🏗️ Self-service execution-environment image creation

Background

container-generator is a self-service Shiny app that generates Dockerfiles/Singularity definitions plus Posit Connect off-host values.yaml, letting a customer pick an OS, R/Python/Quarto versions, and Pro Drivers and download a working build. It's a demand signal for a bakery-native answer — this epic is that answer, scoped to bakery + images-examples rather than a second tool to maintain.

Definition of done

A customer with no bakery experience can go from "I need R 4.4.2 + Python 3.12 + Quarto on Rocky 9" to a tested, buildable Containerfile — and, once the dependent work below lands, a generated Connect off-host values.yaml — using bakery and images-examples alone.

Depends on (not filed here — not yet real issues anywhere)

• Project-level artifact templates rendered over an image's version matrix, to generate Connect values.yaml. Blocking: Image.template_path (posit_bakery/config/image/image.py:299) and the render loop (matrix.py:538-543) scope template rendering to one image at a time; there's no aggregation point across images yet.
• Automatic R system-dependency resolution via pak::pkg_sysreqs, replacing hand-maintained deps/system-packages.txt.

Both were identified as prerequisites while scoping this epic but were never filed as standalone issues anywhere — worth doing before or alongside the sub-issues below.

Checklist (break out into issues when picked up)

• Pro Drivers on a bare-OS base, not just atop Posit's own -min images — could fold into the worked-example sub-issue rather than a standalone macro.
• Apptainer/Singularity output — open question, not yet decided. The Posit Team image fleet management epic scoped this down to a consumption doc only (convert bakery-built OCI images via apptainer build); this epic's actual premise (hand the customer whatever artifact they asked for) is what reopens it.

Non-goals

• GUI front end — resolved in favor of bakery create image --interactive instead.
• "Install every package from a repo" mode.
• Full package-level/environment locks

Start by reading posit_bakery/config/image/image.py around Image.template_path and matrix.py around the render loop, then review bakery create image --interactive and the images-examples project. Map the unresolved dependencies and checklist items before implementation. Done means a customer can use bakery and images-examples to produce a tested, buildable Containerfile for the stated R/Python/Quarto environment.