Replace JObject with object for Message.Payload

[Nigusu-Allehu]

Bug

Fixes: NuGet/Home#14901

Description

Obsoletes Message.Payload (JObject) and stores payloads as object

Message.Payload is marked [Obsolete] and now returns null. Payloads are stored internally as object in PayloadObject, serialized via [JsonProperty("Payload")] so the wire format is unchanged.

MessageUtilities.Create<T> stores typed payloads directly
MessageUtilities.DeserializePayload<T> handles both JObject from JSON deserialization and typed object cases.

This is a slice of #7326. It isolates the breaking API change from the larger STJ behavioral change: when the STJ MessageConverter lands

STJ integration path

When the STJ MessageConverter is introduced, it will:

1. Deserialize payloads directly into typed objects using method-to-type dictionaries
2. Store the typed object in Message.Payload (which is now object)

PR Checklist

• Meaningful title, helpful description and a linked NuGet/Home issue
• Added tests
• Link to an issue or pull request to update docs if this PR changes settings, environment variables, new feature, etc.

[Copilot]

Pull request overview

This PR updates the NuGet plugin protocol Message payload surface to avoid exposing Newtonsoft.Json.Linq.JObject in the public API by changing Message.Payload/constructor payload from JObject to object, while keeping JSON payload handling working via helper/converter updates.

Changes:

• Change NuGet.Protocol.Plugins.Message.Payload and its constructor parameter type from JObject to object, and introduce a custom JSON converter for payload deserialization.
• Update MessageUtilities.DeserializePayload<TPayload> to handle both JObject payloads and already-typed payload instances, and add a localized error string for invalid payload casts.
• Update affected tests to compare payloads via TestUtilities.Serialize(...) rather than JObject.ToString(Formatting.None).

Reviewed changes

Copilot reviewed 26 out of 27 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
test/TestExtensions/TestablePlugin/TestablePlugin.cs	Switches initialization request handling to MessageUtilities.DeserializePayload<T>().
test/NuGet.Core.Tests/NuGet.Protocol.Tests/Plugins/StandardInputReceiverTests.cs	Updates payload assertions to serialize object payloads for comparison.
test/NuGet.Core.Tests/NuGet.Protocol.Tests/Plugins/MessageUtilitiesTests.cs	Updates payload serialization assertion to use TestUtilities.Serialize.
test/NuGet.Core.Tests/NuGet.Protocol.Tests/Plugins/Messages/MessageTests.cs	Updates payload JSON assertions to serialize object payloads.
test/NuGet.Core.Tests/NuGet.Protocol.Tests/Plugins/MessageDispatcherTests.cs	Updates payload JSON assertions to serialize object payloads.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.zh-Hant.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.zh-Hans.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.tr.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.ru.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.pt-BR.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.pl.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.ko.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.ja.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.it.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.fr.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.es.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.de.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/xlf/Strings.cs.xlf	Adds new localization entry for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/Strings.resx	Adds Plugin_InvalidPayloadCast resource string.
src/NuGet.Core/NuGet.Protocol/Strings.Designer.cs	Adds generated accessor for Plugin_InvalidPayloadCast.
src/NuGet.Core/NuGet.Protocol/PublicAPI/net8.0/PublicAPI.Unshipped.txt	Adds updated Message API signatures as unshipped entries.
src/NuGet.Core/NuGet.Protocol/PublicAPI/net8.0/PublicAPI.Shipped.txt	Removes previously shipped Message constructor/payload entries (needs correction).
src/NuGet.Core/NuGet.Protocol/PublicAPI/net472/PublicAPI.Unshipped.txt	Adds updated Message API signatures as unshipped entries.
src/NuGet.Core/NuGet.Protocol/PublicAPI/net472/PublicAPI.Shipped.txt	Removes previously shipped Message constructor/payload entries (needs correction).
src/NuGet.Core/NuGet.Protocol/Plugins/ObjectPayloadConverter.cs	Adds a converter used by Message.Payload to deserialize JSON objects into JObject.
src/NuGet.Core/NuGet.Protocol/Plugins/MessageUtilities.cs	Updates payload deserialization to support object payloads and throw a localized cast error.
src/NuGet.Core/NuGet.Protocol/Plugins/Messages/Message.cs	Changes Payload and constructor payload parameter types from JObject to object and applies the converter attribute.

Files not reviewed (1)

• src/NuGet.Core/NuGet.Protocol/Strings.Designer.cs: Language not supported

[Copilot]

Pull request overview

Copilot reviewed 26 out of 27 changed files in this pull request and generated 5 comments.

Files not reviewed (1)

• src/NuGet.Core/NuGet.Protocol/Strings.Designer.cs: Language not supported

[dotnet-policy-service]

Added needs-breaking-change-doc-created label because this PR has the breaking-change label.

When you commit this breaking change:

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