NewtonsoftJsonSerializationProvider writes object graphs deeper than 64 levels that it then can't read back: Serialize succeeds, Deserialize returns null #155

What's wrong

NewtonsoftJsonSerializationProvider (Essentials.SerializationProviders.NewtonsoftJson/NewtonsoftJsonSerializationProvider.cs:21) uses a default JsonSerializerSettings. In Newtonsoft.Json 13, MaxDepth defaults to 64 and is enforced only when reading.

• TrySerialize writes a graph of any depth and returns true.
• Deserialize<T> on that same output throws JsonReaderException, which the provider catches and turns into default.

The provider can therefore produce data that it cannot read.

Reproduction (on a9a00b9)

A linked chain class Node { string Name; Node? Next; }, round-tripped with Serialize and then Deserialize<Node>:

With a file-backed persistence provider using Newtonsoft, StoreAsync reports success but RetrieveAsync returns null. RetrieveOrCreateAsync would then overwrite the stored data with a fresh instance (see #82).

JsonSerializationProvider (System.Text.Json) handles this consistently: for the 200-deep graph, TrySerialize returns false.

Suggested fix

Make writing and reading enforce the same limit. Either:

• have TrySerialize fail when the output would go deeper than settings.MaxDepth, for example with a JsonTextWriter subclass that checks depth in WriteStartObject/WriteStartArray; or
• set one explicit MaxDepth (including null for unlimited) that applies to both directions.

Combine this with the buffering fix in the companion issue about TrySerialize leaving truncated output, so a depth failure also leaves the writer empty.

Acceptance criteria

• Any graph TrySerialize accepts always deserializes back.
• A test round-trips a 65-deep chain: either both directions succeed, or TrySerialize returns false.