[client] Support parsing grpc-status-details-bin for rich error details

[washanhanzi]

Summary

When interacting with gRPC servers that return rich error details via the grpc-status-details-bin header, the client should be able to parse these details. This header contains base64-encoded protobuf google.rpc.Status messages with typed Any details.

Current Behavior

The client only parses Connect protocol JSON error bodies. When a server returns grpc-status-details-bin, these details are ignored.

Reference Implementation

In connect-go, this is handled in connect-go/error.go and connect-go/protocol_grpc.go:

• Parses the base64-encoded header
• Decodes the google.rpc.Status protobuf
• Extracts typed Any details into the error structure

Proposed Changes

1. Add grpc-status-details-bin header parsing in error handling
2. Decode base64 content to google.rpc.Status protobuf
3. Expose parsed details in ClientError or Status type
4. This enables interoperability with gRPC servers even when using Connect protocol

Note

This is specifically for parsing error details when a server includes them, not for full gRPC protocol support (which is handled by tonic).

References

• gRPC Status Details
• google.rpc.Status

[washanhanzi]

Closing as not planned because grpc-status-details-bin belongs to the gRPC wire protocol, not Connect.

Connect rich error details are already parsed from unary JSON errors and streaming EndStream errors and exposed through ClientError::details(). For gRPC-only servers, generate a Tonic client with with_tonic_client() and use tonic-types::StatusExt to decode google.rpc.Status.

Parsing this field in the Connect client would not provide gRPC interoperability: gRPC also requires its media types, framing, HTTP 200 trailer status handling, grpc-status, grpc-message, trailers-only responses, and different compression semantics.