Citation Grounding Gap

1"use client";
2 
3import { useCallback, useEffect, useId, useLayoutEffect, useRef, useState, type KeyboardEvent } from "react";
4 
5// TrestleGap — grounding coverage drawn as a walkable bridge under a RAG
6// answer. Citation pills (citation-inline-card) and coverage tracks (citation-grounding-hatch)
7// both put the evidence signal in a SEPARATE element beside or below the
8// prose; here it runs directly under the words themselves — one SVG layer,
9// measured off the live sentence buttons with Range.getClientRects() (so it
10// tracks real wrapped line boxes, not a straight synthetic strip), drawing a
11// solid 1px plank under every grounded sentence and letting the plank
12// visibly END — three fading dashes, an open gap, three dashes fading back
13// in — wherever a claim has no retrieved source. The inversion is the point:
14// the ABSENCE of grounding is the loudest mark on the page, not a pill that
15// was simply never placed. A grounded sentence is a real <button>; Enter (or
16// a click anywhere on its plank) springs up a bottom sheet with the source
17// excerpt, matched words underlined in the same plank stroke (again measured
18// with Range.getClientRects, this time over the excerpt's own text node, so
19// resizing the sheet keeps the underlines glued to the words). An ungrounded
20// sentence's gap is live: clicking it (or pressing "f" while it's focused)
21// fires a targeted find-support lookup for just that claim, announced
22// through an aria-live region, and on success the plank draws itself in
23// left-to-right via stroke-dashoffset rather than popping solid. Sentences
24// carry the accessibility semantics (aria-description: "supported by <title>"
25// / "no source found"); the SVG is aria-hidden drawing underneath them, never
26// the other way around. Every stroke is --border/--muted/--foreground —
27// --accent is reserved for the sheet's focus ring and link, never the marks
28// themselves. DOM+SVG+CSS only.
29 
30export interface TrestleSource {
31  title: string;
32  excerpt: string;
33  url?: string;
34}
35 
36export interface TrestleSentence {
37  id: string;
38  text: string;
39  /** omit, or null, for a claim with no retrieval support — its plank is drawn as a gap */
40  source?: TrestleSource | null;
41}
42 
43export interface TrestleGapProps {
44  sentences: TrestleSentence[];
45  /** Runs a retrieval attempt for one ungrounded sentence. Resolve a source on
46   * success, or null/undefined if nothing was found. Defaults to a small
47// … truncated