LZ Bridge (L-02): Emit actual LZ native fee in Bridged event

[zeroxnoodle]

Summary by CodeRabbit

• Bug Fixes

  • Cross-chain bridge now accurately tracks and reports actual fees charged separately from supplied ETH, improving fee transparency.
  • Enhanced handling of excess ETH when bridging with overpayment.

• Tests

  • Added and updated tests to verify correct fee reporting and overpayment handling.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR updates the LayerZero cross-chain bridge to capture and propagate the MessagingReceipt returned by the LayerZero endpoint's send method, exposing the actual charged native fee instead of the caller's supplied msg.value through the Bridged event and the ILZBridgeGateway.burnAndSend interface.

Changes

LayerZero Receipt Propagation

Layer / File(s)	Summary
Interface Contracts src/policies/interfaces/ILZBridgeGateway.sol, src/periphery/interfaces/ILZCrossChainBridge.sol	ILZBridgeGateway.burnAndSend now declares a named return value MessagingReceipt memory receipt. ILZCrossChainBridge.Bridged event signature changes from Bridged(address, uint256, uint32, uint256 fees) to Bridged(address, uint256, uint32, uint256 nativeFee, uint256 msgValue) to distinguish actual LayerZero-charged fee from caller-supplied ETH.
Implementation src/policies/bridge/LZBridgeGateway.sol, src/periphery/bridge/LZCrossChainBridge.sol	LZBridgeGateway.burnAndSend assigns the LayerZero send result to its named return variable instead of a local declaration. LZCrossChainBridge.sendOhm captures the MessagingReceipt from gateway.burnAndSend and emits Bridged with receipt.fee.nativeFee (actual fee) and msg.value (supplied value). Imports updated to include MessagingReceipt.
Tests src/test/policies/bridge/LZBridgeGateway/LZBridgeGateway_BurnAndSend.t.sol, src/test/periphery/bridge/LZCrossChainBridge/LZCrossChainBridge_SendOhm.t.sol	Existing tests capture MessagingReceipt return value and assert fee fields. New test test_sendOhm_emitsActualNativeFeeOnOverpayment verifies that overpayment is not charged—user is debited only the actual native fee while both bridge and gateway retain zero ETH.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• OlympusDAO/olympus-v3#220: Introduced the LayerZero bridge gateway; this PR exposes its MessagingReceipt return value through the cross-chain bridge API.

Suggested reviewers

• 0xJem

Poem

🐰 A bridge now speaks what LayerZero knows,
The receipt returns, true fees it shows,
No more guessing—what's charged comes clear,
Overpayment refunds, user held dear! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically summarizes the main change: emitting the actual LZ native fee in the Bridged event instead of just msg.value, which is the core objective addressed across all modified files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/lz-bridge-upgrade-event-fee

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[0xJem]

@coderabbitai review

[coderabbitai]

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Review triggered.

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[coderabbitai]

🧹 Nitpick comments (1)

src/periphery/interfaces/ILZCrossChainBridge.sol (1)

29-35: Bridged event ABI change breaks existing off-chain consumers.

The event topic (keccak256("Bridged(address,uint256,uint32,uint256)")) changes to keccak256("Bridged(address,uint256,uint32,uint256,uint256)"). Any subgraph, analytics pipeline, or frontend listener that subscribed to the old signature will silently stop receiving events after the contract is upgraded.

Ensure that all subgraphs, indexers, and event decoders (frontend, off-chain services) are updated to the new ABI before or immediately after deployment.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/periphery/interfaces/ILZCrossChainBridge.sol` around lines 29 - 35, The
Bridged event signature was changed (event Bridged(...) now includes msgValue)
which will break any off-chain consumers relying on the old keccak256 topic; to
fix, either restore the original Bridged ABI or preserve backward compatibility
by keeping the original Bridged declaration and adding a new event (e.g.,
BridgedV2 or BridgedWithMsgValue) or emitting both events from the bridging
logic; then update all off-chain artifacts (ABI files, subgraph
mappings/manifest, indexer decoders, frontend listeners) to the new event
name/signature and re-deploy/re-index so consumers pick up the change — check
and modify usages referring to the Bridged symbol and any Graph mappings that
decode its topics.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@src/periphery/interfaces/ILZCrossChainBridge.sol`:
- Around line 29-35: The Bridged event signature was changed (event Bridged(...)
now includes msgValue) which will break any off-chain consumers relying on the
old keccak256 topic; to fix, either restore the original Bridged ABI or preserve
backward compatibility by keeping the original Bridged declaration and adding a
new event (e.g., BridgedV2 or BridgedWithMsgValue) or emitting both events from
the bridging logic; then update all off-chain artifacts (ABI files, subgraph
mappings/manifest, indexer decoders, frontend listeners) to the new event
name/signature and re-deploy/re-index so consumers pick up the change — check
and modify usages referring to the Bridged symbol and any Graph mappings that
decode its topics.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 611802e7-b96b-41c3-b266-30329f46c228

📥 Commits

Reviewing files that changed from the base of the PR and between 8bc9492 and eac1e78.

📒 Files selected for processing (6)

• src/periphery/bridge/LZCrossChainBridge.sol
• src/periphery/interfaces/ILZCrossChainBridge.sol
• src/policies/bridge/LZBridgeGateway.sol
• src/policies/interfaces/ILZBridgeGateway.sol
• src/test/periphery/bridge/LZCrossChainBridge/LZCrossChainBridge_SendOhm.t.sol
• src/test/policies/bridge/LZBridgeGateway/LZBridgeGateway_BurnAndSend.t.sol