feat(evmonly): add eth_getBalance RPC

[codchen]

Describe your changes and provide context

• expose eth_getBalance from the EVM-only JSON-RPC server
• read balances from the current committed EVM state
• support latest, safe, finalized, and pending, while rejecting block heights and hashes until historical state is wired
• add unit, JSON-RPC registration, and Docker integration coverage
• document the endpoint and its supported block selectors in the Autobahn README

Testing performed to validate your change

• go test -race -count=1 ./giga/evmonly/rpc/...
• go test -count=1 ./sei-tendermint/internal/rpc/core/...
• make autobahn-evmonly-integration-test (four local Docker validators, 4,000 finalized transfers, post-transfer balance checks on every validator)
• golangci-lint run ./giga/evmonly/rpc/... ./sei-tendermint/internal/rpc/core/...
• golangci-lint fmt --diff

[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	Sep 14, 2026, 1:52 AM

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.62%. Comparing base (9407b6d) to head (448897f).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
giga/evmonly/rpc/server.go	0.00%	1 Missing and 1 partial ⚠️
sei-tendermint/internal/rpc/core/mempool.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4140      +/-   ##
==========================================
- Coverage   61.58%   60.62%   -0.97%     
==========================================
  Files        2196     2080     -116     
  Lines      193825   180359   -13466     
==========================================
- Hits       119365   109336   -10029     
+ Misses      62888    60605    -2283     
+ Partials    11572    10418    -1154     

Flag	Coverage Δ
sei-chain-pr	37.18% <77.77%> (?)
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
giga/evmonly/rpc/balance.go	100.00% <100.00%> (ø)
giga/evmonly/rpc/server.go	31.25% <0.00%> (-1.01%)	⬇️
sei-tendermint/internal/rpc/core/mempool.go	45.02% <0.00%> (-0.48%)	⬇️

... and 117 files with indirect coverage changes

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[cursor]

PR Summary

Medium Risk
Introduces a new read path over committed EVM balances; scope is limited to current state with historical queries rejected, but balance correctness matters for tooling and offline signing workflows.

Overview
Adds eth_getBalance to the Autobahn EVM-only JSON-RPC server so clients can read an address balance from the current committed EVM state.

The handler accepts latest, safe, finalized, and pending (all mapped to current state); explicit block numbers and hashes return an error until historical state exists. The RPC Backend gains EvmBalance, wired through Environment.EvmBalance to the app, and the method is registered alongside existing eth_* endpoints.

Coverage includes unit tests, an HTTP eth_getBalance smoke test, post-transfer balance checks on every validator in the EVM-only integration load test, and Autobahn README docs (including cast balance).

^{Reviewed by Cursor Bugbot for commit 448897f. Bugbot is set up for automated code reviews on this repo. Configure here.}

[seidroid]

Adds eth_getBalance to the EVM-only JSON-RPC surface, reading the current committed EVM state and rejecting historical selectors, with unit, registration, and Docker integration coverage. The block-selector gating, the nil Sei-address argument (only reachable in EVM-only mode, where it is ignored), the RPC-surface exposure, and the 2^200 + 1 integration assertion all check out; nothing blocking found.

Findings: 0 blocking | 0 non-blocking | 0 posted inline

Blockers

• None at the file/PR level.

Non-blocking

• None at the file/PR level.