fix: log Rand errors

[hanabi1224]

Summary of changes

Changes introduced in this pull request:

• log Rand errors as they are not propagated in fvm
• disable tipset lookup cache in forest-dev state compute to ensure snapshot completeness

Original bug:

> forest-dev state compute --chain mainnet --epoch 6029534 --export-db-to mainnet_6029534.forest.car.zst
epoch: 6029534, state_root: bafy2bzaceagedjhikhjsi2ruwbjmy2gspszqcua5ct5j2o2e6ar7zxsyr5fzk, receipt_root: bafy2bzacebtnqz5kit2i22ggb6aq6u2cyqmsnkvnezudyytlbymqptlqc44xq, db_snapshot_size: 4.4 MiB

> forest-dev state replay-compute --chain mainnet mainnet_6029534.forest.car.zst
Error: state root mismatch, state_root: bafy2bzacebf5ytfseptikwcm2shtzwe6saunt4umytwk3ehl6bkgehhvirpei, expected_state_root: bafy2bzaceagedjhikhjsi2ruwbjmy2gspszqcua5ct5j2o2e6ar7zxsyr5fzk

With the fix:

> forest-dev state compute --chain mainnet --epoch 6029534 --export-db-to mainnet_6029534.forest.car.zst
epoch: 6029534, state_root: bafy2bzaceagedjhikhjsi2ruwbjmy2gspszqcua5ct5j2o2e6ar7zxsyr5fzk, receipt_root: bafy2bzacebtnqz5kit2i22ggb6aq6u2cyqmsnkvnezudyytlbymqptlqc44xq, db_snapshot_size: 11.4 MiB

> forest-dev state replay-compute --chain mainnet mainnet_6029534.forest.car.zst
2026-05-20T06:42:01.712496Z  INFO forest::state_manager::utils::state_compute: epoch: 6029534, state_root: bafy2bzaceagedjhikhjsi2ruwbjmy2gspszqcua5ct5j2o2e6ar7zxsyr5fzk, receipt_root: bafy2bzacebtnqz5kit2i22ggb6aq6u2cyqmsnkvnezudyytlbymqptlqc44xq, took 5s 986ms 689us 922ns.

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

Release Notes

• New Features

  • Added environment variable option to disable tipset lookup table cache for development and testing scenarios.

• Improvements

  • Enhanced error logging for chain randomness operations with contextual information including request details and chain state.

• Documentation

  • Updated environment variable reference guide with new configuration option and usage details.

[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: c465617b-2876-4387-88de-85b6b4398ead

📥 Commits

Reviewing files that changed from the base of the PR and between 7d19be2 and 8b732a2.

📒 Files selected for processing (4)

• docs/docs/users/reference/env_variables.md
• src/chain/store/index.rs
• src/dev/subcommands/state_cmd.rs
• src/state_manager/chain_rand.rs

---

Walkthrough

This PR adds a toggleable environment flag FOREST_TIPSET_LOOKUP_TABLE_DISABLED to conditionally disable tipset lookup-table cache traversal in chain store operations, documents the flag, integrates it into cache-disabling utilities, and adds error-side logging to chain randomness methods.

Changes

Tipset Cache Control and Observability Improvements

Layer / File(s)	Summary
Tipset lookup table disable feature docs/docs/users/reference/env_variables.md, src/chain/store/index.rs, src/dev/subcommands/state_cmd.rs	Environment variable FOREST_TIPSET_LOOKUP_TABLE_DISABLED is documented, then checked in ChainIndex::tipset_by_height to skip checkpoint-based lookup-table resolution when the flag is set. The flag is also set by disable_tipset_cache() alongside FOREST_TIPSET_CACHE_DISABLED to disable both caches together.
Error logging for randomness generation src/state_manager/chain_rand.rs	ChainRand's get_chain_randomness and get_beacon_randomness trait methods now call their v2/v3 implementations and attach inspect_err handlers that emit tracing::warn! logs with the requested round, tipset context, and error details.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• ChainSafe/forest#6705: Both PRs touch the environment-flag surface for tipset caching—chore: update env variables #6705 documents FOREST_TIPSET_CACHE_DISABLED, while the main PR adds/uses FOREST_TIPSET_LOOKUP_TABLE_DISABLED and extends disable_tipset_cache() to disable that cache alongside FOREST_TIPSET_CACHE_DISABLED.

Suggested reviewers

• LesnyRumcajs
• sudo-shashank

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: log Rand errors' accurately summarizes the main change in the PR—adding error logging for Rand trait methods in chain_rand.rs, which is the primary technical change across the files.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
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.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ 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/inpect-rand-errors

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch hm/inpect-rand-errors

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[codecov]

Codecov Report

❌ Patch coverage is 8.33333% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.21%. Comparing base (7d19be2) to head (8b732a2).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/state_manager/chain_rand.rs	0.00%	8 Missing and 2 partials ⚠️
src/dev/subcommands/state_cmd.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/chain/store/index.rs	89.62% <100.00%> (ø)
src/dev/subcommands/state_cmd.rs	0.00% <0.00%> (ø)
src/state_manager/chain_rand.rs	65.64% <0.00%> (-5.90%)	⬇️

... and 6 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7d19be2...8b732a2. Read the comment docs.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.