fix(consensus/XDPoS): stabilize VerifyHeaders across v1-v2 switch, fix #2138 XFN-12

[gzliudan]

Proposed changes

fix:

• issue sync fails at first v2 block only from genesis block #2138
• audit XFN-12: Broken Result Ordering in VerifyHeaders

Problem

• Mixed v1/v2 batches around the switch boundary could produce non-deterministic verification behavior.
• The adaptor previously relied on version-bucket concurrency and did not expose in-batch headers for GetHeaderByNumber lookups.
• In practice this could surface as intermittent sync failures and misleading BAD BLOCK attribution near the switch height.

Root cause

• Verify result ordering and read visibility assumptions were too weak for mixed-boundary batches.
• Engine helpers may query headers by number during verification, but batch context only shadowed hash-based lookups.

Fix

• Keep VerifyHeaders emission strictly aligned with input order.
• Introduce verifyChainReader and shadow both hash and number lookups with in-batch headers:
  • GetHeader(hash, number)
  • GetHeaderByHash(hash)
  • GetHeaderByNumber(number)
• This preserves deterministic per-header verification and avoids stale canonical reads during boundary processing.

Tests

• Add TestAdaptorVerifyHeadersKeepsInputOrderAcrossConsensusSwitch.
• Add TestVerifyChainReaderReturnsBatchHeaderByNumber.

Types of changes

What types of changes does your code introduce to XDC network?
Put an ✅ in the boxes that apply

• 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?
Put an ✅ in the boxes that apply

• 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

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[Copilot]

Pull request overview

This PR fixes a result-ordering bug in XDPoS.VerifyHeaders where splitting headers into v1/v2 buckets and running two concurrent goroutines caused nondeterministic result-to-header mapping around the v1→v2 switch boundary. This led to misleading "BAD BLOCK" log messages (e.g., a v1-style error attributed to a v2-height header) and sync failures (issue #2138).

Changes:

• consensus/XDPoS/XDPoS.go: Replaced the two-bucket/two-goroutine VerifyHeaders implementation with a single goroutine that iterates headers in input order, dispatching each to the appropriate engine version.
• consensus/tests/engine_v2_tests/adaptor_test.go: Added TestAdaptorVerifyHeadersKeepsInputOrderAcrossConsensusSwitch to assert that results arrive in the same order as the input slice across the consensus switch.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
consensus/XDPoS/XDPoS.go	Rewrites VerifyHeaders to a single sequential goroutine preserving input order
consensus/tests/engine_v2_tests/adaptor_test.go	New regression test for result ordering across the v1/v2 switch

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