Interaction: the eye answers in its era's grammar

The five moments (every era has all five)

• Hit test:
  • press feedback (stage): mouse toIris < 1.05R; touch max(1.3R, 28 px);
  • going in (loader): max(56 px, R × (coarse ? 1.3 : 1)), read from the live irisAt().
• Signs live in or on the iris and pupil and never grow past the iris, except while pressing or entering.
• Signs are clipped by the lids (almond) and appear through the era's own dither.
• No two eras share a sign.

Writing an era's sign (decision procedure)

1. What did this era's interface use to say "this opens"? A cursor (1970), an arrow and inverted selection (1981), an underlined link (1991), a visited-link colour and GIF sparkle (1995), a caret (2000), a component's focus and active states (2013), lock-on brackets (2026).
2. Map the verbs. Rest = the era's idle affordance. Hover = its focus or highlight. Press = its active or selected state. Enter = its "open" (a window draws, a selection expands, a flood to the home's colour).
3. Make it physical in the medium. Draw it in the medium's cells, palette and stroke weight, never as an overlay in another style.
4. Make the pupil many parts, not one (2013's keyboard of keys, not one button). Why: a single button read as a sticker.
5. Reduced motion: steady, never gone. The sign's clock keeps running, but the sign holds its "on" state.

The visitor, measured and answered

• ptr is the pointer in top-left UV, damped at λ 8; ptrOn means a mouse is present (a finger is not a cursor).
• track means a pointer or finger was seen within 20 s, including under reduced motion.
• Near the pointer, things react: parts lift and switch on (2013), landmarks are inspected (2026). A reaction is always a state the era really had (focus, active, selected), never a glow invented for the effect.
• listen (pointer and eye speed, up λ 6, down λ 1.2) drives certainty and ripples; it is 0 when still.
• Gaze follows the pointer (eye-motion); while dragging, follow ≥ 0.6.
• The brow feels each moment (rig/brow.ts, docs/EYE_BROW_EMOTION_PLAN.md §4): back after a while → the eyebrow flash; darting in → a startle; hovering → curious ("hm?"); resting still → warm; press → a wince; release to enter → delight; cancel → relief; scribbling → puzzled, and annoyed if it goes on; fast scrub → strain, then relief; leaving the window → a faint wistful; a third dart → wary, eyes wide; three pokes that never go in → annoyed (anger's V); slipping on and off the iris → sceptical, lids lowered; a press held → an intense stare back; 25 s of nothing → gently bored. It's the face's answer, never a sign: no words, no glow, and phones get the same grammar minus hover.

Phones

• The whole almond is in frame (brow and cheek included); there's no pushed-in iris crop.
• Calm mode comes from (pointer: coarse) only: grain ×0.45, gaze ×0.6, cut durations ×1.25.
• Ghost finger demo (phones only):
  • a 44 px fingertip dot drags two eras over 1.2 s with a sine ease, pauses 380 ms and comes back;
  • the peak is 2.6 eras/s, under the 3/s rush threshold, so the eye blinks at each era instead of shutting against the rush;
  • then it glides to the iris and taps with a ring;
  • first play 900 ms after the opening, replays after 8 s idle, at most 3 plays;
  • stopped by any touch, key or wheel; tap only if the visitor has already swiped. No words.
• Touch scrub is relative: one era per clamp(innerWidth/7, 44, 64) pt. Why: ten eras across a phone's width hide the target under the thumb.
• Touch taps off the iris do nothing. Why: half of them are a thumb finding the screen. Every label and line has a phone floor (2026's labels at 1.55% of H; minor callouts drop).
• Sizes follow the iris (kc), so a phone sees the same design at its own scale.

The loader surface (desktop and keyboard)

• Full-screen role="slider" with touch-action: none, focused on mount. aria-valuetext is the era's name, read by screen readers with no visible word.
• Mouse: an absolute sweep with an 8% dead zone each side, so both ends are easy to reach. A click off the iris jumps to the year under the cursor.
• A tap is ≤ 8 px and ≤ 520 ms. Travel never starts on press. Why: a tap on the iris means "take me in", not "take me to this year".
• Keyboard (on window): →/↑ +1, ←/↓ −1, PageUp/PageDown ±3, Home/End; Enter/Space go in. Ignored with modifiers and in inputs.
• Wheel: one gesture is one era, however hard it is pushed.
  • A gesture is a run of deltas on the dominant axis with no gap longer than 450 ms, measured by the event's own timeStamp. Why: the cut keeps the main thread busy, and late-handled deltas would otherwise look like a pause.
  • It steps once its deltas reach 60; the rest of the gesture is spent. Anything within 900 ms of a step belongs to it. A reversal starts a new gesture.
  • Why: a banked wheel let a hard flick run to the last era, and visitors got lost.
• Cursor over the iris is the era's own (cssCursor): the Star arrow for 1981, pointer for 1995/2003/2009, text for 2000. It is set inline, because a global rule forces the arrow.

Realism pass: signs sit on the real eye (C4)

• Pupil signs (1970's cursor, 2000's caret, 2013's keyboard, 2026's brackets and fit) centre on the apparent (refracted) pupil and size by its radius. After R1 or R4, re-shoot rest, hover and press for those four.
• Limbus signs (1995's ring, 2013's segments, 2026's limbus fit) follow the elliptic limbus.
• 1991's underline reads the twin's lower-margin samples, never a guessed curve.
• Hit tests use the apparent iris radius.
• Pupil reactions (near reflex on approach, interest dilation) take R13's dynamics too (0.23 s latency, speed caps). Re-check the hover dilation's timing after R13.

Never

• Never sound, and never a microphone, even for a voice era.
• Never a permission prompt. Use device tilt only where no dialog is needed (Android). On iOS keep finger gaze. Why: a dialog at the front door makes people leave.
• Never a hint of the neighbouring era, an arrow, an edge band or a label at rest.
• Never action on pointer-down.
• Never a hover-only sign.
• On the real loader, Enter and Space are guarded for 0.9 s after the opening and 1.5 s after typing. Why: typing through the hand-off used to enter the site.