Resume Marker — 2026-08-20 (kernel build + GUI session switching)

Context

User restarted the session. Two parallel tasks were in progress when interrupted:

Kernel Rust build config issue (kbuild + nightly rustc)
GUI session switching — install Xfce on workhorse so user can switch GNOME↔Xfce at login

Status: unresolved — root cause found, fix not yet applied

What we know:

Kernel source: /home/CUBELinux/CUBELinux-2/src/CUBELinux-build/ (vanilla v6.19.3 + ipu4 out-of-tree)
CONFIG_RUST=y set in .config
rustc 1.97.1 (stable) is default; rustc 1.100.0-nightly also installed via rustup (default host: x86_64-unknown-linux-gnu)
scripts/target.json exists with rustc-abi: x86-softfloat, llvm-target: x86_64-linux-gnu
make rust/core.o fails: error loading target specification: custom targets are unstable and require -Zunstable-options
The rustc_library command in rust/Makefile:559 does NOT pass -Zunstable-options
rust/Makefile already uses -Zunstable-options in rustdoc paths (lines 136, 324, 333) but NOT in the core rustc_library invocation
KBUILD_RUSTFLAGS (from arch/x86/Makefile) sets --target=.../scripts/target.json but no -Zunstable-options
The rustc_library rule (rust/Makefile:555-567) builds the command as:
```
$(RUSTC) $(filter-out $(skip_flags),$(rust_flags)) $(rustc_target_flags) --emit=...
```
where rust_flags = KBUILD_RUSTFLAGS + rust_common_flags and rustc_target_flags = core-flags (which is --edition=... + cfgs). Neither carries -Zunstable-options.

What needs to happen:

Option A: Patch rust/Makefile to add -Zunstable-options to the rustc_library command (line 559 area) — minimal change, mirrors what rustdoc already does
Option B: Use nightly rustc as RUSTC and ensure it's invoked with -Zunstable-options — but kbuild doesn't add it automatically
The real fix is Option A: add -Zunstable-options to the rustc invocation in the rustc_library rule, since the target.json is a custom target spec that requires it
After that: make rust/all or make rust/core.o should succeed, then full kernel build

Files involved:

/home/CUBELinux/CUBELinux-2/src/CUBELinux-build/rust/Makefile (line 555-567, rustc_library rule)
/home/CUBELinux/CUBELinux-2/src/CUBELinux-build/arch/x86/Makefile (KBUILD_RUSTFLAGS)
/home/CUBELinux/CUBELinux-2/src/CUBELinux-build/scripts/target.json (custom target spec, needs -Zunstable-options)

Status: dpkg interrupted — lightdm stuck half-configured

What we know:

Workhorse runs GNOME (gdm3 + gnome-shell) currently
User wants GNOME ↔ Xfce switching at the login screen (like Cinnamon is available)
apt-get install -y task-xfce-desktop timed out (exit 124) and left dpkg in interrupted state
dpkg --configure -a fails: lightdm is half-configured, depends on itself being configured first
lightdm package status: iF (half-configured), light-locker and task-xfce-desktop also stuck
Xfce components were likely downloaded but not configured due to the dpkg blockage

What needs to happen:

Fix dpkg: either dpkg --remove --force-remove-reinstreq lightdm then dpkg --configure -a, or manually remove the lock/status entries
Re-run apt-get install -y task-xfce-desktop (or just xfce4 + lightdm if minimal)
Verify xfce4-session works: xfce4-session --version
Verify GDM shows Xfce session: check /usr/share/xsessions/xfce.desktop exists, gdm3 is running
Test: log in via Xfce session

Files/dirs involved:

User explicitly does NOT want auto-launching heavy kernel compiles while they're using the machine
Kernel build with make -j$(nproc) will saturate CPU — must ask before launching
The workhorse is Debian-based, root access available
rustup is installed at /root/.rustup, toolchains in /root/.rustup/toolchains/