main doesn't build since #141: CA1506 fails RunCommand.Test (RunCommandTests coupled with 98 types, limit 96), so CI is red and none of the recent fixes can release #152

What's wrong

On main (9e8ed93), dotnet build RunCommand.Test fails with:

RunCommandTests.cs(13,14): error CA1506: 'RunCommandTests' is coupled with '98' different types from '27' different namespaces. Rewrite or refactor the code to decrease its class coupling below '96'.

• CI on main has failed on all three OSes at 9e8ed93, on both the push run and the scheduled run (CI schedule failure, 2026-11-11). The open Dependabot PRs Bump the ktsu group with 11 updates #150 and Bump MSTest.Sdk from 4.4.1 to 4.5.3 #151 fail with the same error.
• I built each commit to find where it started. ce81f0e (Kill the whole process tree from the netstandard builds where the runtime can [patch] #142) and 0aa99fa (Treat a read whose handler threw OperationCanceledException as failed [patch] #146) build. fa125a2 (Ask access(X_OK) whether an overlay PATH match may run, on every target [patch] #141) is the first commit that fails, at 99 types, and 9e8ed93 (Never resolve a bare name to a batch file on the overlay PATH [patch] #140) brings it to 98.
• The fixes landed within minutes of each other. Each push cancelled the CI run before it, so only the last run finished, and that run failed.
• The latest release is still v1.9.6-pre.2 (Oct 10). Nothing from Deliver a line ending in a bare CR at once instead of on the next write [patch] #129, Never resolve a bare name to a batch file on the overlay PATH [patch] #140, Ask access(X_OK) whether an overlay PATH match may run, on every target [patch] #141, Kill the whole process tree from the netstandard builds where the runtime can [patch] #142, Treat a read whose handler threw OperationCanceledException as failed [patch] #146, Strip a leading byte order mark once, not twice, for an encoding with a preamble [patch] #147 or Resolve ".." in a relative executable from where a symlinked working directory points [patch] #149 ships until main builds again.
• With -p:RunAnalyzers=false the suite passes: 108 passed, 3 skipped. Only the analyzer is failing the build, not the behaviour.

Suggested fix

Split RunCommandTests into a few classes by area: overlay PATH resolution, cancellation and process-tree kill, working directory, and output decoding (BOM, CR). The tests are already grouped that way, and splitting them brings each class well under the coupling limit. CLAUDE.md rules out global suppressions.

Acceptance criteria

• dotnet build and dotnet test succeed on main with analyzers on, on all three CI operating systems.
• Bump the ktsu group with 11 updates #150 and Bump MSTest.Sdk from 4.4.1 to 4.5.3 #151 go green after a rebase.