Map the Frame controllers' buttons; make gaze clicks correctable

The Frame controllers aren't input devices on the host, so the pointer
helper reads them with SteamVR input (vrbuttons.h, actions/), one action
set per button, and sends presses to the relay, which does the mapped
action like for a mouse button. Only mapped buttons are taken, at an
overlay-global priority (SteamVR's experimental "Enable global input from
overlays"), and only outside games unless In games is on. Frametop Input
Settings gets a Controllers page to map them.

Gaze mode: a left press while the gaze has the pointer isn't sent at
once. The pointer stops, you drag it onto what you meant with the button
held, and the release clicks there; a press held still for
POINTER_GAZE_HOLD (0.5 s) becomes a real press, for drags. The dot shows
only while the mouse moves it (POINTER_GAZE_SHOW), while a press is held,
and as a pulse per click. Outside games the pointer stays on while gaze
mode is on. ft-gazed takes a third of each lesson's offset instead of all
of it: in the first live test one 6 degree lesson moved everything and put
the next target 7 degrees off. Frametop Input Settings gets a Gaze page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/design.md

@@ -82,7 +82,7 @@ A few overlays need special handling:
 
 Head follow is experimental and off by default. It works, but it's only lightly tested, and the feel is mostly a matter of its settings; polishing it is left open. With it on (`POINTER_FOLLOW=1`, or a mouse button mapped to Head follow on/off), the cursor rides on a reference direction, where you were facing when your head last settled, and keeps its offset from it. The mouse can put the cursor anywhere up to `POINTER_FOLLOW_REACH` (70 degrees) from the reference, a corner of your view included. While your head stays within `POINTER_LEASH_DEG` of the reference, nothing moves on its own. Once your head has been past the leash for `POINTER_LEASH_DELAY` (0.2 s, so a glance out and back doesn't count), the reference eases to where you're facing (time constant `POINTER_LEASH_RETURN`, 0.2 s), never falling further behind than the leash, and the cursor ends up back where it was in your view. Then it waits for the leash again. Two earlier versions didn't work out. Moving the reference only while your head pulled at the end of the leash left it up to the leash off after you turned back, and getting it centred again meant overshooting with your head. Easing it toward your facing all the time moved the cursor on every small head movement. A leash of 0 makes the reference your facing direction, so the cursor is locked to your view, and mouse movement shifts it within the view. Head roll is ignored, so tilting your head doesn't swing the cursor around. While the left button is held the cursor stays put in the room, so your head can't nudge a click or a drag. When you let go, it carries on from where it is instead of jumping.
 
-Gaze mode is experimental and off by default (`POINTER_GAZE=1`, `gaze/ft-gazectl on`, or a mouse button mapped to Gaze pointer on/off). It's MAGIC pointing (Zhai, Morimoto and Ihde, 1999): the pointer goes where you look, and the mouse does the last bit. The gaze service (`gaze/ft-gazed`) sends the helper the corrected gaze at 90 Hz, and while the gaze has the pointer, the cursor ray is that gaze from the eye. The pointer is aimed at the gaze each frame, not steered toward it, so nothing can pile up. An earlier try in the gaze probe steered the pointer with relative moves, and lost it when the pointer went idle or a controller had the laser. Moving the mouse takes the pointer from the gaze. Looking more than `POINTER_GAZE_RETAKE` (5 degrees) away from it, with the mouse still, gives it back, so small eye movements around the pointer don't pull it off what you're doing. A mouse nudge of up to `POINTER_GAZE_NUDGE_MAX` (8 degrees) before a click is sent to the gaze service as a lesson: you were looking at where you clicked when the mouse took over, so the nudge is the eye tracker's error there. Using it is what calibrates it. See `gaze/README.md` for the service, the calibration, and what was measured.
+Gaze mode is experimental and off by default (`POINTER_GAZE=1`, the Gaze page of Frametop Input Settings, `gaze/ft-gazectl on`, or a mouse or controller button mapped to Gaze pointer on/off). It's MAGIC pointing (Zhai, Morimoto and Ihde, 1999): the pointer goes where you look, and the mouse does the last bit. The gaze service (`gaze/ft-gazed`) sends the helper the corrected gaze at 90 Hz, and while the gaze has the pointer, the cursor ray is that gaze from the eye. The pointer is aimed at the gaze each frame, not steered toward it, so nothing can pile up. An earlier try in the gaze probe steered the pointer with relative moves, and lost it when the pointer went idle or a controller had the laser. Moving the mouse takes the pointer from the gaze. A left press while the gaze has the pointer isn't sent at once: the pointer stops where the gaze put it, you drag it onto what you meant with the button still down (panels only see it hover), and the release clicks there. Clicking at once clicked wherever the gaze was, often the wrong thing, before you could correct it. A press held still for `POINTER_GAZE_HOLD` (0.5 s) becomes a real press, so drags still work: hold, then move. Outside games the pointer then stays: the mouse going idle doesn't release it. A moving controller still releases it, as without gaze; the mouse is gaze mode's only pointer device for now. The dot shows only while the mouse moves it (`POINTER_GAZE_SHOW`), while a press is held, and as a pulse for each click; otherwise it's transparent, so the laser still lands on it. The gaze moving the pointer doesn't show it: you know where you're looking. Looking more than `POINTER_GAZE_RETAKE` (5 degrees) away from it, with the mouse still, gives it back, so small eye movements around the pointer don't pull it off what you're doing. A mouse nudge of up to `POINTER_GAZE_NUDGE_MAX` (8 degrees) before a click is sent to the gaze service as a lesson: you were looking at where you clicked when the mouse took over, so the nudge is the eye tracker's error there. Using it is what calibrates it. See `gaze/README.md` for the service, the calibration, and what was measured.
 
 Replacing a loaded driver's files, as re-running the installer used to do, leaves SteamVR honoring the virtual controller's hand role but not its laser claim: the dashboard pointer stays unassigned until SteamVR restarts. The driver installer now leaves an unchanged driver in place.
 
@@ -108,6 +108,8 @@ An ungrabbed keyboard reaches both sides at once. In VR, gamescope reads every i
 
 Volume keys must never reach gamescope. With the openvr backend, gamescope sends volume up and down to Steam by moving keyboard focus to Steam for the key and then back to the previously focused surface. When nothing had focus, the one it moves back to is null, and wlroots aborts on a null focus surface (`wlr_seat_keyboard_notify_enter: Assertion 'surface' failed`), which ends the whole VR session. Keyboard focus is often empty while you work in VR, so one press of the headset's volume button could take everything down. gamescope reads the headset's buttons and every keyboard itself (`InputStealer`), as do SteamVR's processes, so the relay has to stop volume keys at the device. Grabbing `gpio-keys` would also take the headset's click button, so the relay remaps the volume entries in each device's keymap (`EVIOCSKEYCODE`) and handles the stand-in codes itself. That fix covers every device at once, including keyboards that aren't grabbed.
 
+The Frame controllers can be mapped like mouse buttons, but they aren't input devices on the host: they reach SteamVR over the headset's own radio, and no evdev or hidraw node exists for them. So only a SteamVR client can read them. Overlay apps normally get controller input only while they have input focus, which a background helper never has. SteamVR's experimental global action set priority (`steamvr/globalActionSetPriority`, "Enable global input from overlays") lets an overlay's action set receive input anyway, and takes the inputs it binds from the scene app. Binding every button would take them all from games, so the helper's action manifest puts each button in an action set of its own, and it activates only the sets of mapped buttons. The mapping itself stays in the relay, which does the action, so mice and controllers share one list of actions.
+
 ## The desktop session
 
 The session is modeled on SteamOS's `steamos-nested-desktop` and runs beside it. It has its own runtime directory, config (`~/.config/frametop`), and state, so it never disturbs the stock desktop's layout or panels. It runs on a private D-Bus from `dbus-run-session`, which has two consequences. KDE only launches apps in systemd scopes when systemd is on the session bus, so everything started in the desktop lands in its systemd unit, and stopping the unit would kill all of it; `session/keep-apps.sh` moves those programs out first. And tools that need the real user bus, like podman and `distrobox-host-exec`, have to be pointed at it explicitly.