Add dotnet-fsharp plugin

[Copilot]

No dedicated home existed for F# skills — they would otherwise be scattered across unrelated plugins or omitted entirely.

Changes

• plugins/dotnet-fsharp/plugin.json — new plugin registration
• plugins/dotnet-fsharp/skills/fsharp-getting-started/SKILL.md — initial skill covering:
  • Project creation (dotnet new -lang F#)
  • F# file compilation order (the most common beginner gotcha)
  • Idiomatic types: records, discriminated unions, exhaustive pattern matching
  • Pipe operator (|>) for data transformation
  • Null-safety via option<'T> and Result<'T,'E>
  • Async patterns: async { } vs task { }
• tests/dotnet-fsharp/fsharp-getting-started/eval.yaml — two eval scenarios (DU + pattern matching; file order diagnosis)
• .github/plugin/marketplace.json — plugin registered in marketplace

Example: discriminated union eval scenario

- name: "Create an F# console app with discriminated unions and pattern matching"
  prompt: |
    Create a ShapeCalculator F# app using discriminated unions and pattern matching to compute areas.
  assertions:
    - type: output_contains
      value: "dotnet new console"
    - type: output_matches
      pattern: "-lang\\s+F#"
    - type: output_matches
      pattern: "type Shape"
    - type: output_matches
      pattern: "match\\s+shape\\s+with"

Original prompt

---

This section details on the original issue you should resolve

<issue_title>create a new plugin named dotnet-fsharp where all fsharp related skills would go</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes create a new plugin named dotnet-fsharp where all fsharp related skills would go #301

---

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[timheuer]

I know this was Copilot-submitted initially, but we should ensure this type of getting started is necessary for F# -- this also kinda mixes multiple tasks.

[jeffschwMSFT]

/evaluate

[danmoseley]

/evaluate

[github-actions]

Skill Validation Results

Skill	Scenario	Quality	Skills Loaded	Overfit	Verdict
fsharp-getting-started	Create an F# console app with discriminated unions and pattern matching	3.0/5 → 3.7/5 🟢	✅ fsharp-getting-started; tools: skill, view, create / ✅ fsharp-getting-started; tools: skill, view, create	✅ 0.09	✅
fsharp-getting-started	Explain F# file compilation order	3.7/5 → 3.7/5	✅ fsharp-getting-started; tools: report_intent, skill / ✅ fsharp-getting-started; tools: report_intent, skill	✅ 0.09	❌ [1]

[1] (Isolated) Quality unchanged but weighted score is -8.3% due to: tokens (11925 → 26863), tool calls (0 → 2), time (9.7s → 12.9s)

Model: claude-opus-4.6 | Judge: claude-opus-4.6

📖 See InvestigatingResults.md for how to diagnose failures. Additional debugging guidance may be provided by your workflow.

🔍 Full results — includes quality and agent details

To investigate failures, paste this to your AI coding agent:

For PR 302 in dotnet/skills, download eval artifacts with gh run download 23678554667 --repo dotnet/skills --pattern "skill-validator-results-*" --dir ./eval-results, then fetch https://raw.githubusercontent.com/dotnet/skills/c4f657f0d7afe7d9a9816a10aa0da6dff47fdcf4/eng/skill-validator/InvestigatingResults.md and follow it to analyze the results.json files. Diagnose each failure, suggest fixes to the eval.yaml and skill content, and tell me what to fix first.