feat: HypNative routing via HYP_ERC20_COLLATERAL sentinel

[yorhodes]

Summary

Adds native-ETH (HypNative) warp route support to the UniversalRouter BridgeRouter using the existing HYP_ERC20_COLLATERAL branch with token == address(0) as the native sentinel — matching how the rest of the router (Payments.pay/sweep/wrapETH, Dispatcher CONTRACT_BALANCE resolution) already treats address(0) as the native marker.

Client logic is identical to the ERC20 collateral path:

• amount = CONTRACT_BALANCE
• maxTokenFee as a cap (router recomputes actual fee from quoteTransferRemote)
• No caller-side exact-output math

Origin-side composition mirrors the ERC20 pattern too — e.g. TRANSFER_FROM(WETH) + UNWRAP_WETH + BRIDGE_TOKEN(CONTRACT_BALANCE).

Changes

• BridgeRouter: on the HYP_ERC20_COLLATERAL branch, when token == address(0) skip the ERC20 pull/approve and forward the full native amount to transferRemote (covers bridgeAmount + all fees from msg.value).
• Dispatcher: resolve CONTRACT_BALANCE from address(this).balance when token == Constants.ETH (was unconditional ERC20.balanceOf, which reverts on address(0)).
• Tests: integrated alongside the HypERC20Collateral tests in bridgeToken.t.sol, with bidirectional HypNative deployed on root + leaf and cross-chain delivery verified on leaf.

Why the sentinel vs. a new HYP_NATIVE type

• HypNative.token() literally returns address(0), so the sentinel is semantically accurate.
• quoteExactInputBridgeAmount already handles native via quotes[0].token == token.
• Removing the dual-branch dispatch saves bytecode (23,801 bytes runtime, 775 under EIP-170 — 45 bytes less than a separate-branch implementation).
• No new calldata format for clients to learn.

Test coverage (bridgeToken.t.sol)

Every case uses plain amount = CONTRACT_BALANCE client logic — no caller-side fee inflation. Every happy path verifies cross-chain delivery on the leaf fork via leafMailbox.processNextInboundMessage():

Test	What it covers
test_HypNative_WhenNoFees	Baseline, 1:1 credit + leaf delivery
test_HypNative_WithHookFee	Native TestPostDispatchHook fees on required + default hooks; router auto-deducts from balance
test_HypNative_WithLinearWarpFee	Native LinearFee at 1% rate; bridgeAmount = amount² / (amount + f(amount)) = 1 ETH exactly
test_HypNative_WithCombinedFees	Native hook + native linear together; bridge credits exact bridgeAmount, both fee recipients get their cut
test_HypNative_WhenTokenFeeExceedsMax	TokenFeeExceedsMax revert when cap is tight
test_HypNative_WethToNative_ThenBridge	Symmetric ERC20→native→bridge composition via TRANSFER_FROM + UNWRAP_WETH + BRIDGE_TOKEN(CONTRACT_BALANCE)
testGas_HypNativeBridge	Direct native (msg.value) gas snapshot
testGas_HypNativeBridgeRouterBalance	Router-already-holds-native gas snapshot (mirror of testGas_HypXERC20BridgeRouterBalance)

Parity with HypERC20Collateral tests

Collateral test	HypNative equivalent
Happy path + 5 bps linear fee + cross-chain delivery	WithLinearWarpFee (+ WithHookFee, WithCombinedFees)
Permit2 vs direct approval split	N/A — no approvals on native
Token-mismatch revert	N/A — token=address(0) is the sentinel, no mismatch concept
No-approval revert	N/A — no approvals
Gas snapshots	testGas_HypNativeBridge + testGas_HypNativeBridgeRouterBalance

Extras beyond the Collateral suite: no-fees baseline, combined fees, cap-exceeded revert, WETH→native composition.

Test plan

• forge test --mt HypNative -vv (6/6 happy paths + revert passing, cross-chain delivery verified)
• Existing bridgeToken.t.sol suite unchanged (same 4 pre-existing fork-persistence failures as main)
• Bytecode under EIP-170 (23,801 / 24,576 — 775 headroom)

Notes

The earlier exploratory overload test file (bridgeTokenHypNativeOverload.t.sol) from commit 274375a is superseded by the integrated tests; its coverage is preserved in the new cases.

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