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An agent delta should be accepted only after its envelope is validated against the protocol that governs it. Check who emitted it, which session it belongs to, whether that session is still valid, and how the protocol handles ordering, replay, and durability. Arrival alone does not prove that a delta is safe to expose or commit.
What must be true before an agent delta ships?
Here, “ships” means the application accepts, exposes, or commits a delta under its own contract; it does not refer to one vendor’s release pipeline. There is no universal agent envelope. The exact fields and rules depend on the selected protocol, so validate against that protocol rather than assembling a hybrid schema.
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- Validate the schema and protocol version. Confirm the message is well-formed and identifies the protocol version whose rules the consumer will apply.
- Authenticate or establish the emitter. Bind the message to the expected agent or sender using the protocol’s identity mechanism.
- Bind it to the right session scope. Do not assume a session string is globally unique. Use the protocol’s identity scope and session rules.
- Check lifecycle and authority. Reject messages for closed or otherwise invalid sessions, and validate any required capability, delegation, constraints, or revocation state.
- Deduplicate and establish continuity. Use the protocol’s event identity and ordering fields; detect gaps or invalid replays before applying the delta.
- Determine whether it is transient or durable. A streamed update may be useful for display but not retained as a recoverable event.
- Expose or commit only as the application contract permits. Keep provisional UI updates distinct from durable state changes when the protocol does.
This is a decision framework, not a cross-protocol specification. For example, the Agent Event Protocol (AEP), PI Desktop Remote Agent Control Protocol (RACP), MACP, and AIDP use different envelope fields and acceptance models.
How can you tell whether a delta belongs to the right session?
AEP: scope the session to its emitter
AEP 0.1 defines a JSON event with required fields including aep, id, type, time, source, and agent. Session-scoped events also carry session and seq. Its session keys are unique within an emitting agent, not globally, so an aggregated consumer should key session state by (source, session), rather than by the session string alone. AEP also says consumers deduplicate by (source, id). See the AEP-0001 specification.
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MACP: authenticate the sender and check session state
MACP requires a canonical envelope carrying protocol version, session scope, sender identity, message identity, and payload. For session-scoped acceptance, sender identity must be authenticated or derived. The protocol defines session states including open, suspended, resolved, expired, and cancelled; messages that refer to a session that is not open must be rejected. MACP is its own draft/specification ecosystem, not a universal envelope rule. See the MACP specification.
AIDP: validate actor and authority, not just a session label
The July 2026 AIDP Internet-Draft defines an Intent Envelope as a cryptographically attributable execution request, rather than a natural-language prompt. Its fields include an ID, timestamp, actor reference, authority reference, bounded intent, constraints, delegation chain, and observability hooks. At the execution boundary, validation covers actor identity, capability, delegation integrity, revocation, constraints, and non-reuse of the envelope ID. A failed check aborts execution. This is a draft and does not establish broad implementation or final-standard status. See the AIDP Internet-Draft.
Should events be ordered by timestamp or sequence number?
Use the ordering authority defined by the protocol. A timestamp may help display or join records, but it does not necessarily establish causal or replay order.
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In AEP, seq is the ordering, replay, and resume authority; time is display or join metadata. AEP also supports restart-aware ordering and replay with (epoch, seq). Its envelope has optional context fields such as run, step, cause, trace, severity, capture, and payload; optional fields should be omitted when absent rather than filled with null. See the AEP-0001 specification.
RACP uses epoch and sequence for durable continuity
In PI Desktop RACP, the Host allocates durable-event sequence numbers starting at 1 for each epoch. A new epoch begins when continuity cannot be proven. Clients use durable sequence values to detect gaps; ephemeral events instead carry afterSequence and are not part of the durable replay stream. See the RACP protocol documentation.
AIDP gives the envelope ID a different role
AIDP requires the Intent Envelope ID not to be reused, as part of its replay protection. That identity check is not a substitute for AEP’s or RACP’s sequence-based ordering rules; these protocols solve different problems. See the AIDP Internet-Draft.
Can you replay a delta after reconnect?
Only if the protocol treats it as retained, replayable data. In RACP, durable events carry sequence, while ephemeral kinds such as turn.activity, item.delta, tool.progress, and terminal.output carry afterSequence. Ephemeral events are not retained or replayed and do not count against the replay window. The protocol maps message_update to non-durable item.delta, while message_end becomes durable item.completed containing the full UI message. After reconnect, recover from durable events or a snapshot rather than assuming every streamed delta can be replayed. See the RACP protocol documentation.
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How do the protocols differ?
| Protocol | Identity scope | Ordering or replay basis | Lifecycle or durability distinction |
|---|---|---|---|
| AEP 0.1 | source plus session for aggregated session state; deduplicate on (source, id) |
seq, or (epoch, seq) across restarts |
Session scope and optional event context are defined in its envelope |
| PI Desktop RACP | Protocol event stream and its epoch | Durable-event (epoch, sequence) |
Durable events are replayable; ephemeral activity, including item.delta, is not retained or replayed |
| MACP | Authenticated or derived sender identity plus session ID | Message identity is carried in its canonical envelope | Session states include open, suspended, resolved, expired, and cancelled; session-scoped messages require an open session |
| AIDP | Actor and authority references, with delegation and constraints | Unique, non-reusable Intent Envelope ID for replay protection | Execution validation aborts on a failed identity, capability, delegation, revocation, constraint, or replay check |
These are distinct specifications, not interchangeable standards. Apply only the fields and guarantees of the protocol actually in use. Draft status also matters: MACP and the July 2026 AIDP document should be treated as specifications in development, not proof of universal implementation.
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