Godot 4.5 beta 1: Error when saving a scene with a typed dictionary property (presumably a thumbnails problem)

[nuevocharrua]

Tested versions

• Reproducible in: 4.5.beta1 (macOS 15.5)
• Not reproducible in: 4.4.1 (macOS 15.5)

System information

macOS 15.5, Godot 4.5 Beta 1, Vulkan

Issue description

When a scene has a script with a typed dictionary @export like these:

@export var sounds: Dictionary[int, AudioStreamPlayer2D]
@export var faces: Dictionary[String, TextureRect]

when saving that scene (or when opening the editor for the first time) it writes this error in the output:

ERROR: Failed to get property 'sounds' from node 'PlayerHammerSuper1State'
ERROR: Failed to get property 'faces' from node 'MainBars'

Not all typed dictionaries generate this error, I think only the ones that reference Nodes.

I think it's something related to the new way of generating thumbnails (because it happens when opening for the first time and when saving)

Steps to reproduce

1. Create a new scene in Godot
2. Add a script to a node in the scene
3. In the script, add exported typed dictionary properties that reference Node types, such as:

@export var sounds: Dictionary[int, AudioStreamPlayer2D]
@export var faces: Dictionary[String, TextureRect]

4. Save the scene
5. Observe the error messages in the output console

Minimal reproduction project (MRP)

typed-error.zip

[SpockBauru]

With the MRP provided I can reproduce the error message on Windows in the first time loading, or every time I delete the folder %LocalAppData%/Godot.

With my personal project (mobile renderer) it also happens when saving a big scene with typed dictionaries, sometimes preventing the saving. After waiting for a few seconds I can save normally.

Reproducible on 4.5.Beta1
Not reproducible on 4.5.dev5

System information: Godot v4.5.beta1 - Windows 11 (build 22631) - Multi-window, 1 monitor - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3080 (NVIDIA; 32.0.15.6614) - 12th Gen Intel(R) Core(TM) i7-12700KF (20 threads) - 31.81 GiB memory

Edit:
Question: Why are thumbnails stored on the user space instead of the project folder?

[precup]

Bisects to #102313, no longer reproducible in latest master due to the reversion.

[SpockBauru]

Tested the Windows Artifact for #107786, which is the PR that reverts 102313.

The error is gone in the MRP, even after deleting %LocalAppData%/Godot.
On my personal project there's no more loading/saving errors.

Also compiled Master locally just to be sure, all errors above are gone on Windows 😄

[akien-mga]

Fixed by #107786.