Agent Conversation Protocols

Source and implementation boundary

The local trace contract borrows vocabulary from external interaction protocols only where the referenced source establishes it. It is not a wire-conformance claim, and trace identifiers are neither business-operation identifiers nor identity or effect authority. See references/fipa-a2a-mcp-boundary.md.

Design a finite protocol over identities and authority supplied by other systems. A valid trace says which messages were accepted and why. It never creates a principal, body, lease, capability, truth verdict, or permission to cause an effect.

Use this skill when

• already admitted bodies need a request/response, critique, handoff, or gather protocol;
• duplicate, stale, reordered, missing, or replayed messages must fail deterministically;
• a fixed participant set must converge to a closed terminal;
• a transcript must replay to the same semantic state;
• a terminal fence and explicit acknowledgement set are required.

Do not use it for

• choosing, spawning, admitting, resurrecting, or paying agents;
• deciding star, mesh, tree, or runtime placement;
• ordinary human discourse or conflict mediation;
• serialization, queues, sockets, or transport deployment;
• adjudicating claim truth or granting action authority.

Protocol design procedure

flowchart TD
  A[Receive admitted participant snapshot] --> B[Bind protocol, conversation, epoch, scope, and bounds]
  B --> C[Declare closed message types and fixed gather membership]
  C --> D[Accept only current audience-bound envelopes]
  D --> E{Sequence state}
  E -->|duplicate| F[Record duplicate; no reducer transition]
  E -->|gap or reorder| G[Block sender stream pending exact sequence]
  E -->|next exact sequence| H[Verify digest, expiry, generation, and scope]
  H --> I[Apply deterministic reducer]
  I --> J{Terminal predicate?}
  J -->|No| D
  J -->|Yes| K[Append terminal fence]
  K --> L[Collect fixed acknowledgement set]
  L --> M[Close with truthEffect NONE and authorityEffect NONE]

1. Bind the snapshot. Record exact participant principals, body generations, audience labels, protocol epoch, scope, deadline, and message ceiling. This skill does not admit them.
2. Close the language. Enumerate message kinds and payload types. Unknown kinds fail closed.
3. Sequence per sender. Sequence numbers start at 1 and are contiguous inside one epoch and body generation. A duplicate is idempotent only when its full envelope digest matches; otherwise it is equivocation.
4. Filter before reduce. Reject stale epoch/generation, wrong scope/audience, invalid verification receipt, expired message, and unresolved causation before changing semantic state.
5. Freeze gathers. Membership and reducer are fixed when the gather opens. Silence, timeout, majority, and acknowledgement do not imply assent, truth, or authority.
6. Fence termination. Exactly one terminal fence closes semantic mutation. Required participants acknowledge the fence; an acknowledgement means receipt only.
7. Replay semantically. Replaying the accepted envelopes in canonical order must reproduce the state digest and terminal record.

Non-authority invariants

• Messages transport assertions; they do not mint identity, body continuity, admission, leases, capabilities, or permissions.
• ACK proves only protocol receipt by the named participant generation.
• GATHER_RESULT is a deterministic reduction of declared inputs, not a truth verdict.
• A protocol terminal does not prove an external effect stopped, succeeded, failed, or settled.
• Every terminal has truthEffect: NONE and authorityEffect: NONE.

Ordering and replay rules

Condition	Required disposition
exact next sender sequence	validate, then reduce
byte-identical duplicate	record duplicate, no second reduction
same identity/sequence with different digest	E_EQUIVOCATION
sequence gap or later message first	E_SEQUENCE_GAP
stale epoch or body generation	E_STALE_EPOCH / E_STALE_GENERATION
wrong audience or scope	E_AUDIENCE_SCOPE
unknown causation parent	E_CAUSATION_GAP
message after terminal fence	E_POST_TERMINAL_MESSAGE
terminal missing required acknowledgements	valid BLOCKED, never complete

Gather rules

• membership is a sorted, nonempty list of participant refs and cannot change.
• ALL waits for one accepted contribution from every member.
• QUORUM requires an explicit integer threshold and preserves every dissenting contribution.
• FIRST_SUCCESS is permitted only for inert candidate production and must use a deterministic tie-break; it cannot decide truth or authority.
• Timeout yields an explicit partial/blocked result. It never fabricates missing input.
• Reducers consume typed message IDs and return a digest-bound semantic value plus unresolved members.

Terminals

COMPLETED, BLOCKED, TIMED_OUT, CANCELLED, and DISSENT_RECORDED are the only terminals. COMPLETED means only that the protocol's declared semantic predicate was met. Any external lifecycle or effect claim requires independent evidence.

Anti-patterns

Ack means done

Wrong: treat delivery acknowledgement as task completion or stopped process.

Right: receipt, semantic closure, lifecycle state, and external effect state remain separate.

Majority mints truth

Wrong: collapse a quorum result into fact or permission.

Right: preserve inputs and dissent; pass the candidate to an independent evaluator or authority.

Dynamic gather membership

Wrong: add a friendly voter after seeing early results.

Right: freeze membership and epoch before contributions.

Replay by timestamp

Wrong: trust wall-clock order across senders.

Right: verify per-sender sequence and explicit causation, then use a canonical tie-break only for concurrent events.

Validator coverage boundary

The bundled validator checks the local JSON shape, closed enums, participant and gather joins, supplied message ordering, causation references, acknowledgement sets, and digest format. It does not verify cryptographic receipts, payload bytes, reducer output, delivery, storage, identity, canonical concurrency order, runtime liveness, or external effects. A valid stateDigest is format-checked input, not a recomputed semantic result. See the terminal-fence sequence and the supplied-sequence boundary.

Output contract

Emit a JSON trace conforming to schemas/conversation-trace-v2.schema.json. Validate it with:

node skills/agent-conversation-protocols/scripts/validate-conversation-trace.mjs \
  skills/agent-conversation-protocols/examples/valid-trace.json

node skills/agent-conversation-protocols/scripts/test-bundle.mjs

Load only when needed

• references/INDEX.md — short routing for the protocol references.
• references/envelope-and-ordering.md — exact envelope fields, duplicate handling, and canonical replay.
• references/gathers-and-terminals.md — fixed gathers, reducers, terminal fences, and acknowledgements.
• references/pattern-selection-boundary.md — select a conversation pattern before instantiating this closed protocol; a pattern does not grant authority or settle an effect.
• references/fipa-a2a-mcp-boundary.md — external protocol vocabulary and local-trace boundary.
• diagrams/INDEX.md — terminal fence and supplied-sequence diagrams.
• examples/valid-trace.json — canonical closed trace used by the validator.
• scripts/validate-conversation-trace.mjs — closed-shape and semantic validator.
• scripts/test-bundle.mjs — valid fixture plus adversarial mutation suite.
• tests/activation.md — positive and negative activation corpus.

Truth posture

This skill statically validates supplied traces. It does not prove transport delivery, durable storage, independent identity, runtime liveness, containment, or external effects.