]> Nomotic, Inc.

chris@nomotic.ai https://nomotic.ai

Applications and Real-Time Independent Submission AI agents sessions agent communication long-lived connections This document specifies the AGTP Session Protocol (AGTP-SESSION), a companion to that defines session semantics for agent-to-agent and agent-to-API communication. AGTP-SESSION addresses two distinct session models: bounded sessions for time-limited transactional flows, and persistent sessions for long-lived agent contexts. Both inherit identity, authority, and attribution from base AGTP. This revision specifies the session identifier format, the ESTABLISH, RESUME, and TERMINATE methods and their wire format, and resumption after transport loss, in which a session is bound to its participants by a signed session token and to the live sender by the per-request signature of base AGTP; no transport connection is part of the binding.

Introduction Base AGTP defines request-and-response semantics for individual method invocations between agents. Many real-world agent interactions span multiple invocations under shared context: a chatbot conversation that continues across hours, an agentic commerce flow that completes a transaction across a sequence of methods, a research agent maintaining working state across a long-running task. These interactions need session semantics that base AGTP leaves unspecified. AGTP-SESSION defines those semantics as a companion protocol that builds on base AGTP without modifying it. The architectural commitment is simple: a session in AGTP is an agent-level abstraction, distinct from a TLS connection, a QUIC connection, or any transport-level session. It is a logical context shared between two or more agents (or between an agent and an API), within which multiple method invocations carry shared identity, authority scope, and attribution chain. A session may map to a single underlying transport connection, may span multiple connections over time, or may persist while the underlying transport is intermittently disconnected and reestablished. The session state is the agent-level fact; the connection is the mechanism that carries traffic when active.

Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Session:

A logical context shared between AGTP participants under which multiple method invocations are correlated, identity and authority remain consistent, and shared state evolves across the lifetime of the session. Sessions are agent-level abstractions and exist above any transport-level construct.

Bounded Session:

A session with an explicit termination condition: a time limit, an action completion, or a transaction outcome. Bounded sessions are appropriate for commerce flows, multi-step delegations with finite scope, and any agent interaction with a defined end state.

Persistent Session:

A long-lived session intended to span hours, days, or longer. State is maintained across reconnections. Persistent sessions are appropriate for chatbot interactions, research agents, monitoring agents, and other contexts where the agent retains continuity.

Session Identifier:

A 256-bit cryptographically random identifier assigned by the responder at session establishment, encoded as 64 lowercase hexadecimal characters, carried in the Session-ID header of every method invocation within the session. Unique per responder; never derived from either participant's Agent-ID. See .

Session Token:

The signed record of a session's establishment: a compact JWS issued by the responder over the session identifier, the two participant Agent-IDs, the session model, the expiry, the resume window, and the session-scoped Authority-Scope grants. The token binds a session to its participants. See .

Session Root:

A 32-byte rolling SHA-256 commitment over the ordered sequence of Audit-IDs of the responses exchanged under a session, folded by both participants independently. Equal roots mean the two agree on what the session has carried; unequal roots name the point of divergence. See .

Initiator, Responder:

The agent that sends ESTABLISH and the agent that accepts it. The roles persist for the session's lifetime: only the initiator may RESUME, and either may TERMINATE.

Session Context:

The shared state associated with a session, including at minimum participant Agent-IDs, Authority-Scope grants applicable to the session, accumulated Attribution-Records for invocations within the session, and any session-specific governance metadata.

Session Models AGTP-SESSION defines two session models. Implementations MAY support one or both depending on deployment profile.

Bounded Sessions Bounded sessions exist for a finite, often short period and complete when one of the following conditions is met:

• An explicit time limit (session_ttl) expires
• A defined transaction or workflow completes
• A participant explicitly terminates the session
• An authority constraint is violated (e.g., scope limit reached)

Bounded sessions match the semantics of agentic transactions where the session has a clear lifecycle: an agent initiates a purchase flow, exchanges several methods with a merchant, completes the transaction, and the session closes. The session boundary is meaningful to governance and attribution: all method invocations within a bounded session are correlated under a single transactional context.

Persistent Sessions Persistent sessions exist for extended periods and survive transport disconnection, network instability, and platform restarts through the resumption procedure of . The session identifier remains stable; the underlying transport may reconnect any number of times during the session lifetime, and each reconnection is re-bound to the session by the initiator's RESUME. Persistent sessions match the semantics of long-lived agent contexts: a chatbot maintaining conversation continuity, a research agent working on a multi-day task, a monitoring agent maintaining persistent attention to a system. Authority-Scope grants applicable to the session may be re-validated periodically; identity verification follows base AGTP semantics on reconnection.

Session Establishment A session is established explicitly via an ESTABLISH method invoked between two AGTP participants. Implicit establishment via an extended- context flag on a standard method invocation is noted as an alternative under consideration but is NOT RECOMMENDED as the primary mechanism. Explicit establishment provides:

• Unambiguous negotiation of session model (bounded or persistent), session lifetime, and any session-scoped Authority-Scope grants
• A clear root for the session attribution chain, with the ESTABLISH invocation serving as the first signed Attribution-Record under the session
• Clean error semantics when negotiation fails (455 Scope Violation if session-scoped grants exceed the establishing agent's Authority-Scope, 4xx for unsupported session models, 5xx for governance platform unavailability)
• Predictable enforcement boundaries for governance platforms and Scope-Enforcement Points, which can recognize session establishment as a distinct event with no inference from method context

ESTABLISH Wire Format ESTABLISH is invoked on the path /session with no Session-ID header and carries the standard AGTP request headers of , including Request-Signature. The request body is a JSON object: Authority-Scope: documents:query, knowledge:query Request-Signature: Content-Type: application/json Content-Length: ... { "model": "persistent", "session_ttl": 86400, "scopes": ["documents:query", "knowledge:query"], "resume_window": 3600, "initiator_nonce": "" } ]]>

model:

bounded or persistent. REQUIRED.

session_ttl:

Proposed lifetime in seconds from establishment. REQUIRED for bounded; OPTIONAL for persistent, where absence means the responder's default.

scopes:

The session-scoped Authority-Scope grants the initiator proposes, in the grammar of . MUST be a subset of the initiator's claimed or inherited Authority-Scope. OPTIONAL; absence means the session carries no scope narrower than the request's.

resume_window:

Proposed seconds after transport loss during which the responder retains session state for RESUME. OPTIONAL; the responder MAY shorten it.

initiator_nonce:

Random value echoed into the session token so the initiator can bind the token to this request. REQUIRED.

Body Extensions Companion specifications MAY add top-level keys to the ESTABLISH request and response bodies, registered in the ESTABLISH Body Extension Registry of . A responder that recognizes an extension key negotiates it and returns the negotiated value under the same key in the response; a responder that fails to recognize a key MUST ignore it and MUST omit it from the response, so that the absence of the key in the response tells the initiator the extension went unnegotiated. An initiator for which the extension is essential MUST then TERMINATE the session; using it without the extension is prohibited. The first registered extension is communication, defined by . A successful response is 200 OK with the Session-ID response header carrying the new session identifier and a JSON body: ", "model": "persistent", "expires_at": "2026-10-28T22:00:00Z", "resume_window": 3600, "scopes": ["documents:query", "knowledge:query"], "session_token": "" } ]]> The responder MUST verify the initiator at Level 2 or Level 3 per before issuing a token, and the ESTABLISH invocation's Attribution-Record is the first record under the session. Rejection: 455 Scope Violation with reason scope-exceeds-parent when scopes exceeds the initiator's Authority-Scope; 422 when the requested model is unsupported by the responder; 503 when the responder's governance platform cannot be reached to record the session. Implementations MUST NOT establish a session by side effect of any other method invocation; the absence of a successful ESTABLISH response means no session exists.

Session Identifier The responder generates the session identifier as 256 bits from a cryptographically secure random source, encoded as 64 lowercase hexadecimal characters. It MUST NOT be derived from, or correlate with, either participant's Agent-ID or any prior session identifier. It is carried in the Session-ID header on every subsequent invocation within the session, in both directions. Base AGTP assigns Session-ID no semantics; this document assigns it the binding below.

Session Token The session token is a compact JWS , algorithm EdDSA, kid equal to the responder's Agent-ID, signed with the responder's agent_public_key as published in its Identity Document (), over the canonical form of: ", "initiator": "", "responder": "", "model": "bounded" | "persistent", "iat": , "exp": , "resume": , "scopes": [ ... ], "nonce": "" } ]]> The token is the binding between a session identifier and its two participants. A responder's governance platform MAY countersign the token (a second JWS over the same payload, carried in a governance_token body field) where deployment policy requires a platform record of the session; the protocol depends on the responder's signature alone. The initiator retains the token and presents it on RESUME. The responder MAY retain only the session identifier and verify the presented token by signature, which lets a responder that restarted recover the session's binding from the token itself.

Binding to the Live Sender A session identifier and token establish which two agents a session belongs to. They never establish that the sender of a given request is one of them. That proof is the Request-Signature of , present on every invocation and verified under the sender's current key. Within a session the responder MUST additionally check that the request's Agent-ID is one of the two participants in the token for that Session-ID, and MUST reject with 401 and reason session-participant-mismatch otherwise. A session is therefore bound to its participants by signature at establishment and to the live sender by signature on every request, and to no transport connection. A responder MAY also bind each live connection to the session with a TLS exporter or QUIC connection identifier as defense in depth; that binding is per connection, re-established at every RESUME, and separate from the session's identity.

Session Root Two participants in a long session need a compact way to stay in agreement about what the session has carried without resending it. Each response under a session carries an Audit-ID (), the identifier of its Attribution-Record. Both participants fold the sequence of Audit-IDs, in the order the responder emitted them, into a session root: where || is byte concatenation, session_id is the 32 raw bytes of the session identifier, and audit_id_n is the 32 raw bytes of the n-th response's Audit-ID. The root after n responses commits to every response so far and is independent of how long the session has run; it is 32 bytes on the wire however many exchanges precede it. A participant that holds a root and the Audit-IDs since can verify the other's root by refolding, and can fetch any response's full record with INSPECT target=audit () to verify against the raw record later. The root is carried on RESUME, where it lets the responder detect divergence beyond the single lost response that last_response_id covers, and on TERMINATE, where the final Attribution-Record commits to the whole session. Carriage elsewhere (for example on every n-th response as a periodic checkpoint) is permitted and is operator policy. The construction is the rolling-commitment pattern of , restricted here to Audit-IDs so that it composes with the per-agent audit chain of : the per-agent chain records what one agent did; the session root records what two agents agree the session carried. A deployment that needs the full acknowledged history and unacknowledged-window machinery of MAY carry HCTP payloads inside the session as EXECUTE content; the session root is the minimum the session protocol itself needs.

Resumption After Transport Loss When the transport carrying a session is lost (connection reset, network change, responder restart), the session persists in the Suspended-by-transport state for resume_window seconds from the last successful exchange. Within that window the initiator opens a new transport, re-establishing identity at Level 2 or Level 3 as for any new connection, and sends: Session-ID: Request-Signature: Content-Type: application/json Content-Length: ... { "session_token": "", "last_response_id": "", "session_root": "<64 lowercase hex, the initiator's root, or null>" } ]]> The responder MUST verify, in order: the Request-Signature; that the token's signature verifies under its own key and its sid equals the Session-ID header; that the request's Agent-ID equals the token's initiator; that exp is in the future and the resume window is still open; and that the session is in Suspended-by-transport, short of terminated. On success the responder returns 200 OK with the Session-ID header and a body carrying last_response_id and session_root as seen on its side, so the initiator can detect a response lost in transit and re-request it, and the session returns to Active. When the initiator's session_root is present and differs from the responder's, the responder MUST still return 200 OK with its own root and last_response_id, and MUST include divergence: true; the initiator then reconciles by fetching records with INSPECT target=audit from its last agreed point. A divergent root is a signal to reconcile and an insufficient reason to refuse resumption, since the usual cause is a response lost in transit. On failure the responder returns 410 Gone with reason session-expired (window or exp passed), session-terminated (a TERMINATE was processed), or session-unknown; a token that fails verification is 401 with reason session-token-invalid. If a RESUME arrives while an earlier connection for the same session is still open, the responder MUST treat the newer connection as authoritative, release the earlier connection's binding, and log the event; two live connections never share a session. RESUME is an action method for the purposes of and MUST NOT be sent as QUIC early data.

Termination Either participant ends a session with: Request-Signature: { "reason": "", "session_root": "<64 lowercase hex>" } ]]> reason is one of completed, ttl-expired, scope-violation, revoked, operator, or initiator-request. session_root is the terminating party's root over the session (). The response is 200 OK, carries the responder's own session_root, and its Attribution-Record is the session's final record, signed by the terminating party, naming the reason, and committing to the root so that the session's whole history is verifiable from one record. A terminated session identifier MUST NOT be reused and RESUME against it returns 410 Gone with reason session-terminated. Expiry of a bounded session's session_ttl is enforced against the responder's clock and produces the same final record with reason ttl-expired without a TERMINATE invocation.

Method Registration ESTABLISH, RESUME, and TERMINATE are registered in the AGTP Method Registry by this document (). They are session-management methods: none is safe, none is idempotent, and all three are action methods under the properties defined in and its methods companion.

Inheritance from Base AGTP AGTP-SESSION inherits all base AGTP properties:

• Agent-only at the wire level. Sessions exist between agents; general-purpose actors have no session.
• Agent-ID present on every method invocation, including invocations within a session, with Owner-ID resolved from the agent identity document the Agent-ID references.
• Authority-Scope enforced on every method invocation. Scopes stay exactly as granted inside sessions.
• Attribution Records signed for every invocation, including those within sessions, with the session identifier included in the attribution metadata.
• Status codes, including 455 Scope Violation and 551 Authority Chain Broken, apply within sessions exactly as outside them.
• Three-level verification model. Sessions leave verification unchanged.

AGTP-SESSION adds session-specific semantics on top of these properties and leaves every one of them as base AGTP defines it.

Transport Considerations Base AGTP runs over TCP with TLS 1.3 or over QUIC, as specified in . AGTP-SESSION inherits these transport options. QUIC is a particularly natural fit for persistent sessions because of its connection migration capability , which allows a logical connection to survive IP address changes and network path changes without renegotiation. AGTP-SESSION over QUIC can leverage QUIC's connection migration to maintain a persistent session across network transitions transparently. Connection migration is an optimization: when it succeeds no RESUME is needed, and when the QUIC connection is lost outright the resumption procedure of applies as over TCP.

Relationship to MOQT and Real-Time Media The charter discussion that produced the IETF agentproto working group anticipated a session protocol on WebTransport or MOQ as a foundational building block for agent communication. That work and AGTP-SESSION reflect inverse architectural commitments. The agentproto approach treats session and transport semantics as the foundation, with agent-specific concerns (identity, authority, attribution) layered on top by the protocols that compose on the session. Under this model, the session protocol carries agent traffic without knowing it; agent semantics are an application-layer concern. AGTP-SESSION reflects the inverse: agent-specific concerns are the foundation (in base AGTP), and session semantics layer on top of an agent-aware substrate. Under this model, a session is, by definition, an agent session. The protocol carries identity, authority, and attribution at the wire level for every method invocation within the session, because the substrate beneath the session already commits to carrying agent traffic and nothing else. The two architectures can coexist in deployment. MOQT-style relay-based pub/sub patterns and real-time media streaming address use cases (particularly voice with sub-100ms barge-time interruption) that sit outside AGTP-SESSION. is the companion that builds on ESTABLISH for real-time multi-modal communication between agents; composition with MOQT-style transport for real-time agent media, or MOQT-style sessions carrying AGTP semantic envelopes, remains future work. The architectural choice between these two foundations is a question for community discussion. Both deliver session semantics; they differ on which layer commits to knowing the traffic is agent traffic.

Application Layering: Voice and Multi-Modal Agents AGTP-SESSION focuses on session semantics for agent communication. Protocols for real-time voice, video, or multi-modal data exchange are specified in . Voice agents, video agents, and multi-modal agents are application- layer constructs that can compose on top of AGTP and AGTP-SESSION. At the protocol layer they are the same kind of agent; they are agents that produce or consume specific media types. This raises a related architectural question worth surfacing for community discussion: AGTP may benefit from an agent type system, analogous to HTTP Content-Type, that allows the protocol to identify the kind of agent or kind of agent payload involved in a given exchange. This sits outside AGTP-SESSION as currently scoped and is flagged here as adjacent work that may warrant its own companion specification.

Out of Scope for v01 The following are out of scope for this version:

• Real-time voice and barge-time interruption semantics ()
• Pub/sub and relay-based session patterns (MOQT-style multicast)
• Session migration across organizations or governance platforms
• Session state synchronization across multiple agents in a chain
• Multi-party sessions (more than two participants)
• Session encryption beyond what TLS 1.3 or QUIC already provides

These are flagged as future work or as open questions to be resolved through community input.

Security Considerations Base AGTP security considerations apply to every method invocation within a session, including invocations occurring under bounded or persistent session models. This section identifies session-specific risks and mitigations that supplement the base AGTP threat model.

Session Identifier Theft and Replay Threat: An attacker who obtains a session identifier may attempt to inject method invocations into an active session by replaying or forging requests carrying the identifier. Mitigation: Session identifiers are bound at establishment to the participating Agent-IDs by the session token (), and every invocation within a session is bound to its live sender by Request-Signature (). A session identifier in isolation MUST NOT be sufficient to authorize a method invocation: an attacker holding the identifier and the token still lacks the initiator's signing key, and an attacker holding a captured request is stopped by the signature's timestamp and nonce. The receiving party MUST reject invocations whose Agent-ID is outside the token's two participants or whose signature fails. Transport channel binding is permitted as an additional per-connection check and is never what a session's continuity depends on, since the transport is what resumption survives.

Persistent Session Compromise Threat: A persistent session that survives transport disconnection and reconnection has a longer attack window than a bounded session. An attacker who compromises a participant's signing key during the session lifetime can impersonate the participant for the remainder of the session. Mitigation: Persistent sessions SHOULD require periodic Authority-Scope re-validation against the establishing governance platform. Recommended re-validation interval is implementation- defined but SHOULD NOT exceed the lifetime of the underlying Authority-Scope grants. Persistent sessions MUST support revocation propagation: if a participant's Agent Genesis or Agent Certificate is revoked during the session, the session MUST terminate with appropriate status code on the next invocation. Implementations SHOULD subscribe to revocation notifications via mechanisms defined in or .

Cross-Session Correlation Threat: An adversary observing multiple sessions from the same agent may be able to correlate sessions to construct a profile of agent behavior across contexts, even if individual session contents are encrypted. Mitigation: Session identifiers MUST NOT be derived from participant Agent-IDs in a way that enables cross-session linkage. Session identifiers SHOULD be cryptographically random and unique per session. Implementations supporting privacy-sensitive deployments SHOULD consider session identifier rotation policies that limit linkability, with the trade-off that rotation complicates revocation propagation.

Authority Constraint Violation Mid-Session Threat: An agent participating in an established session may attempt to invoke methods that exceed session-scoped Authority-Scope grants, either through scope drift across multiple invocations or through deliberate scope expansion attempts. Mitigation: Authority-Scope is enforced on every invocation regardless of session context. A scope violation MUST trigger 455 Scope Violation per base AGTP. Receiving parties MAY elect to terminate the session on first scope violation instead of accepting further invocations. Termination on scope violation is RECOMMENDED for bounded sessions where the violation suggests the session boundary has been compromised.

QUIC 0-RTT Resumption Considerations Threat: When AGTP-SESSION runs over QUIC, 0-RTT connection resumption allows initial method invocations on a resumed connection to be processed before full handshake completion. Replay of 0-RTT data is a known QUIC consideration. Mitigation: Method invocations transmitted in 0-RTT data MUST NOT be permitted to ESTABLISH, RESUME, or TERMINATE a session; all three are action methods. Session establishment and resumption MUST occur after the QUIC handshake has completed. Invocations within an existing session MAY use 0-RTT only for methods on the early-data eligibility list in the replay-safety profile of ; action methods are excluded there and that exclusion applies unchanged inside sessions. Implementations SHOULD consult QUIC 0-RTT replay guidance ( Section 9.2) when configuring session resumption behavior.

Graceful Termination and Revocation Threat: A session may need to be terminated mid-flow due to revocation, scope violation, time expiry, or governance policy changes. Improper termination handling can leave participants in inconsistent state. Mitigation: TERMINATE ( and following) produces a final Attribution-Record signed by the terminating party identifying the termination reason. Mid-session revocation of either participant's Agent Genesis or Agent Certificate MUST result in session termination. Time-based expiry of bounded sessions MUST be enforced against the establishing governance platform's authoritative time; participant-local clocks are advisory.

IANA Considerations This document requests registration of three methods in the AGTP Method Registry maintained per , with this document as the reference: Session Methods

Method	Group	Safe	Idempotent	Section
ESTABLISH	Mechanics	No	No
RESUME	Mechanics	No	No
TERMINATE	Mechanics	No	No

It also registers the reason tokens session-participant-mismatch, session-token-invalid, session-expired, session-terminated, and session-unknown in the AGTP reason vocabulary for status codes 401 and 410. This document establishes the AGTP ESTABLISH Body Extension Registry (), registration policy Specification Required, with one initial entry: ESTABLISH Body Extensions

Key	Reference
communication

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JSON-based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) specification. Cryptographic operations like hashing and signing need the data to be expressed in an invariant format so that the operations are reliably repeatable. One way to address this is to create a canonical representation of the data. Canonicalization also permits data to be exchanged in its original form on the "wire" while cryptographic operations performed on the canonicalized counterpart of the data in the producer and consumer endpoints generate consistent results. This document describes the JSON Canonicalization Scheme (JCS). This specification defines how to create a canonical representation of JSON data by building on the strict serialization methods for JSON primitives defined by ECMAScript, constraining JSON data to the Internet JSON (I-JSON) subset, and by using deterministic property sorting. Informative References This document defines the core of the QUIC transport protocol. QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and network path migration. QUIC includes security measures that ensure confidentiality, integrity, and availability in a range of deployment circumstances. Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm. This document describes how Transport Layer Security (TLS) is used to secure QUIC.

Open Questions

• Should the session root be carried as a periodic checkpoint on responses within the session, and at what interval, beyond its carriage on RESUME and TERMINATE?
• How are persistent sessions migrated across governance platform changes (e.g., merchant changes governance providers mid-session)?
• Should AGTP define an agent type system (Agent Content-Type) separately, or as part of session establishment?
• What is the right composition story with MOQT for real-time agent media use cases?
• Should multi-party sessions (more than two participants) be in scope for a later revision, or deferred to a separate companion?
• Should a responder be permitted to initiate RESUME toward an initiator that has a reachable attachment, for responder-side transport loss?

Changes from v00 This revision closes the three gaps conceded on the agentproto list in August and refreshes references and terminology. Wire format compatibility: session-00 specified no wire format, so nothing shipped changes.

• Session identifier specified: 256-bit random, 64 lowercase hex, responder-assigned, uncorrelated with Agent-IDs
• ESTABLISH body extensions () and their registry, so companions such as negotiate through the one ESTABLISH grammar with no headers of their own ().
• ESTABLISH wire format specified, with RESUME and TERMINATE added and all three registered (, , ).
• Re-binding after transport loss specified: the session is bound to its participants by a responder-signed session token and to the live sender by the base per-request signature; transport channel binding is demoted to an optional per-connection check, since resumption survives the transport (, ).
• Session root specified (): a 32-byte rolling commitment over the session's Audit-IDs, carried on RESUME for divergence detection and on TERMINATE so the final record commits to the whole session. This answers the session-level attribution question left open in v00 and follows the rolling-commitment pattern of .
• Base reference moved to draft-hood-independent-agtp-10, which supplies Request-Signature and agent_public_key.
• References updated: base AGTP to draft-hood-independent-agtp-09, AGTP-CERT to -03, AGTP-LOG to -02. Informative references added for and .
• Status code for scope violation at ESTABLISH corrected from 451 to 455, matching the base renumbering.
• Principal-ID references replaced. Base AGTP records Owner-ID in the agent identity document referenced by Agent-ID and never in a request header; the ESTABLISH field list and the inheritance section now say so.
• QUIC 0-RTT guidance defers to the replay-safety profile and early-data eligibility list in without restating the rule.
• Real-time voice, video, and multi-modal exchange now points to , which builds on ESTABLISH.
• Working group reference updated from the acp charter proposal to the agentproto working group.
• Editorial pass for house style. No normative change beyond the status code correction.

Contributors This draft is informed by the IETF agent2agent charter formation discussion and by feedback on the architectural layering question raised in that thread.