Fix dotnet tool runner stripping duplicate flags when rollForward is enabled

[Copilot]

When a local tool has "rollForward": true in dotnet-tools.json (or --allow-roll-forward is passed), repeated options like --var a --var b were silently deduplicated before being forwarded to the tool — only the first --var survived.

Root cause

MuxerCommandSpecMaker.CreatePackageCommandSpecUsingMuxer used Enumerable.Except to strip --allow-roll-forward from the forwarded args. Except is a set operation — it deduplicates the source sequence as a side effect, collapsing all repeated arguments.

Fix

Replace Except with a Where predicate that filters only --allow-roll-forward entries:

// Before — silently deduplicates all args
arguments.AddRange(commandArguments.Except(rollForwardArgument));

// After — removes only --allow-roll-forward, preserves duplicates
arguments.AddRange(commandArguments.Where(arg =>
    !arg.Equals("--allow-roll-forward", StringComparison.OrdinalIgnoreCase)));

A test is added to ToolRunCommandTests verifying that --var a --var b survives the forwarding pipeline intact when rollForward is active.

[marcpopMSFT]

Tested in codespaces with lbussell's repro.sh and confirmed the fix. @baronfel this is a regression in 10 but we haven't heard many complaints about it. Port to 4xx and wait for servicing pending feedback?

[baronfel]

I suspect that folks just aren't using --allow-roll-forward in any large amount. Your plan seems sane though!

[Copilot]

Pull request overview

Fixes dotnet tool run argument forwarding when roll-forward is enabled by ensuring repeated flags (e.g., --var a --var b) are not unintentionally deduplicated while stripping the internal --allow-roll-forward marker.

Changes:

• Replace Enumerable.Except with a filtering Where clause to remove only --allow-roll-forward while preserving duplicate arguments.
• Add a regression test to ensure duplicate forwarded arguments survive the roll-forward pipeline.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
test/dotnet.Tests/CommandTests/Tool/Run/ToolRunCommandTests.cs	Adds coverage for duplicate forwarded arguments when roll-forward is active.
src/Cli/dotnet/CommandFactory/CommandResolution/MuxerCommandSpecMaker.cs	Updates arg filtering logic to avoid Except-driven deduplication.

[marcpopMSFT]

/backport to release/10.0.3xx

[github-actions]

Started backporting to release/10.0.3xx (link to workflow run)

[marcpopMSFT]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Merged main into this branch and resolved the conflict in MuxerCommandSpecMaker.cs. The refactored version from main had re-introduced Except (which causes the deduplication bug), so the merge resolution applies our Where fix on top of main's new structure. Commit: fdd4c57.