WiX 7: decide between Open Source Maintenance Fee (OSMF) acceptance and staying on WiX 5/6

[markuslf]

Context

WiX Toolset v7 introduced the Open Source Maintenance Fee (OSMF) EULA: https://wixtoolset.org/osmf/. Unattended CI builds now abort with error WIX7015: You must accept the Open Source Maintenance Fee (OSMF) EULA to use WiX Toolset v7 (seen during the v3.0.0 build attempt).

Current State

.github/workflows/lf-build-windows-x86_64.yml pins the WiX install to 5.0.* as a temporary fix. 5.0.* is the last release line that predates the OSMF requirement and matches what the v2.2.1 release built against.

Decision Needed

• Stay on WiX 5.0.* indefinitely (works, but stops getting maintenance updates)
• Move to WiX 6.x (last pre-OSMF major; check whether the migration introduces breaking changes)
• Move to WiX 7.x with OSMF acceptance, either:
  • accept the OSMF EULA non-interactively in CI (mechanism to be researched), or
  • purchase a commercial OSMF subscription if Linuxfabrik does not qualify as an open-source maintainer under the new terms

Output

• A defendable decision documented in the workflow (or in CONTRIBUTING.md)
• If we stay on 5.0.* / 6.x: a periodic review reminder so we are not blindsided when 5.x stops getting CVE fixes
• If we move to 7.x: the EULA acceptance method documented in the build readme

Links

• WiX OSMF page: https://wixtoolset.org/osmf/
• Failing CI run: https://github.com/Linuxfabrik/monitoring-plugins/actions/runs/25374180462/job/74404956589