runtime

Add a new API to the JIT-VM (aka JIT-EE) interface in the codebase.

Create prototype-backed API proposals for dotnet/runtime. Use when asked to draft an API proposal, write an api-suggestion issue, refine a vague API idea into a complete proposal, or improve a proposal marked api-needs-work. Covers the full pipeline from research through prototyping, ref source generation, and publishing. DO NOT USE FOR bug fixes, code review, performance benchmarking, or internal API changes that don't affect public surface area.

Review code changes in dotnet/runtime for correctness, performance, and consistency with project conventions. Use when reviewing PRs or code changes.

Generate and run ad hoc performance benchmarks to validate code changes. Use this when asked to benchmark, profile, or validate the performance impact of a code change in dotnet/runtime.

Analyze a dotnet/runtime PR's CI failures, skip failures already known to Build Analysis, find matching Known Build Errors, and create or draft new KBEs for the remaining failures. Supports dry-run output to local markdown files instead of creating GitHub issues.

Triage Fuzzlyn CI runs.

Generate breaking change documentation for merged dotnet/runtime PRs. USE FOR: creating breaking change docs, "document this breaking change", "write breaking change issue for PR #NNNNN", processing PRs labeled needs-breaking-change-doc-created. DO NOT USE FOR: general code review (use code-review skill), bug fixes, API proposals (use api-proposal skill).

Domain knowledge for triaging and fixing .NET failures on Apple mobile (iOS, tvOS, MacCatalyst) and Android. Use when runtime-extra-platforms or mobile CI is failing, when investigating iOS, tvOS, MacCatalyst, iossimulator, tvossimulator, or Android build/test failures, or when a change touches mobile pipeline YAML, AppleAppBuilder/AndroidAppBuilder, code signing, provisioning, simulator/emulator startup, platform conditionals, or NativeAOT-on-mobile behavior. Covers failure triage (infrastructure vs code), CI pipeline structure, platform-specific code paths, and NativeAOT compilation on mobile.

Update OS version references in Helix queue definitions to add new versions, replace EOL versions, or audit coverage against the supported-os matrix. USE FOR: adding new OS versions to Helix queues, replacing EOL OS versions, upgrading "oldest" or "latest" version references, auditing Helix coverage. DO NOT USE FOR: creating new container images (that's dotnet-buildtools-prereqs-docker), updating supported-os.json (that's the update-supported-os skill in dotnet/core).

Guidance for writing and modifying System.Net networking code in dotnet/runtime. Covers resource lifecycle, connection pooling, cross-platform interop, protocol compliance, async patterns, and security posture. For full code review, delegates to the @system-net-review agent. Trigger words: system.net, networking, http client, sockets, ssl, tls, quic, http2, http3, socketshttphandler, sslstream, connection pool.

Guidance for writing and modifying Microsoft.Extensions.* and System.IO.Compression code in dotnet/runtime. Covers DI lifetime management, configuration binding, options validation, logging provider patterns, caching semantics, compression format compliance, and host lifecycle. For full code review, delegates to the @extensions-reviewer agent. Trigger words: Microsoft.Extensions, IServiceCollection, IConfiguration, ILogger, IHost, IMemoryCache, IOptions, ZipArchive, HttpClientFactory, IFileProvider, IChangeToken.

Extract a standalone JIT regression test case from a given GitHub issue and save it under the JitBlue folder. USE FOR: creating JIT regression tests, extracting repro code from dotnet/runtime issues, "write a test for this JIT bug", "create a regression test for issue #NNNNN", converting issue repro to xunit test. DO NOT USE FOR: non-JIT tests (use standard test patterns), debugging JIT issues without a known repro, performance benchmarks (use performance-benchmark skill).