[codex] fix giga snapshot storage rollback

[codchen]

Summary

• change Giga StateDB snapshots to use rollbackable CacheMultiStore layers instead of relying on value-writing store journal reverts
• stop store-backed storage, code, nonce, balance, account clear, and mapping changes from being replayed during snapshot rollback
• add regression coverage that verifies reverted storage writes, including same-value SSTOREs, do not flush dirty writes to the parent store

Root cause

Giga used a single transaction cache plus explicit journal entries to undo store-backed writes. The same-value SetState path intentionally wrote through without a storage journal entry, so a same-value SSTORE inside a reverted internal call could survive rollback as a dirty cache write. Value-writing rollback also left a dirty cache entry for non-noop storage changes, which can affect AppHash even when the visible EVM value is restored.

Impact

Reverted EVM snapshots now discard store writes by dropping the snapshot cache layer, matching the V2 rollback model. Persistent store changes only flush from surviving snapshot layers during Finalize, while the journal remains responsible for in-memory EVM state such as logs, refunds, transient storage, access lists, surplus, and account status markers.

Validation

• go test ./giga/deps/xevm/state
• go test ./giga/deps/xevm/...

[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 3, 2026, 2:29 AM

[codecov]

Codecov Report

❌ Patch coverage is 82.53968% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.26%. Comparing base (f8f1af1) to head (17a36da).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
giga/deps/xevm/state/journal.go	14.28%	6 Missing ⚠️
giga/deps/xevm/state/statedb.go	89.58%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3536      +/-   ##
==========================================
- Coverage   59.12%   58.26%   -0.87%     
==========================================
  Files        2213     2140      -73     
  Lines      182774   174353    -8421     
==========================================
- Hits       108072   101587    -6485     
+ Misses      64985    63727    -1258     
+ Partials     9717     9039     -678     

Flag	Coverage Δ
sei-chain-pr	75.62% <82.53%> (?)
sei-db	70.41% <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
giga/deps/xevm/state/balance.go	60.67% <ø> (-0.87%)	⬇️
giga/deps/xevm/state/code.go	76.92% <ø> (-10.04%)	⬇️
giga/deps/xevm/state/nonce.go	100.00% <ø> (ø)
giga/deps/xevm/state/state.go	98.42% <100.00%> (-0.30%)	⬇️
giga/deps/xevm/state/statedb.go	77.24% <89.58%> (-1.47%)	⬇️
giga/deps/xevm/state/journal.go	80.68% <14.28%> (-9.23%)	⬇️

... and 73 files with indirect coverage changes

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