Accept JSON object OR stringified-JSON for stringified-blob tool parameters

[IvanMurzak]

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Summary

MCP tool parameters that carry a "stringified JSON blob" (e.g. jsonPatch on gameobject-component-modify) are declared as C# string. ReflectorNet emits a flat {"type":"string"} input schema for them, so when an LLM sends the value as a raw JSON object instead of a JSON string, the call is rejected up front with:

MCP error -32602: Input validation error: ... { "expected": "string", "code": "invalid_type", "path": ["jsonPatch"], "message": "Invalid input: expected string, received object" }

The model then has to redo the call. We want to accept both forms transparently.

Root cause (verified)

1. Schema too strict. GeneratePrimitiveSchema emits {"type":"string"} for string params — ReflectorNet/src/Utils/Json/JsonSchema.Internal.cs:268-269. The MCP layer validates the call against this schema and rejects an object before binding runs.
2. Binder would also fail. string is IsPrimitive==true (TypeUtils.Helpers.cs:82), so in MethodWrapper.GetParameterValue (both overloads, ~L260 and ~L343) the un-stringify branch is skipped and it calls jsonElement.Deserialize<string>(...), which throws on an object. JsonUtils.TryUnstringifyJson already handles string->object; the reverse (object->string) is missing.

Proposed approach

1. Schema (opt-in): add a parameter attribute (proposed [JsonStringOrObject]) that makes the emitted schema {"anyOf":[{"type":"string"},{"type":"object","additionalProperties":true}]} (consider also array). Reuse the existing JsonArrayJsonConverter.JsonAnySchema pattern (Converter/Json/JsonArrayJsonConverter.cs:21-33). Keep it opt-in — do not loosen every string schema globally.
2. Binder (unconditional, safe): in both MethodWrapper.GetParameterValue overloads, when the target type is string and the incoming JsonElement.ValueKind is Object/Array, bind jsonElement.GetRawText() instead of attempting Deserialize<string>.

Acceptance criteria

• [JsonStringOrObject] attribute exists; applied to a string param it makes the schema an anyOf of string + object.
• Binder coerces an object/array JsonElement into raw JSON text for string params (both overloads).
• Unit tests: schema shape with/without the attribute; binder accepts object (-> stringified JSON); binder still accepts a plain JSON string; an un-annotated string param is unaffected.
• dotnet test --configuration Release green on net8.0 + net9.0.
• No version bump / no release in this PR.

Reported via tool gameobject-component-modify (jsonPatch sent as a nested object).
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