Phase 0: browser X11-overlay inventory + mpv reference cell + tooling installs

Source-level verdict: no browser in the matrix has a code path
to hand NV12 to the X server for plane scanout. Chromium ozone-x11
wires StubOverlayManager (ozone_platform_x11.cc:262); Brave 147 +
chromium-fourier 149 inherit unchanged. Firefox WindowSurfaceX11
is RGB-only. The campaign's load-bearing hypothesis is structurally
weakened — what the X11 cells will measure for browsers is
KWin's per-frame RGB-recomposite cost, not the original
"force-GL-composite of NV12" framing. mpv --vo=xv becomes the
matrix's only direct test of the operator-supplied mechanism.

Matrix updated: 12 cells -> 16 cells (+8 mpv VO sub-points).
revert.log entries 1-5 capture all package + per-user state
mutations from this turn (measurement tools, openbox, XFCE +
xfwm4-no-comp pre-seed, firefox + AUR xtrace, XFCE rotation
+ touchscreen mapping); single SSH-driveable revert chain
returns ohm to its pre-campaign 1169-package state.

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

phase0_evidence/x11_inventory_2026-05-03/pacman.entry3b.xtrace.log

@@ -0,0 +1,20 @@
+loading packages...
+resolving dependencies...
+looking for conflicting packages...
+
+Packages (1) xtrace-1.4.0-2
+
+Total Installed Size:  0.31 MiB
+
+:: Proceed with installation? [Y/n] 
+checking keyring...
+checking package integrity...
+loading package files...
+checking for file conflicts...
+:: Processing package changes...
+installing xtrace...
+Optional dependencies for xtrace
+    xorg-xauth [installed]
+:: Running post-transaction hooks...
+(1/2) Arming ConditionNeedsUpdate...
+(2/2) Refreshing PackageKit...