Firebase Unity SDK – Native crash in Realtime Database (uS WebSocket thread)

# Firebase Unity SDK – Native crash in Realtime Database (uS WebSocket thread)

## Summary

Unity Editor crashes with a **native crash** in `FirebaseCppApp-13_7_0.dll` (Windows) when using Firebase Realtime Database with multiple `ValueChanged` and `ChildAdded`/`ChildRemoved` listeners. The crash occurs on a **worker thread** in the uS (µWebSockets) layer, not in C#.

## Environment

- **Unity**: 6000.3.0f1 (Unity 6)
- **Firebase Unity SDK**: 13.7.0 (Realtime Database)
- **Platform**: Windows 10 (64-bit), Unity Editor
- **Scripting**: .NET / Mono

## Crash details

- **Module**: `FirebaseCppApp-13_7_0.dll`
- **Thread**: Worker thread (stack shows `BaseThreadInitThunk` / `RtlUserThreadStart`)
- **Native stack** (representative frames):
- `uS::TLS::Context::operator bool`
- `uS::Node::...`
- `uS::Socket::write`
- `uS::Socket::freeMessage`

So the failure is in the C++ WebSocket/TLS code, not in managed code.

## Reproduction

1. Open a Unity project with Firebase Realtime Database (SDK 13.7.0).
2. Load a games list from the database and build UI for each game.
3. For each game, attach:
- `DatabaseReference.ValueChanged`
- `DatabaseReference.ChildAdded` (e.g. on a `/Players` child ref)
- `DatabaseReference.ChildRemoved`
4. Trigger a “refresh” that:
- Removes all listeners,
- Fetches a new snapshot (`GetValueAsync` / equivalent),
- Rebuilds the UI,
- Re-attaches the same listeners for each game (either in one frame or over a few frames).
5. The crash can occur during or shortly after re-attaching many listeners, or when many `ValueChanged` callbacks are processed. It is intermittent but reproducible under load.

## Mitigations tried (C# side)

- Coalescing UI rebuilds to at most one per frame.
- Not attaching listeners while a “refresh” is in progress.
- Deferring listener attachment by one frame after the UI rebuild.
- Staggering listener attachment (e.g. 5 games per frame).
- Delaying the single coalesced UI rebuild by one frame.
- In Editor only: adding an extra 2.5 s delay after the UI rebuild before starting listener attachment.

These reduce frequency but do not eliminate the crash; the failure remains in native code.

## Request

Please check whether this uS WebSocket/TLS path is subject to known race conditions or use-after-free when many listeners are added/removed or when many callbacks are delivered, and whether a fix or workaround is available or planned for the Unity SDK.