Offer/listing creation docs missing counter, protocol_address, and EIP-712 typedData format

[0xildefonso]

Problem

The vendor skill references document the offer/listing creation API endpoints but omit fields and context required for an agent to actually create orders programmatically.

An AI agent following the documented workflow (marketplace-api.md "Build an Offer" + seaport.md "Creating Listings") will fail at submission with iterative 400 errors:

1. "Missing required field 'counter'" — not documented anywhere
2. "Missing required field 'protocol_address'" — not shown as a top-level required field in the offer request body
3. "Missing required field 'signature'" — the signing flow (EIP-712 typedData) is mentioned but the exact domain/types/message structure for Seaport orders is not provided

What's missing

1. counter field

The parameters object requires a counter field (the offerer's current Seaport nonce). Neither marketplace-api.md nor seaport.md mention it. Agents need to know:

• That counter is required
• How to get it: getCounter(address) on the Seaport contract, or that "0" works for accounts that haven't incremented

2. protocol_address as top-level field

The offer/listing submission requires protocol_address at the top level alongside parameters and signature:

{
  "protocol_address": "0x0000000000000068f116a894984e2db1123eb395",
  "parameters": { ... },
  "signature": "0x..."
}

The current docs show protocol_address only in fulfillment requests, not in order creation.

3. EIP-712 typedData format for signing

seaport.md says "Sign order with EIP-712" but doesn't provide the typedData structure. Agents need the exact:

• domain: { name: "Seaport", version: "1.6", chainId, verifyingContract }
• types: The OrderComponents type with all field types
• message: How to map the parameters object to the message fields

4. salt format

marketplace-api.md shows "salt": "random_salt_value" — Seaport expects a uint256. Agents don't know if this should be a hex string, decimal string, or how to generate one.

Impact

We tested this with an AI agent (minimax-m2.7) that:

1. Read all vendor references
2. Built the Seaport parameters correctly (offer items, consideration, timestamps)
3. Posted to opensea-post.sh and got "Missing required field 'counter'"
4. Added counter (guessed "0") → "Missing required field 'protocol_address'"
5. Added protocol_address → "Missing required field 'signature'"
6. Got stuck — didn't know the EIP-712 typedData format to sign

The agent got 80% of the way there from the docs but couldn't bridge the gaps.

Suggested fix

Add a complete worked example to seaport.md or marketplace-api.md showing offer creation end-to-end:

# 1. Get counter (usually "0" for new accounts)
cast call 0x0000000000000068F116a894984e2DB1123eB395 "getCounter(address)" 0xYourWallet --rpc-url https://ethereum-rpc.publicnode.com

# 2. Build parameters (with counter, salt as uint256)
# 3. Sign EIP-712 typedData with exact domain/types
# 4. POST with { protocol_address, parameters, signature }

Or alternatively, document these fields inline in the existing "Build an Offer" section.