## What changed
- Record each MCP source and its first turn, including connector and plugin identifiers when available. Cover direct and Code Mode calls, including returned errors and results that are not printed.
- Persist cumulative attribution checkpoints and restore them across compaction, resume, and forks, including forks limited to recent turns.
- Attach fresh attribution to Responses API `client_metadata` under `mcp_attribution`, outside model-visible content. Restrict transmission to allowed OpenAI HTTPS destinations for both HTTP and WebSocket requests.
- Report `attribution_error` for legacy history without checkpoints, malformed or conflicting attribution, and serialized attribution exceeding 16 KiB.
## Testing
Add coverage for source deduplication, checkpoint persistence and restoration, recent-turn forks, direct and Code Mode calls, destination filtering, and the serialized size limit.
GitOrigin-RevId: fd285e152ca9e24bfa000debb20013709d67a86e
## Why
`x-codex-turn-metadata` is sent as an HTTP/WebSocket header, but Codex
was serializing the metadata JSON with raw UTF-8 string contents. When a
workspace path contains non-ASCII characters, common HTTP stacks can
reject or corrupt that header before the request reaches the provider.
Fixes#17468. Also addresses the duplicate WebSocket report in #19581.
## What changed
- Added `codex_utils_string::to_ascii_json_string`, a shared helper that
serializes JSON normally while escaping non-ASCII string content as
`\uXXXX`.
- Switched turn metadata header serialization, including merged
Responses API client metadata, to use the ASCII-safe JSON helper.
- Added coverage for non-ASCII workspace paths and non-ASCII client
metadata while preserving the same parsed JSON values.
## Verification
- `cargo test -p codex-utils-string`
- `cargo test -p codex-core turn_metadata`
- `just bazel-lock-check`
peilin-openai