Dotnet standard 2.0 compat

Skill stevenfackley/opencode-amplifier/.opencode/skills/dotnet-standard-2.0-compat

Contract-governed OpenCode config that amplifies constrained LLMs (Sonnet 4.5, GPT-5.1, cheap corp models) into near-frontier coding agents: multi-agent pipeline with per-agent models, independent test-gen + locked tests, golden-pattern corpus, cross-model review, and an eval harness.

Install

npx -y skills add stevenfackley/opencode-amplifier --skill dotnet-standard-2.0-compat

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

One thing to look at

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What its author says it does

Copied from the file, not written here

Use when writing or contributing to .NET code that must target .NET Standard 2.0 — often multi-targeted with .NET 10 in shared libraries. Lists what is NOT available on the ns2.0 floor so you don't put .NET 10-only APIs in code that must compile for both.

SKILL.md

2.5 KB, as published. Nobody here has run it

.NET Standard 2.0 Compatibility Guardrail

Shared libraries commonly multi-target netstandard2.0;net10.0 — ns2.0 for reach (.NET Framework 4.6.1+, Xamarin, Unity, older runtimes), net10.0 for modern features. Code in the shared (non-#if'd) path must compile for the ns2.0 floor. A constrained model will reach for net10-only APIs and break the ns2.0 build.

Detect first

Read the .csproj. <TargetFrameworks>netstandard2.0;net10.0</TargetFrameworks> = dual floor. Anything outside an #if NET block must be ns2.0-safe.

NOT available on ns2.0 (net-only) — don't use in shared code

DateOnly / TimeOnly (net6+), Half (net5+), Int128/UInt128, generic math + static abstract interface members (net7+).
Default interface methods (ns2.1 / .NET Core 3+ runtime feature).
required members (C# 11) and record/init accessors — compile on ns2.0 ONLY with polyfill attributes (IsExternalInit, RequiredMemberAttribute, CompilerFeatureRequiredAttribute).
[CallerArgumentExpression] and some nullable attributes — need polyfills.

In-box on net, but NEEDS A NuGet PACKAGE on ns2.0

System.Text.Json → add the System.Text.Json package.
Span<T> / Memory<T> → System.Memory.
IAsyncEnumerable<T> / IAsyncDisposable / await foreach → Microsoft.Bcl.AsyncInterfaces.
ValueTask extras → System.Threading.Tasks.Extensions.

Safe on ns2.0

async/await, Task<T>, LINQ, generics, most System.* collections/strings/IO, HttpClient.
Compiler-level C# features: nullable reference type ANNOTATIONS (<Nullable>enable</Nullable> + LangVersion), pattern matching, tuples, local functions, file-scoped namespaces.

Patterns that work

Polyfills: add PolySharp (source-only) or a tiny IsExternalInit/RequiredMember shim so you can use record/init/required while still targeting ns2.0.
Gate modern code: #if NET8_0_OR_GREATER … #else … #endif for net-only fast paths.
Turn on <Nullable>enable</Nullable> even on the ns2.0 floor — annotations cost nothing and catch bugs.

Verify, don't guess

Unsure if an API exists on ns2.0? Check the API reference at learn.microsoft.com/dotnet/api with the version selector set to netstandard-2.0.