eth: cancel milestone subscriber on shutdown

[kamuikatsurgi]

Description

The Heimdall milestone WS subscriber in startMilestoneWhitelistService was launched with context.Background(), so it kept running after close(s.closeCh) and outlived s.chainDb.Close().

Logs:

INFO  Persisting dirty state head=86,085,215 ...                      ← chainDb about to close
INFO  Whitelisting milestone deferred err="chain out of sync"
ERROR error handling milestone ws event err="chain out of sync"
ERROR Failed to store the lock field struct err="pebble: closed"
ERROR Error in writing lock data of milestone to db err="...: pebble: closed for lock field struct"
ERROR Failed to store the future milestone field struct err="pebble: closed"
ERROR connection lost; will attempt to reconnect on heimdall ws subscription error="websocket: close 1006"
INFO  successfully connected on heimdall ws subscription url=ws://localhost:26657/websocket

After the fix, the subscriber returns as soon as closeCh closes, and none of the above appear post-shutdown.

[claude]

Claude Code Review

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Copilot]

Pull request overview

Fixes the Heimdall milestone WebSocket subscriber lifecycle so it shuts down cleanly when the Ethereum service stops, preventing post-shutdown DB writes and noisy reconnect/error logs.

Changes:

• Create a cancellable context for milestone WS subscriptions and cancel it when s.closeCh closes.
• Pass the cancellable context into subscribeAndHandleMilestone to ensure it exits on shutdown.
• Update doc/comments around the milestone whitelist service and retry behavior.

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[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

[codecov]

Codecov Report

❌ Patch coverage is 12.50000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.28%. Comparing base (1a5510f) to head (0459203).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
eth/backend.go	12.50%	7 Missing ⚠️

❌ Your patch status has failed because the patch coverage (12.50%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2199      +/-   ##
===========================================
+ Coverage    52.24%   52.28%   +0.04%     
===========================================
  Files          884      884              
  Lines       155551   155557       +6     
===========================================
+ Hits         81262    81329      +67     
+ Misses       69055    68995      -60     
+ Partials      5234     5233       -1     

Files with missing lines	Coverage Δ
eth/backend.go	52.10% <12.50%> (-0.43%)	⬇️

... and 22 files with indirect coverage changes

Files with missing lines	Coverage Δ
eth/backend.go	52.10% <12.50%> (-0.43%)	⬇️

... and 22 files with indirect coverage changes

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