"error UAC2016: Failed to generate a FunctionPointer<...GetNextBlockDelegate>.Invoke wrapper" is thrown and Package does not compile when the Behavior package is installed

Steps to reproduce:

1. Create a new project
2. Open Window > Package Management > Package Manager
3. Select Unity Registry, search for "Behavior" and click Install
4. Wait for the script compilation to finish and observe the Console

Actual results: The package fails to compile and Play Mode cannot be entered

Library/PackageCache/com.unity.behavior@1b9c0eccba9c/com.unity.serialization/Runtime/Unity.Serialization/Json/Parser/UnsafeSerializedObjectReader.cs(434,25): error UAC2016: Failed to generate a FunctionPointer<global::Unity.Behavior.Serialization.Json.UnsafeSerializedObjectReader.GetNextBlockDelegate>.Invoke wrapper: `Unity.Behavior.Serialization.Json.UnsafeSerializedObjectReader.GetNextBlockDelegate` needs to be public or internal. If exceptions shouldn't be thrown from it, use UncheckedInvoke instead.

All compiler errors have to be fixed before you can enter playmode!

Expected results: The Behavior package compiles and Play Mode can be entered

Reproducible with versions: 1.0.16 (7000.0.0a10)

Not reproducible with versions: 1.0.16 (6000.7.0b6, 7000.0.0a9)

Tested on (OS): macOS 26.6.2

Notes:

• Reopening the project shows the "Enter Safe Mode?" dialog