[codex] Harden gasless tx raw-byte handling

[codchen]

Summary

This PR closes the raw protobuf bloat routes for gasless transactions by making decoded transaction bytes canonical, validating fee data before denom filtering, and adding a hard raw-size cap for gasless txs.

Changes

• Enforce canonical TxRaw, TxBody, and AuthInfo bytes in the default tx decoder.
• Reject duplicate root TxRaw.body_bytes and TxRaw.auth_info_bytes.
• Preserve the relaxed historical decoder for pre-v6.5 tracing compatibility.
• Add MaxGaslessTxBytes = 16 KiB and enforce it in normal gasless ante plus custom CheckTx/DeliverTx paths.
• Validate original decoded fee amounts before allowed-denom filtering.
• Validate fee denoms in Tx.ValidateBasic while preserving existing zero-fee behavior.
• Add regression coverage for canonical decoder rejection, compatibility decoding, gasless size cap, and invalid fee denoms.

Out of scope

• Proposal-level block gas accounting for gasless txs is intentionally unchanged in this PR.

Tests

• go test ./sei-cosmos/x/auth/tx
• go test ./sei-cosmos/x/auth/ante
• go test ./app/antedecorators
• go test ./app/ante
• go test ./sei-cosmos/types/tx
• go test ./evmrpc -run TestTraceBlockByNumberUsesCompatDecoderForHistoricalCosmosTx
• go test ./app -run TestCheckTotalBlockGas_AssociateTxIsGasless
• git diff --check

[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 9, 2026, 9:50 AM

[codecov]

Codecov Report

❌ Patch coverage is 65.11628% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.34%. Comparing base (1f52187) to head (ef5a84a).

Files with missing lines	Patch %	Lines
sei-cosmos/x/auth/tx/decoder.go	82.00%	5 Missing and 4 partials ⚠️
app/ante/cosmos_checktx.go	0.00%	8 Missing ⚠️
app/ante/cosmos_delivertx.go	16.66%	3 Missing and 2 partials ⚠️
sei-cosmos/x/auth/ante/fee.go	55.55%	2 Missing and 2 partials ⚠️
app/antedecorators/gasless.go	75.00%	1 Missing and 1 partial ⚠️
sei-cosmos/x/auth/ante/validator_tx_fee.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3559      +/-   ##
==========================================
- Coverage   59.18%   58.34%   -0.85%     
==========================================
  Files        2225     2151      -74     
  Lines      183625   175150    -8475     
==========================================
- Hits       108677   102188    -6489     
+ Misses      65154    63864    -1290     
+ Partials     9794     9098     -696     

Flag	Coverage Δ
sei-chain-pr	58.77% <65.11%> (?)
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
sei-cosmos/types/tx/types.go	72.22% <100.00%> (+0.79%)	⬆️
app/antedecorators/gasless.go	80.28% <75.00%> (-0.68%)	⬇️
sei-cosmos/x/auth/ante/validator_tx_fee.go	86.04% <0.00%> (-4.20%)	⬇️
sei-cosmos/x/auth/ante/fee.go	80.00% <55.55%> (-3.93%)	⬇️
app/ante/cosmos_delivertx.go	70.58% <16.66%> (-7.68%)	⬇️
app/ante/cosmos_checktx.go	37.60% <0.00%> (-0.51%)	⬇️
sei-cosmos/x/auth/tx/decoder.go	85.31% <82.00%> (-3.04%)	⬇️

... and 74 files with indirect coverage changes

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