Add exp-test-gap-analysis skill for pseudo-mutation test gap detection

[Evangelink]

New experimental skill that performs pseudo-mutation analysis on .NET production code to find gaps in existing test suites. Covers boundary, boolean/logic, return value, exception removal, arithmetic, and null-check mutation categories.

Includes eval.yaml with 4 scenarios (boundary gaps, logic gaps, well-tested code recognition, non-activation) and fixture projects.

[Evangelink]

/evaluate

[github-actions]

Skill Validation Results

Skill	Scenario	Quality	Skills Loaded	Overfit	Verdict
exp-test-gap-analysis	Find boundary mutation gaps in tiered discount and shipping logic	4.7/5 → 5.0/5 🟢	✅ exp-test-gap-analysis; tools: skill, edit / ✅ exp-test-gap-analysis; tools: skill, glob	✅ 0.06	✅
exp-test-gap-analysis	Find logic and null-check mutation gaps in access control code	3.7/5 → 4.7/5 🟢	✅ exp-test-gap-analysis; tools: skill, glob / ✅ exp-test-gap-analysis; tools: skill, edit	✅ 0.06	✅
exp-test-gap-analysis	Acknowledge well-tested code with few surviving mutations	3.3/5 → 3.3/5	✅ exp-test-gap-analysis; tools: skill	✅ 0.06	✅ [1]
exp-test-gap-analysis	Decline request to write new tests from scratch	3.7/5 ⏰ → 4.3/5 🟢	ℹ️ not activated (expected)	✅ 0.06	❌

[1] (Plugin) Quality dropped but weighted score is +2.7% due to: tokens (355377 → 113804), tool calls (26 → 10), time (219.2s → 154.3s)

⏰ timeout — run(s) hit the (120s) scenario timeout limit; scoring may be impacted by aborting model execution before it could produce its full output (increase via timeout in eval.yaml)

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

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

🔍 Full Results - additional metrics and failure investigation steps

[Copilot]

Pull request overview

Adds a new experimental .NET skill (exp-test-gap-analysis) and accompanying evaluation scenarios/fixtures to perform pseudo-mutation style reasoning to identify test suite gaps.

Changes:

• Introduces exp-test-gap-analysis skill documentation describing mutation-point detection and gap reporting.
• Adds eval.yaml with 4 scenarios plus fixture projects covering boundary gaps, logic gaps, and a “well-tested” baseline.
• Updates CODEOWNERS to route ownership for the new skill and tests.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 8 comments.

File	Description
plugins/dotnet-experimental/skills/exp-test-gap-analysis/SKILL.md	Defines the new skill’s purpose, workflow, and mutation categories.
tests/dotnet-experimental/exp-test-gap-analysis/eval.yaml	Adds evaluation scenarios validating boundary/logic gap detection and “well-tested” recognition.
tests/dotnet-experimental/exp-test-gap-analysis/fixtures/**	Adds .NET fixture projects + tests used by the eval scenarios.
.github/CODEOWNERS	Assigns ownership for the new skill + test area.

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