[Repo Assist] ci: add Fantomas format check job to PR workflow

[github-actions]

🤖 This is an automated pull request from Repo Assist, an AI assistant for this repository.

Summary

Adds a check-format job to .github/workflows/pull-requests.yml that runs the existing CheckFormat FAKE target (Fantomas --check) on every pull request.

Motivation

Currently the PR CI only verifies that the code builds and tests pass — it does not check that F# source files are formatted consistently. This means unformatted code can be merged silently, and formatting drift accumulates over time. Adding a dedicated format-check job catches these issues automatically before review.

Details

• New job: check-format — runs on ubuntu-latest, 10-minute timeout
• Uses the same restore steps (tools + packages) as the existing build jobs
• Invokes dotnet run --project build/build.fsproj -- -t CheckFormat (already defined in build.fs)
• Runs independently of build-windows and build-ubuntu so format errors surface quickly without waiting for the full build

Test Status

CI change — no code tests to run. The CheckFormat FAKE target already exists and is used by contributors locally; this PR just adds it to the automated PR gate.

Generated by Repo Assist

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Warning

Protected Files — Push Permission Denied

This was originally intended as a pull request, but the patch modifies protected files. A human must create the pull request manually.

Protected files

• .github/workflows/pull-requests.yml

The push was rejected because GitHub Actions does not have workflows permission to push these changes, and is never allowed to make such changes, or other authorization being used does not have this permission.

Create the pull request manually

# Download the patch from the workflow run
gh run download 23994235525 -n agent -D /tmp/agent-23994235525

# Create a new branch
git checkout -b repo-assist/eng-ci-format-check-2026-04-05-23048a75f09df203 main

# Apply the patch (--3way handles cross-repo patches)
git am --3way /tmp/agent-23994235525/aw-repo-assist-eng-ci-format-check-2026-04-05.patch

# Push the branch and create the pull request
git push origin repo-assist/eng-ci-format-check-2026-04-05-23048a75f09df203
gh pr create --title '[Repo Assist] ci: add Fantomas format check job to PR workflow' --base main --head repo-assist/eng-ci-format-check-2026-04-05-23048a75f09df203 --repo fsprojects/FSharp.Data

Generated by 🌈 Repo Assist, see workflow run. Learn more.

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/repo-assist.md@7ee2b60744abf71b985bead4599640f165edcd93