Answering prompts

The prompts channel takes a prompt from another agent over NATS and runs the agent loop over it. The caller waits and receives an acknowledgement, then the events the run produces, then the answer or the failure.

Configuration

identity: nats-worker
application_path: /usr/local/bin/nats
nats_context: production
system_prompt: |
  You operate NATS. Answer with what you did and what you found.
llm:
  model: claude-sonnet-5
include:
  tools:
    - ^stream_
expose:
  agent:
    a2a:
      serve_tools: true
      tool_timeout: 60s
      prompts:
        workers: 2

Answering a prompt runs the whole agent loop, so the configuration needs identity, system_prompt, llm.model and nats_context. application_path is optional: an agent with only built-in tools, or with none, still answers prompts.

identity must be one you wrote. It is the subject peers reach this worker on and the queue group it joins, so a name taken from the application binary or left at the default would put unrelated agents into one group, sharing each other’s work.

$ fisk serve --config prompts.yaml

Serving nats-worker/1.2.0:

         Endpoints: a2a/prompts
                    a2a
             Model: claude-sonnet-5
     Agent Context: production
          Sessions: file
         Knowledge: disabled
         Telemetry: disabled
    Tool Directory: /var/lib/fisk-ai
      Tool Timeout: 5m0s

  Answering prompts over a2a:

            Requests: choria.fisk-ai.task.nats-worker
             Cancels: choria.fisk-ai.cancel.nats-worker.*
             Workers: 2
    Answering a prompt runs the agent loop and reaches every tool the top-level include and exclude selected.

  Serving tools over a2a:

           Discovery: choria.fisk-ai.discovery.nats-worker
               Tools: choria.fisk-ai.tool.nats-worker
         Concurrency: 4
        Tool Timeout: 1m0s
             Exposed: stream_ls
                      stream_info

workers is how many prompts the process answers at once. --workers does not change it; that flag applies to the queued-jobs channel.

Making requests

A caller publishes a request on choria.fisk-ai.task.<identity>:

{
  "protocol": "io.choria.fisk-ai.v1.request.prompt",
  "id": "3Hzmp2RBLG713TfOTU5aJpATRg2",
  "request": "docs1",
  "conversation": "docs1",
  "sequence": 0,
  "time": "2026-08-16T11:00:00Z",
  "sender": {"name": "peer1"},
  "prompt": "how many streams are there"
}

request names the turn. Every reply to it echoes the value, cancelling the turn addresses it by that value, and so does answering a question the run asks, so pick it before you send and keep it. It must name one turn and one only: two turns sharing a value make their replies indistinguishable, and a cancel aimed at one of them stops both. It is at most 64 characters of letters, digits, - and _, because a worker builds subjects from it.

id names the message rather than the turn, so it is fresh on every message including a resend, and conversation is the caller’s own tag across the turns of one conversation.

The queued-jobs channel takes a request.prompt as its payload and none of the other three.

request.answer is described in Answering after the run ended, and request.read in Reading a conversation.

context is supporting material offered alongside the prompt, stream: false asks for the answer without the event stream, and conversation_token joins an existing conversation, see Follow-up turns.

force is a caller’s decision about its own conversation. Without it a worker refuses a resume across a changed model, system prompt or tool set; with it the run continues under the current configuration and drops the standing approvals it can no longer vouch for.

A budget above the worker’s own configuration is ignored. On a conversation it limits the conversation rather than the turn, since a run measures the whole journal’s token count against it.

The reply set arrives on the request’s own inbox, in order:

The acknowledgement comes first, so a plain nats req receives it and stops there:

$ nats req choria.fisk-ai.task.nats-worker "$(cat request.json)"

{"protocol":"io.choria.fisk-ai.v1.ack","id":"3Hzmp3SCMH824UgPUV6bKqBUSh3","request":"docs1",
 "conversation":"docs1","sequence":1,"time":"2026-08-16T11:24:10.749134Z",
 "sender":{"name":"nats-worker"},"recipient":{"name":"peer1"},"accepted":true}

Every message of the set carries sequence, numbered from the acknowledgement without gaps, so a caller can tell a lost event from a quiet run. Events are advisory. The answer is in the terminal message, and the worker’s run journal is the authoritative transcript.

Event blocks

Each event holds one block. Where an id under io.choria.fisk-ai.v1.event. is one your client does not recognize, keep the message and render what you can rather than rejecting it: a newer worker sends kinds this one does not define.

A text event in full:

{"protocol":"io.choria.fisk-ai.v1.event.text","id":"3Hzmp8kRt1BqA4dQ2v9XnLcYm2T","request":"docs1",
 "conversation":"docs1","sequence":2,"time":"2026-08-16T11:24:11.104217Z",
 "sender":{"name":"nats-worker"},"block":{"text":"the stream is gone","final":true}}

final marks the answer. Only the run knows which message ended the turn, so without the flag a caller cannot tell the answer from the narration on the way to it, and would render it twice when the same text arrives again in the result.

A warning names its kind and gives you the values, not a finished sentence. Your client chooses the wording, and a client that does not recognize a kind can still display the fields.

A tool_call is not answered twice. A call the caller was asked to approve carries the same tool_use_id as the elicit.request.approve that asked, so a caller that drew the question knows it has already shown that call.

Not every call produces a result: a denied confirmation, a tool called without its required arguments, a tool that answers later and an aborted run each end without one, so a caller pairing the two tolerates a call that is never answered.

A status block reports progress, and its usage is what one model call consumed. The call that ends a turn sends no status of its own, so a caller keeping a running total takes the totals from the terminal message rather than summing these. The replay markers use the same block and are described below.

Refusals and endings

The worker refuses a request it cannot parse with a NATS service error, before any acknowledgement:

$ nats req choria.fisk-ai.task.nats-worker '{"protocol":"io.choria.fisk-ai.v1.request.resume","prompt":"...", ...}'

Nats-Service-Error: the request is not a valid v1 message: jsonschema validation failed with
'https://choria.io/schemas/io.choria.fisk-ai.v1/request.resume.json#'
  - at '/prompt': false schema
Nats-Service-Error-Code: 400

A resume takes no prompt. Send io.choria.fisk-ai.v1.request.prompt to run one.

Everything the worker refuses after that is an ack with accepted: false and a reason, followed by an error that closes the set. The error carries a code the caller can branch on:

The worker refuses at capacity rather than queueing the prompt. unknown_call, already_answered and answer_too_large are permanent: sending the same answer again reaches the same reply.

budget_exhausted ends the conversation, not just this request. The allowance belongs to the conversation, so every later turn is refused no matter who sends it. Your prompt did not run and was not recorded. To carry on, send a prompt with no conversation_token to start a new conversation. Only an operator on the machine running the agent can raise llm.budget.max_tokens.

You can also hit this straight away, on a conversation that answered a moment earlier, by lowering budget on your own request below what the conversation has already used.

Every error also has a stop_reason beside its code. budget_exhausted appears there when a run hit the cap part way through a turn instead of before it started.

A deferred run is waiting for a tool answer. The error lists the calls. Answer one on a request carrying the conversation token, or with fisk session on the worker holding the journal.

Canceling

A caller cancels by publishing an io.choria.fisk-ai.v1.cancel on choria.fisk-ai.cancel.<identity>.<request>, where request is the correlation id it sent. The request id is part of the subject, so only the worker running that prompt is subscribed to it. It answers with an ack.

A cancel asks the run to stop where the conversation can be continued. It does not end the run where it stands: the loop polls for it at each boundary and parks there, so the terminal message is suspended with the usage the turn spent, and the conversation takes another turn whenever the caller sends one. A run blocked on a question is included, since a cancel closes the question rather than leaving it asked with nobody to answer.

What that costs is the ability to stop a model call in flight. A run inside a tool that never returns reaches no boundary, and a cancel will not move it; that escape hatch belongs to whoever operates the worker. A caller asks and an operator compels.

Because the id is part of the subject, a caller mints it rather than being told it: set id and request on the request before sending, so the tag is in hand before there is anything to cancel.

A no-responder error means this instance is not running that request: it was never accepted, it already finished, or another instance took it.

Follow-up turns

A caller can send another turn of the same conversation. Every ack that accepts a prompt carries a conversation_token, and a later request carrying that token runs its prompt as the conversation’s next turn:

{"protocol":"io.choria.fisk-ai.v1.ack","id":"3Hzmp3SCMH824UgPUV6bKqBUSh3","request":"docs1",
 "conversation":"docs1","sequence":1,"time":"2026-08-16T11:24:10.749134Z",
 "sender":{"name":"nats-worker"},"recipient":{"name":"peer1"},"accepted":true,
 "conversation_token":"3Hzmp8VqrKL42NmXcPd7bTgWfR1"}

{
  "protocol": "io.choria.fisk-ai.v1.request.prompt",
  "id": "3Hzmq7WdPK628XjRVZ8cLmBUTh4",
  "request": "docs2",
  "conversation": "docs1",
  "sequence": 0,
  "time": "2026-08-16T11:26:00Z",
  "sender": {"name": "peer1"},
  "prompt": "what is the first one called",
  "conversation_token": "3Hzmp8VqrKL42NmXcPd7bTgWfR1"
}

A caller that asks once and stops ignores the token the worker handed it; one that wants another turn sends the token it already has. A follow-up opens a reply set of its own, with its own ack, events, cancel address and terminal message, so it is an ordinary request in every respect but which conversation it joins.

No worker holds a conversation between turns. Each turn loads the journal, runs, and stores the result, so any instance in the queue group serves any turn. That also means a caller sends one turn at a time: a second turn sent while the first is still running is refused with conversation_busy, and it must wait for the first turn’s terminal message rather than try another instance.

A conversation has no end state and no expiry: the journal stays in the session store until an operator removes it.

• A turn cannot join a conversation waiting on a deferred tool result. The worker answers turn_not_taken without running the prompt. With elicit set, a human-in-the-loop question the caller neither answers nor holds open within request_timeout leaves the conversation waiting on a deferred call. Answer the question and it takes turns again.
• A configuration change ends a conversation. Every turn is a resume, and the worker refuses a resume when the model, the system prompt, the thinking mode or the reasoning effort has changed since the conversation started. It answers failed and the caller starts a new conversation. A changed tool set does not end it: the turn runs, and the standing approvals the conversation held are dropped, since an approval names a tool and that tool may have moved under it.

The usage on a result counts the whole conversation rather than the turn, since it is read from the journal. An error that ran and stopped carries it too, so a caller can tell what it owes for a turn it is about to continue. Both also carry trace_id, the trace the worker recorded, which is empty when it exports no telemetry, and content_exported, which says whether this turn’s conversation itself reached that collector.

Asking what an agent is

Ask an agent what it is before you send it anything. Run fisk discover <identity> to make that request. Every agent that answers prompts also answers discovery, whether or not it serves tools as well. An agent that serves no tools to peers answers with a card that lists none.

Two fields on the card describe what the agent does with a conversation:

They are published because a caller should know before it sends a prompt, and they are read off the worker’s resolved telemetry provider rather than its configuration, so a rejected endpoint does not leave the card promising an export that will not happen. The card says what the agent is configured to do; content_exported on a terminal message says what a turn actually did.

Reading a conversation

To read a conversation back, send an io.choria.fisk-ai.v1.request.read with a conversation_token and a replay count. The worker sends that many blocks of the stored conversation and ends the reply set:

{
  "protocol": "io.choria.fisk-ai.v1.request.read",
  "id": "3Hzmr9YfRM839ZlTXb0eNoDVUj6",
  "request": "docs3",
  "conversation": "docs1",
  "sequence": 0,
  "time": "2026-08-16T11:30:00Z",
  "sender": {"name": "peer1"},
  "conversation_token": "3Hzmp8VqrKL42NmXcPd7bTgWfR1",
  "replay": 200
}

Use this to show a conversation your client did not see live, such as one started on another machine. A finished turn leaves a completed journal, and a plain resume will not continue one, so reading it is the only request such a conversation accepts until you send the next prompt.

You get back the same blocks the run sent the first time, between two status blocks:

• phase: "replay_start" opens the history.
• phase: "replay_end" closes it, with count blocks sent, truncated when older ones were left behind, and usage for what the conversation has consumed so far. That usage is the whole conversation rather than one call, which is what lets a caller seed a running total before this turn’s own calls arrive.

Set replay on each request that needs it. Leave it off a follow-up turn, which usually wants only the new blocks. The worker sends at most 200 blocks whatever you ask for, and rounds up to a whole turn so that a result never arrives without the call it answers. The largest useful value is therefore 200; ask for more and you get 200. A read asks for at least 1.

Some of what the journal holds never leaves the worker: thinking signatures, the fingerprint, the caller, the conversation token, the standing approvals, and the notes and handles of deferred calls. Long values are trimmed to fit a block.

io.choria.fisk-ai.v1.request.resume continues a run that stopped part way, which is what a caller sends after a suspended ending. Send it with the token and no replay.

Answering questions

A run puts a question back to the caller when it needs a person: an approval for a confirmation-gated command, or one of the three human-in-the-loop questions. A run asks only when elicit is set.

expose:
  agent:
    a2a:
      prompts:
        workers: 2
        elicit: true

The worker sends the question on the reply set, after the ack and before the result or error:

{
  "protocol": "io.choria.fisk-ai.v1.elicit.request.approve",
  "id": "3Hzq6PkmVLsT9WqrChXkgF7NLwy",
  "request": "docs1",
  "conversation": "docs1",
  "sequence": 4,
  "time": "2026-08-16T11:24:11.912084Z",
  "sender": {"name": "nats-worker"},
  "recipient": {"name": "peer1"},
  "question_id": "3Hzq7RvnWMtU0XstDiYlhG8OMxz",
  "tool_use_id": "toolu_01A9bK2mNpQr",
  "command": "stream rm",
  "display": "stream rm ORDERS --force",
  "tag": "ai:confirm",
  "wait_ms": 120000
}

Every question has question_id, and may have tool_use_id and wait_ms:

tag is absent when the gate could name no trigger, which is a command rewritten to a tool that has none.

The caller answers on choria.fisk-ai.elicit.<identity>.<request>, where request is the correlation id it sent:

$ nats req choria.fisk-ai.elicit.nats-worker.docs1 "$(cat answer.json)"

{
  "protocol": "io.choria.fisk-ai.v1.elicit.reply.approve",
  "id": "3Hzq8TwoXNuV1YtuEjZmiH9PNya",
  "request": "docs1",
  "conversation": "docs1",
  "sequence": 0,
  "time": "2026-08-16T11:24:19.310422Z",
  "sender": {"name": "peer1"},
  "question_id": "3Hzq7RvnWMtU0XstDiYlhG8OMxz",
  "choice": "once"
}

Reply under the id you were asked under, with request swapped for reply:

Send the field even when its value is the zero one. confirmed: false, index: 0 and value: "" are each an answer somebody gave.

io.choria.fisk-ai.v1.elicit.waiting arrives on the same subject and is not an answer. It says the caller is holding the question open, see Holding a question open.

The worker replies with an ack. An answer to a question it is not waiting on gets a 404, as does an answer sent after the question’s window closed, and as does a waiting sent after the question was answered.

once runs the command that one time. always stops the worker asking about that tool for the rest of the run. no and no_operator both leave the command unrun and tell the model the refusal is final.

The worker holds the question for expose.agent.a2a.request_timeout, and its worker slot with it. The question’s wait_ms carries that number, so the caller knows how long it has. An unanswered question ends the run differently depending on what asked it:

• an approval leaves the command unrun, and the run ends with suspended
• a human-in-the-loop tool leaves its call deferred, and the run ends with deferred

Both can be answered later, see Answering after the run ended. An operator on the worker holding the journal answers a deferred call with fisk session instead.

Holding a question open

A person reading a command approval can take longer than two minutes. A caller with the question in front of somebody sends an io.choria.fisk-ai.v1.elicit.waiting, and each one restarts the window:

{
  "protocol": "io.choria.fisk-ai.v1.elicit.waiting",
  "id": "3Hzq9UxpYOvW2ZuvFk0njI0QOzb",
  "request": "docs1",
  "conversation": "docs1",
  "sequence": 0,
  "time": "2026-08-16T11:25:59.104812Z",
  "sender": {"name": "peer1"},
  "question_id": "3Hzq7RvnWMtU0XstDiYlhG8OMxz"
}

The rules a client follows:

• Send a waiting every wait_ms / 3, starting when the question goes on screen. The window restarts when the worker receives the message, so the remaining two thirds cover the round trip and one lost message. In Go, a2a.NewWaitingAck(question, sender) builds the message and question.AckInterval() is the interval.
• Stop before sending the answer. A waiting that arrives after the answer is refused, since the worker has finished with the question.
• A 404 means the question is gone: take it off the screen and send no answer, since that would be refused too.
• A 400, or a question with no wait_ms, comes from a worker older than this feature. Answer inside the window instead.
• Send no_operator when the person walks away. waiting says somebody is there to answer, and no_operator ends the question at once. Silence leaves the command unrun too, but only after a whole window.
• The reply set is silent while the worker holds the question, so a client learns the worker is still there only from the ack to each waiting.

A caller that sends no waiting either answers within the window or answers later, on a request of its own.

Answering after the run ended

A person closes a laptop with a question on screen. The waiting messages stop, the window runs out, and the run ends suspended or deferred. The worker unsubscribes from choria.fisk-ai.elicit.<identity>.<request> with the task, so an hour later their answer reaches no responder.

They send an io.choria.fisk-ai.v1.request.answer instead, with the conversation token:

{
  "protocol": "io.choria.fisk-ai.v1.request.answer",
  "id": "3Hzms0ZgSN940AmUYc1fOpEWVk7",
  "request": "docs4",
  "conversation": "docs1",
  "sequence": 0,
  "time": "2026-08-16T12:40:03Z",
  "sender": {"name": "peer1"},
  "conversation_token": "3Hzmp8VqrKL42NmXcPd7bTgWfR1",
  "answer": {
    "tool_use_id": "toolu_01A9bK2mNpQr",
    "kind": "approve",
    "answer": "choice",
    "choice": "once"
  }
}

Copy tool_use_id and kind from the question. A resumed run mints a new question_id, so the answer names the call instead.

The answer object has kind and answer of its own. answer names the field holding the decision, and kind says what that decision means where the value alone cannot: no_operator looks the same whichever question was asked, and value serves both input and select.

A selection names the option, not its position.

You get back the usual ack, events, and a result or an error. The conversation gains no turn. A deferred call takes the answer as its result; an approval is asked again by the resume and answered from the request.

A 400 means the answer does not fit its kind, or the message has no token, or it came with a prompt.

Concurrency and shutdown

Each prompt holds a worker slot from acknowledgement until the run ends. No setting limits total run time; harness.tool_timeout limits a tool call and llm.budget.call_timeout limits a model call. With workers: 1, one long run makes the worker refuse every other caller until it finishes. A run whose caller keeps sending waiting is one such run, and it holds its slot for as long as the caller sends them.

An interrupt starts a drain, which takes the identity out of its queue group, so the worker accepts no further prompts. The worker waits for runs already under way and answers their callers. A prompt acknowledged but not started ends with draining. A second interrupt cancels the runs in flight and answers each caller with failed.

A drain stops restarting the window of a question already outstanding, so it ends within one window and the runs behind it finish. A caller sending waiting at that point still gets an ack, but the ack no longer restarts the window.

Tool selection

A run started this way reaches every tool the top-level include and exclude selected, exactly as a queued job does. expose.agent.tools selects what peers may invoke directly over MCP and a2a, and does not affect a run.

A command tagged ai:confirm, or a configured confirm tag, needs an approval before it runs. Without elicit the run has no operator to ask, so the model sees the tool, calls it, and the worker refuses the call before the command runs. The worker logs how many such tools the run loaded. With elicit the question goes to the caller, as Answering questions describes.

Sessions

The worker mints a conversation token and journals every run under its hash. A crash leaves a resumable run, and a deferred tool call has a journal to answer into. A caller holding the token continues that conversation; a caller that wants the work redone from scratch sends the prompt without one.

conversation on a request is echoed on every reply and never names a journal. It is the caller’s own correlation tag, free for grouping whatever it likes, and the token names the conversation.

Journals from this channel are named t- and a hash, so an operator reading fisk session ls can tell a prompt’s journal from a queued job’s. A session listing shows the last run’s outcome, so a conversation resting between turns reads as completed, and the prompt column shows the conversation’s first prompt.

The worker records the token and the caller’s claimed name with the journal, so a caller that lost a token can ask an operator for it instead of losing the conversation. Find the conversation with fisk session ls, which lists the first prompt and the time each journal was last touched, then read both values with fisk session show <id>. The listing has no token column, because a token is a credential and ls output is often pasted into tickets.

Safety

NATS publish permission on choria.fisk-ai.task.<identity> is the only access control: anyone holding it runs this agent’s tools against a prompt of their choosing. A request carries no verified caller identity, and sender is an unverified claim the worker records and logs.

A caller needs publish on the request subject. Canceling needs publish on choria.fisk-ai.cancel.<identity>.>, and answering questions needs publish on choria.fisk-ai.elicit.<identity>.>. The reply set arrives on the caller’s own inbox.

Anyone holding the cancel permission who learns a request id can cancel a run they did not start. Anyone holding the answer permission who learns a request id and a question id can approve a confirmation-gated command in a run they did not start, and can hold that run’s worker slot for as long as they keep sending waiting.

A conversation_token is a credential on the same terms: holding it is the authorization to add a turn to that conversation, and any holder can continue a conversation, whoever started it. It carries more than a fresh prompt does, because a standing approval an earlier turn recorded is restored with the conversation, so with elicit set a turn can reach a confirmation-gated command that somebody else approved. Tokens carry 128 bits of randomness and cannot be guessed, so treat one as a secret: this agent neither logs it nor puts it in an error message, and a caller should not either.

The session store is shared with the other channels of this identity, and each names its journals in a space of its own: a conversation here is a hash of the identity and the token, and a queued job is a hash of the identity and its task id. So a queue submitter that learns one of these journal ids and spells it as a task id gets a journal of its own rather than this conversation.

The worker records the token in the conversation’s journal, so anyone who can read the session store can read the token and continue that conversation. This gives away no access that reading the store did not already give, since the same access reads and writes those journals directly, but the store needs the same protection the tokens do. The caller’s name is recorded beside the token, and it is the unverified claim from the sender field.

The worker logs the caller, the request id and the session as a prompt is accepted, runs and ends:

level=INFO msg="Accepted a prompt" channel=a2a/prompts request=docs1 caller=peer1 session=3Hzq5OghUNlK8SnoBgVjfE6MKvx prompt_bytes=26
level=INFO msg=Running channel=a2a/prompts work=3Hzq5OghUNlK8SnoBgVjfE6MKvx caller=peer1 caller_verified=false resume=3Hzq5OghUNlK8SnoBgVjfE6MKvx
level=INFO msg="Ending a run" channel=a2a/prompts request=docs1 caller=peer1 session=3Hzq5OghUNlK8SnoBgVjfE6MKvx code=failed reason="llm call: 401 Unauthorized"

The worker logs the window it gave a question and, when the question closes, how long it held it and how many waiting messages the caller sent. An operator reads from these which caller is holding a worker, and for how long:

level=INFO msg="Asked the caller a question" channel=a2a/prompts request=docs1 caller=peer1 question=3Hzq7RvnWMtU0XstDiYlhG8OMxz kind=approve wait_ms=120000
level=INFO msg="A question was answered" channel=a2a/prompts request=docs1 caller=peer1 question=3Hzq7RvnWMtU0XstDiYlhG8OMxz held=14m32s acks=21

The tool safety rules in the Reference apply here as everywhere else.