Calibration all in the headset panel; the gaze probe is a development tool

Check headset fit now runs in the headset panel too ("fitcheck"): a card per
eye (tracked or lost, the tracker's signal, how much of the last 10 s it was
seen) and the hints, from the probe's fitcheck.py, updated at most twice a
second; left click or Meta+J runs its guided check, right click or Meta+K closes
it. So Quick check, Calibrate, and Check headset fit all happen in one place.

The gaze probe moves to the Gaze page's overflow menu as "Gaze probe
(development)", and its app menu entry says it's a development tool. Texts that
sent users to it ("use Calibrate… with Own tracker") point at Calibrate.

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

gaze/README.md

@@ -5,7 +5,7 @@ The Steam Frame's eye tracking as pointer input: a gaze mode for the 3D mouse (t
 - `ft-gaze` (C++, OpenVR, runs in the dev container) reads the eye tracker and prints one JSON line per sample (90 Hz). For each source, it gives the gaze direction relative to the head and the Frametop screen pixel it lands on.
 - `gazecal.py` has what the probe and the gaze service share: the correction models, filters, and the reader for SteamVR's eye tracking log.
 - `tracker/` is our own eye tracker, an alternative to SteamVR's: `ft-eyes` finds the pupils and glints in the eye-camera frames that `ft-eyegrab` (a small root service) copies out of SteamVR's tracker. See "Our own eye tracker" below.
-- `probe/ft-gazeprobe` (GTK 4, host Python) is a fullscreen playground. It runs ft-gaze, draws where you're looking, measures accuracy, and tries out hold-to-adjust clicking with a calibration that learns from your adjustments.
+- `probe/ft-gazeprobe` (GTK 4, host Python) is a fullscreen playground, for developing the gaze tracking: day to day, the calibration and the checks run in the headset panel (Quick check, Calibrate, and Check headset fit on the Gaze page). It runs ft-gaze, draws where you're looking, measures accuracy, and tries out hold-to-adjust clicking with a calibration that learns from your adjustments.
 
 ```
 gaze/build.sh                 # build ft-gaze
@@ -64,12 +64,14 @@ Ground rules, for anyone changing it:
 
 ## Headset fit
 
-The probe's Headset fit mode (Check headset fit on the Gaze page, or `ft-gazeprobe --mode fit`) shows, for each eye, whether the tracker has it, how open it is, and the tracker's confidence in it, and a map of where you looked coloured by how often it lost that eye there. Hints under the maps say which eye gets lost where, and what to try. Enter runs a guided check: dots around the screen, then looking down at the keyboard, up, left and right. R starts over. Adjust the headset while you watch it.
+Check headset fit on the Gaze page opens it in the headset panel: a card per eye (tracked or lost, the tracker's signal, how much of the last 10 s it was seen) and the hints, live while you adjust the headset. A left click or Meta+J runs the guided check (dots, then looks down, up, left and right), and a right click or Meta+K closes it. The probe's Headset fit mode (`ft-gazeprobe --mode fit`, for development) has the same check with maps: it shows, for each eye, whether the tracker has it, how open it is, and the tracker's confidence in it, and a map of where you looked coloured by how often it lost that eye there. Hints under the maps say which eye gets lost where, and what to try. Enter runs a guided check: dots around the screen, then looking down at the keyboard, up, left and right. R starts over. Adjust the headset while you watch it.
 
 Losing an eye is usually about where you look, not the tracker. On this Frame the left eye was lost 57 to 64 % of the time looking 30 to 50 degrees down (at the keyboard) and the right eye never; at screen height both were seen over 98 % of the time. Looking down, the lids come down over the eyes. That's harmless, since the gaze service ignores looks down past the screens: they show on the maps, but not in the counts or as a problem.
 
 ## Probe
 
+The probe is a development tool (in the Gaze page's overflow menu): calibration experiments, accuracy tests, and practice modes. Users calibrate and check in the headset panel instead.
+
 The trigger is Enter, Space, or a mouse button. Right-click anywhere in the window (or press the Menu key or Shift+F10) for a menu with Run calibration, Start accuracy test, Calibrate from last test, Reset calibration, the modes, the panel, fullscreen, and Quit. The buttons at the top right show and hide the panel, leave fullscreen, and quit. The arrow in the panel's title bar collapses it to just that bar, so the dot and targets behind it stay visible; the collapsed bar stays through tests. The keys do the same (Tab, C, F11, Esc), but only after you click the window once, since Frametop sends typing to the panel you clicked last. If ft-gaze stops, the probe starts it again after 3 s and shows why it stopped. Windowed mode stays on the screen it was on, and a small KWin script tells the probe where the window is, so the dot and targets are still in the right place.
 
 - **Run calibration (start here):** the initial calibration, modeled on Apple Vision Pro's eye setup. Face the centre and keep your head still. Look at one dot and press the trigger, then at each of six dots in a circle. That happens in three rounds, and the screen goes dark, then medium, then bright, because pupil size changes with brightness and the tracker's error with it. Each round turns the ring 20 degrees, and the middle round's ring is half the size, so the 21 dots cover the middle, halfway out, and the edge of your view. The ring's size is `Calibration ring` (degrees, 20 by default, less if the window is too small). Error grows toward the edge, and the calibration can only correct as far out as it has seen dots. The current dot is a bright pulsing dot with a point in the middle; finished dots fade to specks, so your eyes don't go back to them. Samples from blinks and from moments when the tracker lost an eye are dropped: openness under half of what it was during that look (not a fixed level, because your lids come down when you look down, and you squint in the bright round), or the angle between the eyes jumping more than 1.5 degrees from its median (that angle depends on how far away you're looking, so only a jump counts). Each dot is measured with medians, so one bad sample can't fail it. A look that lands where the gaze was for another dot of the round is refused as a look at the wrong dot. Mouse clicks don't count during a calibration run or a test: use Enter or Space. If a dot still fails, the message says why and the next try listens longer. After two failures, S (or the menu) skips the dot. Every attempt is logged to `calibration-attempts.jsonl`. At the end it fits every source's calibration from all the dots, replacing what it had learned (quadratic if the model was none). Esc cancels. The run is saved as `calibration-*.json`. With "Test after calibration" on (the default), the accuracy test starts right after, on new spots.