Function resolve_engine_binary_path 

pub async fn resolve_engine_binary_path(
    config: &EngineResolverConfig,
) -> Result<PathBuf>

Resolves the engine binary path without probing for an already-running engine.

Used by callers that exec the binary directly (for example the CLI engine proxy), where a running engine on the endpoint should not short-circuit resolution to Existing and leave the caller without a path to run.