Function export_dockerfile 

pub fn export_dockerfile(
    session: &Session,
    params: Option<&[Parameter]>,
) -> String

Export a session as a Dockerfile.

Generates a Dockerfile with:

• Metadata header comments (session name, date, command count)
• FROM ubuntu:22.04 base image
• ARG declarations when parameters are provided
• WORKDIR instructions when the working directory changes
• One RUN instruction per command (no escaping needed)
• Annotations for failed commands (non-zero exit codes)

When params is Some, ARG declarations are added after the FROM line and commands use $VAR references.

Empty sessions produce a valid Dockerfile with a “No commands recorded” comment.