src/MyApp.Api/Services/OrderService.cs(42,17): error CS0246: The type or namespace name 'OrderDto' could not be found (are you missing a using directive or an assembly reference?)
src/MyApp.Api/Models/User.cs(15,9): warning CS8618: Non-nullable property 'Name' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

error MSB4019: The imported project "C:\Program Files\dotnet\sdk\9.0.100\Microsoft\VisualStudio\v17.0\WebApplications\Microsoft.WebApplication.targets" was not found. Confirm that the expression in the Import declaration "..." is correct.
error MSB3644: The reference assemblies for .NETFramework,Version=v4.8 were not found. You might need to install the developer pack for this framework version.

error NU1101: Unable to find package Newtonsoft.Json.Extensions. No packages exist with this id in source(s): nuget.org
warning NU1603: Microsoft.EntityFrameworkCore 9.0.0 depends on Microsoft.Extensions.Caching.Memory (>= 9.0.0) but version Microsoft.Extensions.Caching.Memory 8.0.1 was resolved. Approve the package to suppress this warning.
error NU1605: Detected package downgrade: Microsoft.Extensions.Logging from 9.0.0 to 8.0.1. Reference the package directly from the project to select a different version.

src/MyApp.Api/Program.cs(1,1): warning IDE0005: Using directive is unnecessary.
src/MyApp.Api/Models/Order.cs(8,12): warning IDE0044: Make field readonly
src/MyApp.Api/Services/Report.cs(22,5): warning IDE0058: Expression value is never used

src/MyApp.Api/Services/CacheService.cs(34,9): warning CA1848: Use the LoggerMessage delegates instead of calling 'LoggerExtensions.LogInformation(ILogger, string?, params object?[])'. Using LoggerMessage delegates provides better performance.
src/MyApp.Api/Controllers/UserController.cs(12,5): warning CA2007: Consider calling ConfigureAwait on the awaited task
src/MyApp.Api/Crypto/HashService.cs(8,9): warning CA5351: Do Not Use Broken Cryptographic Algorithms (MD5)

  Determining projects to restore...
  Writing assets file to disk. Path: /src/MyApp.Api/obj/project.assets.json
/src/MyApp.Api/MyApp.Api.csproj : error NU1101: Unable to find package MyCompany.Shared.Models. No packages exist with this id in source(s): nuget.org
  Failed to restore /src/MyApp.Api/MyApp.Api.csproj (in 2.14 sec).

undefined

```xml
<!-- Add private feed to nuget.config -->
<configuration>
  <packageSources>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
    <add key="MyCompany" value="https://pkgs.dev.azure.com/myorg/_packaging/myfeed/nuget/v3/index.json" />
  </packageSources>
  <packageSourceMapping>
    <packageSource key="nuget.org">
      <package pattern="*" />
    </packageSource>
    <packageSource key="MyCompany">
      <package pattern="MyCompany.*" />
    </packageSource>
  </packageSourceMapping>
</configuration>

error NU1107: Version conflict detected for Microsoft.Extensions.DependencyInjection.Abstractions.
  MyApp.Api -> Microsoft.EntityFrameworkCore 9.0.0 -> Microsoft.Extensions.DependencyInjection.Abstractions (>= 9.0.0)
  MyApp.Api -> Microsoft.Extensions.Hosting 8.0.1 -> Microsoft.Extensions.DependencyInjection.Abstractions (>= 8.0.1)

<!-- Upgrade the older top-level package to match -->
<PackageReference Include="Microsoft.Extensions.Hosting" Version="9.0.0" />
<!-- Or add a direct reference to force a specific version -->
<PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="9.0.0" />

  Retrying 'FindPackagesByIdAsyncCore' for source 'https://pkgs.dev.azure.com/myorg/_packaging/myfeed/nuget/v3/index.json'.
  Response status code does not indicate success: 401 (Unauthorized).
error NU1301: Unable to load the service index for source https://pkgs.dev.azure.com/myorg/_packaging/myfeed/nuget/v3/index.json.

undefined

---

src/MyApp.Api/Controllers/OrdersController.cs(27,5): warning CA2007: Consider calling ConfigureAwait on the awaited task [/src/MyApp.Api/MyApp.Api.csproj]
src/MyApp.Api/Services/OrderService.cs(15,16): warning CA1062: In externally visible method 'OrderService.Process(string)', validate parameter 'input' is non-null before using it [/src/MyApp.Api/MyApp.Api.csproj]
src/MyApp.Api/Models/UserDto.cs(8,12): warning IDE0032: Use auto-implemented property [/src/MyApp.Api/MyApp.Api.csproj]

undefined

undefined

// ACCEPTABLE: documented justification
[SuppressMessage("Reliability", "CA2007:ConfigureAwait",
    Justification = "ASP.NET Core has no SynchronizationContext")]
public async Task<Order> GetOrderAsync(int id, CancellationToken ct)
{
    return await _repo.GetByIdAsync(id, ct);
}

// NOT ACCEPTABLE: no justification, hides a real issue
#pragma warning disable CA1062
public void Process(string input) { }  // input could be null
#pragma warning restore CA1062

  MyApp.Shared -> /src/MyApp.Shared/bin/Debug/net8.0/MyApp.Shared.dll
src/MyApp.Shared/Services/FeatureService.cs(18,30): error CS1061: 'FrozenDictionary<string, int>' does not contain a definition for 'GetAlternateLookup' [/src/MyApp.Shared/MyApp.Shared.csproj -> net8.0]
  MyApp.Shared -> /src/MyApp.Shared/bin/Debug/net9.0/MyApp.Shared.dll
Build succeeded for net9.0.

Build FAILED for net8.0.

// Use preprocessor directives for TFM-specific code
#if NET9_0_OR_GREATER
    var lookup = frozenDict.GetAlternateLookup<ReadOnlySpan<char>>();
    return lookup.TryGetValue(key, out var value) ? value : default;
#else
    return frozenDict.TryGetValue(key.ToString(), out var value) ? value : default;
#endif

<!-- Or constrain the feature to specific TFMs in the project file -->
<PropertyGroup>
  <TargetFrameworks>net8.0;net9.0</TargetFrameworks>
</PropertyGroup>

<!-- TFM-conditional package reference -->
<ItemGroup Condition="'$(TargetFramework)' == 'net8.0'">
  <PackageReference Include="System.Collections.Immutable" Version="8.0.0" />
</ItemGroup>

Local:  dotnet --version -> 9.0.200
CI:     dotnet --version -> 9.0.100

Build error in CI:
error CS8652: The feature 'field keyword' is currently in Preview and *unsupported*.

// global.json -- pin SDK version for consistent builds
{
  "sdk": {
    "version": "9.0.200",
    "rollForward": "latestPatch"
  }
}

CI error:
error NETSDK1147: To build this project, the following workloads must be installed: maui-android

undefined

undefined

Local restore succeeds (using cached packages).
CI error:
error NU1101: Unable to find package MyCompany.Internal.Lib.

Local (Windows):  Build succeeds
CI (Linux):       error MSB4018: The "ResolveAssemblyReference" task failed.
                  Could not find file '/src/MyApp/../Shared/MyLib.dll'

Local: Build succeeds with 3 warnings
CI:    error CS8602: Dereference of a possibly null reference.
       (because CI sets TreatWarningsAsErrors=true)

<!-- RED FLAG: blanket NoWarn in .csproj -->
<PropertyGroup>
  <NoWarn>CS8600;CS8602;CS8603;CS8604;IL2026;IL2046</NoWarn>
</PropertyGroup>

// RED FLAG: pragma disable without justification
#pragma warning disable CS8618
public class UserModel
{
    public string Name { get; set; } // non-nullable not initialized
    public string Email { get; set; }
}
#pragma warning restore CS8618

// RED FLAG: suppressing security analyzer with no explanation
[SuppressMessage("Security", "CA5351")]
public byte[] HashData(byte[] input)
{
    using var md5 = MD5.Create(); // insecure algorithm
    return md5.ComputeHash(input);
}

undefined

**Fix:** Replace insecure algorithms (MD5 -> SHA-256). If suppression is unavoidable (e.g., interop with a system requiring MD5), add a `Justification` string explaining the constraint.

---