Backport release/v6.6: [codex] Harden multiversion iterator validation

[seidroid]

Backport of #3656 to release/v6.6.

[cursor]

PR Summary

Medium Risk
Touches OCC transaction validation in core state storage; incorrect iterator replay could wrongly accept or reject parallel txs, though behavior is covered by new tests and failures degrade to invalid rather than node panic.

Overview
Hardens OCC multiversion iterateset replay so validation fails safely instead of panicking or hanging when the MVS view races with concurrent writesets.

The validation iterator now skips keys that no longer have a value at replay time (skipRemovedKeys on Valid/Next/Key), reads the underlying iterator key in Value() without re-entering skip logic, treats missing MVS entries as nil, and sends estimate aborts with a non-blocking WriteAbort so a full abort channel cannot deadlock validation.

Iterator validation in store.go runs replay inside a goroutine with panic recovery (logged, returns invalid), splits logic into validateIteratorReplay with explicit iterator cleanup, and poll`select`s the abort channel between steps via iteratorValidationAborted instead of blocking forever when multiple estimates would fill the channel.

Adds regression tests for lower-index writeset rewrites during validation, injected iterator panics, and multiple estimate aborts completing within a timeout.

^{Reviewed by Cursor Bugbot for commit 609343d. 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	Jun 30, 2026, 4:59 PM

[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	Jun 30, 2026, 4:21 PM

[codecov]

Codecov Report

❌ Patch coverage is 88.50575% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.02%. Comparing base (5ed245f) to head (609343d).
⚠️ Report is 1 commits behind head on release/v6.6.

Files with missing lines	Patch %	Lines
sei-cosmos/store/multiversion/store.go	86.66%	4 Missing and 4 partials ⚠️
sei-cosmos/store/multiversion/memiterator.go	92.59%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release/v6.6    #3672      +/-   ##
================================================
- Coverage         58.88%   58.02%   -0.87%     
================================================
  Files              2225     2151      -74     
  Lines            183482   174995    -8487     
================================================
- Hits             108041   101533    -6508     
+ Misses            65733    64451    -1282     
+ Partials           9708     9011     -697     

Flag	Coverage Δ
sei-chain-pr	90.73% <88.50%> (?)
sei-db	70.41% <ø> (-0.22%)	⬇️
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-cosmos/store/multiversion/memiterator.go	86.48% <92.59%> (+2.81%)	⬆️
sei-cosmos/store/multiversion/store.go	89.96% <86.66%> (-2.01%)	⬇️

... and 76 files with indirect coverage changes

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