Add workshop material lint workflow

[cmvcordova]

Moves the lint check trialled in QLS-MiCM/IntroToPython#10 into this repo, so it lives next to the checklist workflow instead of inside one workshop repo. It was prompted by QLS-MiCM/IntroToPython#9, where a missing comma made the notebook invalid JSON and nothing flagged it.

Merging this changes nothing in other repos

• The distributor workflow is untouched, and its path filter does not match the new template, so nothing is pushed anywhere.
• The checklist workflow and its caller are untouched.
• A repo only gets the check when someone adds the caller to it.

What is added

File	Purpose
.github/workflows/reusable_lint_workshop.yml	Reusable workflow: checks out the PR, takes the linter from this repo, lints the changed files
scripts/lint_workshop.py	The linter
.github/workflow-templates/lint_workshop_caller.yml	Thin caller to copy into a workshop repo
README.md	Documents the above

Unlike the checklist workflow, this one runs on pull_request, with a read-only token and no secrets, which is why it is allowed to check out the PR. The linter always comes from this repo, so a PR cannot edit the checks it is held to.

What it checks

It looks at the files a pull request changes.

Fails the check (the file cannot be opened or run at all):

• .ipynb is not valid JSON
• .py, .R or .sh does not parse
• .Rmd / .qmd has a broken YAML header or a code chunk that is never closed
• .mlx is not a valid archive

Warns only (annotations and a job summary):

• a notebook code cell or an Rmd/qmd chunk does not parse
• a notebook was committed with an error output
• a notebook uses a relative image path, which does not render in Colab

Cell-level syntax is a warning on purpose: student notebooks contain intentional blanks.

How it was tested

• Past PRs, locally: the linter was run on the files touched by 29 past pull requests across the organisation (93 files, 16 repos). There were 2 hard failures: IntroToPython#9, and an attendee practice PR in IntroToGitHub (a .R file containing a sentence). None of the 26 merged PRs failed.
• Each check fires: confirmed on deliberately broken copies of real files.
• This reusable workflow, on a runner: called from the IntroToPython trial branch, pointing at this branch. It passes on the clean repo in 13 seconds with 9 warnings (run).
• Failing case, on a runner: tested with the earlier in-repo version of the same script, using the notebook from IntroToPython#9. It fails with line 21: not valid JSON, the notebook cannot be opened (run). The failing case was not re-run through the reusable workflow.

Not covered

• Nothing is executed, so wrong results in code that runs are not caught.
• Runners do not ship R. The workflow installs it only when a PR touches .R, .Rmd or .qmd; that step has not run yet, because IntroToPython has no R files.
• .m files are not checked.

Open questions for rollout

• Distribution: the distributor handles a single template. Rolling this out to every repo means either generalising it or adding the caller by hand to a few repos first.
• IntroToGitHub: attendees open practice PRs there, which would fail the check. It probably should not get the caller, or the caller needs a guard.
• Required or not: as written the check is informative. Making it required is a branch-protection setting per repo.

🤖 Generated with Claude Code