feat: expand chains (+6 testnets) and tokens (+EURC, WETH, USDT)

[AlejandroFabianCampos]

Summary

Chain expansion (testnet): adds 6 testnets to SupportedChain: ethereum-sepolia, arbitrum-sepolia, optimism-sepolia, polygon-amoy, scroll-sepolia, linea-sepolia (chain IDs, USDC addresses, viem chain map, default confirmations = 0, QuickNode slugs).

Token expansion: introduces a SupportedToken union (USDC | EURC | WETH | USDT) with TOKEN_CONTRACTS, TOKEN_DECIMALS, and TOKEN_CREDENTIAL_TYPES. Coverage spans testnet and mainnet. USDC_CONTRACTS is preserved as-is so existing consumers don't break.

evm.charge resolver: now resolves the token contract from (token, chain), validates that the requested credentialTypes are supported by the token (e.g. WETH and USDT lack EIP-3009 transferWithAuthorization), and uses per-token decimals instead of the hardcoded 6.

Public surface (mpp/index.ts): exports the new types and lookup maps so downstream consumers (admin layers, balance views) can validate (chain, token, credentialType) tuples without re-hardcoding the matrix.

Token availability (testnet)

	USDC	EURC	WETH	USDT
ethereum-sepolia	✅	✅	✅	—
arbitrum-sepolia	✅	—	✅	—
optimism-sepolia	✅	—	—	—
polygon-amoy	✅	—	✅	—
scroll-sepolia	✅	—	✅	—
linea-sepolia	✅	—	—	—
base-sepolia	✅	—	—	—

Token availability (mainnet)

	USDC	EURC	WETH	USDT
ethereum	✅	✅	✅	✅
base	✅	✅	✅	—
arbitrum	✅	—	✅	✅
optimism	✅	—	✅	✅
polygon	✅	—	—	✅
avalanche	✅	✅	—	✅
linea	✅	—	✅	—
unichain	✅	—	✅	—

Provenance rules

Tokens added to TOKEN_CONTRACTS must be either issuer-deployed (Circle for USDC/EURC, Tether for mainnet USDT, chain team for canonical native ETH wrappers) or verified on-chain. Community deployments and bridged variants are not first-class. Concrete consequences:

• USDT testnet is omitted — Tether doesn't run an official testnet program; candidate testnet contracts are community deployments without provenance. USDT support is therefore mainnet-only.
• WETH on Polygon and Avalanche is omitted — both chains have native non-ETH gas (MATIC, AVAX) and carry "WETH" only as a bridged ERC-20, which is a different trust model.
• EURC mainnet is shipped only on chains where Circle issues the canonical contract (ethereum, base, avalanche).

Per-token credential-type compatibility

	permit2	authorization (EIP-3009)	hash
USDC	✅	✅	✅
EURC	✅	✅	✅
WETH	✅	—	✅
USDT	✅	—	✅

evm.charge rejects authorization when paired with WETH or USDT at construction time (USDT mainnet uses its own non-standard approve/transferFrom semantics and lacks EIP-3009).

Test plan

• npm run build — clean
• npm run lint — clean
• npm run typecheck — clean
• npm run test — 82/82 pass (existing chain-expansion tests validate the 6 new testnet entries: chain IDs, USDC addresses, default confirmations, viem mapping, slug coverage, RPC URL shape)
• Downstream agent-proxy typecheck — clean

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Note

Medium Risk
Modifies server-side evm.charge construction to resolve token addresses/decimals and validate credential types, which can change runtime behavior or raise new configuration-time errors for existing integrations. Also expands chain matrices (IDs, slugs, viem mappings, confirmations), increasing the surface area for misconfigured constants.

Overview
Adds 6 new testnet chains (ethereum-sepolia, arbitrum-sepolia, optimism-sepolia, polygon-amoy, scroll-sepolia, linea-sepolia) across the chain matrices (chain IDs, USDC addresses, viem chain mapping, QuickNode slugs, and default confirmations).

Introduces multi-token support via SupportedToken plus new exported lookup tables TOKEN_CONTRACTS, TOKEN_DECIMALS, and TOKEN_CREDENTIAL_TYPES (adding EURC, WETH, and mainnet-only USDT).

Updates server charge() to select the ERC-20 contract/decimals from (token, chain), default credentialTypes per token, and reject unsupported (chain, token) pairs or invalid credential types (e.g., disallowing authorization for tokens without EIP-3009).

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