fix(blocks): validate all beacon entries for all covered epochs on quicknet

[EclesioMeloJunior]

Summary of changes

This PR fixes the RawBlockHeader::validate_block_drand method by checking correctly, for quicknet, if the current block header contains the beacon entries from parent_epoch + 1 till self.epoch, meaning that a block built after N null-epoch should have a beacon entry per skipped epoch

Changes introduced in this pull request:

• src/blocks/header.rs: validate_block_drand now checks, for unchained beacons only, that the header carries exactly epoch - parent_epoch entries and that entry i is at max_beacon_round_for_epoch(parent_epoch + i + 1)

Reference issue to close (if applicable)

Closes #7413

Other information and links

• Companion PR fix MinerGetBaseInfo returns the correct BeaconEntries #7427 fixes the producing side, where Filecoin.MinerGetBaseInfo returned too few entries for the same reason. This PR is the validating side.

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 Quicknet block validation to require complete beacon coverage for every epoch between the parent and new block.
  • Beacon entries must appear in ascending epoch order and match each epoch’s maximum beacon round.
  • Blocks with missing, extra, incorrectly ordered, or mismatched beacon entries are now rejected with clear validation errors.
  • Validation now correctly handles epochs with null beacon rounds, improving reliability for affected blocks.

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Walkthrough

Quicknet unchained beacon validation now requires one ascending entry per epoch between the parent and block epochs. Each entry must use that epoch’s maximum beacon round. Public test helpers and coverage for contiguous and null-round epochs were added.

Changes

Quicknet beacon validation

Layer / File(s)	Summary
Unchained beacon coverage validation src/blocks/header.rs, src/beacon/mod.rs, src/beacon/tests/drand.rs, CHANGELOG.md	Validation rejects excessive, missing, unordered, or incorrectly matched beacon entries. Public Quicknet test helpers support contiguous and null-round validation tests. The changelog records the stricter validation.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Possibly related PRs

• ChainSafe/forest#7427: Both changes enforce correctly matched Quicknet beacon entries for every covered epoch.

Suggested reviewers: akaladarshi, lesnyrumcajs

🚥 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 clearly summarizes the main change: stricter validation of all Quicknet beacon entries across covered epochs.
Linked Issues check	✅ Passed	The changes satisfy issue [#7413] by enforcing exact entry counts, per-epoch rounds, ordering, and coverage with tests.
Out of Scope Changes check	✅ Passed	The changelog and public test helpers directly support the validation fix and its tests; no unrelated code changes are evident.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ 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 eclesio/validate-block-drand

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch eclesio/validate-block-drand

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Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@CHANGELOG.md`:
- Line 44: Update the changelog entry for Quicknet block validation to reference
issue `#7413` instead of `#7412`, including the corresponding issue URL, while
preserving the existing description.

In `@src/blocks/header.rs`:
- Around line 188-223: Update src/beacon/drand.rs in
BeaconSchedule::beacon_entries_for_block to generate one unchained beacon entry
for every epoch in parent_epoch + 1..=epoch, matching the validator’s expected
count and rounds. In src/blocks/header.rs:188-223, retain validation against
that full range; in src/blocks/header.rs:481-517, construct the null-epoch
header using BeaconSchedule::beacon_entries_for_block so the test exercises the
producer-validator contract.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

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Run ID: a9cb33ea-85fe-4045-b24e-403c651a75fd

📥 Commits

Reviewing files that changed from the base of the PR and between a379991 and ca53281.

📒 Files selected for processing (4)

• CHANGELOG.md
• src/beacon/mod.rs
• src/beacon/tests/drand.rs
• src/blocks/header.rs

🔗 Linked repositories identified

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

• filecoin-project/lotus (manual)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.12%. Comparing base (a188092) to head (c3dbe8b).
✅ All tests successful. No failed tests found.

Additional details and impacted files

Files with missing lines	Coverage Δ
src/blocks/header.rs	71.25% <100.00%> (+5.43%)	⬆️

... and 9 files with indirect coverage changes

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[LesnyRumcajs]

nit: there are some partially covered lines in the coverage you might want to cover (they're fairly trivial to reason about, so not a huge deal).

I'll approve once CI is green.

[LesnyRumcajs]

LGTM