Phase 0: A1 Wayland baseline + state snapshot — major reframing

3 in-session reps of chromium-fourier 149 / brave_drops_test.html /
Plasma Wayland 6.6.4 (kwin-fourier 6.6.4-3 + qt6-base-fourier
6.11.0-3 carry-overs intact). Tight cluster IQR=0:
drops_total=0, drops_post_warmup=0, frames_total=1685, kwin %CPU
median=0.00, mean=0.04. Perf samples on kwin (~30 over 70s) show
zero composite/dmabuf/GL symbols — only event-loop bookkeeping.

Most likely mechanism: KWin direct-scanout fast-path engaged for
the single-visible-client video case. The campaign's load-bearing
hypothesis ("X11 + non-compositing WM avoids per-frame GL composite
of NV12") is structurally weakened — KWin already avoids that work
under Wayland for this workload. Phase 1 needs to add a
multi-window A1' variant and drm_info-during-playback to confirm
direct-scanout, then revisit matrix cell design.

revert.log entry 6: SDDM autologin + state.conf swap that landed
the Plasma Wayland session for the A1 reps. Backup of original
state.conf preserved at /var/lib/sddm/state.conf.x11-research-bak;
single-command revert documented.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

phase0_evidence/x11_inventory_2026-05-03/revert.log

@@ -382,14 +382,117 @@ regular user.
 
 ---
 
+## Entry 6 — 2026-05-03 ~13:25 CEST
+
+**Trigger:** Operator instructed "okay, 2" — the option-2 path
+from the conversation: SSH-driven session switch from XFCE
+(entry 4 / 5 substrate) to Plasma Wayland for the remaining
+Phase 0 deliverables (state snapshot of Plasma Wayland + A1
+baseline reps), without operator at the SDDM greeter.
+
+**Driven from:** `mfritsche@noether` over SSH to `ohm.fritz.box`,
+passwordless `sudo`.
+
+### What was changed
+
+1. **`/etc/sddm.conf.d/x11-research-autologin.conf` written**
+   then **removed same session**:
+   ```
+   [Autologin]
+   User=mfritsche
+   Session=plasma.desktop
+   Relogin=false
+   ```
+   Removed via `sudo rm` after the autologin succeeded so the
+   campaign doesn't leave a one-shot config behind.
+
+2. **`/var/lib/sddm/state.conf` modified** (still in place at
+   end of this entry — see "Lingering state" below):
+   - Pre-state: `Session=/usr/share/xsessions/xfce.desktop`
+     (cached from the entry-2 XFCE session being the most
+     recently used).
+   - Post-state:
+     `Session=/usr/share/wayland-sessions/plasma.desktop`.
+   - Why: SDDM's autologin section was being **overruled** by
+     the cached last-session in `state.conf` — autologin tried
+     to start `startxfce4` instead of `startplasma-wayland`
+     and crashed in a tight retry loop (visible in
+     `journalctl -u sddm`: `--start startxfce4 ... crashed
+     (exit code 1)` with new transient sessions appearing every
+     ~3 s). Stopping `sddm`, rewriting the state.conf Session
+     line, and restarting `sddm` resolved the loop on the
+     first try — kwin_wayland came up cleanly within ~10 s.
+   - Backup: `/var/lib/sddm/state.conf.x11-research-bak`
+     preserves the original line for revert.
+
+3. **The XFCE session (entry 2/4/5 substrate) was terminated**
+   via `loginctl terminate-session 395`. No cleanup of the
+   user-side `~/.config/autostart/99-rotate-*.desktop` files
+   needed — those scope to `OnlyShowIn=XFCE;` and silently
+   no-op under Plasma Wayland.
+
+### Lingering state
+
+- `/var/lib/sddm/state.conf` continues to point at
+  `Session=/usr/share/wayland-sessions/plasma.desktop`. **This
+  is correct for the current session** (Plasma Wayland is now
+  the most-recently-used). On the next operator-driven session
+  switch, SDDM will rewrite this file naturally to whatever
+  the user picks at the greeter; no campaign-side action
+  needed.
+- The pre-campaign content is preserved at
+  `/var/lib/sddm/state.conf.x11-research-bak` for
+  audit/revert.
+
+### Verification
+
+After SDDM restart:
+- `loginctl show-session 433` → `Type=wayland`, `TTY=tty1`,
+  `Service=sddm-autologin`, `Desktop=KDE`, `Active=yes`.
+- `pgrep -af kwin_wayland` shows
+  `/usr/bin/kwin_wayland_wrapper --xwayland` (PID 35676) and
+  `kwin_wayland --wayland-fd 7 --socket wayland-0 --xwayland-fd
+  ...` (PID 35679).
+- `/run/user/1001/wayland-0` socket present and lockfile.
+
+### Revert procedure
+
+If campaign needs to fully revert:
+```sh
+ssh ohm.fritz.box '
+  sudo systemctl stop sddm
+  sudo cp /var/lib/sddm/state.conf.x11-research-bak /var/lib/sddm/state.conf
+  sudo rm -f /var/lib/sddm/state.conf.x11-research-bak
+  sudo systemctl start sddm
+'
+```
+(The autologin .conf was already removed in-session, so no
+extra delete needed there.)
+
+Note: this revert ONLY restores the state.conf to its
+pre-campaign contents. It doesn't kill the current session;
+the operator can choose whether to log out and back in via
+greeter to fully exit Plasma Wayland.
+
+---
+
 ## How to revert this campaign's installs
 
-Entries reverted in **reverse order** (entry 5 → 4 → 3 → 2 → 1):
+Entries reverted in **reverse order** (entry 6 → 5 → 4 → 3 → 2 → 1):
 
 ```sh
 ssh ohm.fritz.box '
   set -e
 
+  # ----- Entry 6 revert: SDDM state.conf restoration -----
+  if [ -f /var/lib/sddm/state.conf.x11-research-bak ]; then
+    sudo systemctl stop sddm
+    sudo cp /var/lib/sddm/state.conf.x11-research-bak /var/lib/sddm/state.conf
+    sudo rm -f /var/lib/sddm/state.conf.x11-research-bak
+    sudo systemctl start sddm
+  fi
+  # The autologin .conf was already removed in-session.
+
   # ----- Entry 5 revert: touchscreen mapping -----
   rm -f ~/.config/autostart/99-rotate-touchscreen.desktop
   # Live revert: reset Coordinate Transformation Matrix to identity.