[Linux/ChromeOS] Camera snaps back while moving mouse in 26.3 (SDL3); 26.1.2 unaffected

Summary: In Java Edition 26.3, when I move the mouse or touchpad in-game, the camera turns slightly and then snaps back toward its previous position. This does not happen in 26.1.2 on the same machine. Steps to reproduce: 1. Launch 26.3 on a Chromebook, inside the Linux (Crostini) container. 2. Enter any world. 3. Move the mouse or touchpad to look around. Observed result: The view moves a small amount, then snaps back. Expected result: The camera turns smoothly and stays where it was moved. Environment: - Minecraft: Java Edition 26.3, vanilla (also seen with Fabric 26.3) - OS: ChromeOS, Linux container (Crostini), Debian 13 (trixie) - Display: Xwayland running on ChromeOS's Wayland compositor (xinput lists only xwayland-* virtual devices) - Launcher: Legacy Launcher (third-party) - Java: Java 25 (launcher's bundled runtime, as reported by the Fabric log; system Java is OpenJDK 21.0.12.1) - Renderer: llvmpipe (LLVM 19.1.7), Mesa 25.0.7, software rendering, no GPU acceleration. Frame rate is about 6-10 FPS in both 26.3 and 26.1.2. Testing done: - Forced X11 with SDL_VIDEO_DRIVER=x11 and unset WAYLAND_DISPLAY. latest.log confirms "Created window using SDL video driver: x11". The problem still occurs. - Occurs in both windowed and fullscreen. - SDL_MOUSE_RELATIVE_MODE_CENTER=0 and a warp-based relative mouse hint made no difference. - Normal cursor movement over an X11 window (tested with xev) is smooth, so the problem appears specific to mouse capture in-game. - 26.1.2 works correctly on the same device at the same frame rate (about 6-10 FPS), with smooth camera movement and no snap-back. Note on performance: The game runs slowly on this device (about 6-10 FPS in both versions), but 26.1.2 is smooth at that frame rate, so low FPS does not appear to explain the snap-back seen only in 26.3. Other notes: - The log contains a missing libflite.so (narrator) error and Realms/auth 401 errors, which are likely unrelated.