feat(checkout): seamless merchant helpers (adapters, hooks, discovery)

agentscore_commerce/__init__.py

@@ -16,12 +16,77 @@
 from agentscore_commerce.checkout import (
     Checkout,
     CheckoutContext,
+    CheckoutGateConfig,
     CheckoutRailSpec,
     CheckoutRequest,
     CheckoutResult,
+    CheckoutValidationError,
     MppxComposeOutcome,
     PricingResult,
     SettleOutcome,
+    format_pydantic_errors,
+    validation_envelope,
+    validation_response_aiohttp,
+    validation_response_django,
+    validation_response_fastapi,
+    validation_response_flask,
+    validation_response_sanic,
+)
+from agentscore_commerce.checkout_hooks import make_mppx_compose_hook
+
+# Re-export the most commonly used helpers at the package root so consumers
+# don't have to remember which submodule each one lives in. Mirrors node's
+# top-level `index.ts` surface; submodule imports still work for power users.
+from agentscore_commerce.identity import (
+    AGENTSCORE_UCP_CAPABILITY,
+    FIXABLE_DENIAL_REASONS,
+    UCP_A2A_EXTENSION_URI,
+    AgentIdentity,
+    AgentMemoryHint,
+    AgentScoreCore,
+    AgentScoreGatePolicy,
+    AssessResult,
+    CreateSessionOnMissing,
+    DenialCode,
+    DenialReason,
+    PolicyBlock,
+    SignerVerdict,
+    UCPSigningKey,
+    UCPVerificationError,
+    VerifyWalletSignerResult,
+    build_a2a_agent_card,
+    build_agent_memory_hint,
+    build_contact_support_next_steps,
+    build_jwks_response,
+    build_signer_mismatch_body,
+    build_ucp_profile,
+    denial_reason_status,
+    denial_reason_to_body,
+    generate_ucp_signing_key,
+    hash_operator_token,
+    is_fixable_denial,
+    load_ucp_signing_key_from_env,
+    mpp_payment_handler,
+    sign_ucp_profile,
+    stripe_spt_payment_handler,
+    ucp_a2a_extension,
+    verification_agent_instructions,
+    verify_ucp_profile,
+    x402_payment_handler,
+)
+from agentscore_commerce.payment import (
+    PaymentSigner,
+    SignerNetwork,
+    SolanaMppRailSpec,
+    StripeRailSpec,
+    TempoRailSpec,
+    TempoSessionRailSpec,
+    X402BaseRailSpec,
+    extract_payment_signer,
+    extract_signer_for_precheck,
+    format_usd_cents,
+    load_solana_fee_payer,
+    read_x402_payment_header,
 )
 
 try:
@@ -33,13 +98,70 @@
     __version__ = "0.0.0+local"
 
 __all__ = [
+    "AGENTSCORE_UCP_CAPABILITY",
+    "FIXABLE_DENIAL_REASONS",
+    "UCP_A2A_EXTENSION_URI",
+    "AgentIdentity",
+    "AgentMemoryHint",
+    "AgentScoreCore",
+    "AgentScoreGatePolicy",
+    "AssessResult",
     "Checkout",
     "CheckoutContext",
+    "CheckoutGateConfig",
     "CheckoutRailSpec",
     "CheckoutRequest",
     "CheckoutResult",
+    "CheckoutValidationError",
+    "CreateSessionOnMissing",
+    "DenialCode",
+    "DenialReason",
     "MppxComposeOutcome",
+    "PaymentSigner",
+    "PolicyBlock",
     "PricingResult",
     "SettleOutcome",
+    "SignerNetwork",
+    "SignerVerdict",
+    "SolanaMppRailSpec",
+    "StripeRailSpec",
+    "TempoRailSpec",
+    "TempoSessionRailSpec",
+    "UCPSigningKey",
+    "UCPVerificationError",
+    "VerifyWalletSignerResult",
+    "X402BaseRailSpec",
     "__version__",
+    "build_a2a_agent_card",
+    "build_agent_memory_hint",
+    "build_contact_support_next_steps",
+    "build_jwks_response",
+    "build_signer_mismatch_body",
+    "build_ucp_profile",
+    "denial_reason_status",
+    "denial_reason_to_body",
+    "extract_payment_signer",
+    "extract_signer_for_precheck",
+    "format_pydantic_errors",
+    "format_usd_cents",
+    "generate_ucp_signing_key",
+    "hash_operator_token",
+    "is_fixable_denial",
+    "load_solana_fee_payer",
+    "load_ucp_signing_key_from_env",
+    "make_mppx_compose_hook",
+    "mpp_payment_handler",
+    "read_x402_payment_header",
+    "sign_ucp_profile",
+    "stripe_spt_payment_handler",
+    "ucp_a2a_extension",
+    "validation_envelope",
+    "validation_response_aiohttp",
+    "validation_response_django",
+    "validation_response_fastapi",
+    "validation_response_flask",
+    "validation_response_sanic",
+    "verification_agent_instructions",
+    "verify_ucp_profile",
+    "x402_payment_handler",
 ]

agentscore_commerce/challenge/body.py

@@ -11,6 +11,10 @@
 class X402PaymentRequired:
     accepts: list[Any]
     version: Literal[1, 2] = 2
+    extensions: dict[str, Any] | None = None
+    """Per-endpoint x402 ``extensions`` block (e.g. Bazaar discovery declared
+    via ``build_bazaar_discovery_payload``). Emitted on the 402 body as
+    ``body.extensions`` per x402 spec when non-empty."""
 
 
 def build_402_body(
@@ -34,6 +38,8 @@ def build_402_body(
     if x402:
         body["x402Version"] = x402.version
         body["accepts"] = alias_amount_fields(x402.accepts)
+        if x402.extensions:
+            body["extensions"] = x402.extensions
     if amount_usd is not None:
         body["amount_usd"] = amount_usd
     if currency: