chore: update the chain follower logs to report validation

[akaladarshi]

Summary of changes

Changes introduced in this pull request:

• Instead of the max forks epoch remaining to start validation, now log shows min epochs remaining to start validation
• Update the chain follower logs to report the remaining tipset to start validation instead of remaining downloads

Reference issue to close (if applicable)

Closes #5499

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

• This pull request is based on an issue that a maintainer has accepted (see Before Opening a Pull Request).
• 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
  • Improved chain synchronization progress reporting while catching up to the latest chain head by showing the heaviest epoch, expected head, and the computed difference.
  • Progress messages now include clearer stage-based status (e.g., validating tipsets, remaining header fetches, or waiting for tipsets).
  • Log updates are emitted only when the node is significantly behind, reducing unnecessary log noise during normal operation.

[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: e7eb15e3-8c50-43bc-9e3b-22054ec0afc8

📥 Commits

Reviewing files that changed from the base of the PR and between 099662b and 4254e60.

📒 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)

🚧 Files skipped from review as they are similar to previous changes (1)

• src/chain_sync/chain_follower.rs

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Walkthrough

ChainFollower catch-up progress logging now uses the epoch gap to HEAD and reports active fork synchronization stages instead of queued tipset counts.

Changes

Catch-up progress reporting

Layer / File(s)	Summary
Epoch-based fork status logging src/chain_sync/chain_follower.rs	Imports now include Cow and grouped time types. Progress logs skip gaps of 10 epochs or fewer, calculate header-fetch estimates from active forks, and report validating, header-fetching, or tipset-waiting stages.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• ChainSafe/forest#7380: Also updates chain_follower.rs catch-up progress logging based on epoch distance.

Suggested reviewers: hanabi1224

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
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 (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title is concise and accurately describes the logging change around validation progress.
Linked Issues check	✅ Passed	The updated logs estimate remaining tipsets before validation and no longer rely on fork-based download counts.
Out of Scope Changes check	✅ Passed	The changes stay within the logging/reporting scope and do not introduce unrelated behavior.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch akaladarshi/sync-log-validation-start

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch akaladarshi/sync-log-validation-start

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.20%. Comparing base (a6f303b) to head (4254e60).
⚠️ Report is 21 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/chain_sync/chain_follower.rs	0.00%	25 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/chain_sync/chain_follower.rs	30.68% <0.00%> (-0.26%)	⬇️

... and 57 files with indirect coverage changes

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[sudo-shashank]

No green checkmark

[LesnyRumcajs]

LGTM