refactor(p2p,eth): collapse pair-peer dual links into a single prioritized write path, close #2359 #2351

[gzliudan]

Proposed changes

This PR close issue #2359 and replace PR #2351

Replace the pair-peer dual-link write model with a single peer-owned write ingress backed by internal high/low priority queues.

Preserve BFT message priority across wrapper layers, keep synchronous write errors visible to callers, and make queued versus in-flight shutdown handling deterministic.

Update queue metrics and add regression coverage for priority preemption, starvation bounds, ping serialization, wrapper forwarding, and shutdown behavior.

Types of changes

What types of changes does your code introduce to XDC network?
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• build: Changes that affect the build system or external dependencies
• ci: Changes to CI configuration files and scripts
• chore: Changes that don't change source code or tests
• docs: Documentation only changes
• feat: A new feature
• fix: A bug fix
• perf: A code change that improves performance
• refactor: A code change that neither fixes a bug nor adds a feature
• revert: Revert something
• style: Changes that do not affect the meaning of the code
• test: Adding missing tests or correcting existing tests

Impacted Components

Which parts of the codebase does this PR touch?
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• Consensus
• Account
• Network
• Geth
• Smart Contract
• External components
• Not sure (Please specify below)

Checklist

Put an ✅ in the boxes once you have confirmed below actions (or provide reasons on not doing so) that

• This PR has sufficient test coverage (unit/integration test) OR I have provided reason in the PR description for not having test coverage
• Tested on a private network from the genesis block and monitored the chain operating correctly for multiple epochs.
• Provide an end-to-end test plan in the PR description on how to manually test it on the devnet/testnet.
• Tested the backwards compatibility.
• Tested with XDC nodes running this version co-exist with those running the previous version.
• Relevant documentation has been updated as part of this PR
• N/A

[coderabbitai]

Caution

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✨ Finishing Touches

🧪 Generate unit tests (beta)

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[Copilot]

Pull request overview

This PR removes the XDPoS pair-peer dual-connection mechanism and replaces its BFT-latency goal with per-peer high/low priority write scheduling in the p2p message path.

Changes:

• Removes pair-peer state, duplicate-connection allowances, and eth pair writer fallback paths.
• Adds PriorityMsgWriter / SendPriority and routes Vote, Timeout, and SyncInfo messages through the high-priority lane.
• Updates dial/server tests and adds priority scheduler tests for preemption, starvation guard, and fallback behavior.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
p2p/server.go	Rejects duplicate NodeID connections and removes pair-peer tracking.
p2p/server_test.go	Updates server peer tracking tests for single-peer semantics.
p2p/peer.go	Adds high/low write request queues and priority arbitration.
p2p/peer_test.go	Removes pair-peer disconnect behavior test.
p2p/peer_priority_test.go	Adds tests for priority write scheduling behavior.
p2p/peer_error.go	Removes ErrAddPairPeer.
p2p/message.go	Adds SendPriority helper with fallback to normal writes.
p2p/dial.go	Restores duplicate peer dial rejection.
p2p/dial_test.go	Updates dial state expectations for one connection per NodeID.
eth/peer.go	Removes pairRw and uses priority sends for BFT messages.
eth/handler.go	Simplifies peer registration now that pair peers are removed.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated no new comments.