[codex] add dynamic custom precompile gas meter

[codchen]

Summary

Adds dynamic gas accounting for evm-only custom precompiles, with the staking precompile using the shared meter through the existing store, balance-transfer, and log boundaries.

Changes

• Add a reusable precompile gas meter for base gas, SLOAD/SSTORE-style storage costs, keccak slot derivation, native value transfers, and log emission.
• Wrap storageBackedStore, nativeBalanceTransfer, and log emission in the custom precompile adapter so gas is charged based on the actual execution path.
• Reduce staking RequiredGas to only base/input gas, avoiding double charging now that state access is dynamically metered.
• Add executor coverage for dynamic store gas and update staking lifecycle tests to use realistic gas limits.

Validation

• go test ./giga/evmonly/...
• golangci-lint v2.8.0 run ./giga/evmonly/...

[codecov]

Codecov Report

❌ Patch coverage is 59.66851% with 73 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.09%. Comparing base (27e3acc) to head (56bf186).

Files with missing lines	Patch %	Lines
giga/evmonly/precompile_gas.go	68.46%	23 Missing and 18 partials ⚠️
giga/evmonly/precompile_adapter.go	34.69%	19 Missing and 13 partials ⚠️

Additional details and impacted files

@@                         Coverage Diff                          @@
##           codex/evmonly-staking-precompile    #3644      +/-   ##
====================================================================
- Coverage                             58.09%   58.09%   -0.01%     
====================================================================
  Files                                  2186     2184       -2     
  Lines                                178307   178410     +103     
====================================================================
+ Hits                                 103588   103643      +55     
- Misses                                65443    65473      +30     
- Partials                               9276     9294      +18     

Flag	Coverage Δ
sei-chain-pr	54.18% <59.66%> (-0.04%)	⬇️
sei-db	70.41% <ø> (ø)

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

Files with missing lines	Coverage Δ
giga/evmonly/precompiles/staking/staking.go	23.91% <100.00%> (-0.40%)	⬇️
giga/evmonly/precompile_adapter.go	66.35% <34.69%> (-8.65%)	⬇️
giga/evmonly/precompile_gas.go	68.46% <68.46%> (ø)

... and 5 files with indirect coverage changes

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[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 26, 2026, 3:43 AM

[cursor]

PR Summary

Medium Risk
Changes consensus-relevant gas for custom precompiles and staking calls; incorrect metering could allow cheap state writes or break existing txs that relied on the old flat gas schedule.

Overview
Introduces dynamic gas accounting for evm-only custom precompiles so execution cost reflects real work (storage, transfers, logs), not only a flat RequiredGas.

RunAndCalculateGas now drives a shared precompileGasMeter: it charges the contract’s base RequiredGas, then passes the meter into storageBackedStore, nativeBalanceTransfer, and meteredLogSink. Those paths charge EIP-2929/2200-style SLOAD/SSTORE, Keccak for store slot derivation, account access + value transfer costs, and LOG gas, with tracing hooks on each deduction.

The staking precompile drops separate read/write gas constants and uses baseGas + per-input-byte in RequiredGas only, avoiding double billing now that store and balance side effects are metered dynamically.

Tests assert store writes consume more than intrinsic gas, OOG on a tight gas limit leaves no storage changes, and staking flows use 8M gas limits.

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