feat(layerzero): pin one DVN on pathways whose default is dead

[pegahcarter]

Stacked on #57. Decision D1 from the chain checks (#51).

Every LayerZero pathway touching zkSync defaults to the dead DVN, which refuses every message.

• Transceivers follow LayerZero's defaults, except that setDvn(eid, dvn) pins one DVN for a pathway, both directions, on today's default libraries, write-once. A transceiver can be born with it for the governor home's eid (initialize(..., governorHomeDvn), LZ_GOVERNOR_HOME_DVN in DeployLz), since the bootstrap that creates its owner arrives over that pathway.
• The transceiver's delegate is fixed. OApp's setDelegate (not virtual) is refused in _checkOwner; before this, the governor's account could reassign the delegate and reconfigure any pathway.
• Receivers get the transceiver's DVN for their home's eid at creation, before their payload runs, and change it only by their own payload (they have no owner).
• Transmitters: the owner names itself delegate through OApp's existing setDelegate and configures the endpoint directly; no new function.
• LzMessage.pinSendDvn / pinReceiveDvn are public and linked. Every LayerZero transceiver stays under EIP-170 (Tron's has 399 bytes left).

Verified on an Ethereum fork: test/fork/LzDvnFork.t.sol (skipped without ETH_RPC_URL) shows Ethereum to zkSync refusing the quote on the default and quoting once LayerZero Labs' DVN is pinned. The zkSync side cannot be forked (EraVM) and needs a zkSync Sepolia run; tracked in docs/todo.md.

Docs: spec R6.4, deploy/CHECKS.md §5 (with each chain's LayerZero Labs DVN), deploy/README.md, provider-research §8.

782 tests pass, 1 skipped (the fork test); lint clean on both profiles.

Closes #51

[Copilot]

🔵 Needs a closer look

It alters the LayerZero message-authentication security model with irreversible write-once on-chain DVN/delegate configuration whose motivating zkSync path cannot be verified in the test suite, so it warrants human sign-off.

0 open findings

What changed in this PR

This PR resolves issue #51, where every LayerZero pathway touching zkSync Era defaults to the LayerZero "dead DVN" that refuses all messages, and the transceiver — being its own, immovable delegate — previously had no way to reconfigure. It adds a write-once DVN-pinning mechanism so a pathway can be pinned to a single real DVN (both send and receive, on today's default libraries) while otherwise preserving LayerZero's defaults. It fits into the src/protocols/layerzero/ binding, extending the shared LzMessage library (linked, to stay under EIP-170) and the transceiver/receiver initializers.

Changes:

• Adds setDvn(eid, dvn) (owner-gated, write-once, pins both directions) plus birth-time pinning via a new governorHomeDvn initializer arg; LzMessage.pinSendDvn/pinReceiveDvn perform the endpoint setSendLibrary/setReceiveLibrary/setConfig calls.
• Fixes the transceiver's delegate: OApp's setDelegate is refused in _checkOwner (DelegateIsFixed); receivers inherit dvnOf[homeEid] at creation; transmitters' owners self-delegate instead.
• Updates all initializer call sites, deploy script/library (LZ_GOVERNOR_HOME_DVN), the mock endpoint, tests (incl. a skip-gated Ethereum fork test), and docs (spec R6.4, CHECKS §5, README, research, todo).

File	Description
src/​protocols/​layerzero/​LzTransceiver.sol	Adds dvnOf, setDvn/_pinDvn, governorHomeDvn init arg, and _checkOwner override refusing setDelegate.
src/​protocols/​layerzero/​LzMessage.sol	Adds UlnConfig, pinSendDvn/pinReceiveDvn/_onlyDvn and ULN config constants.
src/​protocols/​layerzero/​LzReceiver.sol	Adds homeDvn init arg; pins receive-side DVN for the home eid at creation.
src/​protocols/​layerzero/​LzDivergentTransceiver.sol	Threads governorHomeDvn through zkSync/Tron initializers; _checkOwner overrides resolve to LzTransceiverBase.
script/​DeployLz.s.sol, script/​deploy/​LzDeploy.sol	Pass LZ_GOVERNOR_HOME_DVN; _checkHome asserts the pinned home DVN.
test/​protocols/​layerzero/​MockLzEndpoint.sol	Adds library/config surface with oapp-or-delegate authorization.
test/​protocols/​layerzero/​LzTransceiver.t.sol, LzBinding.t.sol, LzFixture.sol	New DVN/delegate/receiver/transmitter tests; updated init signatures.
test/​fork/​LzDvnFork.t.sol	New skip-gated fork test of Ethereum→zkSync quote before/after pinning.
test/​{CloneDerivation,DestinationNaming,deploy/​DeployChecks,deploy/​ChainConfig}.t.sol	Updated initializer call sites for the new arg.
deploy/​CHECKS.md, deploy/​README.md, docs/​{provider-spec,provider-research,todo}.md	Document the pinning mechanism, per-chain DVNs, and verification status.

🧠 Review effort: Balanced

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