Preserve large gRPC code-mode tool errors (#38621)

## Why

Code-mode tool failure messages larger than 64 KiB were truncated before they
reached the host.

## What changed

- Remove the tool error size limit from the gRPC protocol and host validation.
- Forward failed tool completion messages without truncation.

## Testing

- Verify that a multibyte error larger than 64 KiB is preserved exactly.

GitOrigin-RevId: 264ae4ba4adea5c19b669e4f41ccfd41a0c30fb5

codex-rs/code-mode-host/src/grpc/mod.rs

@@ -83,14 +83,7 @@ impl GrpcCodeModeHost {
                     Status::invalid_argument(format!("invalid code-mode tool output JSON: {error}"))
                 })?,
             ),
-            Some(proto::complete_tool_call_request::Outcome::Failed(error)) => {
-                validation::bounded(
-                    &error.message,
-                    validation::MAX_TOOL_ERROR_BYTES,
-                    "tool error message",
-                )?;
-                Err(error.message)
-            }
+            Some(proto::complete_tool_call_request::Outcome::Failed(error)) => Err(error.message),
             None => {
                 return Err(Status::invalid_argument(
                     "tool completion is missing its outcome",

codex-rs/code-mode-host/src/grpc/validation.rs

@@ -3,7 +3,6 @@ use tonic::Status;
 use uuid::Uuid;
 
 pub(super) use codex_code_mode_protocol::grpc::MAX_IDENTIFIER_BYTES;
-pub(super) use codex_code_mode_protocol::grpc::MAX_TOOL_ERROR_BYTES;
 pub(super) const MAX_TOOL_FILTERS: usize = 64;
 
 pub(super) fn identifier(value: &str, field: &str) -> Result<(), Status> {