ns-ui
Zipper Stall
Merge resolution staged as closing a zipper: two columns of timestamped edit ops, meshed by dragging a handle down the spine that physically jams at the first same-offset conflict until you pick a side.
Use when resolving concurrent edits from two streams (a merge, not a single-author diff) where arrival order and the exact point a conflict blocks progress need to be physical and scrubbable, not a static list of conflict markers — one scalar (closure position down the spine) drives every tooth's state, and dragging past a same-offset conflict genuinely jams rather than being skippable. Pick approval-inline-diff instead for a single agent-proposed change a human edits and approves/denies field by field; that job has one author and no arrival order to interleave.
Install
npx shadcn add https://design.helpmarq.comSource
registry/core/zipper-stall/component.tsx"use client";
import { useEffect, useId, useMemo, useRef, useState } from "react";
// ---------------------------------------------------------------------------
// ZipperStall — merge resolution staged as closing a zipper. Two columns of
// teeth (your ops, their ops), one operation per tooth, laid down the spine
// in arrival order. A single scalar, closureY (px down the spine), governs
// everything: which teeth have meshed flush to the spine, where the drag
// handle sits, the merged-count readout, and which conflict (if any) is
// live. There is no per-tooth animation clock — a tooth's transform is a
// pure function of closureY crossing its row's center, expressed as a CSS
// transition on a state flip, so scrubbing the handle back deterministically
// re-opens teeth in the same order they closed.
//
// A conflict is two ops that land on the same document offset — they share
// a row and neither can mesh until the human picks a side. The real
// mechanism for "the slider physically cannot pass a conflict" is that the
// native <input type="range"> always spans the FULL spine in its min/max
// (so the handle's pixel position always corresponds to real row geometry),
// while the COMMITTED value is clamped in JS to conflictCenter - 8px. Native
// max never shrinks — only the reachable value does — which is what keeps
// "where it stops" honest against the rows actually drawn underneath it,
// rather than a max attribute that would silently rescale the whole track.
// A parallel signal (the raw value reported by the same change event, before
// clamping) drives a small 0-3px "jam" bump on the decorative handle cap via
// a k=500 spring, so pushing past the wall reads as resistance, not a wall
// that silently swallows input. prefers-reduced-motion turns that spring
// into a single instant border flash instead.
//
// A11y: the range input is real (native min/max/step, arrow/Home/End work),
// carries aria-valuetext ("12 of 14 ops merged, stopped at conflict 1 of
// 3"). The spine itself is a plain <ol>, one <li> per row, each named for
// screen readers ("theirs, 14:02, replaced heading"; conflicts name both
// sides plus resolution status). Resolution is two real <button>s that
// appear only once the handle is actually jammed against that row, so a
// prior programmatic click on the handle (which jumps value like any native
// range) still leaves the same buttons re-derivable and clickable.
// ---------------------------------------------------------------------------
export type ZipperSide = "ours" | "theirs";
export interface ZipperOp {
/** stable id */
id: string;
/** which edit stream this op came from */
side: ZipperSide;
/** arrival order — lower sorts first; ties are fine */
t: number;
/** display timestamp, e.g. "14:02" — pre-formatted, never Date-derived, so
* server and client render byte-identical text */
timestamp: string;
/** document offset this op targets. two ops sharing an offset conflict. */
offset: number;
/** short description, e.g. "replaced heading" */
label: string;
}
export interface ZipperStallProps {
/** the two edit streams, unsorted — sorted internally by t */
ops: ZipperOp[];
/** column heading over the left (ours) teeth */
oursLabel?: string;
/** column heading over the right (theirs) teeth */
theirsLabel?: string;
/** px height of one row / one tooth */
rowHeight?: number;
/** called every time a conflict is resolved */
onResolve?: (kept: ZipperOp, droppedOp: ZipperOp) => void;
/** called once the spine is fully closed with nothing left pending */
onComplete?: () => void;
/** extra classes merged onto the rendered root element */
className?: string;
}
type Row = {
key: string;
offset: number;
ours?: ZipperOp;
theirs?: ZipperOp;
conflict: boolean;
center: number; // px, along the spine
};
const TRACK_W = 28;
const CLAMP_GAP = 8;
const BUMP_MAX = 3;
const BUMP_GAIN = 0.6; // px raw overrun -> px of visible bump, pre-clamp
const SPRING_K = 500; // s^-2
const SPRING_ZETA = 0.5;
const FLASH_MS = 150;
function buildRows(ops: ZipperOp[]): Row[] {
const sorted = [...ops].sort((a, b) => a.t - b.t);
const rows: Row[] = [];
const rowForOffset = new Map<number, number>();
for (const op of sorted) {
const existingIdx = rowForOffset.get(op.offset);
const existing = existingIdx !== undefined ? rows[existingIdx] : undefined;
if (existing && !existing[op.side]) {
existing[op.side] = op;
existing.conflict = !!existing.ours && !!existing.theirs;
continue;
}
const row: Row = {
key: `${op.offset}-${rows.length}`,
offset: op.offset,
conflict: false,
center: 0,
[op.side]: op,
} as Row;
rowForOffset.set(op.offset, rows.length);
rows.push(row);
}
return rows;
}
function clamp(v: number, lo: number, hi: number) {
return Math.min(hi, Math.max(lo, v));
}
export function ZipperStall({
ops,
oursLabel = "Yours",
theirsLabel = "Theirs",
rowHeight = 44,
onResolve,
onComplete,
className = "",
}: ZipperStallProps) {
const uid = useId();
const ROW_H = rowHeight > 0 ? rowHeight : 44;
const rows = useMemo(() => {
const built = buildRows(ops);
return built.map((r, i) => ({ ...r, center: i * ROW_H + ROW_H / 2 }));
}, [ops, ROW_H]);
const spineHeight = rows.length * ROW_H;
const totalOps = ops.length;
const [closureY, setClosureY] = useState(0);
const [resolved, setResolved] = useState<Record<string, ZipperSide>>({});
const [bump, setBump] = useState(0);
const [flash, setFlash] = useState(false);
const [announce, setAnnounce] = useState("");
const [focused, setFocused] = useState(false);
const [hovering, setHovering] = useState(false);
const [pressed, setPressed] = useState(false);
const closureYRef = useRef(closureY);
closureYRef.current = closureY;
const reducedRef = useRef(false);
useEffect(() => {
const mq = window.matchMedia("(prefers-reduced-motion: reduce)");
reducedRef.current = mq.matches;
const onChange = () => {
reducedRef.current = mq.matches;
};
mq.addEventListener("change", onChange);
return () => mq.removeEventListener("change", onChange);
}, []);
const conflictRows = useMemo(() => rows.filter((r) => r.conflict), [rows]);
const firstUnresolvedConflict = useMemo(
() => conflictRows.find((r) => !resolved[r.key]),
[conflictRows, resolved]
);
const effectiveMax = firstUnresolvedConflict
? Math.max(0, firstUnresolvedConflict.center - CLAMP_GAP)
: spineHeight;
const jammed = firstUnresolvedConflict !== undefined && closureY >= effectiveMax;
const mergedCount = useMemo(() => {
let n = 0;
for (const row of rows) {
if (row.conflict) {
// a resolved conflict is two decided ops (the kept one meshed, the
// dropped one filed down) — both count toward the total, since the
// filed-down tooth is a decided record, not an unmerged one.
const side = resolved[row.key];
if (side && closureY >= row.center) n += 2;
} else if (closureY >= row.center) {
n += 1;
}
}
return n;
}, [rows, resolved, closureY]);
const completedRef = useRef(false);
useEffect(() => {
const allResolved = conflictRows.every((r) => resolved[r.key]);
const done = allResolved && closureY >= spineHeight && spineHeight > 0;
if (done && !completedRef.current) {
completedRef.current = true;
setAnnounce(`Merge complete: ${totalOps} of ${totalOps} ops merged.`);
onComplete?.();
} else if (!done) {
completedRef.current = false;
}
// eslint-disable-next-line react-hooks/exhaustive-deps
}, [closureY, resolved, conflictRows, spineHeight]);
// -- bump / flash engine (excess drag past the clamp, purely visual) -----
const excessRef = useRef(0);
const bumpRef = useRef(0);
const bumpVelRef = useRef(0);
const rafRef = useRef(0);
const flashTimerRef = useRef<ReturnType<typeof setTimeout> | undefined>(
undefined
);
// excess decays on its own ~100ms after the last push registers it, so a
// single keypress or a drag that ends mid-push still springs back instead
// of sitting jammed forever waiting for a change event that never comes
const excessDecayRef = useRef<ReturnType<typeof setTimeout> | undefined>(
undefined
);
useEffect(() => {
return () => {
if (rafRef.current) cancelAnimationFrame(rafRef.current);
if (flashTimerRef.current) clearTimeout(flashTimerRef.current);
if (excessDecayRef.current) clearTimeout(excessDecayRef.current);
};
}, []);
const wakeSpring = () => {
if (rafRef.current) return;
let last = performance.now();
const tick = (now: number) => {
const dt = Math.min(0.032, Math.max(0, (now - last) / 1000));
last = now;
const target = clamp(excessRef.current * BUMP_GAIN, 0, BUMP_MAX);
const c = 2 * SPRING_ZETA * Math.sqrt(SPRING_K);
const disp = bumpRef.current - target;
bumpVelRef.current += (-SPRING_K * disp - c * bumpVelRef.current) * dt;
bumpRef.current += bumpVelRef.current * dt;
if (
Math.abs(bumpRef.current - target) < 0.05 &&
Math.abs(bumpVelRef.current) < 1 &&
excessRef.current === 0
) {
bumpRef.current = 0;
bumpVelRef.current = 0;
setBump(0);
rafRef.current = 0;
return;
}
setBump(bumpRef.current);
rafRef.current = requestAnimationFrame(tick);
};
rafRef.current = requestAnimationFrame(tick);
};
const registerExcess = (excess: number) => {
excessRef.current = excess;
if (excessDecayRef.current) clearTimeout(excessDecayRef.current);
if (excess > 0) {
excessDecayRef.current = setTimeout(() => {
excessRef.current = 0;
if (!reducedRef.current) wakeSpring();
}, 100);
}
if (excess <= 0 && bumpRef.current === 0) return;
if (reducedRef.current) {
if (excess > 0) {
setFlash(true);
if (flashTimerRef.current) clearTimeout(flashTimerRef.current);
flashTimerRef.current = setTimeout(() => setFlash(false), FLASH_MS);
}
return;
}
wakeSpring();
};
const commit = (raw: number) => {
const bounded = clamp(raw, 0, spineHeight);
const excess = Math.max(0, bounded - effectiveMax);
registerExcess(excess);
const next = Math.min(bounded, effectiveMax);
if (next !== closureYRef.current) setClosureY(next);
};
const inputRef = useRef<HTMLInputElement>(null);
const draggingRef = useRef(false);
// authoritative pointer math — kept independent of native drag-to-value so
// synthetic pointer events (the autoplay driver, dispatched programmatically
// via dispatchEvent) drive the same commit() path a real drag does; a real
// browser's own native slider-drag would otherwise never see a synthetic
// pointerdown/move as a drag gesture at all.
const rawFromClientY = (clientY: number) => {
const rect = inputRef.current?.getBoundingClientRect();
if (!rect || rect.height <= 0) return closureYRef.current;
return ((clientY - rect.top) / rect.height) * spineHeight;
};
const onPointerDownInput = (e: React.PointerEvent<HTMLInputElement>) => {
draggingRef.current = true;
setPressed(true);
e.currentTarget.setPointerCapture(e.pointerId);
commit(rawFromClientY(e.clientY));
};
const onPointerMoveInput = (e: React.PointerEvent<HTMLInputElement>) => {
if (!draggingRef.current) return;
commit(rawFromClientY(e.clientY));
};
const endDrag = () => {
draggingRef.current = false;
setPressed(false);
if (excessDecayRef.current) clearTimeout(excessDecayRef.current);
excessRef.current = 0;
if (!reducedRef.current) wakeSpring();
};
const onChange = (e: React.ChangeEvent<HTMLInputElement>) => {
// fallback for any change the pointer/keyboard handlers above didn't
// already cover (e.g. an assistive-tech-driven value set)
commit(Number(e.target.value));
};
const onKeyDown = (e: React.KeyboardEvent<HTMLInputElement>) => {
const v = closureYRef.current;
let next: number | null = null;
switch (e.key) {
case "ArrowDown":
case "ArrowRight":
next = v + ROW_H;
break;
case "ArrowUp":
case "ArrowLeft":
next = v - ROW_H;
break;
case "PageDown":
next = v + ROW_H * 3;
break;
case "PageUp":
next = v - ROW_H * 3;
break;
case "Home":
next = 0;
break;
case "End":
next = spineHeight;
break;
default:
return;
}
e.preventDefault();
commit(next);
};
const resolve = (row: Row, side: ZipperSide) => {
if (!row.ours || !row.theirs || resolved[row.key]) return;
const kept = side === "ours" ? row.ours : row.theirs;
const dropped = side === "ours" ? row.theirs : row.ours;
setResolved((r) => ({ ...r, [row.key]: side }));
setAnnounce(
`Kept ${kept.side}, ${kept.timestamp}, ${kept.label}. ${dropped.side} version struck through, not taken.`
);
onResolve?.(kept, dropped);
inputRef.current?.focus({ preventScroll: true });
};
const conflictIndex = firstUnresolvedConflict
? conflictRows.indexOf(firstUnresolvedConflict) + 1
: 0;
const valueText = jammed
? `${mergedCount} of ${totalOps} ops merged, stopped at conflict ${conflictIndex} of ${conflictRows.length}`
: `${mergedCount} of ${totalOps} ops merged`;
const capY = closureY + bump;
return (
<div className={`w-full max-w-2xl font-mono ${className}`}>
<style>{`
.zs-tooth{transition:transform 90ms cubic-bezier(0.16,1,0.3,1),opacity 90ms cubic-bezier(0.16,1,0.3,1),color 90ms linear;}
.zs-fold{transition:transform 160ms cubic-bezier(0.16,1,0.3,1),opacity 160ms cubic-bezier(0.16,1,0.3,1);}
.zs-cap{transition:background-color 120ms linear,box-shadow 120ms linear;}
.zs-flash{transition:border-color 60ms linear;}
@media (prefers-reduced-motion: reduce){
.zs-tooth,.zs-fold,.zs-cap{transition:none;}
}
`}</style>
<div className="mb-3 flex items-baseline justify-between gap-3">
<div>
<p className="text-[10px] uppercase tracking-[0.2em] text-ns-muted">
merge closure
</p>
<p className="mt-0.5 text-xs text-ns-muted" aria-hidden>
{jammed
? `stopped at conflict ${conflictIndex} of ${conflictRows.length}`
: `${mergedCount} / ${totalOps} ops merged`}
</p>
</div>
<div className="grid grid-cols-[1fr_28px_1fr] gap-1 px-2 text-[10px] uppercase tracking-[0.15em] text-ns-muted">
<span className="text-right">{oursLabel}</span>
<span aria-hidden />
<span className="text-left">{theirsLabel}</span>
</div>
</div>
<div className="relative" style={{ height: spineHeight }}>
<ol
className="relative list-none divide-y divide-border/60 rounded-md border border-border"
aria-label="Merge operations, in arrival order"
>
{rows.map((row) => (
<li
key={row.key}
style={{ height: ROW_H }}
className="grid grid-cols-[1fr_28px_1fr] items-center gap-1 px-2"
aria-label={rowAriaLabel(row, resolved[row.key])}
>
<div className="flex justify-end">
{row.ours ? (
<Tooth
op={row.ours}
align="right"
state={toothState(row, "ours", closureY, resolved)}
/>
) : null}
</div>
<div aria-hidden />
<div className="flex justify-start">
{row.theirs ? (
<Tooth
op={row.theirs}
align="left"
state={toothState(row, "theirs", closureY, resolved)}
/>
) : null}
</div>
</li>
))}
</ol>
{/* decorative spine: rail, fill, and the visual handle cap — all
pure functions of closureY/bump, no independent animation */}
<div
aria-hidden
className="pointer-events-none absolute inset-y-0 left-1/2"
style={{ width: TRACK_W, transform: "translateX(-50%)" }}
>
<div
className="absolute left-1/2 top-0 bottom-0 w-px"
style={{ transform: "translateX(-50%)", backgroundColor: "var(--border)" }}
/>
<div
className="absolute left-1/2 top-0 w-px"
style={{
height: capY,
transform: "translateX(-50%)",
backgroundColor: "var(--foreground)",
opacity: 0.5,
}}
/>
<div
className={`zs-cap zs-flash absolute left-1/2 rounded-full border ${
flash ? "border-ns-accent" : "border-border"
}`}
style={{
top: capY,
width: TRACK_W,
height: 18,
transform: "translate(-50%, -50%)",
backgroundColor:
focused || hovering || pressed
? "var(--ns-accent)"
: "var(--foreground)",
boxShadow: focused
? "0 0 0 2px var(--background), 0 0 0 4px var(--ns-accent)"
: "none",
}}
/>
</div>
{/* the real control — spans the full spine so its pixel position
always maps to the rows actually drawn beneath it; the reachable
VALUE is clamped in JS, the native max never shrinks */}
<input
ref={inputRef}
type="range"
min={0}
max={spineHeight}
step={1}
value={closureY}
data-zipper-input
aria-label="Merge closure"
aria-valuemin={0}
aria-valuemax={effectiveMax}
aria-valuenow={closureY}
aria-valuetext={valueText}
onChange={onChange}
onKeyDown={onKeyDown}
onFocus={() => setFocused(true)}
onBlur={() => setFocused(false)}
onPointerEnter={() => setHovering(true)}
onPointerLeave={() => setHovering(false)}
onPointerDown={onPointerDownInput}
onPointerMove={onPointerMoveInput}
onPointerUp={endDrag}
onPointerCancel={endDrag}
className="absolute cursor-ns-resize touch-none appearance-none bg-transparent opacity-0 outline-none"
style={{
top: "50%",
left: "50%",
width: spineHeight,
height: TRACK_W,
margin: 0,
transform: "translate(-50%, -50%) rotate(90deg)",
}}
/>
{/* resolution: two real buttons, only present once the handle is
genuinely jammed against this row. z-20 keeps them clickable
above the full-height transparent input they visually sit atop. */}
{jammed && firstUnresolvedConflict?.ours && firstUnresolvedConflict?.theirs ? (
<div
className="absolute left-1/2 z-20 flex -translate-x-1/2 -translate-y-1/2 gap-1.5"
style={{ top: firstUnresolvedConflict.center }}
>
<button
type="button"
data-zipper-choice
onClick={() => resolve(firstUnresolvedConflict, "ours")}
className="whitespace-nowrap rounded-full border border-border bg-background px-2 py-1 text-[10px] font-medium uppercase tracking-wide text-foreground transition-colors hover:border-ns-accent hover:text-ns-accent focus-visible:border-ns-accent focus-visible:text-ns-accent focus-visible:ring-2 focus-visible:ring-ns-accent"
>
Keep {oursLabel.toLowerCase()}
</button>
<button
type="button"
data-zipper-choice
onClick={() => resolve(firstUnresolvedConflict, "theirs")}
className="whitespace-nowrap rounded-full border border-border bg-background px-2 py-1 text-[10px] font-medium uppercase tracking-wide text-foreground transition-colors hover:border-ns-accent hover:text-ns-accent focus-visible:border-ns-accent focus-visible:text-ns-accent focus-visible:ring-2 focus-visible:ring-ns-accent"
>
Keep {theirsLabel.toLowerCase()}
</button>
</div>
) : null}
</div>
<p role="status" aria-live="polite" className="sr-only">
{announce}
</p>
<p className="mt-2 text-[11px] text-ns-muted">
drag, or arrow keys, down the spine to merge · a stall means pick a
side before it can continue
</p>
<p className="sr-only" id={`${uid}-hint`}>
Struck-through rows are edits that were not taken; they stay in the
list as a permanent record.
</p>
</div>
);
}
function toothState(
row: Row,
side: ZipperSide,
closureY: number,
resolved: Record<string, ZipperSide>
): "pending" | "meshed" | "kept" | "folded" {
if (!row.conflict) {
return closureY >= row.center ? "meshed" : "pending";
}
const winner = resolved[row.key];
if (!winner) return "pending";
if (winner === side) return closureY >= row.center ? "kept" : "pending";
return "folded";
}
function rowAriaLabel(row: Row, winner: ZipperSide | undefined): string {
if (!row.conflict) {
const op = (row.ours ?? row.theirs) as ZipperOp;
return `${op.side}, ${op.timestamp}, ${op.label}`;
}
const a = row.ours as ZipperOp;
const b = row.theirs as ZipperOp;
const status = winner
? `resolved, kept ${winner}`
: "conflict, unresolved, stalls the merge here";
return `ours, ${a.timestamp}, ${a.label}; theirs, ${b.timestamp}, ${b.label} — ${status}`;
}
function Tooth({
op,
align,
state,
}: {
op: ZipperOp;
align: "left" | "right";
state: "pending" | "meshed" | "kept" | "folded";
}) {
const dx = align === "right" ? 16 : -16;
const isFolded = state === "folded";
const flush = state === "meshed" || state === "kept";
if (isFolded) {
return (
<div
className="zs-fold max-w-[11rem] truncate rounded-md px-1.5 py-0.5 text-[11px]"
style={{ transform: "translateX(0) scaleY(0.5)", opacity: 0.7 }}
title={`${op.timestamp} · ${op.label} · not taken`}
>
<s className="text-ns-muted decoration-1">{op.label}</s>
<span className="ml-1 text-[9px] uppercase tracking-wide text-ns-muted">
not taken
</span>
</div>
);
}
return (
<div
className="zs-tooth max-w-[11rem] truncate rounded-md border px-1.5 py-1 text-[11px]"
style={{
transform: `translateX(${flush ? 0 : dx}px)`,
borderColor: flush ? "transparent" : "var(--border)",
color: flush ? "var(--foreground)" : "var(--ns-muted)",
}}
title={`${op.timestamp} · ${op.label}`}
>
<span className="tabular-nums text-ns-muted">{op.timestamp}</span>{" "}
{op.label}
</div>
);
}
Build spec
Build a merge-resolution control where two edit streams (ours, theirs) render as two columns of 'teeth' down a shared spine, one operation per tooth, and a single scalar — closureY, px down the spine — is the ONLY thing that drives every tooth's meshed/open state, the drag handle's position, the merged-op count, and which conflict (if any) is currently live; there must be no per-tooth animation clock, since independently-timed teeth could mesh out of arrival order and misrepresent causality. DATA: ops are {id, side, t (arrival order), timestamp (pre-formatted display string, never Date-derived, so server/client render identically), offset (document position), label}. Sort by t, then group into rows keyed by offset: the first op seen at an offset creates a row at the next spine position; a second op arriving later at the SAME offset joins that row on the other side and marks it a conflict — this is the only conflict condition. GEOMETRY: rows are fixed-height (rowHeight, default 44px) list items; row i's mesh threshold (center) is i*rowHeight + rowHeight/2; spineHeight is rows.length*rowHeight. MESHING: a non-conflict tooth is 'meshed' (flush, translateX 0) exactly when closureY >= its row's center, else it sits at a resting column offset of +-16px; that boolean flip drives a 90ms ease-out-expo (cubic-bezier(0.16,1,0.3,1)) CSS transition on transform/opacity/color — nothing else times it, so scrubbing the handle backward deterministically re-opens every tooth in reverse. A conflict row's teeth stay at their +-16px resting offset forever, regardless of closureY, until resolved. THE STALL: the native <input type=range> driving closureY always has min=0, max=spineHeight (constant, never rescaled) so its pixel position always corresponds to the real rows drawn underneath it; the COMMITTED value is clamped in the onChange/keydown handler to at most (firstUnresolvedConflict.center - 8px). Never shrink the native max to fake this — that would silently rescale the whole track and break 'the handle's position IS the row it's stuck at'. The SAME change event's raw (pre-clamp) value drives a 0-3px 'jam' bump on a decorative handle-cap element via a critically-adjacent spring (k=500 s^-2, zeta=0.5, semi-implicit Euler, rAF loop that tears down once settled) so pushing past the wall reads as resistance, not a control that silently stopped responding. RESOLUTION: once jammed, two real <button>s ('keep yours' / 'keep theirs') render inline at that row (a relatively-positioned wrapper at z-index above the full-height transparent input, since the buttons sit inside the same narrow center column the drag control spans); clicking one sets that row's resolved side, fires onResolve(kept, dropped), returns focus to the range input, and announces the decision through a role=status aria-live=polite region. The chosen op then meshes exactly like any normal tooth (closureY vs its row's center, same transition); the OTHER op immediately and permanently transitions to a folded state — scaleY(0.5), reduced opacity, its label in a <s> strikethrough, captioned 'not taken' — that never depends on closureY again and is never removed from the list, since it's a genuine one-way decision, not something scrubbing should undo. Resolving unblocks the max for whatever conflict comes next, if any. KEYBOARD: the input's own onKeyDown intercepts ArrowDown/Right (+1 row), ArrowUp/Left (-1 row), PageDown/PageUp (+-3 rows), Home/End (0 / spineHeight), each going through the exact same commit()-and-clamp path as pointer dragging — native default stepping is preempted so 'down' always means 'more closure' regardless of the control's visual rotation. A11Y: aria-label 'Merge closure', aria-valuemin/now explicit, aria-valuemax explicitly set to the CURRENT reachable max (not the nominal spine total) so assistive tech reports the real boundary, aria-valuetext formatted as '{merged} of {total} ops merged' or, while jammed, '{merged} of {total} ops merged, stopped at conflict {n} of {N}'. The spine is a plain <ol> — one <li> per row — each with an aria-label naming its op(s): 'theirs, 14:02, replaced heading' for a normal row, both sides plus resolution status ('conflict, unresolved, stalls the merge here' or 'resolved, kept ours') for a conflict row. VISUAL: the native input is full-height, fully transparent (opacity 0, outline none) and rotated 90deg via a centered CSS transform (translate(-50%,-50%) rotate(90deg) on a box whose pre-rotation width equals spineHeight) so native click-to-position and drag physics work correctly against the real rotated geometry; every visible pixel (rail, fill, handle cap, focus ring) is a separate aria-hidden decorative layer computed straight from closureY/bump/focus/hover/press React state, tokens only (var(--foreground) resting, var(--ns-accent) only while focused/hovered/pressed, var(--border) for rails and idle tooth borders, var(--ns-muted) for idle tooth text and folded rows). REDUCED MOTION: the spring loop is replaced outright by a single ~150ms border-color flash on the handle cap (no rAF, a setTimeout toggle) and all tooth transitions become instant via a prefers-reduced-motion media query zeroing their transition property — the merge is fully readable and resolvable with zero animation.
Props
| Prop | Type | Default | Description |
|---|---|---|---|
| ops | ZipperOp[] | — | the two edit streams, unsorted — sorted internally by t |
| oursLabel? | string | "Yours" | column heading over the left (ours) teeth |
| theirsLabel? | string | "Theirs" | column heading over the right (theirs) teeth |
| rowHeight? | number | 44 | px height of one row / one tooth |
| onResolve? | (kept: ZipperOp, droppedOp: ZipperOp) => void | — | called every time a conflict is resolved |
| onComplete? | () => void | — | called once the spine is fully closed with nothing left pending |
| className? | string | — | extra classes merged onto the rendered root element |