Investigate compiler failures, test errors, or unexpected behavior through systematic minimal reproduction, 3-hypothesis testing, and verification. Always re-run builds and tests after changes.

Always invoke after editing `.fs` files under `src/Compiler/`. Fast parse/typecheck without `dotnet build`, plus symbol references and inferred type hints. Use whenever the user asks about F# errors, compile errors, type inference, finding usages, or renaming a symbol in the compiler tree.

Detect flaky tests by scanning recent AzDo CI builds for test failures recurring across multiple unrelated PRs. Use when investigating intermittent failures, CI instability, deciding which tests to quarantine, or checking if RunTestCasesInSequence no-ops are causing parallel-safety issues.

Create custom agent capabilities when discovering novel tools, receiving task-agnostic tips from reviewers, or after researching specialized workflows not covered in existing instructions. Teaches structure, YAML optimization for LLM discoverability, and token efficiency.

Use when a code/test/comment diff is called bloated, slop, LLM slop, bullshit, WTF, crap, rubbish, embarrassing, overengineered, adhoc, or "not paid by LOC"; or when symptoms include bloated comments, superfluous planning .md / .tools / one-time setup / phase-or-sprint tags, huge-file growth instead of new-file extraction, 5 copy-pasted tests that should be 1 parametrized test, duplicated test setup, reinvented helpers, near-duplicate logic across files, low reuse, 4+ new module-level helpers for one bugfix, fresh whole-AST/IR/syntax-tree walkers, or 150+ added LOC for one bugfix. Also use proactively before opening a PR whose diff smells like any of the above.

Triage a build / compile / restore / WarnAsError failure from its MSBuild binary log. Fetches the binlog (a local build's, or a failed dotnet/fsharp Azure DevOps PR build's published artifact) and analyzes it live via the `binlog-mcp` MCP server — structured errors, root-cause diagnosis, and an MSBuild perf X-ray. NOT for test failures or CheckCodeFormatting: a build binlog has no errors there.

Implementation details for EF Core SaveChanges and the update pipeline. Use when changing CommandBatchPreparer, UpdateSqlGenerator, ModificationCommand, or related classes.

Use this skill to triage an incoming issue on the EF Core repo (bug report or feature request). Sets the issue type (bug/feature), assigns EF area labels, attempts to arrive at a minimal repro reproducing the bug, checks whether it represents a regression, finds possible duplicates, etc.

Implementation details for the EF Core dotnet-ef CLI and tooling. Use when changing dotnet-ef commands, the ef wrapper, EFCore.Tools (PMC), or EFCore.Tasks MSBuild integration.

Implementation details for EF Core test infrastructure. Use when changing test fixtures, SQL baseline assertions, test helpers, the test class hierarchy, or when adding new tests.

Implementation details for the Microsoft.Data.Sqlite ADO.NET provider. Use when changing files under `src/Microsoft.Data.Sqlite.Core/`.

Create EF Core PRs targeting servicing release branches (release/*). Use when working on a PR that targets a release branch, backporting a fix from main, or when the user mentions servicing, patch, or release branch.

Implementation details for EF Core scaffolding (reverse engineering). Use when changing ef dbcontext scaffold pipeline implementation, database schema reading, CSharpModelGenerator, or related classes.

Run ApiChief in the EF Core repo to emit baselines, summaries, deltas, review files, or breaking-change checks. Use when refreshing `*.baseline.json`, preparing API review artifacts, or validating API changes.

Implementation details for EF Core LINQ query translation, SQL generation, and bulk operations (ExecuteUpdate/ExecuteDelete). Use when changing expression visitors, SqlExpressions, QuerySqlGenerator, ShaperProcessingExpressionVisitor, UpdateExpression, DeleteExpression, or related classes.

Implementation details for EF Core model building. Use when changing ConventionSet, ModelBuilder, IConvention implementations, ModelRuntimeInitializer, RuntimeModel, or related classes.

Implementation details for EF Core migrations. Use when changing MigrationsSqlGenerator, model diffing, migration operations, HistoryRepository, the Migrator or related classes.

Create new Agent Skills for GitHub Copilot. Use when asked to create, scaffold, or add a skill. Generates SKILL.md with frontmatter, directory structure, and optional resources.

Create VS Code file-based instructions (.instructions.md files). Use when asked to create, scaffold, or add file-based instructions for Copilot. Generates .instructions.md with YAML frontmatter and background knowledge content.

Create GitHub Actions workflows for CI, automation, or PR management. Use when asked to create, scaffold, or add a GitHub Actions workflow (.yml file under .github/workflows/).