body — you cannot both preserve the bytes and strip the credential; they are the same bytes.

So byte-preservation is abandoned deliberately: the connector re-serializes the sanitized event and the gateway trusts it. This also unifies the passthrough and relay planes — both are "verify at the edge → emit a normalized event," differing only in transport. See docs/capability-trust-boundary.md (connector repo: gateway-gateway) for the full A2 rationale and the connector-side vault.

6.1 Channel authentication (the connector⇄gateway link itself)

A2 makes the connector the sole holder of platform secrets while the gateway may be customer-managed and internet-exposed, so the connector⇄gateway channel is itself authenticated. The gateway holds an enrollment- or provision-issued per-gateway secret (hermes gateway enroll → connector /relay/enroll, or managed self-provision → /relay/provision) that authenticates its outbound WS upgrade. It is an HMAC-SHA256 scheme with a multi-secret rotation verify list (gateway side: gateway/relay/auth.py; connector side: src/core/relayAuthToken.ts).

Leg	Credential	Mechanism
Gateway → connector WS upgrade	per-gateway secret	An Authorization bearer header on the /relay upgrade. The token is base64url(payload:exp:sig) where payload = gatewayId and sig = HMAC(payload:exp, secret). Connector verifies and rejects the upgrade (close 4401) on mismatch/absence/revocation. The authenticated tenant comes from the connector's store, never the hello frame.
Connector → gateway inbound (inbound / interrupt_inbound frames)	— (rides the authenticated WS)	Inbound is pushed down the gateway's already-authenticated outbound socket (§3), so no per-message signature is needed. A per-tenant delivery key is still issued at enroll/provision and retained for forward-compat, but is no longer used to sign inbound.

This is the channel authenticator — distinct from platform crypto, which the relay path still sheds entirely (§6). The gateway holds zero platform secrets; the per-gateway secret authenticates only the connector link. Full threat model + enrollment/rotation/kill-switch design: docs/connector-gateway-auth-design.md (connector repo).

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7. Versioning policy

• contract_version is an int; bump only for additive changes during the experimental phase (new optional fields, new ops).
• A breaking change (renamed/removed field, changed semantics) requires a coordinated update of both repos and a version bump.
• The connector's first PR references the commit SHA of this file it implements against.