Fix pre-v6.5 debug trace tx decoding

[Kbhat1]

Describe your changes and provide context

• Add a trace-only pre-v6.5 tx decoder that skips the new TxBody bloat check
• Use it when replaying historical debug_trace* blocks so old Cosmos tx bytes don’t break tracing
• Add a regression test for an old tx with explicit memo=""; pre-v6.5 trace works, v6.5+ stays strict

Testing performed to validate your change

• Unit tests
• Verifying on node

[cursor]

PR Summary

Medium Risk
Touches transaction decoding and upgrade-gating logic used by debug_trace* paths; while normal mempool/DeliverTx decoding remains strict, mistakes could cause tracing failures or (if misused) weaken tx validation.

Overview
Fixes debug_trace* on pre-v6.5 blocks by introducing a trace-only Cosmos TxDecoder that skips the new TxBody “bloat” rejection, and wiring it into EVM RPC tracing/replay (BlockByNumber, GetTransaction, and replay helpers) based on whether the v6.5 upgrade is active at the target height.

Adds support utilities to detect upgrade activation (UpgradeKeeper.IsUpgradeActiveAtHeight and TxConfig.ProtoCodec) and extends tests to cover historical bloated TxBody bytes decoding for tracing (while asserting v6.5+ remains strict).

^{Reviewed by Cursor Bugbot for commit 34bfeaa. 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	May 20, 2026, 7:36 PM

[codecov]

Codecov Report

❌ Patch coverage is 94.59459% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.07%. Comparing base (63067ee) to head (34bfeaa).

Files with missing lines	Patch %	Lines
evmrpc/trace_tx_decoder.go	87.50%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3470   +/-   ##
=======================================
  Coverage   59.07%   59.07%           
=======================================
  Files        2186     2187    +1     
  Lines      182269   182299   +30     
=======================================
+ Hits       107671   107702   +31     
  Misses      64947    64947           
+ Partials     9651     9650    -1     

Flag	Coverage Δ
sei-chain-pr	67.94% <94.59%> (?)
sei-db	70.41% <ø> (-0.22%)	⬇️

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

Files with missing lines	Coverage Δ
evmrpc/simulate.go	75.00% <100.00%> (+0.65%)	⬆️
sei-cosmos/x/auth/tx/config.go	93.10% <100.00%> (+0.51%)	⬆️
sei-cosmos/x/auth/tx/decoder.go	88.34% <100.00%> (+0.59%)	⬆️
sei-cosmos/x/upgrade/keeper/keeper.go	92.79% <100.00%> (+0.09%)	⬆️
evmrpc/trace_tx_decoder.go	87.50% <87.50%> (ø)

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit 9fe8237. Configure here.}

[arajasek]

LGTM!

[seidroid]

Created backport PR for release/v6.5:

• Backport release/v6.5: Fix pre-v6.5 debug trace tx decoding #3478 with remaining conflicts!

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin backport-3470-to-release/v6.5
git worktree add --checkout .worktree/backport-3470-to-release/v6.5 backport-3470-to-release/v6.5
cd .worktree/backport-3470-to-release/v6.5
git reset --hard HEAD^
git cherry-pick -x 5098e5b0e902f51d8966003f33aaa440fde9b0d5
git push --force-with-lease