Sheets agent tool: fetch onchain data (read-only RPC / Dune-style sources)

[criptogus]

Inspired by Fileverse's dSheets, which reads smart contracts and imports from Dune/Farcaster. A differentiator for the sheets agent with a small, safe surface.

Proposal

A read-only agent tool in the sheets app, fetch_onchain_data:

• Query public EVM RPC endpoints (configurable; sensible defaults for Ethereum/Base/Gnosis): token balances, contract view calls (ABI-encoded), block/tx lookups.
• Optionally import public datasets from HTTP APIs like Dune (user-supplied API key, stored like other provider keys).
• Results land through the existing propose_operations preview flow — the user reviews the cells before anything is written, and the data-provenance rules apply (dataSource: 'search'-equivalent tagging).

Boundaries

• Read-only, always: no transaction signing, no wallet integration, no private keys anywhere in the app. That keeps the security surface flat.
• Network calls go through the main process with the same SSRF guards used by the existing web tools.
• Feature lives behind a setting (off by default) so the suite stays lean for users who never touch onchain data.

Part of the "off SaaS" track.