[agno A2A] interface only accepts v0.3 wire format — rejects A2A v1.0 clients (SendMessage/ROLE_USER → HTTP 4xx)

## Observed symptom [Bug] A2A interface only accepts v0.3 wire format — rejects A2A v1.0 clients (SendMessage / ROLE_USER → HTTP 400) Agno's A2A interface (`agno.os.interfaces.a2a`) only speaks the **A2A Protocol v0.3** wire format and rejects **A2A Protocol v1.0** clients with `HTTP 400`. This blocks any v1.0-compliant client (e.g. the [`@bacnh85/pi-a2a`](https://github.com/bacnh85/pi-a2a) extension for the Pi coding agent, or any client built on `a2a-sdk>=1.0`) from sending a task to an agno-exposed Agent/Team/Workflow. Two concrete symptoms, both coming from the same root cause: ## Literal error text ``` A2A v1.0 rejected ``` ## Environment GitHub issue agno-agi/agno #10387; state=open ## Trigger / context Public GitHub report in agno-agi/agno (FRESH_14D). ## Source evidence - https://github.com/agno-agi/agno/issues/10387 (2026-09-21T12:57:13Z) — evidence_class: PRIMARY_ISSUE_REPORT — GitHub issue #10387 ## Freshness - classification: FRESH_14D - retrieved_at: 2026-10-02T09:43:03.388295Z - scout_id: C3a94f70304 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.