Add Kokosh plugin (wallet-hygiene audit via x402)

[Kajko25]

Summary

• Adds a Base MCP plugin for Kokosh, a wallet-hygiene sentinel agent on Base mainnet: tracks token/Permit2 allowance exposure and flags scam-airdrop tokens by name/URL/homoglyph heuristics, with a paid /audit report ($0.01 USDC via x402).
• integration: http-api, chains: [base], risk: [irreversible].
• Adds one net-new tag (wallet-hygiene) to the shared vocabulary in plugin-spec.md, per Contribution Scope.

Notable finding

## Submission documents a real compatibility gap rather than a happy-path-only flow: Base MCP's default wallet is a smart contract account, whose sign() returns an ERC-1271/6492-shaped signature. Standard USDC transferWithAuthorization (used by x402's exact scheme) verifies with plain ecrecover only, so it will reject that signature. The plugin was hand-verified working end-to-end (real mainnet USDC settlement) with an EOA signer, and explicitly instructs the agent to stop rather than submit a payment authorization likely to fail settlement when the active wallet is a smart contract. Flagging for maintainers in case this is relevant to other x402-paying plugins.

Self-review

Ran the plugin-review skill against the current spec before opening this PR — verdict 🟡 approve with minor changes (both addressed: file relocated to the correct path, wallet-hygiene tag flagged/added). Full report: https://github.com/Kajko25/kokosh/blob/main/docs/base-mcp-plugin/kokosh-review.md

Test plan

• Frontmatter validated against spec enums (integration, shell, auth, risk)
• All required body sections present in canonical order with canonical headings
• /audit, /exposure, /drops, /healthz endpoints live-tested against the deployed agent (https://kokosh-agent.vercel.app)
• x402 payment flow verified end-to-end on Base mainnet with a real EOA signature (not simulated)
• Not yet verified against Base MCP's own smart-contract wallet (see Notable finding above)

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2

[Kajko25]

Update: live-tested this plugin's smart-wallet caveat against real mainnet settlement.

Paid this exact /audit endpoint from a Coinbase Smart Wallet (Base Account) via Base MCP's native initiate_x402_request/complete_x402_request tools — it settled successfully. Root cause: the facilitator behind /audit (CDP-hosted, via @coinbase/x402) calls USDC's transferWithAuthorization(address,address,uint256,uint256,uint256,bytes32,bytes) overload (selector 0xcf092995), which validates through a signature-checker path accepting ERC-1271/6492 contract-wallet signatures — not the classic (v,r,s) overload (0xe3ee160e) that the original caveat assumed as the only option.

Updated the plugin's "Smart-wallet caveat" section to reflect this and to recommend Base MCP's native x402 tools over the plugin's manual sign → X-PAYMENT path when both are available, since the native path already handled this correctly with no special-casing needed.