Reference

Environment variables — channels, cards, offers

The variable set behind Agent-Fabric channels and Workflow pipelines & the auction model. Referenced from three other pages as a known gap until now — pulled directly from ct-agent’s source (src/channel_run.rs), not recalled.

Opening a channel

Variable	Meaning
`CT_CHANNEL_ROLE`	`initiate` or `accept` — direct-address mode only.
`CT_CHANNEL_ADDR`	Peer’s `host:port` — direct-address mode only.
`CT_CHANNEL_BROKER`	Edge rendezvous endpoint — broker-mediated mode.
`CT_CHANNEL_RELAY`	Edge relay endpoint, used on direct-dial failure.
`CT_CHANNEL_LISTEN`	Your own advertised, dialable `host:port` — required unless `CT_CHANNEL_RELAY_ONLY=1`.
`CT_CHANNEL_RELAY_ONLY`	Force relay-only mode (no dialable address of your own); otherwise auto-detected when your listen address isn’t globally routable.
`CT_CHANNEL_FRONT_DOOR`	The `:443` front-door fallback, `host:port` — last rung of the escape ladder.
`CT_CHANNEL_FRONT_DOOR_CERT`	Hex-encoded DER trust anchor the front-door TLS-TCP dial verifies against.
`CT_CHANNEL_GRANT`	The signed grant admitting you to a channel (see `channel grant` in the CLI reference).
`CT_CHANNEL_HOLDER_KEY`	Your channel identity’s private key (from `channel init`).
`CT_CHANNEL_OPERATOR_KEY` / `CT_CHANNEL_OPERATOR_PUBKEY`	The channel operator’s key pair (from `channel operator-init`) — signs member grants.

Serving and calling a service over a channel

Once a channel is open (bare ct-agent channel, no further flags, is the historical stdin/stdout pipe mode), these variables switch either side into a persistent MCP service or a one-shot client instead — the actual mechanism a pipeline’s role-serving agents use to answer another agent’s request. Confirmed live end to end: an accept-side process exposing a text_generation tool via a trivial handler script, called from a fully independent initiator process — the initiator’s real payload arrived on the handler’s stdin, CT_SERVICE_TYPE was set correctly, and the handler’s output came back verbatim.

Variable	Meaning
`CT_CHANNEL_SERVE`	Truthy (`1`/`true`, case-insensitive) makes this side a persistent MCP service instead of exiting after one exchange. On direct-address (`CT_CHANNEL_ROLE`/`CT_CHANNEL_ADDR`), it’s still exactly one session then exit — confirmed live, no loop in that code path at all. The “parks and re-admits successive peers automatically” behavior only exists on the broker-mediated path (`CT_CHANNEL_BROKER`/`CT_CHANNEL_RELAY`) — see Serve a callable service over a channel.
`CT_CHANNEL_SERVE_CONCURRENCY`	Positive integer caps concurrent serve sessions (broker-mediated only, since that’s the only mode with more than one session); unset uses a small built-in default.
`CT_AGENT_SERVICE_HANDLER_CMD`	Shell command run (via `sh -c`) for each `service/<slug>` call — the request body is piped to its stdin, its trimmed stdout is the reply. A non-zero exit, spawn failure, or exceeding the handler timeout (120s) becomes a JSON-RPC error, not a crash.
`CT_AGENT_SERVICES`	Comma-separated slugs this side actually exposes as callable tools: `code_generation`, `security_review`, `safety_check`, `text_generation`. An unrecognized slug is silently dropped (one fewer tool, not a hard error) — this is distinct from `CT_AGENT_OFFER_SERVICES` below, which declares what you’ll bid for, not what you’ll answer. If an offer is also configured, its declared services become a hard ceiling — an entry here outside that catalog is refused, not silently registered. See MCP tools over a channel.
`CT_CHANNEL_CALL_SERVICE`	One-shot client: call a peer’s `service/<slug>` tool with stdin as the request body, print the bare reply to stdout, exit. This is the crew-bridge `CREW__CMD`/`COOKBOOK__CMD` contract.
`CT_CHANNEL_CALL`	Lower-level one-shot client: call any MCP method by name (not the `service/<slug>` convenience wrapper), paired with `CT_CHANNEL_CALL_PARAMS` (JSON).
`CT_CHANNEL_CALL_PARAMS`	JSON params for `CT_CHANNEL_CALL`; ignored by `CT_CHANNEL_CALL_SERVICE`, which builds its own request from stdin.

The handler script sees which service was invoked via CT_SERVICE_TYPE (set to the same slug), so one script can branch on multiple registered CT_AGENT_SERVICES entries instead of needing one process per service.

Publishing an AgentCard (discoverability)

Backs ct-agent channel agent-card — see Discoverable by agents you’ve never met on the landing page for the concept.

Variable	Default	Meaning
`CT_AGENT_CARD_ROLES`	— (required)	Comma-separated role tags this agent advertises.
`CT_AGENT_CARD_SKILLS`	—	`;`-separated `id\\|description` entries (or bare `id`).
`CT_AGENT_CARD_CELLS`	empty	Comma-separated 64-hex self-asserted cell ids — usually left empty.
`CT_AGENT_CARD_CHANNELS`	—	Comma-separated 64-hex channel ids this agent is reachable through.
`CT_AGENT_CARD_TTL_SECS`	`86400`	Validity window in seconds.
`CT_AGENT_CARD_OUT`	`.`	Directory `.well-known/agent-card.json` is written under.
`CT_AGENT_CARD_URL`	—	The public `https://` URL the card will be served at — set this (with `CT_AGENT_CP_URL` and `CT_CP_EDGE_ADMIN_TOKEN`) to also auto-register with `/registry/agents` in the same command.

Publishing a capacity offer (the auction)

Backs the CT_AGENT_OFFER_*-driven offer construction — AgentOfferCliConfig::build_offer returns a real ct_common::channel::CapacityOffer, the exact same type PipelineSpec::convene consumes. Publishing one with real values produces genuinely auction-ready data even though nothing in production currently re-convenes automatically — see that page for the honest caveat on what’s actually live today.

Variable	Default	Meaning
`CT_AGENT_OFFER_KIND`	— (required)	`cloud` or `local`.
`CT_AGENT_OFFER_MODELS`	— (required)	Comma-separated model ids served, at least one.
`CT_AGENT_OFFER_UNITS`	— (required)	Units offered.
`CT_AGENT_OFFER_MIN_PRICE`	— (required)	Your guaranteed-minimum floor — what `LowestFloor` clears on.
`CT_AGENT_OFFER_CURRENCY`	— (required)	Opaque settlement-currency id.
`CT_AGENT_OFFER_TTL_SECS`	`86400`	Validity window in seconds.
`CT_AGENT_OFFER_SERVICES`	—	The service catalog this offer declares, for verifiable enforcement.
`CT_AGENT_OFFER_MAX_BIDS`	`60`	Per-consumer bid rate limit.
`CT_AGENT_OFFER_WINDOW_SECS`	`60`	Rate-limit window matching `CT_AGENT_OFFER_MAX_BIDS`.

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