devices/d10: the panel cannot sleep, and both ends are blueline-shaped

blueline-screen-toggle does not exist here so the blank no-ops, and Dim is
an absolute that reads as off on a 2047-step backlight. Lit-forever or
black-forever, nothing between, until eb0292c ships.

devices/d10/README.md

@@ -113,6 +113,31 @@ camera, sensor reporters.
 5. **`pgrep -f` matches your own ssh command line.** It has killed a session and
    produced two false "phone is down" readings in one night.
 
+## The panel cannot sleep on this body
+
+Both ends of the blank are blueline-shaped, so there is no idle path that ends
+with a dark, powered-down panel:
+
+- `Blank`/`Unblank` shell out to **`blueline-screen-toggle`**, which does not
+  exist here and ships only in `rootfs-overlay/`. The trail records
+  `panel-off … No such file or directory` — the actuator no-ops.
+- `Dim` is the only thing that changes the panel, and on the shipped sessiond it
+  is `brightnessctl set 10` — an absolute, 0.5% of 2047, indistinguishable from
+  off.
+
+So the device offers lit-forever or black-forever and nothing between, until
+`souveraine eb0292c` lands by package. Meanwhile the timed policy is widened
+(`dim_grace_secs` 600, `lock_blank_after_secs` 1800) rather than left at 15 s.
+To park it by hand:
+
+```sh
+for d in /sys/class/backlight/*/; do echo 0 > $d/brightness; echo 4 > $d/bl_power; done
+```
+
+**This is TASK-63's parity fix.** viewtop owns the CRTC, has `power.rs` with the
+EBUSY deferral, and runs on both bodies — the blank belongs there as a verb, and
+then neither phone needs a script named after the other one.
+
 ## Owed
 
 - `casey` still has password `123456`, which is also the lock PIN.