diff --git a/agentscore_commerce/payment/__init__.py b/agentscore_commerce/payment/__init__.py
index 096facf..589eaaa 100644
--- a/agentscore_commerce/payment/__init__.py
+++ b/agentscore_commerce/payment/__init__.py
@@ -22,6 +22,15 @@
     create_mppx_server,
 )
 from agentscore_commerce.payment.networks import NetworkFamily, network_family, networks
+from agentscore_commerce.payment.rail_spec import (
+    RecipientLike,
+    SolanaMppRailSpec,
+    StripeRailSpec,
+    TempoRailSpec,
+    TempoSessionRailSpec,
+    X402BaseRailSpec,
+    resolve_recipient,
+)
 from agentscore_commerce.payment.rails import RailDefinition, lookup_rail, rails
 from agentscore_commerce.payment.settlement_override import (
     SETTLEMENT_OVERRIDES_HEADER,
@@ -89,14 +98,20 @@
     "ProcessX402SettleResult",
     "ProcessX402SettleSuccess",
     "RailDefinition",
+    "RecipientLike",
     "SignerNetwork",
+    "SolanaMppRailSpec",
     "StripeRail",
+    "StripeRailSpec",
     "TempoChargeRail",
+    "TempoRailSpec",
     "TempoSessionRail",
+    "TempoSessionRailSpec",
     "VerifyX402RequestFailure",
     "VerifyX402RequestResult",
     "VerifyX402RequestSuccess",
     "X402AcceptsBlock",
+    "X402BaseRailSpec",
     "X402FacilitatorChoice",
     "X402SymbolicRail",
     "ZeroSettleRail",
@@ -126,6 +141,7 @@
     "rails",
     "read_x402_payment_header",
     "register_x402_schemes_v1_v2",
+    "resolve_recipient",
     "settle_result_to_json_bytes",
     "settlement_override_header",
     "usd_to_atomic",
diff --git a/agentscore_commerce/payment/rail_spec.py b/agentscore_commerce/payment/rail_spec.py
new file mode 100644
index 0000000..0a362f4
--- /dev/null
+++ b/agentscore_commerce/payment/rail_spec.py
@@ -0,0 +1,139 @@
+"""Canonical `*RailSpec` types — one shape per rail, consumed by every helper.
+
+Pre-304 a merchant accepting Tempo + Base + Solana + Stripe restated the same
+recipient four times in four different shapes (`build_accepted_methods`,
+`build_how_to_pay`, `mpp_payment_handler`, `create_mppx_server` each had its own
+per-rail config). This module unifies those into one `*RailSpec` per rail; every
+helper accepts the same instance.
+
+`RecipientLike` is polymorphic over `str | Callable[[], Awaitable[str]]` so
+per-order recipients (Stripe-multichain mints fresh deposit addresses per
+PaymentIntent) flow through identically to static-treasury recipients. The
+factory is called once per helper invocation; callers cache externally.
+"""
+
+from __future__ import annotations
+
+import inspect
+from collections.abc import Awaitable, Callable
+from dataclasses import dataclass, field
+from typing import Any, Literal, cast
+
+from agentscore_commerce.payment.networks import networks
+from agentscore_commerce.payment.usdc import USDC
+
+RecipientLike = str | Callable[[], Awaitable[str]] | Callable[[], str]
+
+
+async def resolve_recipient(r: RecipientLike) -> str:
+    """Resolve a `RecipientLike` to a concrete address string.
+
+    Accepts a string (returned verbatim), a sync callable (called once), or an
+    async callable (awaited once). The orchestrator (TEC-305) calls this once
+    per session and caches the resolved value; helpers within a session never
+    re-invoke the factory.
+    """
+    if isinstance(r, str):
+        return r
+    result = r()
+    if inspect.isawaitable(result):
+        return cast("str", await result)
+    return cast("str", result)
+
+
+@dataclass
+class TempoRailSpec:
+    """Canonical config for the Tempo MPP rail."""
+
+    recipient: RecipientLike
+    network: str = "tempo-mainnet"
+    chain_id: int = 4217
+    token: str = USDC.tempo.mainnet.address
+    symbol: str = "USDC.e"
+    decimals: int = 6
+    testnet: bool = False
+    recommend: Literal["tempo", "agentscore-pay", "both"] = "both"
+
+
+@dataclass
+class X402BaseRailSpec:
+    """Canonical config for the x402 EVM (Base) rail."""
+
+    recipient: RecipientLike
+    network: str = "eip155:8453"  # CAIP-2 canonical
+    chain_id: int = 8453
+    token: str = USDC.base.mainnet.address
+    symbol: str = "USDC"
+    decimals: int = 6
+    mode: Literal["exact", "upto"] = "exact"
+
+
+@dataclass
+class SolanaMppRailSpec:
+    """Canonical config for the Solana MPP rail.
+
+    `signer` is an optional fee-payer signer for server-side fee sponsorship —
+    typed as `Any` to avoid hard-importing `@solana/kit`-equivalent types here.
+    """
+
+    recipient: RecipientLike
+    network: str = "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp"
+    token: str = USDC.solana.mainnet.mint
+    symbol: str = "USDC"
+    decimals: int = 6
+    rpc_url: str | None = None
+    signer: Any | None = None
+    token_program: str | None = None
+
+
+@dataclass
+class StripeRailSpec:
+    """Canonical config for the Stripe SPT rail.
+
+    `recipient` is intentionally absent — Stripe rails use `profile_id` as the
+    merchant-side network identifier the agent's SPT is scoped to; the
+    transaction recipient is the merchant's Stripe account, not an on-chain
+    address.
+    """
+
+    profile_id: str | None = None
+    rails: list[str] = field(default_factory=lambda: ["card", "link", "shared_payment_token"])
+    payment_method_types: list[str] | None = None
+    product_name: str | None = None
+    secret_key: str | None = None
+
+
+@dataclass
+class TempoSessionRailSpec:
+    """Canonical config for the Tempo session MPP rail (pay-as-you-go channels).
+
+    `escrow_contract` is the merchant-deployed on-chain escrow that holds
+    channel deposits + pays out cumulative vouchers on settlement.
+    `store` is a `ChannelStore` instance (in-memory default for dev; Postgres /
+    Redis-backed in production) — typed as `Any` to avoid hard-importing
+    `mppx`'s store interface here.
+    """
+
+    recipient: RecipientLike
+    escrow_contract: str
+    store: Any
+    currency: str = USDC.tempo.mainnet.address
+    testnet: bool = False
+    chains: Any | None = None
+
+
+__all__ = [
+    "RecipientLike",
+    "SolanaMppRailSpec",
+    "StripeRailSpec",
+    "TempoRailSpec",
+    "TempoSessionRailSpec",
+    "X402BaseRailSpec",
+    "resolve_recipient",
+]
+
+
+# Reference the networks module to keep an explicit dependency edge — the
+# CAIP-2 default values above are sourced from `networks.tempo.mainnet.caip2`
+# and `networks.base.mainnet.caip2` semantics. Asserted via tests.
+_ = networks
diff --git a/tests/test_rail_spec.py b/tests/test_rail_spec.py
new file mode 100644
index 0000000..1b523d5
--- /dev/null
+++ b/tests/test_rail_spec.py
@@ -0,0 +1,137 @@
+"""Tests for the canonical *RailSpec types + RecipientLike resolution."""
+
+from __future__ import annotations
+
+import pytest
+
+from agentscore_commerce.payment import (
+    SolanaMppRailSpec,
+    StripeRailSpec,
+    TempoRailSpec,
+    TempoSessionRailSpec,
+    X402BaseRailSpec,
+    resolve_recipient,
+)
+
+
+def test_tempo_rail_spec_defaults() -> None:
+    """Mainnet defaults match the USDC + networks registries."""
+    spec = TempoRailSpec(recipient="0xfeedface")
+    assert spec.recipient == "0xfeedface"
+    assert spec.network == "tempo-mainnet"
+    assert spec.chain_id == 4217
+    assert spec.symbol == "USDC.e"
+    assert spec.decimals == 6
+    assert spec.testnet is False
+    assert spec.recommend == "both"
+
+
+def test_x402_base_rail_spec_defaults() -> None:
+    """Defaults pin Base mainnet (CAIP-2 `eip155:8453`) + USDC."""
+    spec = X402BaseRailSpec(recipient="0xfeedface")
+    assert spec.network == "eip155:8453"
+    assert spec.chain_id == 8453
+    assert spec.symbol == "USDC"
+    assert spec.decimals == 6
+    assert spec.mode == "exact"
+
+
+def test_x402_base_rail_spec_upto_mode() -> None:
+    """`mode='upto'` is the Permit2 + Settlement-Overrides variant."""
+    spec = X402BaseRailSpec(recipient="0xfeedface", mode="upto")
+    assert spec.mode == "upto"
+
+
+def test_solana_mpp_rail_spec_defaults() -> None:
+    spec = SolanaMppRailSpec(recipient="GEQg2TM4VL315Bd4LLkGrhBjdNfoatKjCJYHBDPM3D74")
+    assert spec.network.startswith("solana:")
+    assert spec.symbol == "USDC"
+    assert spec.decimals == 6
+    assert spec.rpc_url is None
+    assert spec.signer is None
+    assert spec.token_program is None
+
+
+def test_solana_mpp_rail_spec_with_fee_payer_signer() -> None:
+    """Fee-payer signer roundtrips through the spec — opaque object."""
+    sentinel_signer = object()
+    spec = SolanaMppRailSpec(recipient="GEQg2TM4VL315Bd4LLkGrhBjdNfoatKjCJYHBDPM3D74", signer=sentinel_signer)
+    assert spec.signer is sentinel_signer
+
+
+def test_stripe_rail_spec_defaults() -> None:
+    """Stripe has no on-chain recipient; profile_id replaces it."""
+    spec = StripeRailSpec(profile_id="profile_abc")
+    assert spec.profile_id == "profile_abc"
+    assert spec.rails == ["card", "link", "shared_payment_token"]
+    assert spec.payment_method_types is None
+    assert spec.product_name is None
+    assert spec.secret_key is None
+
+
+def test_stripe_rail_spec_default_factory_isolation() -> None:
+    """Each instance gets its own rails list (no shared mutable default)."""
+    a = StripeRailSpec()
+    b = StripeRailSpec()
+    a.rails.append("custom")
+    assert b.rails == ["card", "link", "shared_payment_token"]
+
+
+def test_tempo_session_rail_spec_defaults() -> None:
+    """Session rail requires escrow + store; defaults mirror tempo."""
+    spec = TempoSessionRailSpec(
+        recipient="0xfeedface",
+        escrow_contract="0xescrow",
+        store=object(),
+    )
+    assert spec.escrow_contract == "0xescrow"
+    assert spec.testnet is False
+    assert spec.chains is None
+
+
+@pytest.mark.asyncio
+async def test_resolve_recipient_string_returns_verbatim() -> None:
+    assert await resolve_recipient("0xfeedface") == "0xfeedface"
+
+
+@pytest.mark.asyncio
+async def test_resolve_recipient_sync_callable() -> None:
+    """Sync factory: called once, return value used directly."""
+    calls = 0
+
+    def factory() -> str:
+        nonlocal calls
+        calls += 1
+        return "0xdynamic"
+
+    assert await resolve_recipient(factory) == "0xdynamic"
+    assert calls == 1
+
+
+@pytest.mark.asyncio
+async def test_resolve_recipient_async_callable() -> None:
+    """Async factory: awaited once."""
+    calls = 0
+
+    async def factory() -> str:
+        nonlocal calls
+        calls += 1
+        return "0xdynamic"
+
+    assert await resolve_recipient(factory) == "0xdynamic"
+    assert calls == 1
+
+
+@pytest.mark.asyncio
+async def test_resolve_recipient_called_once_per_resolution() -> None:
+    """Each `resolve_recipient` call invokes the factory once — caching is caller-side."""
+    calls = 0
+
+    async def factory() -> str:
+        nonlocal calls
+        calls += 1
+        return f"0xattempt-{calls}"
+
+    assert await resolve_recipient(factory) == "0xattempt-1"
+    assert await resolve_recipient(factory) == "0xattempt-2"
+    assert calls == 2