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.entry3a.firefox.log

@@ -0,0 +1,30 @@
+resolving dependencies...
+looking for conflicting packages...
+
+Packages (2) mailcap-2.1.54-2  firefox-150.0.1-1
+
+Total Download Size:    63.40 MiB
+Total Installed Size:  256.95 MiB
+
+:: Proceed with installation? [Y/n] 
+:: Retrieving packages...
+ firefox-150.0.1-1-aarch64 downloading...
+ mailcap-2.1.54-2-any downloading...
+checking keyring...
+checking package integrity...
+loading package files...
+checking for file conflicts...
+:: Processing package changes...
+installing mailcap...
+installing firefox...
+Optional dependencies for firefox
+    hunspell-en_US: Spell checking, American English
+    libnotify: Notification integration [installed]
+    networkmanager: Location detection via available WiFi networks [installed]
+    speech-dispatcher: Text-to-Speech
+    xdg-desktop-portal: Screensharing with Wayland [installed]
+:: Running post-transaction hooks...
+(1/4) Arming ConditionNeedsUpdate...
+(2/4) Refreshing PackageKit...
+(3/4) Updating icon theme caches...
+(4/4) Updating the desktop file MIME type cache...