Rust based sourceReader for EVM

[RensR]

All requirements implemented and verified. What changed given the new constraints:

gRPC drop-in replacement

     - rust/proto/ccv/chainaccess/v1/source_reader.proto — ccv.chainaccess.v1.SourceReader service mirroring all five methods. Message travels in its canonical CCIP     LSPs are disabled                       
       v1.7 byte encoding, so the Go side decodes with its existing protocol.DecodeMessage — no fidelity loss.                                                                                                   
     - ccv-chainaccess-grpc (tonic): SourceReaderService<R: SourceReader> adapter, serve() with cooperative shutdown, and the ccv-chainaccess-grpc server binary (                                               
       env-configured, one chain per process, SIGINT → graceful drain, SIGKILL-safe since stateless).                                                                                                            
     - rust/grpc-client-go/ — generated pb code plus a hand-written grpcclient.Client implementing chainaccess.SourceReader (compile-time asserted), with the same                                               
       *big.Int conventions as the Go EVM reader. This is the actual drop-in glue on the Go side.          
                                                                                                      

Constraint compliance

     - No panics: both crates have #![forbid(unsafe_code)] + #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::indexing_slicing)] in non-test                                             
       code. Encoding became fallible (encode() -> Result), all slice access is checked, and code was restructured so error paths are genuinely reachable (no dead                                               
       defensive branches).                                                                                                                                                                                      
     - Chain family: EVM reader covers any chain with standard eth_* RPC; exceptions called out in docs (safe tag unsupported → Ok(None); finalized tag required).                                               
     - Stateless / no persistence below the interface: unchanged by design; the gRPC layer adds none.                                                                                                            
     - Shutdown without notice: tested — SIGKILL mid-serve leaves no bad state; SIGINT drains cleanly.              

Definition of done

    - Coverage: 100% line coverage per llvm-cov/lcov (including the binary's config/error paths, via process-spawn tests; a subtle one — tonic deadlocks graceful                                               
      shutdown if you hold the client open, the test drops it first).                                                                                                                                           
    - Historical backtest: 708 real CCIPMessageSent events from Sepolia's OnRamp v2.0.0 (blocks 10970571–11522733), all parsed and validated live (examples/                                                    
      backtest.rs).                                                                                                                                                                                             
    - Differential vs Go: rust/differential-go CLI exposes the Go pipeline; Rust tests compare per-case outcomes: 7500 codec fuzz cases + 708 historical + 600                                                  
      mutated logs — all agree byte-for-byte, including skip-reason codes.                                                                                                                                      
    - This caught two real divergences I fixed: Alloy's lenient decode masks uint32 overflow where geth rejects it (fixed with a raw-word range walk), and topic                                                
      handling is now masked exactly like Go (topic0 verification kept as documented hardening — unreachable through fetch since the RPC filter pins it).                      

[github-actions]

Code coverage report:

Package	main	rust-reader	Diff
github.com/smartcontractkit/chainlink-ccv/aggregator	50.86%	50.82%	-0.04%
github.com/smartcontractkit/chainlink-ccv/bootstrap	70.72%	70.72%	+0.00%
github.com/smartcontractkit/chainlink-ccv/cli	59.12%	59.12%	+0.00%
github.com/smartcontractkit/chainlink-ccv/cmd	36.93%	36.93%	+0.00%
github.com/smartcontractkit/chainlink-ccv/common	46.51%	46.51%	+0.00%
github.com/smartcontractkit/chainlink-ccv/executor	42.80%	42.80%	+0.00%
github.com/smartcontractkit/chainlink-ccv/indexer	35.54%	35.55%	+0.01%
github.com/smartcontractkit/chainlink-ccv/integration	56.56%	56.56%	+0.00%
github.com/smartcontractkit/chainlink-ccv/internal	0.00%	0.00%	+0.00%
github.com/smartcontractkit/chainlink-ccv/migration	77.66%	77.66%	+0.00%
github.com/smartcontractkit/chainlink-ccv/pkg	100.00%	100.00%	+0.00%
github.com/smartcontractkit/chainlink-ccv/pricer	0.00%	0.00%	+0.00%
github.com/smartcontractkit/chainlink-ccv/protocol	63.06%	63.06%	+0.00%
github.com/smartcontractkit/chainlink-ccv/rust	0.00%	0.00%	+0.00%
github.com/smartcontractkit/chainlink-ccv/tools	43.61%	43.61%	+0.00%
github.com/smartcontractkit/chainlink-ccv/verifier	34.37%	34.37%	+0.00%
Total	49.00%	47.50%	-1.50%

Files added (in rust-reader):

• github.com/smartcontractkit/chainlink-ccv/rust/differential-go/main.go
• github.com/smartcontractkit/chainlink-ccv/rust/grpc-client-go/client.go
• github.com/smartcontractkit/chainlink-ccv/rust/grpc-client-go/pb/ccv/chainaccess/v1/source_reader.pb.go
• github.com/smartcontractkit/chainlink-ccv/rust/grpc-client-go/pb/ccv/chainaccess/v1/source_reader_grpc.pb.go