feat(benchmark): add fgprof, block/mutex profiling and improve profile docs

[pdrobnjak]

Summary

• Add fgprof (wall-clock profiler) to capture off-CPU time (I/O, blocking, GC pauses) invisible to Go's standard CPU profiler. Registered on DefaultServeMux behind benchmark build tag only — no production impact.
• Enable block and mutex contention profiling via runtime.SetBlockProfileRate and runtime.SetMutexProfileFraction, also gated behind benchmark build tag. Uses conservative sampling rates (1us block threshold, 1/5 mutex fraction) to minimize TPS measurement overhead.
• Update benchmark-compare.sh to auto-capture all 6 profile types (CPU, fgprof, heap, goroutine, block, mutex) midway through runs instead of just CPU + heap.
• Add DURATION env var to benchmark.sh (default 120s, 0 = run forever). When set, runs seid in the background, auto-captures all 6 profiles midway, extracts TPS stats (median/avg/min/max), and exits cleanly — enabling fully automated single-scenario profiling.
• Fix CPU/fgprof profile corruption: Switch from parallel background captures to sequential execution. Go's CPU profiler (SIGPROF) and fgprof (runtime.GoroutineProfile) conflict when running concurrently on the same process, producing empty or corrupted profiles. Also measure actual capture duration for accurate remaining-time calculation, and make BASE_DIR overridable so benchmark-compare.sh routes profiles to per-label directories correctly.
• Expand benchmark/CLAUDE.md with profile type reference table, CPU-vs-fgprof guidance, heap metric selection guide, interactive flamegraph docs, and a full optimization loop workflow (profile → analyze → discuss → implement → compare → validate → PR).

Test plan

• Verify go build ./sei-tendermint/node/ succeeds (no fgprof in non-benchmark build)
• Verify go build -tags benchmark ./sei-tendermint/node/ succeeds (fgprof registered)
• Verify go build -tags benchmark ./app/ succeeds (block/mutex profiling enabled)
• Run DURATION=90 benchmark/benchmark.sh and confirm auto-stop, profile capture, and TPS extraction
• Verify all 6 profile files in /tmp/sei-bench/pprof/ with non-zero sizes
• Verify go tool pprof -top works on each captured profile type
• Verify sequential capture produces valid CPU and fgprof profiles (previously corrupted when captured in parallel)

🤖 Generated with Claude Code

[github-actions]

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

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Feb 13, 2026, 5:03 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.19%. Comparing base (127ed99) to head (6dd8b0b).

Additional details and impacted files

@@                  Coverage Diff                  @@
##           pd/benchmark-compare    #2886   +/-   ##
=====================================================
  Coverage                 57.18%   57.19%           
=====================================================
  Files                      2091     2091           
  Lines                    171179   171173    -6     
=====================================================
+ Hits                      97891    97897    +6     
+ Misses                    64578    64557   -21     
- Partials                   8710     8719    +9     

Flag	Coverage Δ
sei-chain	52.65% <ø> (+<0.01%)	⬆️
sei-cosmos	48.15% <ø> (+0.01%)	⬆️
sei-db	68.72% <ø> (ø)

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