Hands: pick the cameras by the light, and detect grips

ft-hands tracks with the mono IR cameras in dim light and with every
camera (or the colour pair, HANDS_BRIGHT) in bright light, going by the
colour frames' mean brightness with hysteresis and a 2 s hold
(HANDS_CAMERAS=auto, the default; mono, color and all fix it). Colour
frames are placed on the mono cameras' clock by their dequeue time, and a
view in a camera a step lacks waits for that camera's next frame.

A grip (a closed hand) is a second gesture next to the pinch, in version 2
of the gestures file: every fingertip curled toward the wrist, beginning
only on a hand seen open within a second and held up in front. On the
2026-09-30 lit recording that leaves 6 false grips of 14, all with the
hands on the desk; pinch counts are unchanged. ft-handreplay logs grips
and finger curl, watch_gestures.py shows them, and tools/cut_sets.py
copies a few sets out of a recording.

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

session/frametop.conf.example

@@ -36,6 +36,17 @@ GAZE_TRACKER=steam         # gaze service: steam = SteamVR's eye tracker | own =
 GAZE_EYE=auto              # gaze service: eye bias. auto = each eye weighted by how far off it was at your recent nudges | left | right = that eye counts twice
 HANDS_SWAP_SIDES=0         # hand tracking (hands/run.sh install): 1 = the side cameras' names are swapped, which some SteamVR restarts cause (hands/tools/check_sides.py --ring tells)
 HANDS_CPUS=5,6,7           # hand tracking: the CPUs its model threads run on
+HANDS_CAMERAS=auto         # hand tracking: auto (by the light) | mono (the IR cameras; also keeps ft-camd off the colour ones) | color | all
+HANDS_BRIGHT=all           # hand tracking, auto: the cameras in bright light, all | color
+HANDS_BRIGHT_ON=40         # hand tracking, auto: the colour frames' mean brightness (0-255) that counts as bright (a dim room reads about 9)
+HANDS_BRIGHT_OFF=25        # ... and back to the mono cameras under this
+HANDS_COLOR_LEFT=color_video0  # hand tracking: which colour camera is passthrough_left (hands/tools/check_color.py tells)
+HANDS_COLOR_CROP=subtract  # hand tracking: how the colour calibration's crop applies, subtract | none (check_color.py tells)
+POINTER_HANDS=1            # 1 = pinches click (on the release; hold and move to nudge the pointer first) and grips press and drag, with hand tracking
+POINTER_PINCH_GAIN=0.5     # hands: the pointer moves this times the pinching hand's angle (precision)
+POINTER_PINCH_DEADZONE=1.5 # hands: degrees the pinching hand moves before the pointer does (a tap's jitter)
+POINTER_GRIP_GAIN=1        # hands: the pointer moves this times the gripping hand's angle
+POINTER_GRIP_BELOW=0.3     # hands: grips beginning more than this (m) below the eyes are ignored (hands on a desk)
 META_DASHBOARD=0   # 1 = a Meta tap on a pass-through keyboard toggles the SteamVR dashboard (pointer mode only)
 SHARE_KEYS=0       # 1 = keys of keyboards grabbed for the desktop also go to @frametop_keys, for hotkey tools (any local process can listen)
 DISPLAY_OFF_MIN=0  # minutes without use before frametop-power turns the displays off, even if the headset seems worn (0 = never)