Address review feedback on cacheScope converter and conformance gate

- CacheScopeConverter.Read now consumes non-string tokens with reader.Skip()
  before returning null. Previously an object or array value for cacheScope
  left the reader mispositioned and threw "read too much or not enough",
  breaking deserialization of the whole result. Added object and array cases
  to the tolerant-deserialization test.
- GetInstalledConformanceVersion no longer calls EnsureNpmDependenciesInstalled.
  The version check backs Theory skip gates and must be side-effect-free; it
  now returns null when the conformance package is absent. The actual scenario
  run path still restores npm dependencies via ConformanceTestStartInfo.

Author: Tarek Mahmoud Sayed

src/ModelContextProtocol.Core/Protocol/CacheScopeConverter.cs

@@ -40,8 +40,15 @@ internal sealed class CacheScopeConverter : JsonConverter<CacheScope?>
             {
                 return CacheScope.Private;
             }
+
+            return null;
         }
 
+        // Any non-string token (number, bool, object, array) is an unrecognized hint. Consume the whole
+        // value, including the contents of an object or array, so the reader is left correctly positioned
+        // before mapping to null. Skipping is required for container tokens: returning without consuming
+        // them would leave the reader mispositioned and break deserialization of the enclosing result.
+        reader.Skip();
         return null;
     }
 

tests/Common/Utils/NodeHelpers.cs

@@ -224,14 +224,10 @@ private static bool HasInstalledConformanceVersionAtLeast(Version minimumVersion
             var packageJsonPath = Path.Combine(
                 repoRoot, "node_modules", "@modelcontextprotocol", "conformance", "package.json");
 
-            // Only trigger an install if the package isn't already present. This avoids a
-            // gate check inadvertently running 'npm ci' (which would restore the pinned
-            // version and clobber a locally installed private build).
-            if (!File.Exists(packageJsonPath))
-            {
-                EnsureNpmDependenciesInstalled();
-            }
-
+            // This is a skip gate for version-conditional conformance scenarios, so it must stay
+            // side-effect-free. If the conformance package isn't installed, report no version (the
+            // scenario is simply gated off); the actual scenario run path restores npm dependencies
+            // separately via ConformanceTestStartInfo.
             if (!File.Exists(packageJsonPath))
             {
                 return null;

tests/ModelContextProtocol.Tests/Protocol/CacheableResultTests.cs

@@ -172,7 +172,8 @@ public static void CacheableResult_DeserializesUnknownCacheScope_AsNull(Type typ
     {
         // A future/unknown cacheScope string must not break deserialization of the entire result; it is
         // tolerated and surfaced as null (equivalent to an absent field, which clients treat as public).
-        foreach (string scope in new[] { "\"shared\"", "\"\"", "123", "true", "null" })
+        // Non-string tokens, including objects and arrays, must likewise be tolerated and fully consumed.
+        foreach (string scope in new[] { "\"shared\"", "\"\"", "123", "true", "null", "{}", "[]", "{\"a\":1}", "[1,2]" })
         {
             string json = $"{{\"cacheScope\":{scope}}}";