[hermes-agent / A2A] outbound text parts advertise mediaType; strict A2A 1.0 peers reject

## Observed symptom A2A: outbound text parts advertise mediaType, which strict A2A 1.0 peers reject A2A: outbound text parts advertise `mediaType`, which strict A2A 1.0 peers reject `a2a_call` fails against an A2A 1.0 server that validates parts on member presence. The peer answers the whole request with a JSON-RPC `InvalidParams` error and Hermes surfaces it as: ## Environment GitHub issue NousResearch/hermes-agent #127707; state=open ## Trigger / context Public GitHub report in NousResearch/hermes-agent (FRESH_7D). ## Source evidence - https://github.com/NousResearch/hermes-agent/issues/127707 (2026-10-02T09:32:26Z) — evidence_class: PRIMARY_ISSUE_REPORT — GitHub issue #127707 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:43:03.388295Z - scout_id: C9e6b1a4009 ## 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.