fix(p2p,eth): synchronize pair peer teardown

[gzliudan]

Proposed changes

Guard PairPeer access with synchronized helpers and snapshot the pair before launching async disconnect during peer shutdown.

Add regression coverage for pair-peer teardown and keep the existing pair tracking checks using the synchronized accessors.

fix panic:

WARN [04-21|13:49:14.217] Failed to unregister sync peer           peer=f14274f155d8b9fd err="peer is not registered"
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x50 pc=0xbf65d6]

goroutine 79891 [running]:
github.com/XinFinOrg/XDPoSChain/p2p.(*Peer).Disconnect(...)
        github.com/XinFinOrg/XDPoSChain/p2p/peer.go:159
github.com/XinFinOrg/XDPoSChain/p2p.(*Peer).run.func2()
        github.com/XinFinOrg/XDPoSChain/p2p/peer.go:239 +0x16
created by github.com/XinFinOrg/XDPoSChain/p2p.(*Peer).run in goroutine 79878
        github.com/XinFinOrg/XDPoSChain/p2p/peer.go:239 +0x3c5

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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
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• fix: A bug fix
• perf: A code change that improves performance
• refactor: A code change that neither fixes a bug nor adds a feature
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• style: Changes that do not affect the meaning of the code
• test: Adding missing tests or correcting existing tests

Impacted Components

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• Consensus
• Account
• Network
• Geth
• Smart Contract
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Checklist

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• 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

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[Copilot]

Pull request overview

Synchronizes access to the p2p “pair peer” pointer and snapshots it before triggering an async disconnect during peer shutdown, addressing a teardown race that can lead to a nil dereference panic.

Changes:

• Replace direct Peer.PairPeer field access with synchronized accessor/mutator helpers.
• Snapshot the pair peer before launching the async disconnect in Peer.run() to avoid nil dereferences.
• Add a regression test ensuring Peer.run() disconnects the paired peer with DiscPairPeerStop.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
p2p/peer.go	Adds mutex-guarded pair-peer accessors and snapshots pair peer before async disconnect on shutdown.
p2p/server.go	Uses synchronized pair-peer helpers when tracking/removing peers and validating handshakes.
p2p/dial.go	Uses synchronized pair-peer getter in dial eligibility checks.
eth/peer.go	Updates eth peer pairing logic to use new synchronized pair-peer setter.
p2p/server_test.go	Updates tests to use the new pair-peer accessors.
p2p/peer_test.go	Adds coverage that pair peer is disconnected when the primary peer stops.

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