Struct SubagentUpdate 

#[non_exhaustive]
pub struct SubagentUpdate {
    pub session_id: SessionId,
    pub title: MaybeUndefined<String>,
    pub description: MaybeUndefined<String>,
    pub capabilities: MaybeUndefined<SubagentSessionCapabilities>,
    pub state: MaybeUndefined<StateUpdate>,
    pub meta: MaybeUndefined<Map<String, Value>>,
}

Available on crate feature unstable_protocol_v2 only.

UNSTABLE

This capability is not part of the spec yet, and may be removed or changed at any point.

Notification that the enclosing parent session created and owns a child session.

Later updates modify the existing association’s metadata, not its ownership.

Sent on the immediate parent session. The first update for an unknown SubagentUpdate::session_id announces the child and MUST be sent before any live request or notification bearing the child’s session ID, including messages naming it as sender or recipient. Child events are delivered automatically; no separate child load, resume, or subscription is needed. Understanding this update, registering child sessions, and applying their operation restrictions are baseline v2 requirements; no Client capability is required.

Only SubagentUpdate::session_id is required. Other fields have patch semantics: omitted fields leave the stored value unchanged, null clears or unsets the value, and concrete values replace it. For state, null removes the current state report and leaves activity unconfirmed; it does not report idle or cancellation. A child whose capabilities are unset permits no Client-initiated session mutations.

The title and description provide the parent’s display metadata for the child. Agents SHOULD mirror known child state changes in the parent’s SubagentUpdate::state using the same StateUpdate snapshot as the ordinary state_update notification on the child session. This reports child state, not a separate parent-owned lifecycle. Consumers should treat duplicate reports idempotently. Completing or cancelling work does not end the association: the parent may message the same child again. Individual messages and their outcomes do not change this association.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

session_id: SessionId

The opaque session ID identifying the child in all ACP messages.

title: MaybeUndefined<String>

The parent’s human-readable display title for this child. It need not be unique.

Optional and nullable. Omitted means unchanged; null clears it. If no title is set, the Client chooses a fallback presentation.

description: MaybeUndefined<String>

The parent’s human-readable description of the child’s role or purpose.

Optional and nullable. Omitted means unchanged; null clears it. This is current display metadata, not the history of instructions sent to the child.

capabilities: MaybeUndefined<SubagentSessionCapabilities>

Client-initiated session mutations permitted for this subagent session.

Read-only operations retain their normal protocol semantics and capability requirements.

state: MaybeUndefined<StateUpdate>

The child’s current foreground state, mirrored onto its parent association.

Optional and nullable. Omitted means unchanged; null removes the current report and leaves activity unconfirmed (not idle or cancelled). A concrete StateUpdate replaces the entire previous snapshot.

meta: MaybeUndefined<Map<String, Value>>

The _meta property is reserved by ACP to allow clients and agents to attach additional metadata to their interactions. Omitted means no metadata update; null is an explicit clear signal. Implementations MUST NOT make assumptions about values at these keys.

See protocol docs: Extensibility

Implementations

impl SubagentUpdate

pub fn new(session_id: impl Into<SessionId>) -> SubagentUpdate

Available on crate feature unstable_subagents only.

Builds a subagent upsert with only its required session ID set.

pub fn title(self, title: impl IntoMaybeUndefined<String>) -> SubagentUpdate

Available on crate feature unstable_subagents only.

Sets, clears, or leaves unchanged the parent’s display title for the child.

pub fn description( self, description: impl IntoMaybeUndefined<String>, ) -> SubagentUpdate

Available on crate feature unstable_subagents only.

Sets, clears, or leaves unchanged the parent’s description of the child.

pub fn capabilities( self, capabilities: impl IntoMaybeUndefined<SubagentSessionCapabilities>, ) -> SubagentUpdate

Available on crate feature unstable_subagents only.

Sets, clears, or leaves unchanged the permitted client-initiated session mutations.

pub fn state( self, state: impl IntoMaybeUndefined<StateUpdate>, ) -> SubagentUpdate

Available on crate feature unstable_subagents only.

Replaces, clears, or leaves unchanged the child’s mirrored state snapshot.

pub fn meta( self, meta: impl IntoMaybeUndefined<Map<String, Value>>, ) -> SubagentUpdate

Available on crate feature unstable_subagents only.

Sets, clears, or leaves unchanged subagent metadata.

Trait Implementations

impl Clone for SubagentUpdate

fn clone(&self) -> SubagentUpdate

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SubagentUpdate

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for SubagentUpdate

fn deserialize<__D>( __deserializer: __D, ) -> Result<SubagentUpdate, <__D as Deserializer<'de>>::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl JsonSchema for SubagentUpdate

fn schema_name() -> Cow<'static, str>

The name of the generated JSON Schema.

fn schema_id() -> Cow<'static, str>

Returns a string that uniquely identifies the schema produced by this type.

fn json_schema(generator: &mut SchemaGenerator) -> Schema

Generates a JSON Schema for this type.

fn inline_schema() -> bool

Whether JSON Schemas generated for this type should be included directly in parent schemas, rather than being re-used where possible using the $ref keyword.

impl PartialEq for SubagentUpdate

fn eq(&self, other: &SubagentUpdate) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl Serialize for SubagentUpdate

fn serialize<__S>( &self, __serializer: __S, ) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for SubagentUpdate