diff --git a/12-fix-rdp-bigres.sh b/12-fix-rdp-bigres.sh
index 3e1f156..2680f81 100755
--- a/12-fix-rdp-bigres.sh
+++ b/12-fix-rdp-bigres.sh
@@ -33,3 +33,41 @@ else
 fi
 
 grep -q XRDP_GFX_MAX_COMPRESSED_BYTES "$DROPIN" && echo "drop-in present: $DROPIN"
+
+###############################################################################
+# Part 2 — kwin_x11 black-screen fix (root-caused 2026-09-01, #611)
+#
+# Symptom: RDP login -> KDE spinner -> BLACK screen. Server-side bisect
+# showed display :10 rendering pure black (colors=1): kwin_x11 was
+# crash-looping (plasma-kwin_x11.service "start operation timed out",
+# restart counter 12+). Cause: software-GL compositing init under
+# xorgxrdp (no DRI) at 5160x2160 never finishes inside the unit's
+# start timeout; systemd kills kwin -> no desktop. The "spinner" the
+# user sees is KSplash firing on every kwin restart.
+#
+# Fix: disable X11 compositing for the RDP accounts (kwin runs
+# uncomposited = instant, no GL) and give the kwin unit start-time
+# headroom. Wayland console session unaffected (Compositing/Enabled is
+# an X11-only key). Verified with the freerdp harness on rdptest:
+# fresh 1408x945 / fresh 5160x2160 / resize up mid-session / resize
+# down on reconnect — all render real desktops.
+###############################################################################
+
+for ACCOUNT in reachableceo reachableceo-offstage; do
+  runuser -u "$ACCOUNT" -- kwriteconfig6 --file kwinrc \
+    --group Compositing --key Enabled false
+  echo "kwinrc Compositing=false: $ACCOUNT"
+done
+
+mkdir -p /etc/systemd/user/plasma-kwin_x11.service.d
+cat > /etc/systemd/user/plasma-kwin_x11.service.d/bigres-timeout.conf <<'EOF'
+[Unit]
+# big-res xorgxrdp sessions: software-GL init is slow; give kwin room
+# instead of kill+crashloop (#611)
+TimeoutStartSec=300
+EOF
+systemctl daemon-reload
+echo "kwin unit override: /etc/systemd/user/plasma-kwin_x11.service.d/bigres-timeout.conf"
+echo
+echo "If a session is currently black: loginctl terminate-session <id> (or"
+echo "loginctl terminate-user <user> for their RDP sessions) and reconnect."
diff --git a/TRACKING.md b/TRACKING.md
index ce1017f..4c074c7 100644
--- a/TRACKING.md
+++ b/TRACKING.md
@@ -16,7 +16,7 @@ One table, updated in place at each checkpoint. States: done ✅ / doing 🔄 /
 | OPT-10 | integ | ⏳ | #605: k8s join (Q11, blocked by #601) + proxmox-ctl token (Q12) |
 | #606 | gpu | 🔄 | Quadro 4000 passthrough STAGED on 5111 (vfio ids + q35 + hostpci0, staged/gpu-passthrough.md); activates at the human's pre-Friday roll; nouveau-only on kernel 6.12 (no CUDA/NVENC — compute cards come with #601) |
 | #610 | fleet | ✅ | Open Terminal 9-account fleet (tailscale-only :30000-30008) + OpenWebUI UAT PASS |
-| #611 | rdp | 🔄 | Jump/iPad + 5160x2160 monitor: EGFX frame-budget fix live (12-fix-rdp-bigres.sh); freerdp UAT all-clean; human UAT pending |
+| #611 | rdp | 🔄 | ROOT CAUSE FOUND + FIXED (black screen = kwin_x11 GL-compositing crash-loop under xorgxrdp; compositing off + unit timeout, EGFX budget kept). Harness matrix ALL GREEN (fresh/resized 1408<->5160). LIVE human UAT now |
 | #612 | dotfiles | ✅ | UAT PASS 2026-09-01 (human): omz+v2 base + kali addendum both accounts; p10k fallback via KALI_PROMPT=0 |
 | #615 | microvm+rebuild | 🔄 | microvm tooling LIVE + REBUILD.md/docs/state + docs synced + regular-VM lane PROVEN (libvirt q35, REGULAR-VMS.md); human UAT pending |
 | #616 | macos | ⏳ | macOS VM on pfv-tsys5 (headless CI + iOS dev) — blocked by #601 |