Bug: system-reactive-7-packages-config-unsupported

[drmoisan]

• Work Mode: minor-audit

Summary

The NuGet upgrade in PR #568 moved System.Reactive to 7.0.0, which explicitly
does not support packages.config. Every build of the solution now emits five
warnings from the package's own guard target stating the configuration is
unsupported. The repository's projects are legacy non-SDK packages.config
projects, so the package is being consumed in a scenario its authors disclaim.

Environment

• OS/version: Windows 11 Pro 10.0.26200
• Python version: n/a (C# / .NET Framework 4.8.1)
• Command/flags used: msbuild TaskMaster.sln /t:Rebuild /m /p:Configuration=Debug "/p:Platform=Any CPU" /p:TreatWarningsAsErrors=true
• Data source or fixture: packages/System.Reactive.7.0.0

Steps to Reproduce

1. Check out main at or after merge commit 97065e55.
2. Run nuget restore TaskMaster.sln.
3. Run the analyzer or nullable toolchain stage, for example
   msbuild TaskMaster.sln /t:Rebuild /m /p:Configuration=Debug "/p:Platform=Any CPU" /p:TreatWarningsAsErrors=true.
4. Observe the warning summary at the end of the build.

Expected Behavior

The solution builds with zero warnings from its dependency set, and the reactive
dependency is consumed in a configuration its maintainers support.

Actual Behavior

The build succeeds with 5 warnings, all of the following form:

packages\System.Reactive.7.0.0\build\System.Reactive.PackagesConfigCheck.targets(31,5):
warning : The project contains a packages.config file, which is not supported by
System.Reactive v7.0 or later. Please migrate to PackageReference. (You can
suppress this message by setting the RxUseUnsupportedPackagesConfig property to
true, but be aware this is an unsupported scenario.)

Affected projects: ToDoModel, QuickFiler, TaskMaster, UtilitiesCS.Test,
and one further project in the same build.

Logs / Screenshots

• Attached minimal logs or screenshot
• Snippet: see the warning text quoted above; reproduced verbatim from the
  local analyzer and nullable toolchain stages on 2026-08-15.

Impact / Severity

• Blocker
• High
• Medium
• Low

The build is not broken today and both protected gates pass. The severity is
Medium rather than Low because the package guard is not cosmetic: the vendor
states the scenario is unsupported, so assembly-binding or runtime-loading
behavior for Rx may diverge from a supported configuration without further
warning, and the warning count masks any new warning that appears later.

Source

From: docs/features/potential/2026-08-15-system-reactive-7-packages-config-unsupported.md