fix: more server logs for snapshot export

[hanabi1224]

Summary of changes

It should be useful to track snapshot export progress on the server side, to troubleshoot transient stuckness issue.

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

• Chores
  • Enhanced logging for snapshot export operations with duration tracking and frame count reporting during write operations.

[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: e2ceff79-eb3a-44e6-9a4a-17ec5c32c385

📥 Commits

Reviewing files that changed from the base of the PR and between 0ad035e and ba3c9e4.

📒 Files selected for processing (2)

• src/chain/mod.rs
• src/db/car/forest.rs

🔗 Linked repositories identified

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

• filecoin-project/lotus (manual)

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Walkthrough

This PR adds observability instrumentation to snapshot export operations. The export_to_forest_car function now measures export duration and logs initial parameters, while the CAR frame encoder tracks frame counts and emits progress logs for each export stage.

Changes

Snapshot Export Observability

Layer / File(s)	Summary
Export-level timing instrumentation src/chain/mod.rs	export_to_forest_car captures Instant::now() at the start, logs epoch, lookup depth, and prefix-frame count, then logs the total elapsed export duration formatted via humantime::format_duration after completion.
CAR frame writing progress logging src/db/car/forest.rs	Encoder::write maintains an n_frames counter incremented per zstd frame, and emits tracing::info! logs after completing zstd CAR frame writes, skip-frame index writes, and footer serialization.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Suggested reviewers

• LesnyRumcajs
• sudo-shashank

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% 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 accurately describes the main change: adding logging for snapshot export operations in two files to track export progress and duration.
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

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch hm/chain-export-logs

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch hm/chain-export-logs

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[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.32%. Comparing base (0ad035e) to head (ba3c9e4).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/chain/mod.rs	50.00%	3 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/db/car/forest.rs	84.10% <100.00%> (+0.23%)	⬆️
src/chain/mod.rs	83.47% <50.00%> (-1.85%)	⬇️

... and 14 files with indirect coverage changes

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