fix: broadcast head changes only when subscribed

[hanabi1224]

Summary of changes

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

Release Notes

• Performance

  • Optimized head-change notification publishing to occur only when active listeners are present.
  • Extracted shared subscriber detection utility for reuse across components.

• Tests

  • Added tests validating subscriber status detection behavior.

[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: d4baf59d-bfcd-428a-9a30-73184bee95ef

📥 Commits

Reviewing files that changed from the base of the PR and between bb3bf11 and 2121ef7.

📒 Files selected for processing (5)

• src/chain/store/chain_store.rs
• src/db/parity_db.rs
• src/utils/broadcast/mod.rs
• src/utils/broadcast/tests.rs
• src/utils/mod.rs

🚧 Files skipped from review as they are similar to previous changes (2)

• src/utils/broadcast/tests.rs
• src/db/parity_db.rs

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Walkthrough

This PR introduces a shared has_subscribers utility function to check for active broadcast channel subscribers and applies it to guard expensive path-change computations in the chain store and database layer, preventing unnecessary work when no subscribers are present.

Changes

Cohort / File(s)	Summary
Broadcast Utility Module src/utils/broadcast/mod.rs, src/utils/broadcast/tests.rs, src/utils/mod.rs	New broadcast utility module with public has_subscribers<T>() function for checking active subscribers on tokio broadcast channels, including comprehensive test coverage for subscriber lifecycle scenarios.
Chain Store Integration src/chain/store/chain_store.rs	Applied subscriber guard around head-change path computation and broadcast; work is now performed only when has_subscribers confirms active subscribers exist.
Database Integration src/db/parity_db.rs	Replaced local has_subscribers helper with imported centralized version from broadcast utility module, removing redundant code and unused import.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• Revive the previous Filecoin.EthSubscribe PR #5749: Integrates subscriber-aware head-change broadcasts into EthSubscribe/EthPubSub implementation, building upon this PR's new shared subscriber-checking utility.

Suggested reviewers

• akaladarshi
• sudo-shashank

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: broadcast head changes only when subscribed' accurately and concisely describes the main change: adding a subscriber check before publishing head changes to avoid unnecessary broadcast operations.

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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/check-subscribers-before-publishing-head-changes

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch hm/check-subscribers-before-publishing-head-changes

📝 Coding Plan

• Generate coding plan for human review comments

---

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@src/utils/broadcast/tests.rs`:
- Around line 6-25: The test test_has_subscribers should assert the public
helper has_subscribers instead of inspecting tx.closed().now_or_never()
directly; replace each assertion that checks
tx.closed().now_or_never().is_none()/is_some() with the corresponding
has_subscribers(&tx) boolean check (e.g., assert!(has_subscribers(&tx)) or
assert!(!has_subscribers(&tx))) so the test verifies the has_subscribers
function contract rather than duplicating its implementation; update all four
occurrences and add any necessary use/import for has_subscribers.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 1d8ed2a1-da0f-4c22-9c65-ddd9ad65c6c7

📥 Commits

Reviewing files that changed from the base of the PR and between 37418a6 and bb3bf11.

📒 Files selected for processing (7)

• src/chain/store/chain_store.rs
• src/db/parity_db.rs
• src/shim/executor.rs
• src/state_manager/mod.rs
• src/utils/broadcast/mod.rs
• src/utils/broadcast/tests.rs
• src/utils/mod.rs

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.60%. Comparing base (37418a6) to head (2121ef7).
⚠️ Report is 6 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/chain/store/chain_store.rs	7.69%	12 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/db/parity_db.rs	67.74% <ø> (-0.26%)	⬇️
src/utils/broadcast/mod.rs	100.00% <100.00%> (ø)
src/utils/mod.rs	82.45% <ø> (ø)
src/chain/store/chain_store.rs	67.33% <7.69%> (-3.07%)	⬇️

... and 14 files with indirect coverage changes

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