Backport release/v6.7: Fix pruning issue in SS causing huge disk spike

[seidroid]

Backport of #4321 to release/v6.7.

[cursor]

PR Summary

Medium Risk
Changes MVCC descending prune lifecycle timing around Pebble iterators and compaction; low logic change but affects disk reclamation during retention.

Overview
Fixes a state-store pruning disk spike by closing the full-DB scan iterator before compactPrunedRange runs, instead of keeping it open until function return.

An open Pebble iterator pins readState, which blocks deletion of obsolete SSTables while compaction runs—so tombstoned data could accumulate on disk during long post-prune compactions. A guarded closeItr() avoids double-close on errors and still defers cleanup if the scan loop fails early.

Also adds seilog and an info log for prune compaction duration, version, and error.

^{Reviewed by Cursor Bugbot for commit 86e6496. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Oct 8, 2026, 9:13 AM

[seidroid]

This is a clean backport of #4321 to release/v6.7. pruneDescending now closes its scan iterator before compactPrunedRange runs, so the iterator no longer pins Pebble's readState and stops obsolete sstables from being deleted during a long compaction. The guarded double-close is correct, the deleted-key bounds are cloned so closing the iterator early is safe, and the new seilog logger matches how other sei-db packages create theirs. I found no issues.

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 84.61538% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.80%. Comparing base (fccc24e) to head (86e6496).

Files with missing lines	Patch %	Lines
sei-db/db_engine/pebbledb/mvcc/db.go	84.61%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release/v6.7    #4508      +/-   ##
================================================
- Coverage         61.84%   60.80%   -1.04%     
================================================
  Files              2168     2068     -100     
  Lines            188740   176791   -11949     
================================================
- Hits             116727   107501    -9226     
+ Misses            61159    59406    -1753     
+ Partials          10854     9884     -970     

Flag	Coverage Δ
sei-chain-pr	64.74% <84.61%> (?)
sei-db	69.80% <ø> (ø)
sei-db-state-db	?

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

Files with missing lines	Coverage Δ
sei-db/db_engine/pebbledb/mvcc/db.go	67.43% <84.61%> (+0.21%)	⬆️

... and 100 files with indirect coverage changes

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