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A2A Agent Tools

Kagent has two distinct subagent mechanisms. They should not be confused.

flowchart TB
    PARENT[Parent agent]
    PARENT -->|Shared binding compiled into one runtime| LOCAL[Native in-process subagent]
    PARENT -->|remote A2A tool call| REMOTE[Addressable A2A agent]
    REMOTE -->|task + context IDs retained| CONTINUE[input-required continuation]
    PUBLIC[Public cross-session delegation] -. deferred .-> POLICY[credential and lineage policy]
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Shared agent tools

An AgentTemplate can bind another template as a Shared tool through spec.tools[].subAgent.templateRef. The translator resolves the referenced template in the same compilation tree and the selected harness compiler emits its native, in-process representation. Kagent, Codex, and Claude support Shared bindings according to their runtime capabilities.

For example, in an AgentTemplate spec (or an Agent's inline spec.template.inline):

tools:
  - subAgent:
      name: reviewer
      description: Review proposed changes before applying them.
      templateRef:
        name: review-context

Tree resolution detects missing references and cycles before compilation.

Dedicated agent tools

Dedicated bindings would select an independently configured Agent with its own Harness and Session, invoked over A2A. This execution path is deferred. The agentRef field is commented out in the source and absent from the served API; subagent bindings currently require templateRef.

Runtime remote A2A tools

The Go and Python ADKs also contain a remote A2A tool. Each call sends an A2A message to an already-addressable remote agent and preserves the child task and context IDs. If the child enters input-required, the parent can retain those identifiers and continue the same child task after receiving human input.

Implementations:

This runtime helper is not public cross-Session delegation. Gateway-level delegation still requires scoped credentials, lineage/depth/cycle enforcement, and streamed child execution; that work remains deferred.