Changes in this PR

Extension package — align with spec

• Server API — declareBuilderCodeExtension() now returns { info, schema } (JSON Schema Draft 2020-12); resourceServer.ts → server.ts
• s ownership — moved from server-declared string[] to client-provided string per spec
• Client extension — new BuilderCodeClientExtension: echoes server a, attaches client s
• Facilitator — buildCalldataSuffix(payload) → buildDataSuffix(ctx):
  • reads a from PaymentRequired.extensions (server truth)
  • soft echo validation against client payload (warn + fallback, never fail settlement)
  • reads s from client payload
  • always adds facilitator w
• CBOR — added parseBuilderCodeSuffixFromCalldata() for off-chain parsing

Core — validate client payload echoes server defined extension fields

• Add validateExtensions utility

EVM mechanisms — calldata suffix append (TypeScript)

• New shared/extensions/builderCode.ts: resolveDataSuffix(), appendDataSuffix(); gas sponsoring split out of shared/extensions.ts
• Wire suffix into all major EVM settle paths:
  • exact — EIP-3009, Permit2, v1
  • upto — Permit2
  • batch-settlement — deposit, claim, refund, settle
• Remove duplicated suffix logic from eip3009-utils.ts

Tests & examples

• Unit + integration tests in typescript/packages/extensions
• Core test updates for paymentRequiredExtensions in HTTP facilitator client
• TypeScript examples: examples/typescript/{servers,clients,facilitator}/builder-code/