Fix: Stop the display link retraining and blanking

This panel's DP link is marginal. 4500x3000@60 at 10bpc is around 24 Gbps,
right at the edge of DP 1.4 HBR3 and reliant on DSC, so every modeset
retrains the link and blanks the screen. 8bpc keeps headroom.

Steam games are the other trigger. Everything Hyprland does only for a real
fullscreen window (direct scanout, VRR, tearing, auto HDR) forces that
retrain, so steam_app windows get fullscreen_state "1 2": maximized
internally while the game believes it is fullscreen, which is what
borderless windowed looks like from the game's side.

Recorded alongside the related Panama settings already at 0,
directScanoutPolicy and vrrPolicy.

config/dot/hypr/monitors.lua

@@ -244,10 +244,20 @@ local shipped_mode = "4500x3000@60"
 local shipped_scale = 1.5
 local shipped_transform = 0
 
--- 10-bit output. 4500x3000@60 at 10bpc is ~24 Gbps, right at the edge of DP 1.4
--- HBR3, so this relies on DSC. If the display fails to light up or falls back to
--- a lower mode, drop this to 8 first.
-local shipped_bitdepth = 10
+-- 8-bit output. 4500x3000@60 at 10bpc is ~24 Gbps, right at the edge of DP 1.4
+-- HBR3 and reliant on DSC, and this panel's link is marginal: every modeset
+-- retrains it and blanks the screen. 8bpc keeps headroom on the link.
+--
+-- Related: directScanoutPolicy is 0 in Panama settings (2026-09-13). With
+-- scanout on, a fullscreen game whose buffer depth differs from the desktop
+-- (games ship both 8- and 10-bit swapchains) makes Hyprland change the output
+-- format, and on amdgpu a format change is a full modeset. Compositing always
+-- keeps the format fixed, so the link never retrains mid-game.
+--
+-- vrrPolicy is also 0 there. VRR on this panel loses sync and blacks out
+-- (seen on GNOME in July 2026 and again here); a 60Hz panel gains little
+-- from it anyway.
+local shipped_bitdepth = 8
 
 -- "auto" = sRGB at 8bpc, wide gamut at 10bpc. Not HDR; see header.
 local shipped_cm = "auto"

config/dot/hypr/rules.lua

@@ -125,6 +125,16 @@ hl.window_rule({
     no_dim    = true,
 })
 
+-- Steam games never get true fullscreen. Everything Hyprland does only for a
+-- real fullscreen window (direct scanout, VRR, tearing, auto HDR) makes this
+-- panel's marginal DP link retrain and blank (2026-09-13). "1 2" keeps the
+-- window maximized internally while the game believes it is fullscreen, which
+-- is what borderless windowed looks like from the game's side.
+hl.window_rule({
+    match = { class = "^steam_app_\\d+$" },
+    fullscreen_state = "1 2",
+})
+
 -- Steam itself is a normal window, but its transient popups are a mess.
 hl.window_rule({
     match = { class = "^steam$", title = "^(Friends List|Steam Settings|Special Offer.*)$" },