feat(metrics): track blocks synchronized by source

[auricom]

Summary

• Add sequencer_blocks_synchronized_total Prometheus counter with source label (DA/P2P)
• Counter increments each time a block is synced in the syncer
• Resets on process restart

Test plan

• Run node and verify sequencer_blocks_synchronized_total{source="DA"} and sequencer_blocks_synchronized_total{source="P2P"} appear in /metrics
• Confirm counters increment as blocks are synced from each source

🤖 Generated with Claude Code

[claude]

Claude finished @auricom's task in 1m 31s —— View job

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Code Review

• Gather context and read changed files
• Review code quality & architecture
• Review error handling & resilience
• Review testing & reliability
• Post final review

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Overall this is a clean, well-scoped addition that follows existing codebase patterns. A few issues worth addressing before merging:

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Issues

1. EventSource value case change is a silent breaking change for log consumers

SourceDA and SourceP2P were changed from "DA" / "P2P" to lowercase "da" / "p2p". These values appear in structured log output across the syncer:

// block/internal/syncing/syncer.go:548, 561, 671, 717
Str("source", string(event.Source))

Any dashboards, alerts, or log parsers that filter on source="DA" or source="P2P" will silently break. This should be called out explicitly in the CHANGELOG under a Breaking Changes section. The motivation for lowercasing is valid (Prometheus label convention), but the impact is broader than Prometheus alone.

2. CHANGELOG and PR description reference wrong label values

The CHANGELOG entry and the PR test plan both reference source="DA" and source="P2P", but the actual registered values are lowercase "da", "p2p", "raft". Fix this →

3. Stale field comment on BlocksSynchronized

// block/internal/common/metrics.go:72
BlocksSynchronized map[EventSource]metrics.Counter // Blocks synchronized by source (P2P or DA)

SourceRaft is now a valid third source. The comment should read // Blocks synchronized by source (DA, P2P, or Raft). Fix this →

4. No test coverage for the new counter increment

Codecov reports 0% patch coverage on syncer.go. The two new lines (787–789) increment BlocksSynchronized after a successful commit, but no test verifies that the counter actually fires. The NopMetrics are already used in syncer tests — it would be straightforward to add an assertion that BlocksSynchronized[SourceDA] increments after a successful TrySyncNextBlock call.

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Positives

• Correct placement — the counter increment is after batch.Commit(), so only successfully committed blocks are counted. Blocks that fail validation, fail to apply, or fail to commit are not counted.
• Defensive map lookup — the if counter, ok := s.metrics.BlocksSynchronized[event.Source]; ok guard prevents a nil map panic if an unexpected source appears.
• SourceRaft fix — the empty string in RecoverFromRaft was a latent bug; tagging it as SourceRaft is the right fix and ensures Raft-recovered blocks are tracked.
• Consistent with existing patterns — ConstLabels-per-source approach matches DASubmitterFailures and DASubmitterLastFailure.
• NopMetrics properly populated — no-op counters are initialized for all sources, preventing nil-pointer panics in test contexts.

[github-actions]

The latest Buf updates on your PR. Results from workflow CI / buf-check (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	⏩ skipped	✅ passed	✅ passed	Apr 16, 2026, 10:02 AM

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

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Run ID: e0fa38c4-45b7-48ed-8ba9-d1f962c40a79

📥 Commits

Reviewing files that changed from the base of the PR and between 2865d6d and 8c43e66.

📒 Files selected for processing (4)

• CHANGELOG.md
• block/internal/common/event.go
• block/internal/common/metrics.go
• block/internal/syncing/syncer.go

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• Create PR with unit tests
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.32%. Comparing base (2865d6d) to head (8c43e66).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3259      +/-   ##
==========================================
- Coverage   62.33%   62.32%   -0.01%     
==========================================
  Files         122      122              
  Lines       12873    12877       +4     
==========================================
+ Hits         8024     8026       +2     
- Misses       3968     3970       +2     
  Partials      881      881              

Flag	Coverage Δ
combined	62.32% <100.00%> (-0.01%)	⬇️

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[julienrbrt]

lgtm!