Launcher crashes (std::bad_function_call in liblauncher.so) when clicking "Sign in with Microsoft"

## Summary

The official Minecraft Launcher (Flatpak, `com.mojang.Minecraft` v2.1.3) crashes with SIGABRT every time I click **"Sign in with Microsoft"**, immediately after the CEF sign-in window opens. The crash always happens ~4-8 seconds after clicking the button, well before the actual Microsoft login page has a chance to load.

Instead of the sign-in page, the launcher UI shows a garbled/nonsensical error dialog:

```
Error Code: 0x80004005 code: Eroded Badlands. A file that the Windows
Product Activation (WPA) requires is damaged or missing. Please reboot,
verify system permissions, and make sure your operating system is
up-to-date. For more information, go HERE or contact Customer Support
directly.
```

This text is clearly a leftover/generic Windows error template (referencing "Windows Product Activation") that should never appear on Linux, combined with what looks like an uninitialized/garbage string ("Eroded Badlands" - a Minecraft biome name) used as the error "code" placeholder - consistent with memory corruption following the crash below.

## Environment

- OS: Fedora Linux 44 (Workstation Edition)
- Session: GNOME, Wayland
- Flatpak: 1.18.2
- App: `com.mojang.Minecraft` v2.1.3
- Runtime: `org.freedesktop.Platform/x86_64/25.08`
- Fresh install (first launch, no prior `.minecraft` data)

## Steps to reproduce

1. `flatpak install flathub com.mojang.Minecraft`
2. `flatpak run com.mojang.Minecraft`
3. Click "Sign in with Microsoft"
4. Crash occurs within ~5 seconds; error dialog above is shown

## What I've already ruled out

- **Not a GPU/driver issue**: reproduces identically with `LIBGL_ALWAYS_SOFTWARE=1` forcing software rendering.
- **Not a portal/D-Bus availability issue**: `xdg-desktop-portal`, `xdg-desktop-portal-gnome`, and the system D-Bus are all active and working on the host.
- **Partially related but not the cause**: the log shows `OSCrypt tried Libsecret but couldn't initialise` and `Failed to connect to the bus: ... /run/dbus/system_bus_socket`. Granting `flatpak override --user --talk-name=org.freedesktop.secrets com.mojang.Minecraft` makes the Libsecret warning disappear (gnome-keyring's Secret Service is reachable), but **the crash still happens identically afterward** - so this is a separate, secondary issue (the app likely also needs `--talk-name=org.freedesktop.secrets` declared by default in the manifest for keyring-based token storage to work at all under GNOME), not the root cause of the crash itself.
- **Not fixed by pinning an older build**: history shows a commit "Remove shared-modules/libsecret (#167)" but per that PR's own description libsecret is provided by the runtime regardless, so this isn't a regression from that change.

## Crash details

`journalctl` shows the process aborts with an uncaught `std::bad_function_call`:

```
terminate called after throwing an instance of 'std::bad_function_call'
what(): bad_function_call
```

`coredumpctl info` backtrace (thread that aborts) - the crash originates inside **`liblauncher.so`** (Mojang's own native launcher library), not in CEF/Chromium:

```
Stack trace of thread 188:
#0 ... libc.so.6 + 0x9c51c
#1 ... libc.so.6 + 0x422be
#2 ... libc.so.6 + 0x298ed
#3 ... libstdc++.so.6.0.34 + 0xb304b
#4 ... libstdc++.so.6.0.34 + 0xcc38a
#5 ... libstdc++.so.6.0.34 + 0xb2912
#6 ... libstdc++.so.6.0.34 + 0xcbb7b
#7 ... libgcc_s.so.1 + 0x2202a
#8 ... libgcc_s.so.1 + 0x22b4a
#9 ... liblauncher.so + 0x1360a3
#10 ... liblauncher.so + 0x29f2f1
#11 ... liblauncher.so + 0x29f43d
#12 ... liblauncher.so + 0x29e9c2
#13 ... liblauncher.so + 0x1e0b06
#14 RunLauncher (liblauncher.so + 0x1b270e)
#15 ... minecraft-launcher + 0x1ba9e0
#16 ... minecraft-launcher + 0x49ad9
#17 ... minecraft-launcher + 0x34ec9
#18 ... libc.so.6 + 0x2b975
#19 ... libc.so.6 + 0x2ba28
#20 _start (minecraft-launcher + 0x36bda)
```

Frames #9–#14 are all inside `liblauncher.so`, culminating in the exported `RunLauncher` symbol - this points to an unhandled/empty `std::function` callback being invoked somewhere in the native sign-in flow, not a CEF/rendering problem.

## Possibly related existing issues

This looks like the same recurring class of bug reported (with different launcher versions, over several years) in:
- #111 "Can't log in on from fresh install"
- #120 "Launcher crashes upon invocation"
- #143 "application launcher fails to complete" (login hangs/fails ~9 times out of 10)

If useful I have the full `coredumpctl` core file (16 MB, `zstd`-compressed) and can attach or share more of it on request.

Start by reproducing the crash with the documented Flatpak install and sign-in steps, then inspect the coredump and journal output around RunLauncher in liblauncher.so. Review related issues #111, #120, and #143 and the Flatpak manifest's keyring permissions. Done would require identifying a fix for the native sign-in crash and verifying that Microsoft sign-in completes without aborting.

Written by the indexing model from the issue text.