# AgentServer v2.1 — System Primitives (Magic Tags) These payload root elements receive special routing and/or side effects in the message pump. They reside in the reserved namespace `https://xml-pipeline.org/ns/core/v1`. ## `` ### `` - Emitted exclusively by the system - Routes back to the listener that triggered the error - Payload structure: ```xml Brief canned error message (e.g., "Invalid payload structure") Base64-encoded raw bytes of the failed attempt (truncated if large) ``` - Purpose: Safe, LLM-friendly diagnostic feedback - Security note: Error messages are abstract and canned — no raw validator output is exposed to agents - Security note: - Certain classes of errors (payload schema violations, unknown root tags, etc.) are intentionally reported with identical abstract messages. - This prevents topology probing: an agent or external caller cannot distinguish between "wrong schema for existing capability" and "capability does not exist". - Authorized introspection is available only via controlled meta queries. ## `` - May be emitted by any listener - Routes to self (uses the emitting listener's unique root tag mechanism) - No side effects - Purpose: Optional visible scaffolding for structured reasoning and iteration planning ## `` - May be emitted by any listener - Routes to the immediate parent listener in the private thread hierarchy - Side effect: The Current subthread below the current listener is pruned after successful delivery of message.
the current thread tail is the current listener. - Purpose: Explicit return-to-caller semantics with automatic cleanup ## `` - May be emitted by any listener - Routes to the immediate parent listener in the private thread hierarchy - Side effect: The Entire thread is pruned up to and including the current listener.
the current thread tail is the parent listener. - Purpose: Explicit termination of the current thread and all its subthreads