## 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`
calculated a hashed user ID from either auth user id or API key
Also correctly populates OS.
These will make our metrics more useful and powerful for analysis.
# Tool System Refactor
- Centralizes tool definitions and execution in `core/src/tools/*`:
specs (`spec.rs`), handlers (`handlers/*`), router (`router.rs`),
registry/dispatch (`registry.rs`), and shared context (`context.rs`).
One registry now builds the model-visible tool list and binds handlers.
- Router converts model responses to tool calls; Registry dispatches
with consistent telemetry via `codex-rs/otel` and unified error
handling. Function, Local Shell, MCP, and experimental `unified_exec`
all flow through this path; legacy shell aliases still work.
- Rationale: reduce per‑tool boilerplate, keep spec/handler in sync, and
make adding tools predictable and testable.
Example: `read_file`
- Spec: `core/src/tools/spec.rs` (see `create_read_file_tool`,
registered by `build_specs`).
- Handler: `core/src/tools/handlers/read_file.rs` (absolute `file_path`,
1‑indexed `offset`, `limit`, `L#: ` prefixes, safe truncation).
- E2E test: `core/tests/suite/read_file.rs` validates the tool returns
the requested lines.
## Next steps:
- Decompose `handle_container_exec_with_params`
- Add parallel tool calls
