feat(ui): touch and small-screen support (U-13)

[timurbazhirov]

Stacked on claude/uiux-p2-figure-export — review that one first; this PR's diff is U-13 only.

Touch and small-screen support, the last item of the UI/UX proposal (docs/design/uiux-improvements-2026-08.md, U-13). Kept separate because it is the only item in the set that changes how input the viewer already receives is handled, rather than adding a surface — so it is worth being reviewable, and revertable, on its own.

What was actually wrong

Measured on a 390×844 touch profile before changing anything:

• The canvas had touch-action: auto, so the browser claimed every touch drag for page scroll and pinch-zoom and sent pointercancel to whatever had begun tracking it. No touch drag ever reached any handler — not orbiting, not moving an atom, not marquee select — even though every pointer handler in the editor is already pointer-event based. A one-finger swipe left the rendered frame byte-identical.
• The quick-toggle row was 32 px, and it is the primary control surface on a phone.
• The only surface documenting how to drive the viewer opened on ? alone — unreachable without a keyboard.
• isMobile was computed from the viewport width and forwarded to exactly one dropdown. That is also the wrong question twice over: a narrow window on a desktop is not touch input, and a touch laptop is touch input at any width.

Changes

• touch-action: none on the renderer canvas. One declaration, and every existing pointer handler starts working with a finger.
• Edit mode reserves the first finger, mirroring what it already does with the left mouse button (D-4): touches.ONE comes off the camera and orbit moves to two fingers (DOLLY_ROTATE). There is no right button to move it to. Restored on exit, verified across repeated round trips.
• utils/inputCapabilities.ts replaces the viewport guess with capability queries read at call time — a window can move to another display and a tablet can gain a keyboard mid-session. hasCoarsePointer gates sizing; hasTouchSupport gates documentation, so a touch laptop gets the gestures listed and keeps its compact chrome.
• Quick toggles reach 44 px under (pointer: coarse) only.
• The shortcut sheet is reachable from View ▸ Shortcuts & gestures, gains a visible Close, lists the touch gestures, and puts them first when the pointer is coarse — the sheet reflows to one column there, so group order is scroll distance, and the gestures were sitting below three groups of keyboard shortcuts.
• Nothing names an input the device lacks. The edit pill reads drag atom = move · 2 fingers = orbit on touch instead of RMB/Del/Esc; the sheet is titled "Shortcuts & gestures" rather than "Keyboard shortcuts" and drops its "? or Esc to close" hint on a coarse pointer.

Verification

• 32 new tests. Whole suite 457 passing, 32 suites, 0 failing; npm run lint and tsc --noEmit clean.
• Re-measured on the same 390×844 touch profile: main canvas touch-action: none, every button ≥ 44×44, one-finger drag rotates the camera, the sheet opens from the View menu with the touch group first and lists pinch, pill wording correct, no console errors.
• Desktop rendering and wording unchanged (checked at 1280 and 1600).

Two of the defects here came only from looking at the rendered result rather than the suite: the sheet still promised ? and Escape on a device with neither and had no visible way out, and the touch group rendered last.

🤖 Generated with Claude Code

https://claude.ai/code/session_0185JNEgEJLfZZEx7jKHgwu5

---

Generated by Claude Code

[timurbazhirov]

Closing — superseded, not dropped.

U-13 ships in #214, which carries the same commits plus the rest of the UI/UX work. The plan is #216 first (everything except U-13), then #214 on top of it, so this stacked branch has nothing left to add.

Nothing here is lost: claude/uiux-p2-touch-input stays on the remote at 7588dab if the split is ever wanted again, and every line of it is in #214.

---

Generated by Claude Code