Add evidence-based SqlClient code review skill

.github/copilot-instructions.md

@@ -11,9 +11,9 @@
 
 ## 📚 Project Overview
 This project is a .NET data provider for SQL Server, enabling .NET applications to interact with SQL Server databases. It supports various features like connection pooling, transaction management, and asynchronous operations.
-The project builds from a **single unified project** at `src/Microsoft.Data.SqlClient/src/Microsoft.Data.SqlClient.csproj`. It targets `net8.0` and `net9.0` on all supported hosts, and adds `net462` only when building on Windows. The legacy `netfx/` and `netcore/` directories are being phased out — only their `ref/` folders (which define the public API surface) remain active.
+The project builds from a **single unified project** at `src/Microsoft.Data.SqlClient/src/Microsoft.Data.SqlClient.csproj`. Its framework and platform selection is defined by the project and imported build files. Public API declarations are unified under `src/Microsoft.Data.SqlClient/ref/`; the legacy `netfx/` and `netcore/` directories are no longer used.
 The project includes:
-- **Public APIs**: Defined in `netcore/ref/` and `netfx/ref/` directories.
+- **Public APIs**: Defined by `src/Microsoft.Data.SqlClient/ref/Microsoft.Data.SqlClient.csproj` and the reference source files beside it.
 - **Implementations**: All source code in `src/Microsoft.Data.SqlClient/src/`.
 - **Tests**: Located in the `tests/` directory, covering unit and integration tests.
   - **Unit Tests**: Located in `src/Microsoft.Data.SqlClient/tests/UnitTests/`.
@@ -137,7 +137,7 @@ When a new issue is created, follow these steps:
 
 ## 🧠 Contextual Awareness
 - All source code is in `src/Microsoft.Data.SqlClient/src/`. Do NOT add code to legacy `netfx/src/` or `netcore/src/` directories.
-- Only `ref/` folders in `netcore/ref/` and `netfx/ref/` remain active for defining the public API surface.
+- Public API changes must update the unified `src/Microsoft.Data.SqlClient/ref/` sources for each affected target framework.
 - Check for platform-specific differences using file suffixes (`.netfx.cs`, `.netcore.cs`, `.windows.cs`, `.unix.cs`) and conditional compilation (`#if NETFRAMEWORK`, `#if NET`, `#if _WINDOWS`, `#if _UNIX`).
 - Respect API compatibility rules across .NET versions
 - Do not introduce breaking changes without proper justification and documentation

.github/instructions/api-design.instructions.md

@@ -15,10 +15,10 @@ Microsoft.Data.SqlClient follows strict API design guidelines to ensure:
 ### Structure
 ```
 src/Microsoft.Data.SqlClient/
-├── netcore/ref/          # .NET Core/.NET public APIs
-│   └── Microsoft.Data.SqlClient.cs
-└── netfx/ref/            # .NET Framework public APIs
-    └── Microsoft.Data.SqlClient.cs
+└── ref/                              # Unified public API declarations
+    ├── Microsoft.Data.SqlClient.csproj
+    ├── Microsoft.Data.SqlClient.cs
+    └── Microsoft.Data.SqlTypes.cs     # Other namespace-specific files alongside
 ```
 
 ### API Surface
@@ -32,8 +32,8 @@ The reference assemblies do **not** use C# nullable context (`#nullable enable`)
 
 ### Updating Public APIs
 When adding or modifying public APIs:
-1. Update reference assembly in BOTH `netcore/ref/` and `netfx/ref/`
-2. Ensure signatures match across platforms
+1. Update the corresponding sources under `src/Microsoft.Data.SqlClient/ref/`
+2. Ensure signatures match the implementation for each affected framework, including conditional declarations
 3. Add XML documentation
 4. Consider backward compatibility
 5. Do not use nullable annotations (`?`) in ref assemblies (see above)

.github/instructions/architecture.instructions.md

@@ -11,11 +11,8 @@ This repository contains the official Microsoft ADO.NET data provider for SQL Se
 src/
 ├── Microsoft.Data.SqlClient/
 │   ├── add-ons/                    # Azure Key Vault provider
-│   ├── netcore/                    # ⚠️ LEGACY - being phased out
-│   │   └── ref/                    # Reference assemblies for .NET Core/.NET
-│   ├── netfx/                      # ⚠️ LEGACY - being phased out
-│   │   └── ref/                    # Reference assemblies for .NET Framework
-│   ├── ref/                        # Shared reference assembly files
+│   ├── ref/                        # Unified public API declarations
+│   │   └── Microsoft.Data.SqlClient.csproj # Multi-target reference project
 │   ├── src/                        # ✅ PRIMARY - Unified source for all platforms
 │   │   ├── Microsoft.Data.SqlClient.csproj  # Multi-target project file
 │   │   ├── Interop/               # P/Invoke and native interop
@@ -34,19 +31,13 @@ src/
 ## Unified Project Model
 
 ### Architecture Goal
-The driver is transitioning away from separate `netfx/` and `netcore/` project files toward a **single unified project** at `src/Microsoft.Data.SqlClient/src/Microsoft.Data.SqlClient.csproj`. This project targets the modern .NET TFMs on every host and conditionally adds .NET Framework on Windows:
-
-```xml
-<TargetFrameworks>net8.0;net9.0</TargetFrameworks>
-<TargetFrameworks Condition="'$(NormalizedTargetOs)' == 'windows_nt'">$(TargetFrameworks);net462</TargetFrameworks>
-```
+The driver implementation is built from `src/Microsoft.Data.SqlClient/src/Microsoft.Data.SqlClient.csproj`; its public API declarations are built from `src/Microsoft.Data.SqlClient/ref/Microsoft.Data.SqlClient.csproj`. Check those projects and their imported build files for framework and platform selection.
 
 **All new code MUST go into `src/Microsoft.Data.SqlClient/src/`**. Do NOT add files to the legacy `netcore/src/` or `netfx/src/` directories.
 
 ### Legacy Folders
-The `netcore/` and `netfx/` directories are legacy artifacts from the old dual-project model:
-- `netcore/src/` and `netfx/src/` — **DEPRECATED**. These contain legacy project files that are being phased out. Do not add new code here.
-- `netcore/ref/` and `netfx/ref/` — **STILL ACTIVE**. Reference assemblies remain in these directories and define the public API surface for each target framework.
+The former `netcore/` and `netfx/` source and reference directories are no longer
+used. Do not recreate them; use the unified `src/` and `ref/` directories.
 
 ### OS Targeting with `TargetOs`
 The unified project uses a `TargetOs` build property to handle OS-specific compilation:
@@ -97,12 +88,12 @@ The unified project uses conditional `ItemGroup` elements for dependencies:
 - **Shared**: `Azure.Core`, `Azure.Identity`, `Microsoft.Bcl.Cryptography`, `Microsoft.Extensions.Caching.Memory`, `Microsoft.IdentityModel.*`, `System.Security.Cryptography.Pkcs`
 
 ### Reference Assemblies
-The `ref/` directories define the public API surface:
-- `netcore/ref/` — Public APIs for .NET Core/.NET (includes `Microsoft.Data.SqlClient.cs`, `Microsoft.Data.SqlClient.Manual.cs`)
-- `netfx/ref/` — Public APIs for .NET Framework (includes `Microsoft.Data.SqlClient.cs`)
-- `ref/` — Shared reference assembly files (e.g., `Microsoft.Data.SqlClient.Batch.cs`, `Microsoft.Data.SqlClient.Batch.NetCoreApp.cs`)
+`src/Microsoft.Data.SqlClient/ref/Microsoft.Data.SqlClient.csproj` builds the unified
+reference sources for `net462`, `net8.0`, `net9.0`, and `netstandard2.0`. Declarations
+are grouped by namespace, with conditional compilation for framework differences.
 
-**IMPORTANT**: Any public API changes MUST update the corresponding reference assembly in the appropriate `ref/` directory.
+**IMPORTANT**: Public API changes MUST update the corresponding files under
+`src/Microsoft.Data.SqlClient/ref/` for every affected target framework.
 
 ### Build Output
 Build artifacts are organized by reference mode, configuration, OS, and framework:

.github/prompts/fix-bug.prompt.md

@@ -37,7 +37,7 @@ Follow this workflow step-by-step:
 - Ensure the fix compiles for ALL target frameworks: `net462`, `net8.0`, `net9.0`.
 - If the fix requires platform-specific code, use the appropriate conditional compilation directives.
 - Do NOT introduce breaking changes to public APIs.
-- If a public API must change, update the reference assemblies in `netcore/ref/` and `netfx/ref/`.
+- If a public API must change, update the corresponding sources under `src/Microsoft.Data.SqlClient/ref/`, including conditional declarations for each affected framework.
 
 ## 5. Validate
 - Verify the failing test now passes with the fix applied.

.github/prompts/implement-feature.prompt.md

@@ -27,10 +27,8 @@ Before writing code, produce a brief implementation plan covering:
 - **Documentation plan** — XML docs, samples, release notes entries.
 
 ## 3. Update Reference Assemblies (if public API changes)
-- If adding new public APIs, update reference assemblies FIRST:
-  - `netcore/ref/Microsoft.Data.SqlClient.cs` and/or `Microsoft.Data.SqlClient.Manual.cs` for .NET Core/.NET APIs
-  - `netfx/ref/Microsoft.Data.SqlClient.cs` for .NET Framework APIs
-  - `ref/` shared files if the API applies to batch or cross-framework features
+- If adding or changing public APIs, update the corresponding namespace-specific sources under `src/Microsoft.Data.SqlClient/ref/` FIRST.
+- Ensure signatures match the implementation for each affected framework, including conditional declarations.
 - Include only the method/property signatures with no implementation.
 - Add XML documentation comments on all public members.