feat(dapi): return actual fees paid in state transition broadcast responses

[pauldelucia]

Issue being fixed or feature implemented

It would be nice if clients (like dash-evo-tool) could know the actual fees paid for state transitions without having to fetch identity balances before and after. Something similar to how Ethereum returns gasUsed in transaction receipts. Previously, WaitForStateTransitionResultResponse only returned proof or error without the fee breakdown, even though the fee information was calculated internally in StateTransitionExecutionResult::SuccessfulExecution.

What was done?

• Proto: Added FeeResult message with processing_fee, storage_fee, and removed_from_system fields. Added optional fee_result field to WaitForStateTransitionResultResponseV0.

• Drive: Encode fee result into ExecTxResult.data during state transition execution (20 bytes: 8 + 8 + 4 for processing_fee, storage_fee, removed_bytes). Included for both successful executions and paid consensus errors.

• DAPI: Decode fee data from Tenderdash transaction results (both websocket events and existing tx queries). Populate fee_result field in gRPC responses for success and paid error cases.

• SDK: Added FeeResult struct and StateTransitionBroadcastResult<T> wrapper. Added new trait methods broadcast_and_wait_with_fee() and wait_for_response_with_fee() that return fee information alongside the proof result. Existing methods unchanged for backwards compatibility.

How Has This Been Tested?

• Unit tests added for fee encoding in Drive (test_encode_fee_result, test_encode_fee_result_zero_values, test_encode_fee_result_max_values)
• Unit tests added for fee decoding in DAPI (test_decode_fee_result_valid, test_decode_fee_result_zero_values, test_decode_fee_result_too_short, test_decode_fee_result_empty, test_decode_fee_result_extra_bytes)
• Unit tests added for SDK FeeResult conversion (test_fee_result_from_grpc, test_fee_result_total_no_overflow)
• All tests pass with cargo test

Breaking Changes

None - existing broadcast_and_wait() and wait_for_response() methods remain unchanged. New methods are additive.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

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[github-actions]

✅ gRPC Query Coverage Report

================================================================================
gRPC Query Coverage Report - NEW QUERIES ONLY
================================================================================

Total queries in proto: 53
Previously known queries: 47
New queries found: 6

================================================================================

New Query Implementation Status:
--------------------------------------------------------------------------------
✓ getAddressInfo                                /home/runner/work/platform/platform/packages/rs-sdk/src/platform/query.rs
✓ getAddressesBranchState                       /home/runner/work/platform/platform/packages/rs-sdk/src/platform/address_sync/mod.rs
✓ getAddressesInfos                             /home/runner/work/platform/platform/packages/rs-sdk/src/platform/fetch_many.rs
✓ getAddressesTrunkState                        /home/runner/work/platform/platform/packages/rs-sdk/src/platform/query.rs
✓ getRecentAddressBalanceChanges                /home/runner/work/platform/platform/packages/rs-sdk/src/platform/query.rs
✓ getRecentCompactedAddressBalanceChanges       /home/runner/work/platform/platform/packages/rs-sdk/src/platform/query.rs

================================================================================
Summary:
--------------------------------------------------------------------------------
New queries implemented: 6 (100.0%)
New queries missing: 0 (0.0%)

Total known queries: 53
  - Implemented: 50
  - Not implemented: 2
  - Excluded: 1

Not implemented queries:
  - getConsensusParams
  - getTokenPreProgrammedDistributions

[QuantumExplorer]

Closing during housekeeping. The original author is no longer with the project, this never came out of draft, and there's no human review on record.

The underlying idea — surfacing actual fees paid back to the client in the broadcast response, the way Ethereum returns gasUsed in a receipt — is still wanted, and the hand-written delta here is fairly small (~540 lines of real code; the rest is generated proto clients). I'm not opening a new tracking issue because the surrounding workstream already exists:

• feat(sdk): expose transitionHash from state transition broadcast functions #3352 — exposing transitionHash from broadcast functions (sibling concern: more info in the broadcast response surface).
• fix(drive-abci): bill batch transformer drive reads (B7) #3670 / Fee under-billing in non-batch paid-error state transition paths (follow-up to #3670) #3673 — paid-error fee-billing correctness audit (what gets charged). A fee receipt is only useful when those are settled, because the receipt only echoes what Drive computed.

Anyone picking this up later: the feat/feeResult branch has a working draft of the proto message (FeeResult with processing/storage/removed fields), the Drive-side encoding into ExecTxResult.data, the DAPI decode for both websocket and tx-query paths, and SDK broadcast_and_wait_with_fee() / wait_for_response_with_fee() trait methods. Targets v3.0-dev, but the affected files have had little churn on v3.1-dev, so a rebase should be largely mechanical. Worth coordinating with #3670/#3673 so the returned numbers reflect the corrected billing.