[BUG] `otelHeadersHelper` does not get used for OTLP gRPC exporter

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

This is a duplicate of #18000 because that was closed due to being "stale".

When otelHeadersHelper is set in the settings, the headers from that script output are not added to gRPC metadata when the gRPC exporter is in use, i.e. OTEL_EXPORTER_OTLP_PROTOCOL=grpc.

It does work and be added to HTTP request headers when using the HTTP exporter, i.e. OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf or OTEL_EXPORTER_OTLP_PROTOCOL=http/json.

What Should Happen?

When otelHeadersHelper is set in the settings, the headers from that script output are not added to gRPC metadata

Error Messages/Logs

Steps to Reproduce

Set a config like

{
	"otelHeadersHelper": "... some script ...",
	"env": {
		"CLAUDE_CODE_ENABLE_TELEMETRY": "1",
		"OTEL_METRICS_EXPORTER": "otlp",
		"OTEL_LOGS_EXPORTER": "otlp",
		"OTEL_EXPORTER_OTLP_PROTOCOL": "grpc",
		"OTEL_EXPORTER_OTLP_ENDPOINT": "https://some-host:4317"
	}
}

Run claude.

Observe that the values returned by the script are not included in gRPC metadata.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.77

Platform

Other

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_