Mcp-ts support for batch-settlement

[phdargen]

Description

• add missing mcp hook primitives aligning with http transport: skipHandler, cancellation dispatcher etc
• changed the core v2 matcher so paymentPayload.accepted.extra may include additive client fields, while all server-declared fields still have to match -> this allows corrective 402 retries with payloads based on either original 402 or corrective 402 requirements
• add batch-settlement to mcp-ts e2e tests

Tests

Checklist

• I have formatted and linted my code
• All new and existing tests pass
• My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits
• I added a changelog fragment for user-facing changes (docs-only changes can skip)

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[ryanRfox]

Hey @phdargen, I just opened #2250 (issue #2249) which makes the e2e harness chain-pluggable for any EVM chain in DEFAULT_STABLECOINS. We're touching some of the same files and are directionally aligned: we both widened MCP scheme registration to eip155:* independently.

Two spots where we picked different patterns and it might be worth comparing notes:

Chain selection. I went with a catalog lookup (resolveViemChain(caip2) walks viem's chain DB and falls back to defineChain for any chain viem hasn't packaged), so any chain in DEFAULT_STABLECOINS works without harness edits. You used a binary eip155:8453 ? base : baseSepolia ternary in e2e/clients/mcp-typescript/index.ts:21, so any non-Base-mainnet CAIP-2 (e.g. eip155:31611, Mezo Testnet, which also has batch-settlement) silently falls through to Base Sepolia's RPC.

EIP-712 token name. Same binary in e2e/servers/mcp-typescript/index.ts:103 (EVM_NETWORK === "eip155:84532" ? "USDC" : "USD Coin"). I replaced the corresponding ternaries in the four other EVM servers with EVM_PERMIT2_ASSET_NAMES: Record<string, string> keyed by EVM_NETWORK. FWIW Permit2's EIP-712 domain doesn't include token name or version, so this one's largely cosmetic. Mentioning it more for symmetry across the EVM servers than correctness.

Also: #2250 wires EVM_PERMIT2_ASSET from the resolved NetworkConfig in generic-server.ts, so spawned servers get it set per-network without reading the env directly.

Your new env vars in test.config.json optional arrays lgtm. Same table-driven pattern I'm using.