Preserve typed nested unions in SDK codegen

.github/workflows/update-copilot-dependency.yml

@@ -91,7 +91,7 @@ jobs:
         env:
           VERSION: ${{ inputs.version }}
         working-directory: ./java/scripts/codegen
-        run: npm install "@github/copilot@$VERSION"
+        run: npm install --save-exact "@github/copilot@$VERSION"
 
       - name: Update Java POM CLI version property
         env:

dotnet/test/Unit/DiscriminatedUnionConformanceTests.cs

@@ -0,0 +1,173 @@
+using System.Text.Json;
+using System.Text.Json.Serialization.Metadata;
+using GitHub.Copilot.Rpc;
+using Xunit;
+
+#pragma warning disable GHCP001 // The catalogue search schema is experimental.
+
+namespace GitHub.Copilot.Test.Unit;
+
+public class DiscriminatedUnionConformanceTests
+{
+    private const string OpaqueMcpHandle = "opaque:mcp/01-do-not-parse";
+    private const string OpaqueSkillHandle = "opaque:skill/02-do-not-parse";
+    private static readonly JsonSerializerOptions SerializerOptions = new(JsonSerializerDefaults.Web)
+    {
+        TypeInfoResolver = new DefaultJsonTypeInfoResolver(),
+    };
+
+    [Fact]
+    public void CatalogSearchResult_PreservesTypedCandidatesAndOpaqueHandles()
+    {
+        const string json = """
+            {
+              "kind": "succeeded",
+              "rawCard": { "secret": "must-not-survive" },
+              "searchId": "search-01",
+              "candidates": [
+                {
+                  "kind": "mcp-server",
+                  "handle": "opaque:mcp/01-do-not-parse",
+                  "handleExpiresAt": "2026-09-02T12:00:00Z",
+                  "mediaType": "application/mcp-server-card+json",
+                  "installability": "installable",
+                  "displayName": "Example MCP",
+                  "rawCard": { "secret": "must-not-survive" },
+                  "source": { "kind": "url", "url": "https://catalog.example/mcp.json", "rawCard": { "secret": "must-not-survive" } },
+                  "provenance": {
+                    "authority": "catalog.example",
+                    "observedAt": "2026-09-02T11:00:00Z",
+                    "mediaType": "application/mcp-server-card+json"
+                  }
+                },
+                {
+                  "kind": "ai-skill",
+                  "handle": "opaque:skill/02-do-not-parse",
+                  "handleExpiresAt": "2026-09-02T12:00:00Z",
+                  "mediaType": "application/ai-skill",
+                  "installability": "not-installable-kind",
+                  "displayName": "Example skill",
+                  "rawCard": { "secret": "must-not-survive" },
+                  "source": { "kind": "embedded", "rawCard": { "secret": "must-not-survive" } },
+                  "provenance": {
+                    "authority": "catalog.example",
+                    "observedAt": "2026-09-02T11:00:00Z",
+                    "mediaType": "application/ai-skill"
+                  }
+                }
+              ],
+              "truncated": false,
+              "negotiated": {
+                "runtimeProtocolVersion": 1,
+                "grantedCapabilities": ["mcp-server-card", "ai-skill-discovery"]
+              }
+            }
+            """;
+
+        var result = Assert.IsType<CatalogSearchResultSucceeded>(
+            JsonSerializer.Deserialize<CatalogSearchResult>(json, SerializerOptions));
+        var mcp = Assert.IsType<CatalogCandidateMcpServer>(result.Candidates[0]);
+        var skill = Assert.IsType<CatalogCandidateAiSkill>(result.Candidates[1]);
+        Assert.Equal(OpaqueMcpHandle, mcp.Handle);
+        Assert.Equal(OpaqueSkillHandle, skill.Handle);
+        Assert.IsType<CatalogCandidateSourceUrl>(mcp.Source);
+        Assert.IsType<CatalogCandidateSourceEmbedded>(skill.Source);
+
+        using var encoded = JsonDocument.Parse(JsonSerializer.Serialize<CatalogSearchResult>(
+            result, SerializerOptions));
+        Assert.False(encoded.RootElement.TryGetProperty("rawCard", out _));
+        foreach (var candidate in encoded.RootElement.GetProperty("candidates").EnumerateArray())
+        {
+            Assert.False(candidate.TryGetProperty("card", out _));
+            Assert.False(candidate.TryGetProperty("cardData", out _));
+            Assert.False(candidate.TryGetProperty("rawCard", out _));
+            Assert.False(candidate.GetProperty("source").TryGetProperty("rawCard", out _));
+        }
+    }
+
+    [Fact]
+    public void CatalogSearchResult_PreservesRefusalsAndFailures()
+    {
+        var authentication = JsonSerializer.Deserialize<CatalogSearchResult>(
+            """{"kind":"authentication-required","reason":"no-credential","message":"Sign in is required."}""",
+            SerializerOptions);
+        Assert.IsType<CatalogSearchResultAuthenticationRequired>(authentication);
+
+        var network = Assert.IsType<CatalogSearchResultNetworkFailure>(
+            JsonSerializer.Deserialize<CatalogSearchResult>(
+                """{"kind":"network-failure","reason":"timeout","retryAfterSeconds":30,"message":"The catalogue timed out."}""",
+                SerializerOptions));
+        Assert.Equal(30, network.RetryAfterSeconds);
+    }
+
+    [Fact]
+    public void ClosedUnions_RejectUnknownAndMissingDiscriminators()
+    {
+        string[] invalidPayloads =
+        [
+            """{"kind":"future-result","rawCard":{"secret":"must-not-survive"}}""",
+            """{"rawCard":{"secret":"must-not-survive"}}""",
+            """
+            {
+              "kind":"succeeded",
+              "searchId":"search-invalid",
+              "candidates":[{"kind":"future-candidate","rawCard":{"secret":"must-not-survive"}}],
+              "truncated":false,
+              "negotiated":{"runtimeProtocolVersion":1,"grantedCapabilities":[]}
+            }
+            """,
+            """
+            {
+              "kind":"succeeded",
+              "searchId":"search-invalid",
+              "candidates":[{"rawCard":{"secret":"must-not-survive"}}],
+              "truncated":false,
+              "negotiated":{"runtimeProtocolVersion":1,"grantedCapabilities":[]}
+            }
+            """,
+            """
+            {
+              "kind":"succeeded",
+              "searchId":"search-invalid",
+              "candidates":[{
+                "kind":"mcp-server",
+                "handle":"opaque:mcp/01-do-not-parse",
+                "handleExpiresAt":"2026-09-02T12:00:00Z",
+                "mediaType":"application/mcp-server-card+json",
+                "installability":"installable",
+                "displayName":"Example MCP",
+                "source":{"kind":"future-source","rawCard":{"secret":"must-not-survive"}},
+                "provenance":{"authority":"catalog.example","observedAt":"2026-09-02T11:00:00Z","mediaType":"application/mcp-server-card+json"}
+              }],
+              "truncated":false,
+              "negotiated":{"runtimeProtocolVersion":1,"grantedCapabilities":[]}
+            }
+            """,
+            """
+            {
+              "kind":"succeeded",
+              "searchId":"search-invalid",
+              "candidates":[{
+                "kind":"mcp-server",
+                "handle":"opaque:mcp/01-do-not-parse",
+                "handleExpiresAt":"2026-09-02T12:00:00Z",
+                "mediaType":"application/mcp-server-card+json",
+                "installability":"installable",
+                "displayName":"Example MCP",
+                "source":{"rawCard":{"secret":"must-not-survive"}},
+                "provenance":{"authority":"catalog.example","observedAt":"2026-09-02T11:00:00Z","mediaType":"application/mcp-server-card+json"}
+              }],
+              "truncated":false,
+              "negotiated":{"runtimeProtocolVersion":1,"grantedCapabilities":[]}
+            }
+            """,
+        ];
+
+        foreach (string json in invalidPayloads)
+        {
+            Exception? exception = Record.Exception(() =>
+                JsonSerializer.Deserialize<CatalogSearchResult>(json, SerializerOptions));
+            Assert.True(exception is JsonException, $"Invalid closed union payload was accepted: {json}");
+        }
+    }
+}