fix: RPC cache prefilling for eth pending tag

[hanabi1224]

Summary of changes

The validated tipset key might be expanded before updating chain head, we should warm up with the expanded key or eth pending tipset might not be warmed up

Changes introduced in this pull request:

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Outside contributions

• I have read and agree to the CONTRIBUTING document.
• I have read and agree to the AI Policy document. I understand that failure to comply with the guidelines will lead to rejection of the pull request.

Summary by CodeRabbit

• Bug Fixes
  • Corrected the validated tipset broadcast during chain synchronization to ensure consistent use of the current heaviest tipset information, improving alignment in head-key expansion scenarios.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: dfa9b180-0446-4e97-9fd7-7df92be128a6

📥 Commits

Reviewing files that changed from the base of the PR and between 2c1f7e6 and 39518c3.

📒 Files selected for processing (1)

• src/chain_sync/chain_follower.rs

🔗 Linked repositories identified

CodeRabbit considers these linked repositories for cross-repo context during reviews:

• filecoin-project/lotus (manual)

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Walkthrough

The change modifies SyncStateMachine::update to broadcast the heaviest tipset key from the chain store rather than the validated tipset key to validated_tipset_broadcast_tx subscribers, aligning the broadcast with any head-key expansion when the validated tipset is the proposed head.

Changes

Validated Tipset Broadcast Key

Layer / File(s)	Summary
Broadcast heaviest tipset key instead of validated tipset key src/chain_sync/chain_follower.rs	SyncStateMachine::update broadcasts self.cs.heaviest_tipset().key().clone() instead of the validated tipset.key() to subscribers, maintaining subscription checks and error handling while aligning with head-key expansion logic.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• ChainSafe/forest#7068: Both PRs modify src/chain_sync/chain_follower.rs to change how validated_tipset_broadcast_tx/SyncStateMachine::update selects and emits the validated_tipset key to subscribers (this PR adjusts the heaviest-key used; related PR adds/conditions the broadcast itself).

Suggested reviewers

• LesnyRumcajs
• akaladarshi

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Title check	⚠️ Warning	The PR title mentions 'RPC cache prefilling for eth pending tag', but the actual changes focus on broadcasting the validated tipset using the current heaviest tipset key from the chain store rather than the key from the tipset being validated.	Update the title to accurately reflect that the fix addresses tipset key expansion in chain sync validation, not specifically RPC cache prefilling. For example: 'fix: use expanded tipset key when broadcasting validated tipset' or 'fix: broadcast tipset with current heaviest chain key for proper head expansion handling'.
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
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

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• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch hm/fix-rpc-cache-prefill

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch hm/fix-rpc-cache-prefill

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 64.32%. Comparing base (2c1f7e6) to head (39518c3).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/chain_sync/chain_follower.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/chain_sync/chain_follower.rs	33.62% <0.00%> (+0.04%)	⬆️

... and 4 files with indirect coverage changes

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