2) Only signed control-plane prompts are accepted - All pri…

2) Only signed control-plane prompts are accepted
- All privileged instructions must arrive wrapped in a signed “prompt envelope.” Everything else is treated as data only.
- Use standard signing flows:
- EIP‑712 typed data (recommended for structured, replay-safe prompts), or
- SIWE (EIP‑4361) with resources and statements that bind the instruction to a specific agent and scope.
- Mandatory fields to prevent replay and misbinding:
- agent: on-chain agent identifier (address or NFT reference)
- chainId + domain separation (verifyingContract or SIWE domain)
- scope: capability or list of capabilities for this prompt
- contentHash (or CID/URI + hash): hash of the natural-language instruction
- nonce (monotonic or session-scoped), expiresAt/deadline
- optional sessionKey id (see below)