Backport giga-1: Add Giga fetch/serve and BlockDB prune metrics (CON-438)

[seidroid]

Backport of #4329 to giga-1.

[cursor]

PR Summary

Low Risk
Observability-only changes (metric registration and counters); P2P and prune behavior is unchanged aside from labeling pruned vs not-found on block serve.

Overview
Adds Prometheus observability for autobahn block retention and giga P2P sync, following the existing metricsgen pattern.

Blockstore: exposes tendermint_autobahn_blockstore_prune_watermark and updates it when the store opens and after PruneBefore, so operators can see the lowest retained global block. Prune tests assert the gauge matches the clamped floor.

Giga P2P: adds tendermint_p2p_giga_fetch and tendermint_p2p_giga_serve counters labeled by resource (block, full commit QC, app QC, commit QC, lane proposal) and reason (e.g. ok, unavailable, pruned, not_found, stream/decode/process failures). Client streaming and GetBlock paths are instrumented; GetBlock serve now records distinct reasons for pruned vs not-found empty responses. Integration tests check that fetch/serve counters move during replication.

^{Reviewed by Cursor Bugbot for commit 5d95f77. Bugbot is set up for automated code reviews on this repo. Configure here.}

[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	Sep 24, 2026, 11:49 PM

[seidroid]

This is a clean backport of #4329 to giga-1. It adds counters for Giga fetch and serve outcomes, plus a BlockDB prune-watermark gauge. The dependencies it uses (utils.Clamp, BlockDB.GetPruneWatermark, the tmprometheus vec types) exist on this branch. The instrumentation leaves control flow unchanged and has test coverage; I found nothing to block the merge.

Findings: 0 blocking | 0 non-blocking | 0 posted inline

Blockers

• None at the file/PR level.

Non-blocking

• None at the file/PR level.

[codecov]

Codecov Report

❌ Patch coverage is 69.33333% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.32%. Comparing base (7e3ca24) to head (5d95f77).
⚠️ Report is 51 commits behind head on giga-1.

Files with missing lines	Patch %	Lines
sei-tendermint/internal/p2p/giga/data.go	46.15%	14 Missing ⚠️
sei-tendermint/internal/p2p/giga/avail.go	30.76%	9 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           giga-1    #4331       +/-   ##
===========================================
+ Coverage   65.55%   79.32%   +13.76%     
===========================================
  Files        2081       12     -2069     
  Lines      157460      827   -156633     
===========================================
- Hits       103222      656   -102566     
+ Misses      54097      171    -53926     
+ Partials      141        0      -141     

Flag	Coverage Δ
sei-chain	?
sei-chain-pr	79.32% <69.33%> (?)
sei-db	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sei-tendermint/autobahn/blockstore/metrics.gen.go	100.00% <100.00%> (ø)
sei-tendermint/autobahn/blockstore/store.go	87.50% <100.00%> (+0.10%)	⬆️
sei-tendermint/internal/p2p/giga/metrics.gen.go	100.00% <100.00%> (ø)
sei-tendermint/internal/p2p/giga/metrics.go	100.00% <100.00%> (ø)
sei-tendermint/internal/p2p/giga/avail.go	69.79% <30.76%> (-7.41%)	⬇️
sei-tendermint/internal/p2p/giga/data.go	71.15% <46.15%> (-5.95%)	⬇️

... and 2071 files with indirect coverage changes

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[masih]

What is in giga-1 that's not on main which makes us wnat to backport this @wen-coding @philipsu522 ?

[wen-coding]

What is in giga-1 that's not on main which makes us wnat to backport this @wen-coding @philipsu522 ?

All the panic fixes? Without them the giga testnet will die. I have a plan to replace the evmonly cursor persistence with #4306, but it has a dependency on #4341, so I'm fine if we just persist the cursors for now.

[masih]

All the panic fixes? Without them the giga testnet will die. I have a plan to replace the evmonly cursor persistence with #4306, but it has a dependency on #4341, so I'm fine if we just persist the cursors for now.

All good discussed in DM, happy to land anything in giga-1 as long as it is a backport from main 🙌