Add the model matching engine and make capabilities a flags enum

app/Tests/Models/CapabilityTests.cs

@@ -0,0 +1,68 @@
+using AIStudio.Models;
+using AIStudio.Provider;
+
+namespace AIStudio.Tests.Models;
+
+/// <summary>
+/// Checks the two things about the capability enum which the rest of the app relies on.
+/// </summary>
+/// <remarks>
+/// Capabilities became a set carried in one value, which only works while each member owns a bit of
+/// its own. And the names are what an override written years ago addresses, so a member which is no
+/// longer handed out still has to answer to its name.
+/// </remarks>
+[TestFixture]
+public sealed class CapabilityTests
+{
+    /// <summary>
+    /// Every capability the app has ever written into a configuration.
+    /// </summary>
+    /// <remarks>
+    /// Deliberately spelled out instead of read from the enum: a test which asks the enum about
+    /// itself would agree with any change made to it, including a member being deleted. Removing
+    /// one of these names silently drops the override an organization wrote for it.
+    /// </remarks>
+    private static readonly string[] NAMES_THAT_MUST_KEEP_WORKING =
+    [
+        "NONE", "UNKNOWN",
+        "TEXT_INPUT", "AUDIO_INPUT", "SINGLE_IMAGE_INPUT", "MULTIPLE_IMAGE_INPUT", "SPEECH_INPUT", "VIDEO_INPUT",
+        "TEXT_OUTPUT", "AUDIO_OUTPUT", "IMAGE_OUTPUT", "SPEECH_OUTPUT", "VIDEO_OUTPUT",
+        "OPTIONAL_REASONING", "ALWAYS_REASONING", "REASONING_BY_DEFAULT",
+        "EMBEDDING", "REALTIME", "FUNCTION_CALLING", "WEB_SEARCH",
+        "CHAT_COMPLETION_API", "RESPONSES_API",
+    ];
+
+    [Test]
+    public void EveryCapabilityOwnsOneBitOfItsOwn()
+    {
+        var bits = new Dictionary<ulong, Capability>();
+
+        Assert.Multiple(() =>
+        {
+            foreach (var capability in Enum.GetValues<Capability>())
+            {
+                if (capability is Capability.NONE)
+                    continue;
+
+                var value = (ulong) capability;
+                Assert.That(ulong.IsPow2(value), Is.True, $"{capability} is not a single bit, so it cannot be part of a set.");
+
+                if (bits.TryGetValue(value, out var other))
+                    Assert.Fail($"{capability} and {other} share a bit, so the app cannot tell them apart.");
+
+                bits[value] = capability;
+            }
+        });
+    }
+
+    [Test]
+    public void NoCapabilityLostItsName() => Assert.That(Enum.GetNames<Capability>(), Is.SupersetOf(NAMES_THAT_MUST_KEEP_WORKING));
+
+    [Test]
+    public void TheReasoningVocabularyIsExactlyTheThreeReasoningMembers()
+    {
+        const Capability THE_THREE = Capability.OPTIONAL_REASONING | Capability.ALWAYS_REASONING | Capability.REASONING_BY_DEFAULT;
+
+        Assert.That(ModelProfile.REASONING_VOCABULARY, Is.EqualTo(THE_THREE));
+    }
+}