docling_pdf/

assemble.rs

//! Layout-driven assembly: map detected [`Region`]s + text cells to a
//! [`DoclingDocument`], mirroring docling's page-assembly + reading-order.
//!
//! Overlapping detections are resolved greedily by score, each text cell is
//! assigned to its best-containing region, regions are ordered in reading order
//! (two-column aware), and each becomes a typed node by its layout label.

use docling_core::{CaptionParent, Node, PictureClass, PictureImage, Table};
#[cfg(feature = "ml")]
use image::RgbImage;

use crate::layout::Region;
use crate::pdfium_backend::{PdfPage, TextCell};

fn area(l: f32, t: f32, r: f32, b: f32) -> f32 {
    ((r - l).max(0.0)) * ((b - t).max(0.0))
}

/// Intersection area of two boxes.
fn inter(a: &Region, l: f32, t: f32, r: f32, b: f32) -> f32 {
    let il = a.l.max(l);
    let it = a.t.max(t);
    let ir = a.r.min(r);
    let ib = a.b.min(b);
    area(il, it, ir, ib)
}

/// Wrapper (structured-region) labels, ported from docling
/// `LayoutPostprocessor.WRAPPER_TYPES`: a region that *contains* other regions
/// and renders as a structured block (a table / table-of-contents index), not as
/// its own flat text.
fn is_wrapper(label: &str) -> bool {
    matches!(
        label,
        "table" | "document_index" | "form" | "key_value_region"
    )
}

/// Labels docling's table-structure (TableFormer) model runs on and that render
/// as a Markdown table: a plain `table` and a `document_index` (a table of
/// contents), which docling assembles as a `TableItem` too.
pub fn is_table_like(label: &str) -> bool {
    matches!(label, "table" | "document_index")
}

/// Greedily keep regions by descending score, dropping a region that is mostly
/// covered by an already-kept one (RT-DETR emits overlapping duplicates).
fn greedy(mut regions: Vec<Region>) -> Vec<Region> {
    regions.sort_by(|a, b| b.score.total_cmp(&a.score));
    let mut kept: Vec<Region> = Vec::new();
    for r in regions {
        let ra = area(r.l, r.t, r.r, r.b).max(1.0);
        let covered = kept.iter().any(|k| {
            let i = inter(&r, k.l, k.t, k.r, k.b);
            let ka = area(k.l, k.t, k.r, k.b).max(1.0);
            // drop if most of r is inside k, or they strongly mutually overlap
            i / ra > 0.7 || i / (ra + ka - i) > 0.5
        });
        if !covered {
            kept.push(r);
        }
    }
    kept
}

/// Resolve overlapping RT-DETR detections, ported from the bucket structure of
/// docling's `LayoutPostprocessor`: regular, picture and wrapper clusters live in
/// **separate** spatial indexes and are de-overlapped independently, so a
/// high-score picture never suppresses a lower-score table or table-of-contents
/// index (the redp5110 TOC that was otherwise replaced by a picture box). A
/// cross-type pass first drops a picture that nearly coincides with a table
/// (`_handle_cross_type_overlaps`), keeping the structured table.
/// docling's `_remove_overlapping_clusters("picture")`: same-label picture
/// detections whose boxes heavily overlap (IoU > 0.8, or either box > 80 %
/// contained in the other) form one group, and a single survivor is kept per
/// group. Survivor selection ports `_should_prefer_cluster` /
/// `_select_best_cluster_from_group` with the picture params
/// (`area_threshold` 2.0, `conf_threshold` 0.3): a candidate is rejected only
/// when a rival is both comparable in size (candidate ≤ 2× its area) and
/// clearly more confident (> 0.3); among the survivors the *larger* box wins
/// unless it is > 0.3 less confident. Net effect on the corpus: a figure the
/// detector proposes both whole and as its sub-panels (2206's four-thumbnail
/// Figure 1) collapses to the whole-figure box, exactly like docling.
pub(crate) fn dedup_pictures(regions: &mut Vec<Region>) {
    remove_overlapping_specials(regions, |l| l == "picture", 2.0, 0.3);
}

/// docling's `_remove_overlapping_clusters` for one special bucket (the
/// regions whose label satisfies `in_bucket`), with that bucket's
/// `OVERLAP_PARAMS`: picture (2.0, 0.3) — see [`dedup_pictures`] — or wrapper
/// (2.0, 0.2) for the table bucket in [`resolve`]. Regions outside the bucket
/// are untouched; a bucket member overlapping nothing is always kept.
fn remove_overlapping_specials(
    regions: &mut Vec<Region>,
    in_bucket: impl Fn(&str) -> bool,
    area_threshold: f32,
    conf_threshold: f32,
) {
    let idx: Vec<usize> = (0..regions.len())
        .filter(|&i| in_bucket(regions[i].label))
        .collect();
    if idx.len() < 2 {
        return;
    }
    // Union-find over the bucket.
    let mut parent: Vec<usize> = (0..idx.len()).collect();
    fn find(parent: &mut [usize], i: usize) -> usize {
        let mut root = i;
        while parent[root] != root {
            root = parent[root];
        }
        let mut cur = i;
        while parent[cur] != root {
            let next = parent[cur];
            parent[cur] = root;
            cur = next;
        }
        root
    }
    let boxed = |r: &Region| (r.l, r.t, r.r, r.b);
    for a in 0..idx.len() {
        for b in (a + 1)..idx.len() {
            let (ra, rb) = (&regions[idx[a]], &regions[idx[b]]);
            let (al, at, ar, ab_) = boxed(ra);
            let (bl, bt, br, bb) = boxed(rb);
            let ix = (ar.min(br) - al.max(bl)).max(0.0);
            let iy = (ab_.min(bb) - at.max(bt)).max(0.0);
            let inter = ix * iy;
            let aa = area(al, at, ar, ab_).max(f32::EPSILON);
            let ba = area(bl, bt, br, bb).max(f32::EPSILON);
            let iou = inter / (aa + ba - inter).max(f32::EPSILON);
            if iou > 0.8 || inter / aa > 0.8 || inter / ba > 0.8 {
                let (pa, pb) = (find(&mut parent, a), find(&mut parent, b));
                if pa != pb {
                    parent[pa] = pb;
                }
            }
        }
    }
    // Per group, run docling's pairwise preference + larger-wins selection.
    let mut groups: std::collections::HashMap<usize, Vec<usize>> = std::collections::HashMap::new();
    for i in 0..idx.len() {
        let root = find(&mut parent, i);
        groups.entry(root).or_default().push(i);
    }
    let mut drop = vec![false; regions.len()];
    for group in groups.values() {
        if group.len() < 2 {
            continue;
        }
        let area_of = |i: usize| {
            let r = &regions[idx[i]];
            area(r.l, r.t, r.r, r.b).max(f32::EPSILON)
        };
        let mut best: Option<usize> = None;
        for &cand in group {
            let passes = group.iter().all(|&other| {
                if other == cand {
                    return true;
                }
                let area_ratio = area_of(cand) / area_of(other);
                let conf_diff = regions[idx[other]].score - regions[idx[cand]].score;
                !(area_ratio <= area_threshold && conf_diff > conf_threshold)
            });
            if passes {
                best = Some(match best {
                    None => cand,
                    Some(cur) => {
                        if area_of(cand) > area_of(cur)
                            && regions[idx[cur]].score - regions[idx[cand]].score <= conf_threshold
                        {
                            cand
                        } else {
                            cur
                        }
                    }
                });
            }
        }
        // Every candidate rejected can't happen with docling's rule (rejection
        // needs a strictly better rival); guard with highest score anyway.
        let keep = best.unwrap_or_else(|| {
            *group
                .iter()
                .max_by(|&&a, &&b| regions[idx[a]].score.total_cmp(&regions[idx[b]].score))
                .expect("non-empty group")
        });
        for &i in group {
            if i != keep {
                drop[idx[i]] = true;
            }
        }
    }
    let mut keep_iter = drop.into_iter();
    regions.retain(|_| !keep_iter.next().expect("aligned"));
}

/// docling's `_remove_overlapping_clusters("regular")` for what [`greedy`]
/// leaves standing, run on OCR'd pages before the region-scoped OCR (found
/// with #471's synthetic scan: every line of the page came out twice).
///
/// `greedy` keeps regions by descending score and drops a candidate mostly
/// inside an already-kept one — so a *lower*-score block that contains
/// several higher-score line boxes (RT-DETR's favourite reading of a sparse
/// scanned page: every line, plus the paragraph) survives alongside them.
/// On a digital page that is harmless: [`fit_regions_to_cells`] hands each
/// text cell to one owner and drops the regions left empty. On a scanned
/// page the cells don't exist yet — they come from OCR of *each* region's
/// crop — so the block and its lines were each recognized, and the block,
/// which then owned both cell sets, read every line twice.
///
/// Upstream never has this problem because its OCR runs over the bitmap
/// before layout postprocessing and each cell is assigned once; the
/// postprocessor's regular pass then groups clusters that overlap (IoU > 0.8,
/// or either > 80 % contained in the other) with a union-find, keeps one
/// survivor per group via `_should_prefer_cluster` /
/// `_select_best_cluster_from_group` (`area_threshold` 1.3, `conf_threshold`
/// 0.05; a LIST_ITEM beats a same-sized TEXT, a CODE box beats what it
/// contains) and merges the losers' cells into it, whose box is then fitted
/// to those cells. The equivalent for region-scoped OCR: one survivor per
/// group, keeping its label and score, with the group's **union** box so the
/// single crop still covers every merged line. Pictures and wrappers are not
/// regulars and are left alone ([`dedup_pictures`], [`resolve`]).
pub(crate) fn merge_overlapping_regulars(regions: &mut Vec<Region>) {
    let idx: Vec<usize> = (0..regions.len())
        .filter(|&i| regions[i].label != "picture" && !is_wrapper(regions[i].label))
        .collect();
    if idx.len() < 2 {
        return;
    }
    let mut parent: Vec<usize> = (0..idx.len()).collect();
    fn find(parent: &mut [usize], i: usize) -> usize {
        let mut root = i;
        while parent[root] != root {
            root = parent[root];
        }
        let mut cur = i;
        while parent[cur] != root {
            let next = parent[cur];
            parent[cur] = root;
            cur = next;
        }
        root
    }
    for a in 0..idx.len() {
        for b in (a + 1)..idx.len() {
            let (ra, rb) = (&regions[idx[a]], &regions[idx[b]]);
            let i = inter(ra, rb.l, rb.t, rb.r, rb.b);
            let aa = area(ra.l, ra.t, ra.r, ra.b).max(f32::EPSILON);
            let ba = area(rb.l, rb.t, rb.r, rb.b).max(f32::EPSILON);
            if i / (aa + ba - i).max(f32::EPSILON) > 0.8 || i / aa > 0.8 || i / ba > 0.8 {
                let (pa, pb) = (find(&mut parent, a), find(&mut parent, b));
                if pa != pb {
                    parent[pa] = pb;
                }
            }
        }
    }
    let mut groups: std::collections::BTreeMap<usize, Vec<usize>> =
        std::collections::BTreeMap::new();
    for i in 0..idx.len() {
        let root = find(&mut parent, i);
        groups.entry(root).or_default().push(i);
    }
    const AREA_THRESHOLD: f32 = 1.3;
    const CONF_THRESHOLD: f32 = 0.05;
    let area_of = |i: usize| {
        let r = &regions[idx[i]];
        area(r.l, r.t, r.r, r.b).max(f32::EPSILON)
    };
    // `_should_prefer_cluster(candidate, other)` with the regular params.
    let prefer = |cand: usize, other: usize| -> bool {
        let (c, o) = (&regions[idx[cand]], &regions[idx[other]]);
        let area_ratio = area_of(cand) / area_of(other);
        if c.label == "list_item" && o.label == "text" && (1.0 - area_ratio).abs() < 0.2 {
            return true;
        }
        if c.label == "code" && inter(o, c.l, c.t, c.r, c.b) / area_of(other) > 0.8 {
            return true;
        }
        !(area_ratio <= AREA_THRESHOLD && o.score - c.score > CONF_THRESHOLD)
    };
    let mut drop = vec![false; regions.len()];
    let mut unions: Vec<(usize, (f32, f32, f32, f32))> = Vec::new();
    for group in groups.values() {
        if group.len() < 2 {
            continue;
        }
        let mut best: Option<usize> = None;
        for &cand in group {
            if group
                .iter()
                .all(|&other| other == cand || prefer(cand, other))
            {
                best = Some(match best {
                    None => cand,
                    Some(cur)
                        if area_of(cand) > area_of(cur)
                            && regions[idx[cur]].score - regions[idx[cand]].score
                                <= CONF_THRESHOLD =>
                    {
                        cand
                    }
                    Some(cur) => cur,
                });
            }
        }
        // docling falls back to the group's first cluster; the highest score
        // is the deterministic equivalent for a set with no insertion order.
        let keep = best.unwrap_or_else(|| {
            *group
                .iter()
                .max_by(|&&a, &&b| regions[idx[a]].score.total_cmp(&regions[idx[b]].score))
                .expect("non-empty group")
        });
        let mut u = (
            f32::INFINITY,
            f32::INFINITY,
            f32::NEG_INFINITY,
            f32::NEG_INFINITY,
        );
        for &i in group {
            let r = &regions[idx[i]];
            u = (u.0.min(r.l), u.1.min(r.t), u.2.max(r.r), u.3.max(r.b));
            if i != keep {
                drop[idx[i]] = true;
            }
        }
        unions.push((idx[keep], u));
    }
    for (i, (l, t, r, b)) in unions {
        let k = &mut regions[i];
        (k.l, k.t, k.r, k.b) = (l, t, r, b);
    }
    let mut keep_iter = drop.into_iter();
    regions.retain(|_| !keep_iter.next().expect("aligned"));
}

/// `intersection_over_union` of two regions.
fn iou(a: &Region, b: &Region) -> f32 {
    let i = inter(a, b.l, b.t, b.r, b.b);
    let u = area(a.l, a.t, a.r, a.b) + area(b.l, b.t, b.r, b.b) - i;
    if u > 0.0 {
        i / u
    } else {
        0.0
    }
}

/// docling's `_resolve_coincident_pairs` (#4059, 2.122): for every (loser,
/// winner) pair at a near-identical box (IoU > 0.8) whose confidences are
/// within 0.1 (`loser.score - winner.score < 0.1`), the loser label is dropped
/// so the label with the richer downstream semantic survives. Nothing else —
/// containment, area — is considered; a clearly more confident loser stays.
fn coincident_losers(regions: &[Region], losers: &[usize], winners: &[usize]) -> Vec<usize> {
    let mut out = Vec::new();
    for &li in losers {
        for &wi in winners {
            if iou(&regions[li], &regions[wi]) > 0.8 && regions[li].score - regions[wi].score < 0.1
            {
                out.push(li);
                break;
            }
        }
    }
    out
}

/// docling's `_handle_cross_type_overlaps` (2.122/2.123 shape): the layout
/// model can emit one grounded region under several labels, and the picture /
/// table / container buckets are de-overlapped independently, so such a region
/// survives twice. Elect a winner for the near-identical pairs:
///
/// | pair                                  | loser     | winner              |
/// |---------------------------------------|-----------|---------------------|
/// | TABLE vs DOCUMENT_INDEX               | table     | document_index      |
/// | PICTURE vs TABLE / DOCUMENT_INDEX     | picture   | the table-like      |
/// | FORM / KEY_VALUE_REGION vs *surviving* TABLE / DOCUMENT_INDEX / PICTURE | container | structured element |
///
/// IoU (not containment) so a genuine small figure inside a large table region
/// is not removed; the confidence tolerance keeps a clearly more confident
/// loser (an earlier port dropped every coincident picture regardless).
fn handle_cross_type_overlaps(regions: Vec<Region>) -> Vec<Region> {
    let by = |pred: &dyn Fn(&str) -> bool| -> Vec<usize> {
        (0..regions.len())
            .filter(|&i| pred(regions[i].label))
            .collect()
    };
    let tables = by(&|l| l == "table");
    let doc_indices = by(&|l| l == "document_index");
    let pictures = by(&|l| l == "picture");
    let containers = by(&|l| matches!(l, "form" | "key_value_region"));
    let mut drop = vec![false; regions.len()];
    for i in coincident_losers(&regions, &tables, &doc_indices) {
        drop[i] = true;
    }
    let table_like: Vec<usize> = tables.iter().chain(&doc_indices).copied().collect();
    for i in coincident_losers(&regions, &pictures, &table_like) {
        drop[i] = true;
    }
    let structured: Vec<usize> = table_like
        .iter()
        .chain(&pictures)
        .copied()
        .filter(|&i| !drop[i])
        .collect();
    for i in coincident_losers(&regions, &containers, &structured) {
        drop[i] = true;
    }
    let mut drop = drop.into_iter();
    let mut regions = regions;
    regions.retain(|_| !drop.next().expect("aligned"));
    regions
}

pub fn resolve(regions: Vec<Region>) -> Vec<Region> {
    let regions = handle_cross_type_overlaps(regions);
    // De-overlap each bucket on its own.
    let pictures = greedy(
        regions
            .iter()
            .filter(|r| r.label == "picture")
            .cloned()
            .collect(),
    );
    // Tables and containers are separate buckets since docling 2.123
    // (`TABLE_TYPES` vs `CONTAINER_TYPES`, docling#4064): a form drawn around a
    // table no longer competes with it for survival — the table nests inside
    // the container instead (`order_with_containers`).
    let mut tables = greedy(
        regions
            .iter()
            .filter(|r| is_table_like(r.label))
            .cloned()
            .collect(),
    );
    // `greedy` only drops a table mostly inside a *more* confident one, so a
    // low-score whole-page table proposed over the column tables it contains
    // (a two-column glossary page: 0.53 over 0.71/0.67/0.66) survived next to them and every
    // cell was emitted twice. docling's `_remove_overlapping_clusters(tables,
    // "wrapper")` groups tables whose boxes overlap (IoU > 0.8, or either one
    // > 80 % inside the other) and keeps one per group: run it on what
    // `greedy` leaves, like `merge_overlapping_regulars` does for regulars.
    remove_overlapping_specials(&mut tables, |_| true, 2.0, 0.2);
    let containers = greedy(
        regions
            .iter()
            .filter(|r| matches!(r.label, "form" | "key_value_region"))
            .cloned()
            .collect(),
    );
    let mut kept = greedy(
        regions
            .iter()
            .filter(|r| r.label != "picture" && !is_wrapper(r.label))
            .cloned()
            .collect(),
    );
    dedup_nested_code(&mut kept);
    kept.extend(pictures);
    kept.extend(tables);
    kept.extend(containers);
    kept
}

/// Drop a regular region that is >80% contained in a surviving special region we
/// render **as a single unit** — a table/table-of-contents index — ported from
/// docling's "Remove regular clusters that are included in wrappers" step: the
/// special absorbs it as a child (a table cell), so it must not also be emitted
/// as its own paragraph/list-item. This stops the survey list-items from
/// appearing both inside the detected table and again as bullets
/// (`table_mislabeled_as_picture`).
///
/// `picture` regions stay in the swallow set even after #165: docling keeps a
/// picture's contained clusters as the `PictureItem`'s *children* in the
/// document JSON (`ReadingOrderModel._add_child_elements`), but its
/// `MarkdownPictureSerializer` prints only the caption and the image — the
/// children never reach the Markdown (verified against the corpus groundtruth:
/// `amt_handbook`'s in-figure callout labels are absent). Dropping the
/// fully-contained regulars here reproduces exactly that. What #165 *does*
/// change is upstream, in [`add_orphan_regions`]: pictures no longer claim
/// cells, so a line only partially under a figure box (straddling its border,
/// ≤80 % contained) now forms an orphan region that survives this drop — those
/// words were silently erased before, and docling emits them.
///
/// `form` / `key_value_region` wrappers are deliberately **excluded**: this
/// pipeline does not render them as a structured block (they are skipped), so
/// their textual content comes precisely from the contained regular regions —
/// dropping those would erase the page (e.g. `right_to_left_03`'s form-heavy
/// pages). Runs *after* [`drop_false_pictures`] so a phantom picture can't
/// swallow real text on its way out.
pub fn drop_contained_regulars(regions: &mut Vec<Region>) {
    let specials: Vec<(f32, f32, f32, f32)> = regions
        .iter()
        .filter(|r| r.label == "picture" || is_table_like(r.label))
        .map(|r| (r.l, r.t, r.r, r.b))
        .collect();
    if specials.is_empty() {
        return;
    }
    regions.retain(|r| {
        if r.label == "picture" || is_wrapper(r.label) {
            return true;
        }
        let ra = area(r.l, r.t, r.r, r.b).max(1.0);
        !specials
            .iter()
            .any(|&(l, t, rr, b)| inter(r, l, t, rr, b) / ra > 0.8)
    });
}

/// True for a bare, single-token source-code language label (`XML`, `C#`, `JSON`,
/// `bash`, …) — the little header the docs render above a code block. Matched
/// case-insensitively; anything with whitespace or longer than a token is out.
fn is_code_language(t: &str) -> bool {
    let t = t.trim();
    if t.is_empty() || t.chars().any(char::is_whitespace) || t.chars().count() > 12 {
        return false;
    }
    const LANGS: &[&str] = &[
        "xml",
        "html",
        "xhtml",
        "json",
        "jsonc",
        "yaml",
        "yml",
        "toml",
        "ini",
        "c#",
        "csharp",
        "f#",
        "fsharp",
        "vb",
        "c",
        "c++",
        "cpp",
        "java",
        "kotlin",
        "scala",
        "go",
        "golang",
        "rust",
        "swift",
        "javascript",
        "js",
        "typescript",
        "ts",
        "jsx",
        "tsx",
        "python",
        "py",
        "ruby",
        "rb",
        "php",
        "perl",
        "lua",
        "r",
        "dart",
        "bash",
        "sh",
        "shell",
        "powershell",
        "zsh",
        "batch",
        "cmd",
        "sql",
        "tsql",
        "plsql",
        "graphql",
        "dockerfile",
        "makefile",
        "css",
        "scss",
        "sass",
        "less",
        "markdown",
        "md",
        "tex",
        "latex",
        "diff",
        "proto",
        "razor",
        "cshtml",
        "xaml",
        "aspx",
        "http",
    ];
    let lower = t.to_ascii_lowercase();
    LANGS.contains(&lower.as_str())
}

/// Mark the region indices that are a code block's **language label** — a bare
/// `XML`/`C#`/… token sitting directly above a `code` region — so they are consumed
/// rather than emitted as their own stray paragraph/heading. The label may also be
/// captured inside a wider code box (rendered as the fence's first line); dropping
/// the standalone copy just removes the duplicate.
fn code_language_labels(regions: &[Region], cells: &[TextCell]) -> Vec<bool> {
    let mut drop = vec![false; regions.len()];
    for (i, r) in regions.iter().enumerate() {
        if matches!(r.label, "code" | "picture" | "table") {
            continue;
        }
        if !is_code_language(&region_text(r, cells)) {
            continue;
        }
        // The label sits just above the code (a blank line's gap) or is swallowed
        // into the top of a wider code box; either way it is that block's label.
        // The window is generous because the label's own font is small, so a
        // one-line gap is several times its height.
        let line_h = (r.b - r.t).abs().max(1.0);
        let window = (line_h * 4.0).max(28.0);
        let labels_code = regions.iter().enumerate().any(|(j, c)| {
            if j == i || c.label != "code" {
                return false;
            }
            let gap = c.t - r.b; // >0 when the code is below the label
            let h_overlap = (r.r.min(c.r) - r.l.max(c.l)).max(0.0);
            gap > -line_h * 3.0 && gap < window && h_overlap > 0.0
        });
        if labels_code {
            drop[i] = true;
        }
    }
    drop
}

/// Collapse `code` regions where one is nested inside another, keeping the larger.
///
/// RT-DETR sometimes emits a tight code box *and* a wider near-duplicate that also
/// captures the block's language label (`XML`, `C#`, …). When the tight box scores
/// higher it is kept first, and the wider container — not "mostly inside" the tight
/// box — survives [`resolve`]'s greedy pass, so the block is emitted twice. Keeping
/// the **larger** box (rather than dropping it) collapses the pair without leaking
/// the container's extra cells back out as orphan text, since the larger box still
/// covers every cell. Restricted to `code` so genuinely distinct nested regions of
/// other kinds are untouched.
fn dedup_nested_code(kept: &mut Vec<Region>) {
    let mut drop = vec![false; kept.len()];
    for i in 0..kept.len() {
        if kept[i].label != "code" {
            continue;
        }
        let ai = area(kept[i].l, kept[i].t, kept[i].r, kept[i].b).max(1.0);
        for j in 0..kept.len() {
            if i == j || drop[j] || kept[j].label != "code" {
                continue;
            }
            let aj = area(kept[j].l, kept[j].t, kept[j].r, kept[j].b).max(1.0);
            // Drop i when it is mostly inside a strictly larger code box j.
            let overlap = inter(&kept[i], kept[j].l, kept[j].t, kept[j].r, kept[j].b);
            if aj > ai && overlap / ai > 0.7 {
                drop[i] = true;
                break;
            }
        }
    }
    let mut keep = drop.iter();
    kept.retain(|_| !*keep.next().unwrap());
}

/// Fraction of the page's non-empty text cells that some detected region
/// claims (>0.2 intersection-over-self, docling's assignment rule). 1.0 for a
/// page without text cells.
///
/// The int8-layout guard keys off this: a dense digital page whose detections
/// cover almost none of its text is the signature of quantized confidences
/// flipping under the 0.5 label thresholds on this CPU's kernels — not of a
/// genuinely empty layout — and is worth re-running on the fp32 graph.
pub fn layout_cell_coverage(regions: &[Region], cells: &[TextCell]) -> f32 {
    let mut total = 0usize;
    let mut covered = 0usize;
    for c in cells {
        if c.text.trim().is_empty() {
            continue;
        }
        total += 1;
        let ca = area(c.l, c.t, c.r, c.b).max(1.0);
        if regions
            .iter()
            .any(|r| inter(r, c.l, c.t, c.r, c.b) / ca > 0.2)
        {
            covered += 1;
        }
    }
    if total == 0 {
        1.0
    } else {
        covered as f32 / total as f32
    }
}

/// Append `text` regions for cells the layout left uncovered ("orphan cells"),
/// the way docling's `LayoutPostprocessor` does (`create_orphan_clusters`): any
/// non-empty cell that no kept region covers (>50% of the cell's area) becomes a
/// text region of its own, so text the detector missed (a stray `.`, a small
/// label) is still emitted instead of silently dropped. Adjacent orphan cells on a
/// line are merged so a missed paragraph doesn't shatter into one block per line.
pub fn add_orphan_regions(regions: &mut Vec<Region>, cells: &[TextCell]) {
    // docling assigns each cell to its single best-overlapping cluster at
    // intersection-over-self > 0.2 and serializes exactly the assigned cells —
    // and since [`region_texts_exclusive`] now emits under that very rule, the
    // claim test here matches it: any cell over 0.2 will actually render in
    // its best region, everything else becomes an orphan. Completeness by
    // construction, with no (0.2, 0.5] hole (the old > 0.5 serializer needed
    // the claim test raised to > 0.5 to keep right_to_left_03's `20300` from
    // vanishing; the exclusive port closes that structurally).
    //
    // Only *regular* clusters claim cells: docling's `_find_unassigned_cells`
    // walks `regular_clusters` alone, so a cell under a `picture` or a wrapper
    // (`table`/`document_index`/`form`/`key_value_region`) that no regular
    // cluster covers still becomes an orphan text cluster (#165). The orphans
    // that end up *fully* inside the special are re-dropped by
    // [`drop_contained_regulars`] (docling's Markdown drops them the same way
    // — a picture's children never reach its `MarkdownPictureSerializer`
    // output, a table's text renders through the reconstructed grid). The
    // observable fix is the border-straddlers: a line only partially under a
    // figure box used to lose its cells to the picture's 0.2 claim and vanish
    // — now it forms an orphan region and is emitted, as docling does.
    let assigned = |c: &TextCell| {
        let ca = area(c.l, c.t, c.r, c.b).max(1.0);
        regions
            .iter()
            .filter(|r| r.label != "picture" && !is_wrapper(r.label))
            .any(|r| inter(r, c.l, c.t, c.r, c.b) / ca > 0.2)
    };
    // Collect orphan cells (non-empty, unassigned), in page order.
    let mut orphans: Vec<&TextCell> = cells
        .iter()
        .filter(|c| !c.text.trim().is_empty() && !assigned(c))
        .collect();
    if orphans.is_empty() {
        return;
    }
    orphans.sort_by(|a, b| a.t.total_cmp(&b.t).then(a.l.total_cmp(&b.l)));
    // Merge cells that sit on the same line and nearly touch into one region, so a
    // dropped multi-word line stays one block (docling's refinement merges these).
    let mut merged: Vec<Region> = Vec::new();
    for c in orphans {
        let h = (c.b - c.t).abs().max(1.0);
        if let Some(last) = merged.last_mut() {
            let same_line = (last.t - c.t).abs() < h * 0.5;
            let touching = c.l <= last.r + h && c.l >= last.l - h;
            if same_line && touching {
                last.l = last.l.min(c.l);
                last.r = last.r.max(c.r);
                last.t = last.t.min(c.t);
                last.b = last.b.max(c.b);
                continue;
            }
        }
        merged.push(Region {
            label: "text",
            score: 0.0,
            l: c.l,
            t: c.t,
            r: c.r,
            b: c.b,
        });
    }
    regions.extend(merged);
}

/// Demote a `picture` region that is really a **text panel** — a paragraph block
/// the layout model boxed as a figure because it is typeset on a colored
/// background (terms-and-conditions callouts, quote boxes) — into ordinary
/// `text` regions, one per paragraph, so its words are read instead of shipped
/// as pixels. docling loses this text the same way (cells assigned to a picture
/// cluster are never serialized); this is a deliberate improvement, not parity.
///
/// The gate is conservative so a genuine figure keeps its crop: the region must
/// contain at least three text lines whose median width spans most of the panel
/// (axis labels and chat bubbles are narrow and varied) and whose cells cover a
/// substantial fraction of its area (a photo or chart with sparse labels does
/// not). Paragraph boundaries are re-derived from the line pitch: a vertical gap
/// clearly larger than the panel's own leading starts a new `text` region, so
/// the panel doesn't collapse into one giant paragraph.
///
/// Works on any cell source — the digital text layer or OCR lines recognized
/// from the picture crop — so the native and browser paths, with or without
/// force-OCR, demote identically.
pub fn recover_text_panels(regions: &mut Vec<Region>, cells: &[TextCell]) {
    // A *captioned* picture is a genuine figure whatever it contains — the
    // corpus is full of document screenshots ("Figure 3: …" above a page
    // image) that are exactly as dense and wide as a text panel. Only an
    // uncaptioned picture is a demotion candidate.
    let captioned: Vec<bool> = regions
        .iter()
        .map(|r| {
            r.label == "picture"
                && regions.iter().any(|c| {
                    c.label == "caption" && c.r.min(r.r) - c.l.max(r.l) > 0.0 && {
                        let gap = if c.t >= r.b {
                            c.t - r.b
                        } else if r.t >= c.b {
                            r.t - c.b
                        } else {
                            f32::MAX // vertically overlapping: not a caption
                        };
                        gap <= 25.0
                    }
                })
        })
        .collect();
    let mut out: Vec<Region> = Vec::with_capacity(regions.len());
    // Synthesized paragraphs and the demoted panels' boxes are kept separate
    // from `out` until the end: the dedup filter below must not confuse a
    // paragraph we just built with a pre-existing region inside the panel.
    let mut demoted_paras: Vec<Region> = Vec::new();
    let mut demoted_boxes: Vec<(f32, f32, f32, f32)> = Vec::new();
    for (i, r) in regions.drain(..).enumerate() {
        if r.label != "picture" || captioned[i] {
            out.push(r);
            continue;
        }
        let inside: Vec<&TextCell> = cells
            .iter()
            .filter(|c| {
                !c.text.trim().is_empty() && {
                    let ca = area(c.l, c.t, c.r, c.b).max(1.0);
                    inter(&r, c.l, c.t, c.r, c.b) / ca > 0.5
                }
            })
            .collect();
        // Group the contained cells into lines by vertical overlap (the same
        // rule region_text orders by), tracking each line's union box.
        let mut lines: Vec<(f32, f32, f32, f32)> = Vec::new(); // (t, b, l, r)
        for c in &inside {
            let (ct, cb) = (c.t.min(c.b), c.t.max(c.b));
            match lines.iter_mut().find(|(lt, lb, _, _)| {
                let ov = cb.min(*lb) - ct.max(*lt);
                ov > 0.5 * (cb - ct).min(*lb - *lt).max(1.0)
            }) {
                Some((lt, lb, ll, lr)) => {
                    *lt = lt.min(ct);
                    *lb = lb.max(cb);
                    *ll = ll.min(c.l);
                    *lr = lr.max(c.r);
                }
                None => lines.push((ct, cb, c.l, c.r)),
            }
        }
        if lines.len() < 3 {
            out.push(r);
            continue;
        }
        let panel_w = (r.r - r.l).max(1.0);
        let coverage = inside.iter().map(|c| area(c.l, c.t, c.r, c.b)).sum::<f32>()
            / area(r.l, r.t, r.r, r.b).max(1.0);
        let mut widths: Vec<f32> = lines.iter().map(|(_, _, l, rr)| rr - l).collect();
        widths.sort_by(f32::total_cmp);
        // A figure's text is ragged: a title line, small axis/tick labels, and
        // OCR boxes over the plot area come out at wildly different heights,
        // whereas a real text panel is set in one face with constant leading.
        // Require near-uniform line heights (median absolute deviation ≤ 35%
        // of the median) so an uncaptioned chart keeps its crop even when its
        // labels are dense enough to pass the coverage gate (#173) — garbled
        // OCR of its bars is not content.
        let mut heights: Vec<f32> = lines.iter().map(|(t, b, _, _)| b - t).collect();
        heights.sort_by(f32::total_cmp);
        let h_med = heights[heights.len() / 2].max(1.0);
        let mut devs: Vec<f32> = heights.iter().map(|h| (h - h_med).abs()).collect();
        devs.sort_by(f32::total_cmp);
        let uniform = devs[devs.len() / 2] <= 0.35 * h_med;
        let text_panel = coverage >= 0.2 && widths[widths.len() / 2] >= 0.45 * panel_w && uniform;
        if !text_panel {
            out.push(r);
            continue;
        }
        lines.sort_by(|a, b| a.0.total_cmp(&b.0));
        let mut heights: Vec<f32> = lines.iter().map(|(t, b, _, _)| b - t).collect();
        heights.sort_by(f32::total_cmp);
        let h = heights[heights.len() / 2].max(1.0);
        let mut gaps: Vec<f32> = lines
            .windows(2)
            .map(|w| (w[1].0 - w[0].1).max(0.0))
            .collect();
        gaps.sort_by(f32::total_cmp);
        let leading = if gaps.is_empty() {
            0.0
        } else {
            gaps[gaps.len() / 2]
        };
        let brk = (1.8 * leading).max(0.75 * h);
        let mut para: Option<(f32, f32, f32, f32)> = None; // (l, t, r, b) union
        for (t, b, l, rr) in &lines {
            match &mut para {
                Some((pl, _, pr, pb)) if *t - *pb <= brk => {
                    *pl = pl.min(*l);
                    *pr = pr.max(*rr);
                    *pb = pb.max(*b);
                }
                _ => {
                    if let Some((pl, pt, pr, pb)) = para.take() {
                        demoted_paras.push(Region {
                            label: "text",
                            score: r.score,
                            l: pl,
                            t: pt,
                            r: pr,
                            b: pb,
                        });
                    }
                    para = Some((*l, *t, *rr, *b));
                }
            }
        }
        if let Some((pl, pt, pr, pb)) = para {
            demoted_paras.push(Region {
                label: "text",
                score: r.score,
                l: pl,
                t: pt,
                r: pr,
                b: pb,
            });
        }
        demoted_boxes.push((r.l, r.t, r.r, r.b));
    }
    // The paragraphs are rebuilt from *all* of the panel's cells, so any
    // surviving text region inside a demoted panel (an orphan cluster or a
    // layout-detected fragment — pictures no longer swallow them, #165) would
    // say the same words twice. Consume those; wrappers and pictures stay.
    if !demoted_boxes.is_empty() {
        out.retain(|r| {
            r.label == "picture" || is_wrapper(r.label) || {
                let ra = area(r.l, r.t, r.r, r.b).max(1.0);
                !demoted_boxes
                    .iter()
                    .any(|&(l, t, rr, b)| inter(r, l, t, rr, b) / ra > 0.5)
            }
        });
    }
    // docling's "Remove regular clusters that are included in wrappers" (a
    // regular > 80 % inside a table is absorbed by it) already ran as
    // [`drop_contained_regulars`], but before this demotion created new
    // regulars. Apply it to them too: a panel that coincides with a table (a
    // dense data table detected as picture 0.80 and table 0.62 on one box;
    // `_handle_cross_type_overlaps` keeps both once the picture is ≥ 0.1 more
    // confident) rebuilds the table's words as a paragraph the grid already
    // renders. A panel inside another picture is left as it was.
    demoted_paras.retain(|p| {
        let pa = area(p.l, p.t, p.r, p.b).max(1.0);
        !out.iter()
            .any(|s| is_table_like(s.label) && inter(p, s.l, s.t, s.r, s.b) / pa > 0.8)
    });
    out.extend(demoted_paras);
    *regions = out;
}

/// Drop a `picture` detection covering more than 90 % of the page — docling's
/// `LayoutPostprocessor._process_special_clusters` "Filter out full-page
/// pictures" (upstream since 2.15), applied to the thresholded detections
/// before overlap resolution. A box that big is the page itself, not a figure
/// on it: the layout model emits one for a whole-page diagram (a LaTeX figure
/// PDF cropped to its drawing), a plate, or a scan, and keeping it would swallow
/// every text cell on the page as picture children — the diagram's labels and
/// caption vanish behind a lone `<!-- image -->`, where docling reads them out as
/// text. `page_w`/`page_h` is the display-frame page box.
pub fn drop_full_page_pictures(regions: &mut Vec<Region>, page_w: f32, page_h: f32) {
    let page_area = (page_w * page_h).max(1.0);
    regions.retain(|r| r.label != "picture" || area(r.l, r.t, r.r, r.b) / page_area <= 0.90);
}

/// Drop a `picture` detection that is a small, empty, low-confidence margin box on
/// a **text page** — a false positive the RT-DETR layout sometimes emits (e.g.
/// `right_to_left_02`'s phantom right-column picture, score 0.40); docling does not
/// emit it. The gate is deliberately narrow so a genuine figure is never dropped:
/// (1) only on pages with a digital text layer — image/scanned/figure pages have
/// no `cells` yet at this point (OCR runs later), so their pictures, which *are*
/// the content, are kept; (2) only a box covering < 25 % of the page (a margin
/// artifact, not a dominant figure); (3) only when it contains no text and scores
/// below 0.5 (real empty figures in the corpus all score ≥ 0.86).
pub fn drop_false_pictures(
    regions: &mut Vec<Region>,
    cells: &[TextCell],
    page_w: f32,
    page_h: f32,
) {
    if cells.iter().all(|c| c.text.trim().is_empty()) {
        return; // no digital text layer (image/scanned page) — keep all pictures
    }
    // A text-document page carries several text-bearing non-picture regions (so a
    // spurious margin picture is clearly extra). A slide / figure page has at most
    // one — there the picture is the content, so never drop it.
    let content_regions = regions
        .iter()
        .filter(|r| r.label != "picture" && !region_text(r, cells).trim().is_empty())
        .count();
    if content_regions < 2 {
        return;
    }
    let page_area = (page_w * page_h).max(1.0);
    regions.retain(|r| {
        if r.label != "picture" || r.score >= 0.5 {
            return true;
        }
        if area(r.l, r.t, r.r, r.b) / page_area >= 0.25 {
            return true; // a dominant figure, not a margin artifact
        }
        // Keep it if any text cell falls mostly inside (a real captioned/labelled
        // figure); drop only the genuinely empty low-confidence boxes.
        cells.iter().any(|c| {
            let ca = area(c.l, c.t, c.r, c.b).max(1.0);
            !c.text.trim().is_empty() && inter(r, c.l, c.t, c.r, c.b) / ca > 0.5
        })
    });
}

/// A small digit-only region in the top/bottom margin: a page number. docling
/// emits `right_to_left_02`'s bottom `11` as the page's *first* text item (its
/// reading-order model floats the page number to the front), whereas our
/// position-based ordering would place a bottom region last.
fn is_page_number(region: &Region, cells: &[TextCell], page_h: f32) -> bool {
    let t = region_text(region, cells);
    let t = t.trim();
    !t.is_empty()
        && t.chars().all(|c| c.is_ascii_digit())
        && (region.b - region.t).abs() < 30.0
        && (region.t < page_h * 0.12 || region.b > page_h * 0.88)
}

/// docling's `form` / `key_value_region` *containers* (2.123, docling#4064):
/// every region sitting > 0.8 inside one — text, list items, and since #4064
/// tables and pictures too — is that container's child. Children are
/// reading-ordered among themselves and emitted as one block where the
/// container falls in the page's top-level order (a `form_area` /
/// `key_value_area` group upstream), instead of interleaving with the text
/// around the form. A child inside several containers belongs to the smallest
/// (then most confident, then first); a container with children shrinks to
/// their union for the top-level ordering, like upstream's bbox adjustment.
///
/// The containers themselves are still not emitted (`is_skipped`), so the
/// Markdown is exactly upstream's — a group prints only its children.
///
/// `cids` are the items' positions in docling's assembly order
/// ([`cluster_cids`]) — the reading-order predictor's same-row rule (#424)
/// pairs consecutive ones, within the top level and within each container.
fn order_with_containers<T: Clone>(
    items: &mut Vec<T>,
    cids: &[usize],
    page_w: f32,
    page_h: f32,
    reg: impl Fn(&T) -> &Region,
) {
    let is_container = |r: &Region| matches!(r.label, "form" | "key_value_region");
    let containers: Vec<usize> = (0..items.len())
        .filter(|&i| is_container(reg(&items[i])))
        .collect();
    if containers.is_empty() {
        order_regions(items, cids, page_w, page_h, reg);
        return;
    }
    // Parent container per item (containers never nest in each other here —
    // upstream assigns regulars and tables/pictures only).
    let mut parent: Vec<Option<usize>> = vec![None; items.len()];
    for i in 0..items.len() {
        let r = reg(&items[i]);
        if is_container(r) {
            continue;
        }
        let ra = area(r.l, r.t, r.r, r.b).max(1.0);
        let mut best: Option<(usize, f32, f32)> = None; // (idx, area, -score)
        for &c in &containers {
            let cr = reg(&items[c]);
            if inter(r, cr.l, cr.t, cr.r, cr.b) / ra > 0.8 {
                let key = (area(cr.l, cr.t, cr.r, cr.b), -cr.score);
                if best.is_none_or(|(_, a, s)| key.0 < a || (key.0 == a && key.1 < s)) {
                    best = Some((c, key.0, key.1));
                }
            }
        }
        parent[i] = best.map(|(c, _, _)| c);
    }
    // Top-level pass: non-children plus the containers, the latter shrunk to
    // their children's union.
    let mut top: Vec<(usize, Region)> = Vec::new();
    for i in 0..items.len() {
        if parent[i].is_some() {
            continue;
        }
        let mut r = reg(&items[i]).clone();
        if is_container(&r) {
            let kids: Vec<&Region> = (0..items.len())
                .filter(|&k| parent[k] == Some(i))
                .map(|k| reg(&items[k]))
                .collect();
            if !kids.is_empty() {
                r.l = kids.iter().map(|k| k.l).fold(f32::INFINITY, f32::min);
                r.t = kids.iter().map(|k| k.t).fold(f32::INFINITY, f32::min);
                r.r = kids.iter().map(|k| k.r).fold(f32::NEG_INFINITY, f32::max);
                r.b = kids.iter().map(|k| k.b).fold(f32::NEG_INFINITY, f32::max);
            }
        }
        top.push((i, r));
    }
    let top_cids: Vec<usize> = top.iter().map(|(i, _)| cids[*i]).collect();
    order_regions(&mut top, &top_cids, page_w, page_h, |it| &it.1);
    let mut out: Vec<T> = Vec::with_capacity(items.len());
    for (i, _) in top {
        if is_container(reg(&items[i])) {
            let kid_idx: Vec<usize> = (0..items.len()).filter(|&k| parent[k] == Some(i)).collect();
            let mut kids: Vec<T> = kid_idx.iter().map(|&k| items[k].clone()).collect();
            let kid_cids: Vec<usize> = kid_idx.iter().map(|&k| cids[k]).collect();
            order_regions(&mut kids, &kid_cids, page_w, page_h, &reg);
            out.push(items[i].clone());
            out.extend(kids);
        } else {
            out.push(items[i].clone());
        }
    }
    *items = out;
}

/// Furniture / not-yet-emitted labels.
fn is_skipped(label: &str) -> bool {
    matches!(
        label,
        "page_header" | "page_footer" | "form" | "key_value_region"
    )
}

/// Reading-order sort of a page's regions, via the ported rule-based
/// [`reading_order`](crate::reading_order) predictor (docling's
/// `ReadingOrderPredictor`): an up/down geometry graph with same-row links
/// between `cids`-consecutive elements (#424), horizontal dilation and a
/// depth-first traversal, with `page_header`/`page_footer` ordered as their own
/// groups (first/last) as docling does.
fn order_regions<T: Clone>(
    items: &mut Vec<T>,
    cids: &[usize],
    page_w: f32,
    page_h: f32,
    reg: impl Fn(&T) -> &Region,
) {
    let boxes: Vec<(f32, f32, f32, f32)> = items
        .iter()
        .map(|it| {
            let r = reg(it);
            (r.l, r.t, r.r, r.b)
        })
        .collect();
    let is_header: Vec<bool> = items
        .iter()
        .map(|it| reg(it).label == "page_header")
        .collect();
    let is_footer: Vec<bool> = items
        .iter()
        .map(|it| reg(it).label == "page_footer")
        .collect();
    let order =
        crate::reading_order::order_page(&boxes, cids, &is_header, &is_footer, page_w, page_h);
    *items = order.iter().map(|&i| items[i].clone()).collect();
}

/// docling's assembly order of a page's clusters (`LayoutPostprocessor`'s
/// final `_sort_clusters(mode="id")`, #424): each region's rank when sorted by
/// its first source cell, then by top edge, then left edge; a region with no
/// cells sorts after every one that has some. docling numbers its page
/// elements (`cid`) in this order, and the reading-order predictor's same-row
/// rule pairs elements with consecutive numbers, so the ranks are what
/// [`order_with_containers`] hands the predictor.
///
/// A regular region's first cell is the smallest index among the cells it
/// claims. A table, picture or container has no cells of its own upstream
/// either — its cells are its *children's*: the regular clusters > 0.8 inside
/// it, and upstream every cell no regular cluster claimed is an orphan cluster
/// of its own, so a table's interior text (which no regular cluster claims)
/// reaches the table through those orphans. Here that is the cells > 0.8
/// inside the region plus the claimed cells of the regular regions > 0.8
/// inside it. Without the interior cells every table would sort last, and two
/// side-by-side tables would then be consecutive and row-linked — reading the
/// right table's caption ahead of the left column's headings (2206 page 8).
pub fn cluster_cids(regions: &[Region], cells: &[TextCell]) -> Vec<usize> {
    let owned = assign_cells(regions, cells);
    let first_cell: Vec<usize> = regions
        .iter()
        .enumerate()
        .map(|(i, r)| {
            if claims_cells(r) {
                return owned[i].iter().copied().min().unwrap_or(usize::MAX);
            }
            let interior = cells
                .iter()
                .enumerate()
                .filter(|(_, c)| {
                    !c.text.trim().is_empty()
                        && inter(r, c.l, c.t, c.r, c.b) / area(c.l, c.t, c.r, c.b).max(1.0) > 0.8
                })
                .map(|(ci, _)| ci)
                .min();
            let children = regions
                .iter()
                .enumerate()
                .filter(|(j, child)| {
                    *j != i && claims_cells(child) && {
                        let ca = area(child.l, child.t, child.r, child.b).max(1.0);
                        inter(r, child.l, child.t, child.r, child.b) / ca > 0.8
                    }
                })
                .filter_map(|(j, _)| owned[j].iter().copied().min())
                .min();
            interior
                .into_iter()
                .chain(children)
                .min()
                .unwrap_or(usize::MAX)
        })
        .collect();
    let mut by_source: Vec<usize> = (0..regions.len()).collect();
    // Stable, like Python's `sorted`: full ties keep the layout order.
    by_source.sort_by(|&a, &b| {
        first_cell[a]
            .cmp(&first_cell[b])
            .then(regions[a].t.total_cmp(&regions[b].t))
            .then(regions[a].l.total_cmp(&regions[b].l))
    });
    let mut cids = vec![0; regions.len()];
    for (rank, &i) in by_source.iter().enumerate() {
        cids[i] = rank;
    }
    cids
}

/// Clean a region's assembled text: undo soft-hyphen line wraps, map curly
/// quotes and the ellipsis to ASCII (matching docling), and collapse runs of
/// whitespace. pdfium emits the line-wrap hyphen as U+0002 in this corpus
/// (U+00AD elsewhere), so `word\u{2} continuation` is one hyphenated word —
/// drop the hyphen + the joining space and merge (`com\u{2} pact` → `compact`,
/// `end-to\u{2} end` → `end-toend`), exactly as docling does.
///
/// Token spacing is otherwise left as the geometric join produced it. We do not
/// tighten punctuation spacing: docling preserves the PDF's own spaces (it keeps
/// `{ ahn }`, `Name 1 .`, `[ 9 ]`), and a geometric gap heuristic diverges from
/// it more than a plain single-space join does.
/// An ordered-list enumeration marker at the start of a list item: leading ASCII
/// digits followed by `.`, e.g. `1. Undo/Redo` → `(1, "Undo/Redo")`. Returns
/// `None` when the text doesn't start with `digits.`.
fn parse_ordered_marker(s: &str) -> Option<(u64, String)> {
    let digits: String = s.chars().take_while(|c| c.is_ascii_digit()).collect();
    if digits.is_empty() {
        return None;
    }
    let rest = s[digits.len()..].strip_prefix('.')?;
    let number = digits.parse().ok()?;
    Some((number, rest.trim_start().to_string()))
}

/// Escape markdown special characters the way docling-core's markdown serializer
/// does (`markdown.py` post_process): `_` → `\_`, then HTML-escape `&`, `<`, `>`
/// (quote=False, so quotes are left). Applied to prose (headings, list items,
/// paragraphs); code blocks, the formula placeholder, and table cells are left raw.
fn md_escape(text: &str) -> String {
    text.replace('_', "\\_")
        .replace('&', "&amp;")
        .replace('<', "&lt;")
        .replace('>', "&gt;")
}

fn clean_text(text: &str) -> String {
    // Typographic-quote normalization follows docling-parse's sanitizer table
    // (`pdf_sanitators/constants.h`): every curly quote — single *and double* —
    // becomes the ASCII apostrophe `'`, and `‚` a comma. A `"` in docling's
    // output only ever comes from a literal `quotedbl` glyph, never from `“ ”`
    // (2206's `'text in the wild"` pairs a curly open with a literal-quote
    // close). This replaces an earlier Hangul-only special case that patched
    // one symptom of mapping `“ ”` to `"`.
    let replaced = text
        .replace("\u{2} ", "")
        .replace("\u{ad} ", "")
        .replace(['\u{2}', '\u{ad}'], "") // any stray wrap hyphens not at a join
        .replace(
            [
                '\u{2018}', '\u{2019}', '\u{201b}', '\u{201c}', '\u{201d}', '\u{201e}', '\u{201f}',
            ],
            "'",
        ) // ‘ ’ ‛ “ ” „ ‟ → '
        .replace('\u{201a}', ",") // ‚ → ,
        .replace(
            [
                '\u{2010}', '\u{2011}', '\u{2012}', '\u{2013}', '\u{2014}', '\u{2015}', '\u{2212}',
            ],
            "-",
        ) // hyphen/dash family → -
        .replace('\u{2044}', "/") // ⁄ fraction slash → /
        .replace('\u{2022}', "\u{b7}") // • → · (docling never emits •; inline CCS-concept separators)
        .replace('\u{2026}', "..."); // … → ...
    let out = if crate::pdfium_backend::use_dp_lines() {
        // The docling-parse sanitizer already placed the correct spacing (e.g.
        // justified double spaces); preserve internal runs of spaces, only
        // normalizing line breaks/tabs and trimming the ends.
        replaced.replace(['\n', '\r', '\t'], " ").trim().to_string()
    } else {
        // Legacy: collapse all whitespace runs to single spaces.
        replaced.split_whitespace().collect::<Vec<_>>().join(" ")
    };
    fix_arabic_lam_alef(&out)
}

/// pdfium decomposes the Arabic lam-alef ligature (لا / لإ / لأ / لآ) into its
/// glyph constituents in *visual* order — `alef-variant, lam` — but docling keeps
/// logical order, `lam, alef-variant`. Swap a mid-word `alef-variant + lam` back
/// to `lam + alef-variant`. "Mid-word" (the previous char is an Arabic letter)
/// distinguishes the ligature from the definite article `ال` (word-initial
/// `alef + lam`), which must stay. No-op for non-Arabic text.
fn fix_arabic_lam_alef(s: &str) -> String {
    let is_arabic_letter = |c: char| ('\u{0620}'..='\u{064A}').contains(&c);
    let chars: Vec<char> = s.chars().collect();
    if !chars.iter().any(|&c| is_arabic_letter(c)) {
        return s.to_string(); // no-op for non-Arabic text
    }
    // Pass 1: swap mid-word `alef-variant + lam` → `lam + alef-variant`. Only the
    // hamza/madda alef variants (إ أ آ) are safe: the definite article is always
    // plain `ا + ل`, so plain `alef + lam` is ambiguous (a legitimate `فعالة` vs a
    // reversed `لا` ligature look identical) — leaving plain alef alone avoids
    // corrupting legitimate words.
    let mut a: Vec<char> = Vec::with_capacity(chars.len());
    let mut i = 0;
    while i < chars.len() {
        let c = chars[i];
        if matches!(c, '\u{0622}' | '\u{0623}' | '\u{0625}')
            && chars.get(i + 1) == Some(&'\u{0644}')
            && i > 0
            && is_arabic_letter(chars[i - 1])
            // A preceding lam means this alef-variant is *already* the logical
            // `lam + alef` ligature; the following lam is the next syllable's
            // letter, not a reversed ligature — swapping it corrupts `لآل` → `للآ`
            // (e.g. التعلم الآلي → الآلي, not اللآي).
            && chars[i - 1] != '\u{0644}'
        {
            a.push('\u{0644}');
            a.push(c);
            i += 2;
            continue;
        }
        a.push(c);
        i += 1;
    }
    // Pass 2: insert a space at Arabic↔Latin boundaries (bidi script switch) that
    // pdfium runs together — docling separates the embedded Latin run (`وPython`
    // → `و Python`).
    let mut out: Vec<char> = Vec::with_capacity(a.len());
    for (j, &c) in a.iter().enumerate() {
        if j > 0 {
            let p = a[j - 1];
            if (is_arabic_letter(p) && c.is_ascii_alphabetic())
                || (p.is_ascii_alphabetic() && is_arabic_letter(c))
            {
                out.push(' ');
            }
        }
        out.push(c);
    }
    out.into_iter().collect()
}

/// docling's `PageAssembleModel._match_hyperlink`: the URI whose link
/// annotations cover at least half of the region's box, or `None`. Coverage is
/// intersection-over-region-area, **accumulated per URI** — a URL that wraps
/// across lines carries several annotation rects that sum toward the same
/// target. Ties resolve to the first-seen URI (Python's `max` over dict
/// insertion order); the winner still needs `>= 0.5`
/// (`_HYPERLINK_COVERAGE_THRESHOLD`).
pub(crate) fn region_hyperlink(
    region: &Region,
    links: &[crate::pdfium_backend::LinkAnnot],
) -> Option<String> {
    if links.is_empty() {
        return None;
    }
    let area = (region.r - region.l).max(0.0) * (region.b - region.t).max(0.0);
    if area <= 0.0 {
        return None;
    }
    let mut coverage: Vec<(&str, f32)> = Vec::new();
    for link in links {
        let ix = (region.r.min(link.r) - region.l.max(link.l)).max(0.0);
        let iy = (region.b.min(link.b) - region.t.max(link.t)).max(0.0);
        let c = ix * iy / area;
        match coverage.iter_mut().find(|(uri, _)| *uri == link.uri) {
            Some((_, acc)) => *acc += c,
            None => coverage.push((&link.uri, c)),
        }
    }
    let mut best: Option<(&str, f32)> = None;
    for (uri, c) in coverage {
        // Strictly greater keeps the first-seen URI on ties, like Python's max.
        if best.is_none_or(|(_, bc)| c > bc) {
            best = Some((uri, c));
        }
    }
    let (uri, c) = best?;
    (c >= 0.5).then(|| normalize_uri(uri))
}

/// The pydantic-`AnyUrl` normalization docling's hyperlink value passes
/// through on its way to the serializer: a URL with an authority but no path
/// gains a trailing `/` (`https://arxiv.org` → `https://arxiv.org/`). Other
/// AnyUrl canonicalizations (scheme/host lowercasing, percent-encoding) don't
/// occur in PDF link annotations in practice, so they are not reproduced.
fn normalize_uri(uri: &str) -> String {
    if let Some((_, rest)) = uri.split_once("://") {
        if !rest.is_empty() && !rest.contains(['/', '?', '#']) {
            return format!("{uri}/");
        }
    }
    uri.to_string()
}

/// Resolve each page hyperlink to the visible text it covers, as `(anchor, uri)`
/// in reading order. The anchor is the cells whose centre falls in the link rect,
/// joined left-to-right and cleaned the same way prose is (so it matches the
/// serialized text), deduped against the immediately-preceding link so pdfium's
/// occasional duplicate annotation doesn't double-list. Empty anchors are dropped.
pub(crate) fn resolve_link_anchors(page: &PdfPage) -> Vec<(String, String)> {
    let mut out: Vec<(String, String)> = Vec::new();
    // Use per-word cells, not the line-merged `cells`: a link rect covers a few
    // words on a line, and a whole merged line cell would over-capture (its centre
    // lands in one link's rect, grabbing the entire line as that link's anchor).
    let words = if page.word_cells.is_empty() {
        &page.cells
    } else {
        &page.word_cells
    };
    for link in &page.links {
        // A cell participates when its centre row is inside the rect and it
        // overlaps the rect horizontally. A cell can be *wider* than the rect:
        // PDFs often draw a whole header line as one text run ("LinkedIn |
        // GitHub | Credly"), which docling-parse's word grouping keeps as one
        // cell even though each label carries its own link annotation —
        // centre-in-rect alone would hand the entire line to every link.
        // [`cell_text_in_rect`] clips such a cell to the tokens under the rect.
        let mut inside: Vec<(&TextCell, String)> = words
            .iter()
            .filter(|c| {
                let cy = (c.t + c.b) / 2.0;
                cy >= link.t && cy <= link.b && c.r.min(link.r) > c.l.max(link.l)
            })
            .filter_map(|c| {
                let text = cell_text_in_rect(c, link.l, link.r);
                (!text.is_empty()).then_some((c, text))
            })
            .collect();
        // Reading order: top band then left-to-right (link anchors are LTR).
        let band = inside
            .iter()
            .map(|(c, _)| (c.b - c.t).abs())
            .fold(0.0f32, f32::max)
            .max(1.0);
        inside.sort_by_key(|(c, _)| ((c.t / band).round() as i64, (c.l * 10.0) as i64));
        let anchor = clean_text(
            &inside
                .iter()
                .map(|(_, t)| t.trim())
                .filter(|t| !t.is_empty())
                .collect::<Vec<_>>()
                .join(" "),
        );
        if anchor.is_empty() {
            continue;
        }
        if out
            .last()
            .is_some_and(|(a, u)| a == &anchor && u == &link.uri)
        {
            continue;
        }
        out.push((anchor, link.uri.clone()));
    }
    out
}

/// The part of a cell's text that lies under a link rect's x-range. A cell
/// fully inside the rect (by centre) returns its whole text. A wider cell is
/// split into whitespace tokens whose x-spans are estimated proportionally to
/// their character positions (kerning makes this approximate, so selection
/// snaps to whole tokens, never characters); tokens whose estimated centre
/// falls inside the rect are kept. Returns "" when nothing falls inside.
fn cell_text_in_rect(c: &TextCell, l: f32, r: f32) -> String {
    let cx = (c.l + c.r) / 2.0;
    if cx >= l && cx <= r && c.l >= l - (c.r - c.l) * 0.25 && c.r <= r + (c.r - c.l) * 0.25 {
        return c.text.trim().to_string();
    }
    let chars: Vec<char> = c.text.chars().collect();
    let n = chars.len();
    if n == 0 || c.r <= c.l {
        return String::new();
    }
    let per = (c.r - c.l) / n as f32;
    let mut out: Vec<String> = Vec::new();
    let mut token = String::new();
    let mut start = 0usize;
    // A trailing sentinel space flushes the last token.
    for (i, &ch) in chars.iter().enumerate().chain(std::iter::once((n, &' '))) {
        if ch.is_whitespace() {
            if !token.is_empty() {
                let mid = c.l + (start as f32 + (i - start) as f32 / 2.0) * per;
                if mid >= l && mid <= r {
                    out.push(std::mem::take(&mut token));
                } else {
                    token.clear();
                }
            }
        } else {
            if token.is_empty() {
                start = i;
            }
            token.push(ch);
        }
    }
    out.join(" ")
}

/// Cells assigned to a region (best container), in reading order, joined.
fn region_text(region: &Region, cells: &[TextCell]) -> String {
    let inside: Vec<&TextCell> = cells
        .iter()
        .filter(|c| {
            let ca = area(c.l, c.t, c.r, c.b).max(1.0);
            inter(region, c.l, c.t, c.r, c.b) / ca > 0.5
        })
        .collect();
    cells_text(inside)
}

/// docling's exclusive cell assignment (`_assign_cells_to_clusters`): every
/// non-empty cell goes to the single best-overlapping *regular* region at
/// intersection-over-self > 0.2, and each region serializes exactly its
/// assigned cells. A cell under two overlapping boxes is emitted once (by the
/// better-covering one), and a cell only partially under its region — e.g.
/// normal_4pages' big section numeral, ~30 % inside the heading box — still
/// joins it (`## 들어가며 1`) instead of leaking as an orphan. Pictures and
/// wrappers never claim (docling walks regular clusters only); ties go to the
/// first region, like docling's strict `>` best-overlap scan.
pub fn region_texts_exclusive(regions: &[Region], cells: &[TextCell]) -> Vec<String> {
    let owned = assign_cells(regions, cells);
    // Non-claimers (tables/wrappers/pictures) keep the inclusive > 0.5 text:
    // docling fills a special cluster's cells from its contained children, and
    // downstream table assembly gates on that text being non-empty.
    regions
        .iter()
        .zip(owned)
        .map(|(r, cs)| {
            if claims_cells(r) {
                cells_text(cs.iter().map(|&i| &cells[i]).collect())
            } else {
                region_text(r, cells)
            }
        })
        .collect()
}

/// A *regular* region in docling's sense — one that claims cells. Pictures and
/// the wrappers (`table`, `document_index`, `form`, `key_value_region`) fill
/// their cells from contained children instead.
fn claims_cells(r: &Region) -> bool {
    r.label != "picture" && !is_wrapper(r.label)
}

/// docling's `_assign_cells_to_clusters`: each non-empty cell's index goes to
/// the single best-overlapping regular region at intersection-over-self > 0.2
/// (ties to the first region, like docling's strict `>` scan). One entry per
/// region, in region order.
fn assign_cells(regions: &[Region], cells: &[TextCell]) -> Vec<Vec<usize>> {
    let mut owned: Vec<Vec<usize>> = vec![Vec::new(); regions.len()];
    for (ci, c) in cells.iter().enumerate() {
        if c.text.trim().is_empty() {
            continue;
        }
        let ca = area(c.l, c.t, c.r, c.b).max(1.0);
        let mut best: Option<(usize, f32)> = None;
        for (i, r) in regions.iter().enumerate() {
            if !claims_cells(r) {
                continue;
            }
            let ov = inter(r, c.l, c.t, c.r, c.b) / ca;
            if ov > 0.2 && best.is_none_or(|(_, b)| ov > b) {
                best = Some((i, ov));
            }
        }
        if let Some((i, _)) = best {
            owned[i].push(ci);
        }
    }
    owned
}

/// docling's regular-cluster refinement after cell assignment
/// (`LayoutPostprocessor._process_regular_clusters`, #419), run once the page's
/// cells are final and before reading order:
///
/// 1. every regular region's box becomes the union of the cells it claimed
///    (`_adjust_cluster_bboxes` — a regular cluster's bbox *is* its cells'
///    bbox; a table's is the union with the model box, and pictures keep
///    theirs, so neither is touched here);
/// 2. a regular region that claimed no cell is dropped (`keep_empty_clusters`
///    is off; a `formula` is kept, as upstream keeps it);
/// 3. an orphan text region (`score == 0.0`, from [`add_orphan_regions`]) that
///    now sits > 0.8 inside another regular region's fitted box is folded into
///    it (`_remove_overlapping_clusters` at containment 0.8, the larger box
///    winning the group) — up to three rounds, like upstream's loop.
///
/// Why it matters: the layout model's box can end partway through a line. That
/// line fails the 0.2 claim and becomes an orphan — recoverable — but the
/// *model* box still overlaps the orphan's line by a few points, so the
/// reading-order graph, which links only strictly-above pairs, gets no edge
/// between them and may emit the next paragraph first, stranding the line
/// after the paragraph it belongs in (1540 of 6050 text blocks on the #419
/// book began mid-sentence). Fitted to its cells, the box ends on a line
/// boundary and the orphan slots in between; an orphan the fitted box
/// swallows joins the paragraph outright. Cell assignment is untouched: a
/// region's fitted box contains every cell it claimed, so
/// [`region_texts_exclusive`] hands it the same cells afterwards.
///
/// A page with no cells yet (a scan before OCR) is left alone: dropping every
/// text region for want of cells would be wrong, and the OCR paths call this
/// again once the cells exist.
pub fn fit_regions_to_cells(regions: &mut Vec<Region>, cells: &[TextCell]) {
    if !cells.iter().any(|c| !c.text.trim().is_empty()) {
        return;
    }
    for _ in 0..3 {
        let owned = assign_cells(regions, cells);
        let mut fitted: Vec<Region> = Vec::with_capacity(regions.len());
        for (r, own) in regions.iter().zip(&owned) {
            if !claims_cells(r) {
                fitted.push(r.clone());
                continue;
            }
            if own.is_empty() {
                if r.label == "formula" {
                    fitted.push(r.clone());
                }
                continue;
            }
            let mut f = r.clone();
            f.l = own
                .iter()
                .map(|&i| cells[i].l)
                .fold(f32::INFINITY, f32::min);
            f.t = own
                .iter()
                .map(|&i| cells[i].t)
                .fold(f32::INFINITY, f32::min);
            f.r = own
                .iter()
                .map(|&i| cells[i].r)
                .fold(f32::NEG_INFINITY, f32::max);
            f.b = own
                .iter()
                .map(|&i| cells[i].b)
                .fold(f32::NEG_INFINITY, f32::max);
            fitted.push(f);
        }
        let mut changed = fitted.len() != regions.len();
        // Fold orphans into the regular region whose fitted box holds them.
        let mut drop = vec![false; fitted.len()];
        for i in 0..fitted.len() {
            let o = &fitted[i];
            if !(o.score == 0.0 && o.label == "text") {
                continue;
            }
            let oa = area(o.l, o.t, o.r, o.b).max(1.0);
            let mut best: Option<(usize, f32)> = None;
            for (j, r) in fitted.iter().enumerate() {
                if j == i || drop[j] || r.score == 0.0 || !claims_cells(r) {
                    continue;
                }
                let ov = inter(r, o.l, o.t, o.r, o.b) / oa;
                if ov > 0.8 && best.is_none_or(|(_, b)| ov > b) {
                    best = Some((j, ov));
                }
            }
            if let Some((j, _)) = best {
                let (l, t, r, b) = (o.l, o.t, o.r, o.b);
                let host = &mut fitted[j];
                host.l = host.l.min(l);
                host.t = host.t.min(t);
                host.r = host.r.max(r);
                host.b = host.b.max(b);
                drop[i] = true;
                changed = true;
            }
        }
        let mut drop = drop.into_iter();
        fitted.retain(|_| !drop.next().expect("aligned"));
        *regions = fitted;
        if !changed {
            break;
        }
    }
}

/// Join a prefiltered cell list into the region's text (docling's
/// `sanitize_text` on the docling-parse path, gap-aware band join on legacy).
fn cells_text(mut inside: Vec<&TextCell>) -> String {
    // Quantize the top coordinate into ~line bands so cells on the same line
    // sort in reading order; this is a strict total order (a raw fuzzy comparator
    // is not transitive and makes Rust's sort panic). For a right-to-left
    // (Arabic-majority) region, cells on a line read right→left, so sort the band
    // by descending left edge.
    let band = inside
        .iter()
        .map(|c| (c.b - c.t).abs())
        .fold(0.0f32, f32::max)
        .max(1.0);
    let arabic = inside
        .iter()
        .flat_map(|c| c.text.chars())
        .filter(|&c| ('\u{0600}'..='\u{06FF}').contains(&c))
        .count();
    let latin = inside
        .iter()
        .flat_map(|c| c.text.chars())
        .filter(|c| c.is_ascii_alphabetic())
        .count();
    let rtl = arabic > latin;
    let dp = crate::pdfium_backend::use_dp_lines();
    if dp {
        // docling orders a cluster's cells by their docling-parse cell index
        // alone (`LayoutPostprocessor._sort_cells`: `sorted(cells, key=c.index)`)
        // — the sanitizer's output order, which our `cells` slice already is.
        // No geometric re-sort: normal_4pages' big section numerals paint
        // *after* their heading text, and docling's `## 들어가며 1` (numeral
        // last) only falls out of pure index order — a band sort dragged the
        // numeral to the front. The overlap-grouped line restore this replaced
        // measured strictly worse on the corpus (it fixed nothing the index
        // order broke, and broke the numerals).
    } else {
        inside.sort_by_key(|c| {
            let x = (c.l * 10.0) as i64;
            ((c.t / band).round() as i64, if rtl { -x } else { x })
        });
    }
    let joined = if dp {
        // docling's `PageAssembleModel.sanitize_text`, ported verbatim over the
        // parse-index-ordered lines: append a separating space to a line —
        // unless it ends with `-`. A dash-ending line whose last word and the
        // next line's first word are both alphanumeric is a wrapped word: the
        // dash is dropped and the lines fuse (`platforms-` + `reflects` →
        // `platformsreflects`, `pp. 545-` + `561` → `545561`). Any other
        // dash-ending line — e.g. the *bare* `-` cell a superscript ORCID or an
        // inline `–` bullet splits off (its word list is empty, so the fuse
        // test fails) — keeps its dash and still takes no trailing space:
        // `[0000` `-` `0002` joins as docling's `[0000 -0002`, and the OTSL
        // list's `-` + `"C" cell -` + `a new table cell` collapses to
        // `-"C" cell a new table cell`. Our cells still carry the raw dash
        // family (docling-parse normalizes to `-` before this; clean_text does
        // it after), so the endswith test matches them all.
        let texts: Vec<&str> = inside
            .iter()
            .map(|c| c.text.trim())
            // Skip whitespace-only cells (a justified line's trailing space
            // glyph): an empty line would double the separator.
            .filter(|t| !t.is_empty())
            .collect();
        let last_word_alnum = |s: &str| {
            s.split(|c: char| !(c.is_alphanumeric() || c == '_'))
                .rfind(|w| !w.is_empty())
                .is_some_and(|w| w.chars().all(char::is_alphanumeric))
        };
        let first_word_alnum = |s: &str| {
            s.split(|c: char| !(c.is_alphanumeric() || c == '_'))
                .find(|w| !w.is_empty())
                .is_some_and(|w| w.chars().all(char::is_alphanumeric))
        };
        let mut out = String::new();
        for (i, t) in texts.iter().enumerate() {
            if i > 0 {
                let prev = texts[i - 1];
                let dashish = matches!(
                    prev.chars().last(),
                    Some(
                        '-' | '\u{2010}'
                            | '\u{2011}'
                            | '\u{2012}'
                            | '\u{2013}'
                            | '\u{2014}'
                            | '\u{2015}'
                            | '\u{2212}'
                    )
                );
                // docling#4052 (2.122): a dash only splits a word when it is
                // *attached* to one — the character before it is alphanumeric.
                // A dash that follows whitespace (a separator dash, a bullet
                // marker, a wrapped `-prefixed` token, the bare `-` cell an
                // ORCID splits off) is a literal character: it is kept and the
                // lines join with the ordinary space.
                let attached = prev.chars().rev().nth(1).is_some_and(char::is_alphanumeric);
                if dashish && attached {
                    if last_word_alnum(prev) && first_word_alnum(t) {
                        out.pop(); // wrapped word: fuse without the dash
                    }
                    // an attached dash never takes a separating space
                } else {
                    out.push(' ');
                }
            }
            out.push_str(t);
        }
        out
    } else {
        // Legacy reconstruction: join same-band cells with a space only across a
        // real gap, because it can split a word into abutting segments
        // (`الت`|`ي` → `التي`).
        let mut out = String::new();
        let mut prev: Option<&&TextCell> = None;
        for c in &inside {
            let t = c.text.trim();
            if t.is_empty() {
                continue;
            }
            if let Some(p) = prev {
                let same_band = ((p.t / band).round() as i64) == ((c.t / band).round() as i64);
                let h = (c.b - c.t).abs().max((p.b - p.t).abs()).max(1.0);
                let gap = if rtl { p.l - c.r } else { c.l - p.r };
                if !same_band || gap > h * 0.25 {
                    out.push(' ');
                }
            }
            out.push_str(t);
            prev = Some(c);
        }
        out
    };
    clean_text(&joined)
}

/// Tighten the spaces pdfium leaves around tight punctuation in a code line
/// (`console .log` → `console.log`, `add (3 , 5)` → `add(3, 5)`), matching
/// docling-parse's source spacing.
fn tighten_code_punct(s: &str) -> String {
    s.replace(" .", ".")
        .replace(" ,", ",")
        .replace(" ;", ";")
        .replace(" )", ")")
        .replace(" (", "(")
}

/// Assemble a **code** region's text with its line structure preserved.
///
/// Unlike [`region_text`] — which joins every cell with a single space, the right
/// thing for prose reflow — a code block's line breaks and indentation are
/// significant. The `code_cells` are already one physical source line each
/// (grouped space-glyph-only, so monospace runs keep their spacing), so this:
///
/// 1. groups the cells into vertical line bands and orders them top→bottom,
///    left→right;
/// 2. joins the lines with `\n` (rather than spaces), keeping the carriage
///    returns; and
/// 3. reconstructs each line's leading indentation from its left offset, in units
///    of the block's estimated monospace character width, so nesting survives.
///
/// Typography is normalized per line via [`clean_text`] (smart quotes, dashes,
/// ellipsis), which never merges lines. Returns an empty string if the region has
/// no code cells (the caller falls back to the prose text).
fn code_region_text(region: &Region, cells: &[TextCell]) -> String {
    let mut inside: Vec<&TextCell> = cells
        .iter()
        .filter(|c| {
            let ca = area(c.l, c.t, c.r, c.b).max(1.0);
            inter(region, c.l, c.t, c.r, c.b) / ca > 0.5
        })
        .filter(|c| !c.text.trim().is_empty())
        .collect();
    if inside.is_empty() {
        return String::new();
    }

    // Quantize the top edge into ~line bands (like `region_text`), then order the
    // cells by band (top→bottom) and, within a band, by left edge.
    let band = inside
        .iter()
        .map(|c| (c.b - c.t).abs())
        .fold(0.0f32, f32::max)
        .max(1.0);
    let line_of = |c: &TextCell| (c.t / band).round() as i64;
    inside.sort_by_key(|c| (line_of(c), (c.l * 10.0) as i64));

    // Estimate one monospace character's width (total ink width / total glyphs) to
    // convert a line's left offset into a count of leading spaces. Measured over
    // all lines so a single short line can't skew it.
    let (mut total_w, mut total_chars) = (0.0f32, 0usize);
    for c in &inside {
        let n = c.text.trim().chars().count();
        if n > 0 {
            total_w += (c.r - c.l).max(0.0);
            total_chars += n;
        }
    }
    let char_w = if total_chars > 0 {
        (total_w / total_chars as f32).max(1.0)
    } else {
        1.0
    };
    // The block's own left margin is the zero-indent baseline.
    let base_l = inside.iter().map(|c| c.l).fold(f32::INFINITY, f32::min);

    let mut lines: Vec<String> = Vec::new();
    let mut cur: Option<i64> = None;
    for c in &inside {
        // Tighten pdfium's spaced punctuation per line (on the trimmed content, so
        // the reconstructed leading indentation is never nibbled).
        let text = tighten_code_punct(&clean_text(c.text.trim()));
        if Some(line_of(c)) == cur {
            // A second cell sharing this band (rare — e.g. split columns): keep it
            // on the same source line, separated by a space.
            if let Some(last) = lines.last_mut() {
                last.push(' ');
                last.push_str(&text);
            }
            continue;
        }
        let indent = ((c.l - base_l) / char_w).round().max(0.0) as usize;
        lines.push(format!("{}{}", " ".repeat(indent), text));
        cur = Some(line_of(c));
    }
    lines.join("\n")
}

/// Reconstruct a table's grid geometrically from the text cells inside its
/// region: cluster cells into rows (by vertical centre) and columns (by clustered
/// left edges), then place each cell. A model-free stand-in for TableFormer that
/// recovers grid-aligned tables from the precise PDF text layer (it does not
/// resolve row/column spans).
pub fn reconstruct_table(region: &Region, cells: &[TextCell]) -> Vec<Vec<String>> {
    let mut inside: Vec<&TextCell> = cells
        .iter()
        .filter(|c| {
            let ca = area(c.l, c.t, c.r, c.b).max(1.0);
            inter(region, c.l, c.t, c.r, c.b) / ca > 0.5
        })
        .collect();
    if inside.is_empty() {
        return Vec::new();
    }
    inside.sort_by(|a, b| a.t.total_cmp(&b.t));

    // Rows: consecutive cells whose vertical centre is within ~0.7 line height.
    let mut rows: Vec<(f32, Vec<&TextCell>)> = Vec::new();
    for c in &inside {
        let cyc = (c.t + c.b) / 2.0;
        let lh = (c.b - c.t).abs().max(1.0);
        if let Some((ryc, row)) = rows.last_mut() {
            if (cyc - *ryc).abs() < lh * 0.7 {
                row.push(c);
                continue;
            }
        }
        rows.push((cyc, vec![c]));
    }

    // Columns: cluster left edges (merge those within a tolerance).
    let tol = {
        let mut hs: Vec<f32> = inside.iter().map(|c| (c.b - c.t).abs()).collect();
        hs.sort_by(f32::total_cmp);
        hs[hs.len() / 2].max(4.0) * 1.5
    };
    let mut lefts: Vec<f32> = inside.iter().map(|c| c.l).collect();
    lefts.sort_by(f32::total_cmp);
    let mut col_starts: Vec<f32> = Vec::new();
    for l in lefts {
        if col_starts.last().is_none_or(|&last| l - last > tol) {
            col_starts.push(l);
        }
    }
    let ncols = col_starts.len().max(1);
    let col_of = |l: f32| -> usize {
        col_starts
            .iter()
            .rposition(|&s| l + tol * 0.5 >= s)
            .unwrap_or(0)
            .min(ncols - 1)
    };

    let mut grid = Vec::with_capacity(rows.len());
    for (_, mut row) in rows {
        row.sort_by(|a, b| a.l.total_cmp(&b.l));
        let mut cols = vec![String::new(); ncols];
        for c in row {
            let ci = col_of(c.l);
            // Strip the wrap-hyphen control char so it never lands in a cell.
            let t = c.text.trim().replace(['\u{2}', '\u{ad}'], "");
            if cols[ci].is_empty() {
                cols[ci] = t;
            } else {
                cols[ci].push(' ');
                cols[ci].push_str(&t);
            }
        }
        grid.push(cols);
    }
    grid
}

/// Does the geometric reconstruction of a table look trustworthy enough to use
/// as-is, instead of paying for TableFormer?
///
/// [`reconstruct_table`] derives columns by clustering cell **left edges**. On a
/// clean grid that is exact, but when a column's entries are not left-aligned
/// (or the OCR boxes wobble) the clustering splits one real column into several,
/// and the result is a wide, mostly-empty grid — the "spurious empty columns"
/// failure TableFormer exists to fix.
///
/// Two symptoms separate the two cases, and both are properties of the grid
/// alone (no model needed):
/// * **density** — a real table is mostly full; a split-up one is mostly holes;
/// * **thin columns** — a column carrying at most one entry across several rows
///   is almost always a split artefact rather than a real column.
///
/// Deliberately conservative: it answers `true` only for grids that are plainly
/// well-formed, so the expensive path stays the default whenever there is doubt.
/// A caller that skips TableFormer on `true` trades no quality for the time.
pub fn geometric_table_is_reliable(rows: &[Vec<String>]) -> bool {
    let ncols = rows.iter().map(Vec::len).max().unwrap_or(0);
    // Fewer than two columns is not a grid this heuristic can vouch for: it is
    // exactly the shape a collapsed table takes, and TableFormer may recover
    // real structure from it.
    if rows.len() < 2 || ncols < 2 {
        return false;
    }
    let filled = |c: &String| !c.trim().is_empty();
    let total = rows.len() * ncols;
    let full = rows.iter().flatten().filter(|c| filled(c)).count();
    if (full as f32) < MIN_TABLE_FILL * total as f32 {
        return false;
    }
    // A column used by at most one row, when there are rows enough to tell.
    if rows.len() >= 3 {
        for ci in 0..ncols {
            let used = rows
                .iter()
                .filter(|r| r.get(ci).is_some_and(filled))
                .count();
            if used <= 1 {
                return false;
            }
        }
    }
    true
}

/// Share of a geometric grid's cells that must carry text for it to be trusted
/// without TableFormer. Chosen well above the density a left-edge split
/// produces (those land nearer a third) and below what a genuine table with a
/// few blank cells reaches.
const MIN_TABLE_FILL: f32 = 0.6;

/// The union bbox of the text cells assigned to a region (same >50%-overlap
/// rule as [`region_text`]), or `None` when no cell lands in it. docling's
/// LayoutPostprocessor shrinks a regular cluster's bbox to its cells, and the
/// enrichment crops are taken from that cell-tight box — cropping the raw
/// detector box instead hands the VLM surrounding chrome (e.g. the `Listing N:`
/// caption under a code block) that changes its output.
pub fn region_cell_bbox(region: &Region, cells: &[TextCell]) -> Option<[f32; 4]> {
    let mut bbox: Option<[f32; 4]> = None;
    for c in cells {
        let ca = area(c.l, c.t, c.r, c.b).max(1.0);
        if inter(region, c.l, c.t, c.r, c.b) / ca <= 0.5 {
            continue;
        }
        bbox = Some(match bbox {
            None => [c.l, c.t, c.r, c.b],
            Some([l, t, r, b]) => [l.min(c.l), t.min(c.t), r.max(c.r), b.max(c.b)],
        });
    }
    bbox
}

/// One region's enrichment-model result, produced by the pipeline's opt-in
/// passes (issue #76) and applied during assembly.
#[derive(Debug, Clone)]
pub enum Enrichment {
    /// DocumentPictureClassifier predictions, descending confidence.
    PictureClasses(Vec<PictureClass>),
    /// CodeFormulaV2 output for a `code` region: the rewritten source text and
    /// the `<_language_>` prefix (when the model emitted one).
    Code {
        language: Option<String>,
        text: String,
    },
    /// CodeFormulaV2 output for a `formula` region: the decoded LaTeX.
    Formula { latex: String },
}

/// Crop a region (page points, already expanded by the caller if needed) from
/// the rendered page image and resize it to `target_scale` pixels per point —
/// the enrichment-model equivalent of docling's
/// `page.get_image(scale=…, cropbox=…)`, sourced from the existing
/// [`crate::pdfium_backend::RENDER_SCALE`] render instead of a fresh pdfium
/// pass (the page bitmap is already the exact docling render at scale 2).
#[cfg(feature = "ml")]
pub fn crop_region_scaled(page: &PdfPage, bbox: [f32; 4], target_scale: f32) -> Option<RgbImage> {
    let s = page.scale;
    let [l, t, r, b] = bbox;
    let (iw, ih) = (page.image.width(), page.image.height());
    let x = (l * s).max(0.0) as u32;
    let y = (t * s).max(0.0) as u32;
    if x >= iw || y >= ih {
        return None;
    }
    let w = (((r - l.max(0.0)) * s) as u32).min(iw - x);
    let h = (((b - t.max(0.0)) * s) as u32).min(ih - y);
    if w == 0 || h == 0 {
        return None;
    }
    let crop = image::imageops::crop_imm(&page.image, x, y, w, h).to_image();
    // docling renders the crop at `target_scale` directly; from the scale-2
    // page render that is a resize to the same pixel geometry
    // (`round(width_points * scale)`, PIL's BICUBIC ≙ CatmullRom).
    let tw = ((w as f32 / s) * target_scale).round().max(1.0) as u32;
    let th = ((h as f32 / s) * target_scale).round().max(1.0) as u32;
    if (tw, th) == (w, h) {
        return Some(crop);
    }
    Some(image::imageops::resize(
        &crop,
        tw,
        th,
        image::imageops::FilterType::CatmullRom,
    ))
}

/// Crop a layout region from the rendered page image and encode it as PNG (the
/// figure bytes docling stores on a `PictureItem`). Region coordinates are page
/// points; the image is rendered at `page.scale`.
#[cfg(feature = "ocr-prep")]
fn crop_region(page: &PdfPage, region: &Region) -> Option<PictureImage> {
    let s = page.scale;
    let (iw, ih) = (page.image.width(), page.image.height());
    let x = (region.l * s).max(0.0) as u32;
    let y = (region.t * s).max(0.0) as u32;
    if x >= iw || y >= ih {
        return None;
    }
    let w = (((region.r - region.l) * s) as u32).min(iw - x);
    let h = (((region.b - region.t) * s) as u32).min(ih - y);
    if w == 0 || h == 0 {
        return None;
    }
    let sub = image::imageops::crop_imm(&page.image, x, y, w, h).to_image();
    let mut buf = std::io::Cursor::new(Vec::new());
    sub.write_to(&mut buf, image::ImageFormat::Png).ok()?;
    Some(PictureImage {
        mimetype: "image/png".into(),
        width: w,
        height: h,
        data: buf.into_inner(),
    })
}

/// For each `picture` region, find the `caption` region closest below it (and
/// horizontally overlapping); docling pairs them and emits the caption first.
/// Each caption is claimed by at most one picture.
fn pair_captions(regions: &[Region]) -> Vec<Option<usize>> {
    let mut pairs = vec![None; regions.len()];
    let mut taken = vec![false; regions.len()];
    for (pi, p) in regions.iter().enumerate() {
        if p.label != "picture" {
            continue;
        }
        let mut best: Option<(usize, f32)> = None;
        for (ci, c) in regions.iter().enumerate() {
            if c.label != "caption" || taken[ci] {
                continue;
            }
            let line_h = (c.b - c.t).abs().max(1.0);
            let gap = c.t - p.b; // caption sits below the picture
            let h_overlap = (p.r.min(c.r) - p.l.max(c.l)).max(0.0);
            if gap > -line_h && gap < line_h * 3.0 && h_overlap > 0.0 {
                let dist = gap.abs();
                if best.is_none_or(|(_, bd)| dist < bd) {
                    best = Some((ci, dist));
                }
            }
        }
        if let Some((ci, _)) = best {
            pairs[pi] = Some(ci);
            taken[ci] = true;
        }
    }
    pairs
}

/// Pair each `code` region with the `caption` region just **above** it (a
/// `Listing N:` label). docling renders the code block first, then its caption,
/// so the caption is consumed from its own (earlier) reading-order slot and
/// re-emitted after the code.
fn pair_code_captions(regions: &[Region]) -> Vec<Option<usize>> {
    let mut pairs = vec![None; regions.len()];
    let mut taken = vec![false; regions.len()];
    for (pi, p) in regions.iter().enumerate() {
        if p.label != "code" {
            continue;
        }
        let mut best: Option<(usize, f32)> = None;
        for (ci, c) in regions.iter().enumerate() {
            if c.label != "caption" || taken[ci] {
                continue;
            }
            let line_h = (c.b - c.t).abs().max(1.0);
            let gap = p.t - c.b; // caption sits above the code
            let h_overlap = (p.r.min(c.r) - p.l.max(c.l)).max(0.0);
            if gap > -line_h && gap < line_h * 3.0 && h_overlap > 0.0 {
                let dist = gap.abs();
                if best.is_none_or(|(_, bd)| dist < bd) {
                    best = Some((ci, dist));
                }
            }
        }
        if let Some((ci, _)) = best {
            pairs[pi] = Some(ci);
            taken[ci] = true;
        }
    }
    pairs
}

/// Pair each `table`/`document_index` region with its `caption` (#265) the way
/// docling's `ReadingOrderPredictor._find_to_captions` does: by **reading-order
/// adjacency**, not geometry. A caption claims the media element
/// (table/picture/code) immediately next to it in the ordered region sequence,
/// and only when exactly one side holds one — a caption sandwiched between two
/// media elements stays unattached, and a text paragraph between caption and
/// table breaks the bond. This is what lets a flush-left "Table 3: …" label
/// bind a centered grid it doesn't horizontally overlap, while a caption in
/// the neighbouring column of a two-column page — geometrically close — never
/// pairs across the gutter. Runs after the picture and code pairings (the
/// picture/code arms of the same upstream matcher), so a caption they claimed
/// stays claimed. docling attaches these as `TableItem.captions` refs; the
/// paired caption is consumed from its own reading-order slot and rides on the
/// table node instead.
fn pair_table_captions(regions: &[Region], taken: &mut [bool]) -> Vec<Option<usize>> {
    let is_media = |label: &str| is_table_like(label) || matches!(label, "picture" | "code");
    let mut pairs: Vec<Option<usize>> = vec![None; regions.len()];
    for ci in 0..regions.len() {
        if regions[ci].label != "caption" || taken[ci] {
            continue;
        }
        // Furniture (headers/footers, form chrome) is not part of docling's
        // body-element sequence, so it neither bonds nor blocks.
        let prev = regions[..ci].iter().rposition(|r| !is_skipped(r.label));
        let next = regions[ci + 1..]
            .iter()
            .position(|r| !is_skipped(r.label))
            .map(|off| ci + 1 + off);
        let prev_media = prev.is_some_and(|j| is_media(regions[j].label));
        let next_media = next.is_some_and(|j| is_media(regions[j].label));
        let target = match (prev_media, next_media) {
            (true, false) => prev,
            (false, true) => next,
            // Ambiguous (media on both sides) or no media at all: leave the
            // caption in its own reading-order slot, as docling does.
            _ => None,
        };
        if let Some(ti) = target {
            // A first claim wins (a table with captions above *and* below
            // keeps the earlier one — docling's nearest-first tiebreak).
            if is_table_like(regions[ti].label) && pairs[ti].is_none() {
                pairs[ti] = Some(ci);
                taken[ci] = true;
            }
        }
    }
    pairs
}

/// Assemble one page from its (already overlap-resolved) layout regions and
/// text cells.
/// Normalize a layout region (page points, top-left origin) to DocLang's 0–511
/// location grid: `clamp(round(512 · coord / page_dim), 0, 511)`, per axis,
/// order `[x0, y0, x1, y1]`. Mirrors docling_core's
/// `_doclang_utils._create_location_tokens_for_bbox` (resolution 512) so the
/// emitted `<location>` tokens line up with the Python groundtruth. Our heron
/// cluster boxes match docling's to within ~1 grid unit; the residual (mainly
/// the aspect-ratio-stretch vs letterbox preprocessing difference) is absorbed
/// by the conformance harness's geometry tolerance.
fn norm_loc(region: &Region, page_w: f32, page_h: f32) -> [u16; 4] {
    let q = |v: f32, dim: f32| -> u16 {
        if dim <= 0.0 {
            return 0;
        }
        let g = (512.0 * (v as f64) / (dim as f64)).round() as i64;
        g.clamp(0, 511) as u16
    };
    [
        q(region.l, page_w),
        q(region.t, page_h),
        q(region.r, page_w),
        q(region.b, page_h),
    ]
}

/// Wrap a node in its layout provenance so the DocLang serializer emits the four
/// `<location>` tokens as the element's head (Markdown/JSON render `inner`
/// unchanged).
fn located(loc: [u16; 4], inner: Node) -> Node {
    Node::Located {
        location: loc,
        inner: Box::new(inner),
    }
}

/// Stamp the real 1-based page number onto a page's leading marker (see
/// [`assemble_page`], which emits it with `page_no: 0` because only the
/// document-level collector knows the true index — `--pages` windows shift it).
pub fn stamp_page_no(nodes: &mut [Node], page_no: usize) {
    if let Some(Node::PageInfo { page_no: p, .. }) = nodes.first_mut() {
        *p = page_no;
    }
}

/// A dense table grid plus its first-class cells (#240): `rows` is the text
/// grid every serializer renders (spans replicate their anchor's text);
/// `cells` are the docling-parity per-cell records (text, page-point bbox,
/// span rectangle, OTSL header roles). Produced by the TableFormer paths
/// (`tf_core`); lives in this always-compiled module so the pure-text (wasm
/// `pdf-text`) build sees the type.
#[derive(Clone, Debug)]
pub struct TableGrid {
    pub rows: Vec<Vec<String>>,
    pub cells: Vec<docling_core::TableCell>,
}

/// docling's `_RICH_CELL_PICTURE_COVERAGE_THRESHOLD`.
const RICH_CELL_PICTURE_COVERAGE: f32 = 0.8;

/// docling `ReadingOrderModel._match_table_pictures` (#3906, 2.118.1): every
/// picture ≥ 80 % inside a TableFormer-structured table on the page is matched
/// to the cell covering it, and returned per table as `cell index → pictures`.
/// A picture that pairs with a caption stays a standalone figure (upstream
/// would nest it and lose the caption; keeping the caption is the better
/// failure). Tables without first-class cells (geometric fallback) have no cell
/// boxes to match against and nest nothing.
fn match_table_pictures(
    regions: &[Region],
    table_rows: &[Option<TableGrid>],
    caption_for: &[Option<usize>],
) -> std::collections::HashMap<usize, Vec<(usize, Vec<usize>)>> {
    let mut out: std::collections::HashMap<usize, Vec<(usize, Vec<usize>)>> =
        std::collections::HashMap::new();
    for (p, pic) in regions.iter().enumerate() {
        if pic.label != "picture" || caption_for.get(p).is_some_and(Option::is_some) {
            continue;
        }
        let pa = area(pic.l, pic.t, pic.r, pic.b).max(1.0);
        let mut best: Option<(f32, usize, usize)> = None; // (coverage, table, cell)
        for (t, tbl) in regions.iter().enumerate() {
            if !is_table_like(tbl.label) {
                continue;
            }
            let Some(grid) = table_rows.get(t).and_then(Option::as_ref) else {
                continue;
            };
            if inter(pic, tbl.l, tbl.t, tbl.r, tbl.b) / pa < RICH_CELL_PICTURE_COVERAGE {
                continue;
            }
            if let Some((cov, cell)) = match_picture_to_cell(pic, &grid.cells) {
                if best.is_none_or(|(b, _, _)| cov > b) {
                    best = Some((cov, t, cell));
                }
            }
        }
        if let Some((_, t, cell)) = best {
            let entry = out.entry(t).or_default();
            match entry.iter_mut().find(|(c, _)| *c == cell) {
                Some((_, pics)) => pics.push(p),
                None => entry.push((cell, vec![p])),
            }
        }
    }
    out
}

/// docling `_match_picture_to_table_cell`: among the cells covering ≥ 80 % of
/// the picture, prefer the one at the picture's inferred grid position (the
/// row / column whose median cell center is nearest the picture's center —
/// cell boxes can overlap across logical rows and columns), else the best
/// coverage. Returns `(coverage, cell index)`.
fn match_picture_to_cell(pic: &Region, cells: &[docling_core::TableCell]) -> Option<(f32, usize)> {
    let pa = area(pic.l, pic.t, pic.r, pic.b).max(1.0);
    let cover = |b: &[f32; 4]| inter(pic, b[0], b[1], b[2], b[3]) / pa;
    let eligible: Vec<(f32, usize)> = cells
        .iter()
        .enumerate()
        .filter_map(|(i, c)| {
            let b = c.bbox.as_ref()?;
            let cov = cover(b);
            (cov >= RICH_CELL_PICTURE_COVERAGE).then_some((cov, i))
        })
        .collect();
    if eligible.is_empty() {
        return None;
    }
    let mut row_centers: std::collections::BTreeMap<usize, Vec<f32>> = Default::default();
    let mut col_centers: std::collections::BTreeMap<usize, Vec<f32>> = Default::default();
    for c in cells {
        let Some(b) = c.bbox.as_ref() else { continue };
        for r in c.start_row..c.start_row + c.row_span {
            row_centers.entry(r).or_default().push((b[1] + b[3]) / 2.0);
        }
        for k in c.start_col..c.start_col + c.col_span {
            col_centers.entry(k).or_default().push((b[0] + b[2]) / 2.0);
        }
    }
    let median = |v: &mut Vec<f32>| -> f32 {
        v.sort_by(f32::total_cmp);
        let n = v.len();
        if n % 2 == 1 {
            v[n / 2]
        } else {
            (v[n / 2 - 1] + v[n / 2]) / 2.0
        }
    };
    let (px, py) = ((pic.l + pic.r) / 2.0, (pic.t + pic.b) / 2.0);
    let nearest = |centers: &mut std::collections::BTreeMap<usize, Vec<f32>>, target: f32| {
        centers
            .iter_mut()
            .map(|(&i, v)| (i, (median(v) - target).abs()))
            .min_by(|a, b| a.1.total_cmp(&b.1))
            .map(|(i, _)| i)
    };
    let row = nearest(&mut row_centers, py);
    let col = nearest(&mut col_centers, px);
    let logical: Vec<(f32, usize)> = eligible
        .iter()
        .copied()
        .filter(|&(_, i)| {
            let c = &cells[i];
            row.is_some_and(|r| c.start_row <= r && r < c.start_row + c.row_span)
                && col.is_some_and(|k| c.start_col <= k && k < c.start_col + c.col_span)
        })
        .collect();
    let pool = if logical.is_empty() {
        &eligible
    } else {
        &logical
    };
    // Python's `max` over `(coverage, cell_index, cell)` tuples: highest
    // coverage, ties to the higher index.
    pool.iter()
        .copied()
        .max_by(|a, b| a.0.total_cmp(&b.0).then(a.1.cmp(&b.1)))
}

/// The DocLang structure overlay derived from first-class cells: span
/// continuations (`lcel`/`ucel`/`xcel`) and per-cell header roles, so the
/// PDF path's DCLX carries real spans instead of a flat grid.
fn structure_from_cells(
    cells: &[docling_core::TableCell],
    nrows: usize,
    ncols: usize,
) -> docling_core::TableStructure {
    let grid = || vec![vec![false; ncols]; nrows];
    let mut col_cont = grid();
    let mut row_cont = grid();
    let mut row_header = grid();
    let mut col_header = grid();
    for c in cells {
        for r in c.start_row..(c.start_row + c.row_span).min(nrows) {
            for k in c.start_col..(c.start_col + c.col_span).min(ncols) {
                col_cont[r][k] = k > c.start_col;
                row_cont[r][k] = r > c.start_row;
                row_header[r][k] = c.row_header;
                col_header[r][k] = c.column_header;
            }
        }
    }
    docling_core::TableStructure {
        header_row: Vec::new(),
        col_continuation: col_cont,
        row_continuation: row_cont,
        row_header,
        col_header,
    }
}

pub fn assemble_page(
    page: &PdfPage,
    regions: Vec<Region>,
    table_rows: &[Option<TableGrid>],
    enrichments: &[Option<Enrichment>],
) -> (Vec<Node>, Vec<(String, String)>) {
    let mut nodes: Vec<Node> = Vec::new();
    // Every page opens with an invisible page marker carrying its size in
    // points — what the JSON export needs to build docling's `pages` map and
    // denormalize the 0–511 `<location>` grid into point bboxes (#171). The
    // page *number* is stamped by the document-level collector (which knows
    // the real 1-based index, `--pages` windows included); every serializer
    // except JSON skips the marker, so Markdown/DocLang stay byte-identical.
    nodes.push(Node::PageInfo {
        page_no: 0,
        width: page.width,
        height: page.height,
    });
    // Recover this page's hyperlinks (anchor-precise pairs for strict
    // Markdown; whole-item docling-parity links are baked below and their
    // pairs dropped from this list so strict output doesn't double-wrap).
    let mut links = resolve_link_anchors(page);
    // Pair each region with its precomputed TableFormer grid and enrichment
    // (indexed by original order) and order by reading order together, so they
    // stay aligned.
    // docling's assembly order of the regions — what its reading-order
    // predictor knows as `cid` (#424) — before they are shuffled.
    let cids = cluster_cids(&regions, &page.cells);
    type RegionItem = (Region, Option<TableGrid>, Option<Enrichment>);
    let mut items: Vec<RegionItem> = regions
        .into_iter()
        .enumerate()
        .map(|(i, r)| {
            (
                r,
                table_rows.get(i).cloned().flatten(),
                enrichments.get(i).cloned().flatten(),
            )
        })
        .collect();
    order_with_containers(&mut items, &cids, page.width, page.height, |it| &it.0);
    // Float a margin page number to the front of reading order (docling parity:
    // right_to_left_02's bottom `11` is its first item). Stable, so everything
    // else keeps its order; no-op on pages without such a region.
    let page_h = page.height;
    items.sort_by_key(|(r, _, _)| !is_page_number(r, &page.cells, page_h));
    let table_rows: Vec<Option<TableGrid>> = items.iter().map(|(_, t, _)| t.clone()).collect();
    let enrichments: Vec<Option<Enrichment>> = items.iter().map(|(_, _, e)| e.clone()).collect();
    let regions: Vec<Region> = items.into_iter().map(|(r, _, _)| r).collect();
    // docling emits a figure's caption *before* the image marker. Pair each
    // picture with the caption region nearest below it and consume that caption,
    // so it isn't also emitted in its own (lower) reading-order position.
    let caption_for = pair_captions(&regions);
    let code_caption_for = pair_code_captions(&regions);
    let mut consumed = vec![false; regions.len()];
    for ci in caption_for.iter().flatten() {
        consumed[*ci] = true;
    }
    for ci in code_caption_for.iter().flatten() {
        consumed[*ci] = true;
    }
    // Table captions (#265) claim from what the picture/code pairings left.
    let mut caption_taken = consumed.clone();
    let table_caption_for = pair_table_captions(&regions, &mut caption_taken);
    for ci in table_caption_for.iter().flatten() {
        consumed[*ci] = true;
    }
    // Pictures inside a table become rich-cell content (docling#3906, 2.118.1):
    // the picture is nested in the cell it covers and not emitted standalone.
    let rich_cell_pictures = match_table_pictures(&regions, &table_rows, &caption_for);
    for (_, pics) in rich_cell_pictures.values().flatten() {
        for &p in pics {
            consumed[p] = true;
        }
    }
    // A code block's language label (`XML`, `C#`, …) is chrome, not content — the
    // detector emits it as its own region above the code; consume it.
    for (i, is_label) in code_language_labels(&regions, &page.cells)
        .into_iter()
        .enumerate()
    {
        if is_label {
            consumed[i] = true;
        }
    }

    // docling `ReadingOrderPredictor.predict_merges`: join a text fragment with a
    // following text fragment strictly to its right (an author column that wraps
    // into the next, a paragraph continuing in the next column) into one block —
    // the intra-page half of docling's reading-order merges (cross-page/vertical
    // continuations stay with [`merge_continuations`]). Already-consumed regions
    // (paired captions, code labels) are excluded.
    // Exclusive docling cell assignment: computed once for the ordered region
    // list and reused for every serialization below, so a cell can never render
    // in two regions.
    let region_texts: Vec<String> = region_texts_exclusive(&regions, &page.cells);
    let is_text: Vec<bool> = regions
        .iter()
        .enumerate()
        .map(|(i, r)| r.label == "text" && !consumed[i])
        .collect();
    let is_skip: Vec<bool> = regions
        .iter()
        .enumerate()
        .map(|(i, r)| {
            consumed[i]
                || matches!(
                    r.label,
                    "page_header" | "page_footer" | "table" | "picture" | "caption" | "footnote"
                )
        })
        .collect();
    let boxes: Vec<(f32, f32, f32, f32)> = regions.iter().map(|r| (r.l, r.t, r.r, r.b)).collect();
    if docling_core::env::flag("DOCLING_RS_DEBUG_MERGES") {
        for (i, r) in regions.iter().enumerate() {
            eprintln!(
                "MRG {i:2} {} text={} skip={} [{:.0},{:.0},{:.0},{:.0}] {:?}",
                r.label,
                is_text[i],
                is_skip[i],
                r.l,
                r.t,
                r.r,
                r.b,
                region_texts[i].chars().take(40).collect::<String>()
            );
        }
    }
    let mut merge_suffix: Vec<String> = vec![String::new(); regions.len()];
    for (head, children) in
        crate::reading_order::predict_merges(&boxes, &region_texts, &is_text, &is_skip)
            .into_iter()
            .enumerate()
    {
        for c in children {
            let t = region_texts[c].trim();
            if !t.is_empty() {
                merge_suffix[head].push(' ');
                merge_suffix[head].push_str(t);
            }
            consumed[c] = true;
        }
    }

    for (i, region) in regions.iter().enumerate() {
        if consumed[i] {
            continue;
        }
        // Page headers/footers: docling emits them as furniture blocks
        // (`<page_header>`/`<page_footer>` with a layer + location + text) at
        // their reading-order position, not as body — emit them, don't skip.
        if matches!(region.label, "page_header" | "page_footer") {
            let text = region_texts[i].clone();
            if !text.is_empty() {
                nodes.push(Node::PageFurniture {
                    footer: region.label == "page_footer",
                    location: norm_loc(region, page.width, page_h),
                    text: md_escape(&text),
                });
            }
            continue;
        }
        if is_skipped(region.label) {
            continue;
        }
        // Layout provenance for this region, normalized to docling's 0–511 grid.
        let loc = norm_loc(region, page.width, page_h);
        if region.label == "picture" {
            // The figure pixels are cropped from the page render for image export.
            // Captions are prose: markdown-escaped like a paragraph (the JSON
            // export unescapes back to the raw text, matching docling).
            let caption = caption_for[i]
                .map(|ci| md_escape(&region_texts[ci]))
                .filter(|t| !t.is_empty());
            let classification = match &enrichments[i] {
                Some(Enrichment::PictureClasses(classes)) => Some(classes.clone()),
                _ => None,
            };
            // Without the page render (text-layer-only build) a picture keeps
            // its caption/classification but carries no cropped pixels.
            #[cfg(feature = "ocr-prep")]
            let image = crate::timing::timed("crop_region", || crop_region(page, region));
            #[cfg(not(feature = "ocr-prep"))]
            let image: Option<PictureImage> = None;
            nodes.push(located(
                loc,
                Node::Picture {
                    caption,
                    caption_href: None,
                    image,
                    classification,
                    // docling's layout pipeline parents a figure's caption to
                    // the picture itself (#390) — the one backend that does.
                    caption_parent: CaptionParent::Item,
                },
            ));
            continue;
        }
        let mut text = region_texts[i].clone();
        text.push_str(&merge_suffix[i]);
        if text.is_empty() {
            continue;
        }
        match region.label {
            // docling assembles checkboxes as TEXT_ELEM items (the region's
            // cells are the option label, e.g. right_to_left_03's بلی/خير)
            // and its Markdown serializer renders them as task-list lines
            // (`- [x] …`) — mirrored by [`Node::CheckboxItem`].
            "checkbox_selected" | "checkbox_unselected" => nodes.push(Node::CheckboxItem {
                checked: region.label == "checkbox_selected",
                text: md_escape(&text),
            }),
            // docling renders both the document title and section headers as
            // `##` (it never emits a top-level `#` for PDFs), so match that.
            "title" | "section_header" => nodes.push(located(
                loc,
                Node::Heading {
                    level: 2,
                    text: md_escape(&text),
                },
            )),
            // docling drops the rendered bullet glyph; the Markdown serializer
            // adds its own `- ` marker. An item whose text opens with an `N.`
            // enumeration marker is an ordered item (rendered `N. text`).
            // A leading dash stays: it is an ordinary text glyph that
            // docling-parse keeps, and docling's items carry it into the
            // Markdown (2305's OTSL list renders `- -"C" cell …`) — only the
            // symbol-font bullets docling-parse filters out are stripped.
            "list_item" => {
                let stripped = text
                    .trim_start_matches(['•', '◦', '▪', '·', '*'])
                    .trim_start()
                    .to_string();
                if let Some((number, rest)) = parse_ordered_marker(&stripped) {
                    nodes.push(Node::ListItem {
                        ordered: true,
                        number,
                        first_in_list: false,
                        text: md_escape(&rest),
                        level: 0,
                        marker: None,
                        location: Some(loc),
                        dclx: None,
                        href: None,
                        layer: None,
                    });
                } else {
                    nodes.push(Node::ListItem {
                        ordered: false,
                        number: 0,
                        first_in_list: false,
                        text: md_escape(&stripped),
                        level: 0,
                        // docling keeps the bullet as the DocLang list marker
                        // (`<ldiv><marker>·</marker></ldiv>`); Markdown ignores it.
                        marker: Some("·".into()),
                        location: Some(loc),
                        dclx: None,
                        href: None,
                        layer: None,
                    });
                }
            }
            // TableFormer structure (cells + spans, text matched from word cells)
            // when available; otherwise geometric grid reconstruction; finally a
            // single cell.
            "table" | "document_index" => {
                // TableFormer grids carry first-class cells (#240: text +
                // page-point bbox + span rectangle + OTSL header roles) into
                // the public model, and the DocLang structure overlay derives
                // from them so DCLX emits real span/header tokens. The
                // geometric fallback has no per-cell records.
                let (mut rows, cells, structure) = match table_rows[i].clone() {
                    Some(grid) => {
                        let nrows = grid.rows.len();
                        let ncols = grid.rows.first().map_or(0, Vec::len);
                        let structure = structure_from_cells(&grid.cells, nrows, ncols);
                        (grid.rows, Some(grid.cells), Some(structure))
                    }
                    None => {
                        let rows = reconstruct_table(region, &page.cells);
                        let rows = if rows.iter().any(|r| r.len() > 1) {
                            rows
                        } else {
                            vec![vec![text.clone()]]
                        };
                        (rows, None, None)
                    }
                };
                // The paired caption (#265) rides on the table — docling's
                // TableItem.captions ref; Markdown prints it above the grid,
                // the JSON export emits the $ref, DocLang the <caption>.
                let caption = table_caption_for[i]
                    .map(|ci| md_escape(&region_texts[ci]))
                    .filter(|t| !t.is_empty());
                // Rich cells (docling#3906): the covering cell's blocks are its
                // text followed by the nested picture(s). docling's Markdown
                // renders a `RichTableCell` through the serializer — the
                // group's children joined by blank lines, newlines flattened
                // to spaces — so the flat `rows` text becomes
                // `text  <!-- image -->`; the first-class `cells` (the JSON
                // `table_cells` / `grid`) keep the plain text, as upstream.
                let mut cell_blocks: Option<Vec<Vec<Vec<Node>>>> = None;
                if let (Some(by_cell), Some(fc)) = (rich_cell_pictures.get(&i), cells.as_ref()) {
                    let nrows = rows.len();
                    let ncols = rows.iter().map(Vec::len).max().unwrap_or(0);
                    let mut blocks = vec![vec![Vec::<Node>::new(); ncols]; nrows];
                    for (cell_idx, pics) in by_cell {
                        let cell = &fc[*cell_idx];
                        let (r, c) = (cell.start_row, cell.start_col);
                        if r >= nrows || c >= ncols {
                            continue;
                        }
                        let mut parts: Vec<String> = Vec::new();
                        let mut cell_nodes: Vec<Node> = Vec::new();
                        if !cell.text.trim().is_empty() {
                            parts.push(cell.text.clone());
                            cell_nodes.push(Node::Paragraph {
                                text: cell.text.clone(),
                            });
                        }
                        for &p in pics {
                            parts.push("<!-- image -->".to_string());
                            let classification = match &enrichments[p] {
                                Some(Enrichment::PictureClasses(classes)) => Some(classes.clone()),
                                _ => None,
                            };
                            #[cfg(feature = "ocr-prep")]
                            let image = crop_region(page, &regions[p]);
                            #[cfg(not(feature = "ocr-prep"))]
                            let image: Option<PictureImage> = None;
                            cell_nodes.push(located(
                                norm_loc(&regions[p], page.width, page_h),
                                Node::Picture {
                                    caption: None,
                                    caption_href: None,
                                    image,
                                    classification,
                                    caption_parent: Default::default(),
                                },
                            ));
                        }
                        let rendered = parts.join("  ");
                        for row in rows.iter_mut().skip(r).take(cell.row_span) {
                            for slot in row.iter_mut().skip(c).take(cell.col_span) {
                                *slot = rendered.clone();
                            }
                        }
                        blocks[r][c] = cell_nodes;
                    }
                    cell_blocks = Some(blocks);
                }
                nodes.push(located(
                    loc,
                    Node::Table(Table {
                        rows,
                        location: None,
                        structure,
                        cell_blocks,
                        cells,
                        caption,
                        // As for pictures: the caption is the table's child.
                        caption_parent: CaptionParent::Item,
                    }),
                ));
            }
            // With formula enrichment the CodeFormula model decodes the region
            // to LaTeX; otherwise docling emits a placeholder comment rather
            // than the (garbled) raw glyph text.
            "formula" => match &enrichments[i] {
                Some(Enrichment::Formula { latex }) => nodes.push(Node::Formula {
                    latex: latex.clone(),
                    orig: text.clone(),
                    location: Some(loc),
                }),
                _ => nodes.push(Node::Paragraph {
                    text: "<!-- formula-not-decoded -->".into(),
                }),
            },
            // Code blocks: use the space-glyph-only grouping (monospace keeps its
            // source spacing) and emit a fenced block, preserving the line breaks
            // and indentation of the source (unlike prose, which reflows). pdfium
            // still inserts spaces around tight punctuation (`console .log`,
            // `add (3 , 5)`); tighten them to match docling-parse's source spacing.
            "code" => {
                // `code_region_text` preserves line breaks/indentation and tightens
                // each line itself; the fallback prose `text` is tightened here.
                let code = code_region_text(region, &page.code_cells);
                let code = if code.is_empty() {
                    tighten_code_punct(&text)
                } else {
                    code
                };
                // With code enrichment the CodeFormula model rewrites the block
                // (and names its language); `orig` keeps the raw extraction in
                // docling's shape — its parser has no line-preserving code
                // path, so its `orig` is the same code with the lines joined
                // by single spaces (indentation collapsed).
                // docling's parser has no line-preserving code path — its code
                // items carry the lines joined by single spaces. That flat
                // form is what every byte-conformance surface serializes
                // (legacy Markdown, JSON, DocLang); the line-preserving
                // extraction rides in `pretty` for strict Markdown only.
                let flat = code
                    .lines()
                    .map(str::trim)
                    .filter(|l| !l.is_empty())
                    .collect::<Vec<_>>()
                    .join(" ");
                let node = match &enrichments[i] {
                    Some(Enrichment::Code {
                        language,
                        text: enriched,
                    }) => Node::Code {
                        language: language.clone(),
                        text: enriched.clone(),
                        orig: Some(flat),
                        pretty: None,
                    },
                    _ => Node::Code {
                        language: None,
                        text: flat,
                        orig: None,
                        pretty: Some(code),
                    },
                };
                nodes.push(located(loc, node));
                // docling emits the `Listing N:` caption after the code block.
                if let Some(ci) = code_caption_for[i] {
                    let cap = md_escape(&region_texts[ci]);
                    if !cap.is_empty() {
                        nodes.push(Node::Paragraph { text: cap });
                    }
                }
            }
            // text, caption, footnote → paragraph
            _ => {
                // docling parity (`PageAssembleModel._match_hyperlink`): when
                // link annotations cover ≥ half of the region's box, the
                // hyperlink attaches to the item and the legacy Markdown
                // serializer wraps its full text — 2206.01062's footnote URLs
                // render as `[1 https://…](https://…)`. Sparse in-paragraph
                // citation links stay below the 0.5 coverage threshold and
                // remain plain text, exactly like docling.
                //
                // Scope: **footnote regions only.** Upstream's page_assemble
                // matches every TEXT_ELEM label, but published docling
                // observably carries the hyperlink into the document only for
                // footnote items — in both committed groundtruth generations
                // (docling-JSON and Markdown, independent runs) the fully
                // covered plain-text DOI line of 2206.01062 page 1 has
                // `hyperlink: None` while the equally covered footnotes carry
                // theirs. The corpus is the conformance reference, so match
                // the observed behavior; widen the label set if a future
                // groundtruth refresh starts linking plain text too.
                let escaped = md_escape(&text);
                let hyperlink = (region.label == "footnote")
                    .then(|| region_hyperlink(region, &page.links))
                    .flatten();
                let text = match hyperlink {
                    Some(uri) => {
                        // The strict-mode anchor pairs this item covers are
                        // superseded by the baked whole-item link.
                        links.retain(|(anchor, href)| {
                            !(href == &uri && region_texts[i].contains(anchor.as_str()))
                        });
                        format!("[{escaped}]({uri})")
                    }
                    None => escaped,
                };
                nodes.push(located(loc, Node::Paragraph { text }))
            }
        }
    }
    // A `/Rotate`-normalized scanned page (see `pdfium_backend`) was assembled
    // in upright space; rotate the finished geometry back so locations and the
    // page size are display-space, like docling and every viewer report them.
    if page.rotation != 0 {
        rotate_nodes_to_display(&mut nodes, page.rotation);
    }
    (nodes, links)
}

/// Rotate one 0–511 location bbox 90° clockwise on the grid (top-left origin):
/// `(x, y) → (511 - y, x)`.
fn rot_loc_cw(l: [u16; 4]) -> [u16; 4] {
    [511 - l[3], l[0], 511 - l[1], l[2]]
}

/// Map upright-space geometry back to display space for a page whose `/Rotate`
/// was normalized away before inference: every `<location>` rotates `rot`°
/// clockwise on the 0–511 grid (the grid is per-axis normalized, so no page
/// dims are needed), and the `PageInfo` size returns to the display box. Node
/// text and order are untouched — reading order was decided upright, which is
/// the whole point.
fn rotate_nodes_to_display(nodes: &mut [Node], rot: u16) {
    let quarter_turns = (rot / 90) as usize;
    let rot_loc = |l: &mut [u16; 4]| {
        for _ in 0..quarter_turns {
            *l = rot_loc_cw(*l);
        }
    };
    fn walk(node: &mut Node, rot_loc: &impl Fn(&mut [u16; 4]), swap_dims: bool) {
        match node {
            Node::PageInfo { width, height, .. } => {
                if swap_dims {
                    std::mem::swap(width, height);
                }
            }
            Node::Located { location, inner } => {
                rot_loc(location);
                walk(inner, rot_loc, swap_dims);
            }
            Node::Furniture { inner, .. } => walk(inner, rot_loc, swap_dims),
            Node::Group { children, .. } => {
                for c in children {
                    walk(c, rot_loc, swap_dims);
                }
            }
            Node::ListItem { location, .. }
            | Node::Formula { location, .. }
            | Node::Chart { location, .. } => {
                if let Some(l) = location {
                    rot_loc(l);
                }
            }
            Node::PageFurniture { location, .. } => rot_loc(location),
            Node::Table(t) => {
                if let Some(l) = &mut t.location {
                    rot_loc(l);
                }
            }
            _ => {}
        }
    }
    let swap_dims = quarter_turns % 2 == 1;
    for node in nodes {
        walk(node, &rot_loc, swap_dims);
    }
}

/// Merge paragraph fragments split across a column or page break. docling joins a
/// paragraph whose previous fragment ends mid-sentence (a letter, not sentence
/// punctuation) with a lowercase continuation: `…definition of` + `lists in…` →
/// `…definition of lists in…`. The fragments are consecutive paragraphs, or
/// separated only by figure(s) the text wraps around: a column whose body flows
/// past a figure resumes below it (`…The wing type that is` ⟶[figure]⟶ `the most
/// common…`), and docling emits the whole paragraph before the figure. A heading,
/// table, or list between them ends the paragraph (no merge).
/// A paragraph that is really a figure/table caption (`Fig. 1. …`, `Table 2 …`).
/// Used to skip an unpaired caption when stitching a paragraph that wraps around
/// a figure.
fn looks_like_caption(text: &str) -> bool {
    let head: String = text.trim_start().chars().take(14).collect();
    (head.starts_with("Fig") || head.starts_with("Table"))
        && head.contains(|c: char| c.is_ascii_digit())
}

/// A paragraph fragment is "open" — i.e. it might continue into the next
/// paragraph — when it ends mid-word (a letter) or with a wrap hyphen/dash.
/// docling joins `vocab-` + `ulary` → `vocab- ulary`.
fn paragraph_is_open(text: &str) -> bool {
    // docling's merge head test (`.+([a-z,\-\u00AD])\s*`): at least two chars,
    // ending in an ASCII lowercase letter, a comma, a hyphen, or a soft
    // hyphen. The comma matters: 2206's "…In phase four," resumes across the
    // page break. Uppercase/non-Latin endings do not merge, exactly as
    // upstream (the dash family is already `-` here — clean_text normalized).
    let t = text.trim_end();
    t.chars().count() >= 2
        && t.chars()
            .next_back()
            .is_some_and(|c| matches!(c, 'a'..='z' | ',' | '-' | '\u{ad}'))
}

/// The paragraph text inside a node, looking through a [`Node::Located`]
/// provenance wrapper (PDF body paragraphs are wrapped since they carry a
/// `<location>`). Returns `None` for non-paragraph nodes.
fn as_paragraph(n: &Node) -> Option<&str> {
    match n {
        Node::Paragraph { text } => Some(text),
        Node::Located { inner, .. } => match inner.as_ref() {
            Node::Paragraph { text } => Some(text),
            _ => None,
        },
        _ => None,
    }
}

/// Whether a node is a picture, looking through a [`Node::Located`] wrapper.
fn is_picture_node(n: &Node) -> bool {
    match n {
        Node::Picture { .. } => true,
        Node::Located { inner, .. } => matches!(inner.as_ref(), Node::Picture { .. }),
        _ => false,
    }
}

/// A node a forward paragraph merge looks straight past: a figure or *table*
/// the text wraps around, or a page header/footer that falls between the two
/// fragments of a paragraph continuing across a page break (docling's merge
/// skip-labels: page_header, page_footer, table, picture, caption, footnote —
/// 2206's "…In phase four," resumes after a full caption+table+figure block).
fn is_merge_trailer(n: &Node) -> bool {
    is_picture_node(n)
        || matches!(
            n,
            Node::PageFurniture { .. } | Node::PageInfo { .. } | Node::Table(_)
        )
        || matches!(n, Node::Located { inner, .. } if matches!(inner.as_ref(), Node::Table(_)))
        || as_paragraph(n).is_some_and(looks_like_caption)
}

/// Rebuild node `i` as a paragraph with `text`, preserving its `<location>`
/// wrapper (and thus provenance) if it had one.
fn reparagraph(node: &Node, text: String) -> Node {
    match node {
        Node::Located { location, .. } => located(*location, Node::Paragraph { text }),
        _ => Node::Paragraph { text },
    }
}

pub(crate) fn merge_continuations(nodes: &mut Vec<Node>) {
    let mut i = 0;
    while i + 1 < nodes.len() {
        let Some(a) = as_paragraph(&nodes[i]) else {
            i += 1;
            continue;
        };
        // A figure/table caption is a self-contained unit; body text resuming
        // after a figure is the continuation case, not the caption itself. Never
        // stitch *from* a caption — otherwise a caption that ends in a lone glyph
        // (`Fig. 5. … PubTabNet. μ`) would swallow a following stray figure label
        // (a standalone `μ`) into `… μ μ`.
        if looks_like_caption(a) {
            i += 1;
            continue;
        }
        if !paragraph_is_open(a) {
            i += 1;
            continue;
        }
        // The continuation is the next paragraph, looking past any figures the
        // text wraps around — and a figure/table caption that was emitted as its
        // own paragraph (an above-the-figure caption that didn't pair), since the
        // body text resumes after the whole figure+caption block.
        let mut j = i + 1;
        while nodes.get(j).is_some_and(is_merge_trailer) {
            j += 1;
        }
        // docling's continuation regex allows either case, but its merge runs
        // over the pre-assembly element stream; at node level an uppercase
        // start is overwhelmingly a new sentence/heading fragment (allowing it
        // swallowed 2305's formula blocks and redp's chapter openers), so the
        // continuation stays lowercase-start here.
        let cont = nodes.get(j).and_then(as_paragraph).is_some_and(|b| {
            b.trim_start()
                .chars()
                .next()
                .is_some_and(char::is_lowercase)
        });
        if cont {
            let a = as_paragraph(&nodes[i]).unwrap().trim_end().to_string();
            let b = as_paragraph(&nodes[j]).unwrap().trim_start().to_string();
            // A soft hyphen -- or a hard hyphen followed by a lowercase
            // continuation (guaranteed lowercase by the `cont` gate above) --
            // is a word split across the break: strip it and join without a
            // space, docling#3888 ("vocab-" + "ulary" -> "vocabulary");
            // docling's older serializer kept the artifact ("vocab- ulary").
            // Everything else joins with the space, as before.
            let merged = match a.strip_suffix('\u{ad}').or_else(|| a.strip_suffix('-')) {
                Some(stem) => format!("{stem}{b}"),
                None => format!("{a} {b}"),
            };
            // Keep node i's provenance wrapper; docling's merged paragraph keeps
            // the first fragment's geometry as its primary location.
            nodes[i] = reparagraph(&nodes[i], merged);
            nodes.remove(j);
            // Re-check i: the merged paragraph may continue further.
        } else {
            i += 1;
        }
    }
}

/// How many leading nodes of `nodes` are safe to flush now — i.e. cannot be
/// rewritten by a future [`merge_continuations`] once more pages are appended.
///
/// A forward merge can only start from an "open" paragraph (ends mid-word) and
/// only reaches across trailing pictures and figure/table captions. So we scan
/// from the end past those skippable trailers: if the first non-skippable node is
/// an open paragraph, it (and the trailers after it) must be held; anything else —
/// a closed paragraph, a heading, a table, a list — blocks any forward merge, so
/// the whole buffer is safe to flush.
fn hold_start(nodes: &[Node]) -> usize {
    for k in (0..nodes.len()).rev() {
        // Skippable trailers (figures, page furniture, captions): a forward merge
        // looks straight past them.
        if is_merge_trailer(&nodes[k]) {
            continue;
        }
        match as_paragraph(&nodes[k]) {
            // An open body paragraph might still pull a continuation off the next
            // page — hold from here to the end.
            Some(text) if paragraph_is_open(text) => return k,
            // A closed paragraph, heading, table, list, etc. ends the paragraph:
            // nothing after it can merge backwards across it. Flush everything.
            _ => return nodes.len(),
        }
    }
    // Only skippable trailers (or empty) and no open paragraph to anchor a merge.
    nodes.len()
}

/// Streaming counterpart of [`merge_continuations`]: feed per-page node batches in
/// document order and get back the prefix that is final (its cross-page merges are
/// resolved and no future page can change it), holding back only the small tail
/// that might still merge into the next page. Concatenating every flushed batch
/// (then [`finish`](Self::finish)) yields exactly the same nodes as running
/// [`merge_continuations`] once over the whole document.
pub(crate) struct StreamAssembler {
    pending: Vec<Node>,
}

impl StreamAssembler {
    pub(crate) fn new() -> Self {
        Self {
            pending: Vec::new(),
        }
    }

    /// Append one page's nodes, resolve merges within the buffer, and return the
    /// now-final prefix to emit (possibly empty).
    pub(crate) fn push(&mut self, mut nodes: Vec<Node>) -> Vec<Node> {
        self.pending.append(&mut nodes);
        merge_continuations(&mut self.pending);
        let cut = hold_start(&self.pending);
        let tail = self.pending.split_off(cut);
        std::mem::replace(&mut self.pending, tail)
    }

    /// Flush whatever is left after the last page (the held tail is final once no
    /// more pages can follow).
    pub(crate) fn finish(self) -> Vec<Node> {
        self.pending
    }
}

#[cfg(test)]
mod tests {
    use super::{cells_text, clean_text, merge_overlapping_regulars};

    /// docling drops a picture covering > 90 % of the page (its labels then
    /// read out as text); a dominant-but-not-full figure and any other label
    /// stay whatever their size.
    #[test]
    fn full_page_pictures_are_dropped_like_docling() {
        use super::drop_full_page_pictures;
        use crate::layout::Region;
        let region = |label: &'static str, l, t, r, b| Region {
            label,
            score: 0.99,
            l,
            t,
            r,
            b,
        };
        let mut regions = vec![
            region("picture", 0.0, 0.5, 478.9, 241.8),
            region("picture", 10.0, 10.0, 400.0, 200.0),
            region("table", 0.0, 0.0, 480.0, 243.0),
            region("text", 5.0, 5.0, 100.0, 20.0),
        ];
        drop_full_page_pictures(&mut regions, 480.75, 243.75);
        let labels: Vec<_> = regions.iter().map(|r| (r.label, r.l)).collect();
        assert_eq!(
            labels,
            vec![("picture", 10.0), ("table", 0.0), ("text", 5.0)]
        );
    }
    use super::{code_region_text, merge_continuations, resolve_link_anchors, StreamAssembler};
    use crate::layout::Region;
    use crate::pdfium_backend::{LinkAnnot, PdfPage, TextCell};
    use docling_core::Node;

    /// The int8-layout guard's coverage metric: cells under detections count,
    /// cells outside don't, whitespace cells are ignored, and a cell-less page
    /// reads as fully covered (nothing to rescue).
    #[test]
    fn layout_cell_coverage_counts_claimed_text_cells() {
        let cell = |text: &str, l: f32, t: f32| TextCell {
            text: text.into(),
            l,
            t,
            r: l + 40.0,
            b: t + 10.0,
        };
        let region = Region {
            label: "text",
            score: 0.9,
            l: 0.0,
            t: 0.0,
            r: 100.0,
            b: 50.0,
        };
        let cells = vec![
            cell("inside", 10.0, 10.0),
            cell("also inside", 10.0, 30.0),
            cell("outside", 10.0, 200.0),
            cell("   ", 10.0, 210.0), // whitespace: not counted at all
        ];
        let cov = super::layout_cell_coverage(std::slice::from_ref(&region), &cells);
        assert!((cov - 2.0 / 3.0).abs() < 1e-6, "got {cov}");
        assert_eq!(super::layout_cell_coverage(&[], &[]), 1.0);
        assert_eq!(super::layout_cell_coverage(&[], &cells), 0.0);
    }

    /// #165: a picture no longer claims cells at 0.2 intersection-over-self.
    /// A line straddling the figure border (≤80 % contained) becomes an orphan
    /// region and survives the contained-regulars drop — before the fix its
    /// cells were silently erased. A line fully inside the picture is still
    /// re-dropped, matching docling's Markdown (a picture's children never
    /// reach its serializer's output).
    #[test]
    fn border_straddling_lines_survive_picture_interior_is_still_dropped() {
        let pic = Region {
            label: "picture",
            score: 0.9,
            l: 0.0,
            t: 0.0,
            r: 100.0,
            b: 100.0,
        };
        // ~35 % of this cell overlaps the picture (l=90..120 of 0..100): above
        // the old 0.2 claim (was swallowed), below full containment (survives).
        let straddler = TextCell {
            text: "axis label".into(),
            l: 90.0,
            t: 40.0,
            r: 120.0,
            b: 48.0,
        };
        let interior = TextCell {
            text: "in-figure callout".into(),
            l: 10.0,
            t: 10.0,
            r: 60.0,
            b: 18.0,
        };
        let mut regions = vec![pic];
        super::add_orphan_regions(&mut regions, &[straddler, interior]);
        assert_eq!(
            regions.iter().filter(|r| r.label == "text").count(),
            2,
            "both unclaimed lines become orphans"
        );
        super::drop_contained_regulars(&mut regions);
        let texts: Vec<(f32, f32)> = regions
            .iter()
            .filter(|r| r.label == "text")
            .map(|r| (r.l, r.r))
            .collect();
        assert_eq!(
            texts,
            [(90.0, 120.0)],
            "the straddler is emitted, the fully-contained callout is not"
        );
    }

    /// docling#3906's concern, pinned on our side: a picture detected fully
    /// inside a table region must survive the containment drop (upstream now
    /// attaches it to the table's cell; we keep it as a body sibling — either
    /// way it must not vanish). The text region inside the same table is the
    /// control: regulars are the ones the drop swallows.
    #[test]
    fn picture_inside_a_table_region_survives_the_containment_drop() {
        let mut regions = vec![
            region("table", 0.9, 0.0, 0.0, 200.0, 200.0),
            region("picture", 0.9, 20.0, 20.0, 120.0, 120.0),
            region("text", 0.9, 20.0, 140.0, 180.0, 180.0),
        ];
        super::drop_contained_regulars(&mut regions);
        let labels: Vec<&str> = regions.iter().map(|r| r.label).collect();
        assert_eq!(
            labels,
            ["table", "picture"],
            "the in-table picture stays; the in-table regular is the special's child"
        );
    }

    /// Table–caption pairing (#265) is reading-order adjacency, docling's
    /// `_find_to_captions`: a caption binds the table directly next to it in
    /// the region sequence — above-caption and below-caption both work, and
    /// geometry is irrelevant (a same-page caption in the other column of a
    /// two-column layout is *not* adjacent, however close its box is). A
    /// caption with media on both sides, or separated from the table by a
    /// text paragraph, stays unattached.
    #[test]
    fn table_captions_pair_by_reading_order_adjacency() {
        // caption → table (above-caption), then table → caption (below-caption),
        // then a caption fenced off by a paragraph, then one between two tables.
        let regions = vec![
            region("text", 0.9, 0.0, 0.0, 100.0, 10.0), // 0 body text
            region("caption", 0.9, 0.0, 12.0, 60.0, 20.0), // 1 above-caption
            region("table", 0.9, 20.0, 22.0, 90.0, 60.0), // 2 ← pairs with 1
            region("table", 0.9, 0.0, 70.0, 100.0, 110.0), // 3 ← pairs with 4
            region("caption", 0.9, 0.0, 112.0, 60.0, 120.0), // 4 below-caption
            region("text", 0.9, 0.0, 130.0, 100.0, 140.0), // 5 body text
            region("caption", 0.9, 0.0, 142.0, 60.0, 150.0), // 6 fenced by 5/7
            region("text", 0.9, 0.0, 152.0, 100.0, 162.0), // 7 body text
            region("table", 0.9, 0.0, 170.0, 100.0, 200.0), // 8 unpaired
            region("caption", 0.9, 0.0, 202.0, 60.0, 210.0), // 9 ambiguous
            region("table", 0.9, 0.0, 212.0, 100.0, 240.0), // 10 unpaired
        ];
        let mut taken = vec![false; regions.len()];
        let pairs = super::pair_table_captions(&regions, &mut taken);
        assert_eq!(pairs[2], Some(1), "caption directly above its table pairs");
        assert_eq!(pairs[3], Some(4), "caption directly below its table pairs");
        assert_eq!(
            pairs[8], None,
            "a text paragraph between caption and table breaks the bond"
        );
        assert_eq!(
            pairs[10], None,
            "a caption between two tables is ambiguous and stays loose"
        );
        assert!(taken[1] && taken[4] && !taken[6] && !taken[9]);
    }

    /// A colored terms-and-conditions panel detected as `picture` demotes into
    /// per-paragraph `text` regions (the blank line between C.7 and C.8 splits
    /// them); a chart whose only text is a few narrow axis labels keeps its
    /// crop untouched.
    #[test]
    fn text_panels_demote_to_paragraphs_but_charts_keep_their_crop() {
        let cell = |text: &str, l: f32, t: f32, r: f32, b: f32| TextCell {
            text: text.to_string(),
            l,
            t,
            r,
            b,
        };
        let panel = Region {
            label: "picture",
            score: 0.9,
            l: 0.0,
            t: 0.0,
            r: 100.0,
            b: 100.0,
        };
        // Three tight lines, a blank-line gap, two more: two paragraphs.
        let cells = vec![
            cell(
                "C.7. Wenn Sie diesen Vertrag widerrufen,",
                5.0,
                10.0,
                95.0,
                18.0,
            ),
            cell(
                "haben wir Ihnen alle Zahlungen, die wir",
                5.0,
                20.0,
                95.0,
                28.0,
            ),
            cell(
                "von Ihnen erhalten haben, zurückzuzahlen.",
                5.0,
                30.0,
                90.0,
                38.0,
            ),
            cell(
                "C.8. Wir können die Rückzahlung verweigern,",
                5.0,
                52.0,
                95.0,
                60.0,
            ),
            cell(
                "bis wir die Waren wieder zurückerhalten haben.",
                5.0,
                62.0,
                92.0,
                70.0,
            ),
        ];
        let mut regions = vec![panel.clone()];
        super::recover_text_panels(&mut regions, &cells);
        assert_eq!(
            regions.iter().map(|r| r.label).collect::<Vec<_>>(),
            ["text", "text"],
            "dense panel must demote into one text region per paragraph"
        );
        assert!(regions[0].b < regions[1].t, "paragraphs split at the gap");
        // Sparse narrow labels (a chart): picture survives.
        let labels = vec![
            cell("0", 5.0, 90.0, 8.0, 95.0),
            cell("50", 5.0, 50.0, 10.0, 55.0),
            cell("100", 5.0, 10.0, 12.0, 15.0),
            cell("t, s", 45.0, 96.0, 55.0, 100.0),
        ];
        let mut regions = vec![panel];
        super::recover_text_panels(&mut regions, &labels);
        assert_eq!(
            regions.iter().map(|r| r.label).collect::<Vec<_>>(),
            ["picture"]
        );
    }

    /// An uncaptioned chart on a scanned page whose title, axis labels, and
    /// OCR boxes over the plot area are dense and wide enough to pass the
    /// coverage/width gates still keeps its crop: its line heights are ragged
    /// (title face vs tick labels vs bar-area OCR), failing the uniform-leading
    /// gate — a real text panel is set with constant leading (#173).
    #[test]
    fn dense_titled_chart_keeps_its_crop() {
        let cell = |text: &str, l: f32, t: f32, r: f32, b: f32| TextCell {
            text: text.to_string(),
            l,
            t,
            r,
            b,
        };
        let chart = Region {
            label: "picture",
            score: 0.9,
            l: 0.0,
            t: 0.0,
            r: 100.0,
            b: 100.0,
        };
        // Five wide lines at wildly different heights: a 12-pt title, 20-pt OCR
        // boxes over the bars, 4–5-pt tick/axis labels. Coverage and median
        // width both clear the panel thresholds.
        let cells = vec![
            cell("Underground Water Storage", 10.0, 5.0, 90.0, 17.0),
            cell("aquifer recharge zone", 15.0, 30.0, 75.0, 50.0),
            cell("confined | unconfined | perched", 12.0, 55.0, 80.0, 59.0),
            cell("saturated thickness", 8.0, 70.0, 60.0, 90.0),
            cell("distance from well, km", 20.0, 92.0, 85.0, 97.0),
        ];
        let mut regions = vec![chart];
        super::recover_text_panels(&mut regions, &cells);
        assert_eq!(
            regions.iter().map(|r| r.label).collect::<Vec<_>>(),
            ["picture"],
            "ragged line heights mark a figure, not a text panel"
        );
    }

    /// docling serializes a cluster's cells in docling-parse index order
    /// (`_sort_cells`) and joins them with `PageAssembleModel.sanitize_text`:
    /// a space after every line except one ending in `-`, which either fuses a
    /// wrapped word (alnum on both sides — dash dropped) or glues verbatim (a
    /// bare `-` cell: `[0000` `-` `0002` → `[0000 -0002`, the 2305 ORCID line;
    /// `-` + `"C" cell -` + `a new table cell` → `-"C" cell a new table cell`,
    /// its OTSL list). Verified against the corpus: pure index order beats any
    /// geometric re-sort (normal_4pages' heading numerals paint after their
    /// text and belong last: `## 들어가며 1`).
    #[test]
    fn cells_join_in_index_order_with_sanitize_text_rules() {
        let cell = |text: &str, l: f32, t: f32, r: f32, b: f32| TextCell {
            text: text.to_string(),
            l,
            t,
            r,
            b,
        };
        let region = Region {
            label: "text",
            score: 1.0,
            l: 0.0,
            t: 95.0,
            r: 200.0,
            b: 130.0,
        };
        // ORCID superscript: a bare dash cell is a *detached* dash — kept, and
        // since docling#4052 (2.122) it joins with the ordinary space on both
        // sides (`[0000 -0002 -6960]` before that fix).
        let orcid = vec![
            cell("[0000", 10.0, 100.0, 30.0, 110.0),
            cell("−", 30.0, 100.0, 34.0, 110.0),
            cell("0002", 34.0, 100.0, 50.0, 110.0),
            cell("−", 50.0, 100.0, 54.0, 110.0),
            cell("6960]", 54.0, 100.0, 70.0, 110.0),
        ];
        assert_eq!(super::region_text(&region, &orcid), "[0000 - 0002 - 6960]");
        // Wrapped word: dash dropped, lines fused (both boundary words alnum).
        let wrapped = vec![
            cell("platforms-", 10.0, 100.0, 60.0, 110.0),
            cell("reflects the design", 10.0, 112.0, 90.0, 122.0),
        ];
        assert_eq!(
            super::region_text(&region, &wrapped),
            "platformsreflects the design"
        );
        // Dash-ending lines that are *detached* dashes (a bare bullet cell, a
        // `cell -` separator): the dash stays and the lines join with a space
        // — docling#4052; before it they glued (`-"C" cell a new table cell`,
        // 2305's OTSL list bullets).
        let otsl = vec![
            cell("–", 10.0, 100.0, 14.0, 110.0),
            cell("\"C\" cell -", 16.0, 100.0, 60.0, 110.0),
            cell("a new table cell", 10.0, 112.0, 80.0, 122.0),
        ];
        assert_eq!(
            super::region_text(&region, &otsl),
            "- \"C\" cell - a new table cell"
        );
        // Index order is authoritative — no geometric re-sort.
        let numeral = vec![
            cell("들어가며", 30.0, 100.0, 80.0, 110.0),
            cell("1", 10.0, 98.0, 25.0, 112.0), // big numeral painted last
        ];
        assert_eq!(super::region_text(&region, &numeral), "들어가며 1");
    }

    /// The geometric-reliability gate, on the two shapes it has to tell apart.
    #[test]
    fn geometric_reliability_rejects_split_column_grids() {
        let g = |rows: &[&[&str]]| -> Vec<Vec<String>> {
            rows.iter()
                .map(|r| r.iter().map(|c| c.to_string()).collect())
                .collect()
        };
        // A genuine grid: dense, every column carrying entries. Nothing for
        // TableFormer to improve, so geometry is used as-is.
        assert!(super::geometric_table_is_reliable(&g(&[
            &["Datum", "Leistung", "Anzahl", "Kosten"],
            &["04.07", "Internet", "1", "40.30"],
            &["04.07", "Telefon", "2", "8.06"],
        ])));
        // The left-edge split artefact (the shape a scanned invoice produced):
        // one real label column plus values scattered across three sparse ones.
        assert!(!super::geometric_table_is_reliable(&g(&[
            &["www.magenta.at/faq", "", "", ""],
            &["Serviceteam", "", "", ""],
            &["Telefon", "0676/2000", "", ""],
            &["Kundennummer", "", "", "1.21699482"],
            &["Rechnungsnummer", "", "922769430725", ""],
            &["Rechnungsdatum", "", "", "04.07.2025"],
        ])));
        // A column only one row ever uses is a split artefact even when the
        // grid is otherwise dense.
        assert!(!super::geometric_table_is_reliable(&g(&[
            &["a", "b", ""],
            &["c", "d", ""],
            &["e", "f", "g"],
        ])));
        // Degenerate shapes are never vouched for — TableFormer may recover
        // structure a collapsed reconstruction lost.
        assert!(!super::geometric_table_is_reliable(&g(&[&[
            "only one column"
        ]])));
        assert!(!super::geometric_table_is_reliable(&[]));
    }

    /// A `picture` region is cropped out of the rendered page, whatever built
    /// that page. The browser pipeline (#157) has no pdfium but does hand over
    /// the rasterized bitmap through `from_cells_with_image`, so it must get
    /// the same figure bytes the native path does — that is what makes
    /// `images = "embedded"` inline real pixels instead of a placeholder.
    #[cfg(feature = "ocr-prep")]
    #[test]
    fn picture_regions_are_cropped_from_a_host_supplied_page_image() {
        let mut img = image::RgbImage::new(200, 200);
        // Paint the figure area so the crop is distinguishable from the page.
        for y in 100..160 {
            for x in 20..120 {
                img.put_pixel(x, y, image::Rgb([255, 0, 0]));
            }
        }
        // scale 2.0: the region is in page points, the bitmap in pixels.
        let page = PdfPage::from_cells_with_image(100.0, 100.0, 2.0, Vec::new(), img);
        let region = Region {
            label: "picture",
            score: 0.9,
            l: 10.0,
            t: 50.0,
            r: 60.0,
            b: 80.0,
        };
        let (nodes, _) = super::assemble_page(&page, vec![region], &[None], &[None]);
        // Layout-derived nodes carry provenance, so the picture arrives wrapped.
        let image = nodes
            .iter()
            .find_map(|n| match n {
                Node::Located { inner, .. } => match &**inner {
                    Node::Picture { image, .. } => image.as_ref(),
                    _ => None,
                },
                Node::Picture { image, .. } => image.as_ref(),
                _ => None,
            })
            .expect("a picture node with cropped pixels");
        assert_eq!(image.mimetype, "image/png");
        assert_eq!((image.width, image.height), (100, 60), "region × scale");
        assert!(!image.data.is_empty(), "PNG bytes were encoded");
    }

    #[test]
    fn link_anchors_split_a_shared_word_cell_between_adjacent_links() {
        // A common header layout: one text run holds several pipe-separated
        // labels, each carrying its own link annotation. Every link must get
        // its own label as the anchor (and the "|" separators must belong to
        // none), not the whole run.
        let annot = |l: f32, r: f32, uri: &str| LinkAnnot {
            l,
            t: 100.0,
            r,
            b: 114.0,
            uri: uri.into(),
        };
        let page = PdfPage {
            width: 600.0,
            height: 800.0,
            scale: 2.0,
            cells: Vec::new(),
            code_cells: Vec::new(),
            // "LinkedIn | GitHub | Credly" = 26 chars over x 100..360.
            word_cells: vec![cell(
                "LinkedIn | GitHub | Credly",
                100.0,
                100.0,
                360.0,
                114.0,
            )],
            image: image::RgbImage::new(1, 1),
            image_layout: None,
            links: vec![
                annot(100.0, 180.0, "https://l"),
                annot(200.0, 260.0, "https://g"),
                annot(290.0, 360.0, "https://c"),
            ],
            rotation: 0,
        };
        assert_eq!(
            resolve_link_anchors(&page),
            vec![
                ("LinkedIn".to_string(), "https://l".to_string()),
                ("GitHub".to_string(), "https://g".to_string()),
                ("Credly".to_string(), "https://c".to_string()),
            ]
        );
    }

    /// A one-line code cell at `[l, r] × [t, b]` (top-left coords).
    fn cell(text: &str, l: f32, t: f32, r: f32, b: f32) -> TextCell {
        TextCell {
            text: text.into(),
            l,
            t,
            r,
            b,
        }
    }

    /// OCR-path grouping (docling's `_remove_overlapping_clusters("regular")`):
    /// the low-score paragraph box RT-DETR draws over its own high-score line
    /// boxes collapses to one region — the group's union, with the survivor's
    /// label and score — so region-scoped OCR reads each line once. Regions
    /// that merely sit near each other, and specials, are untouched.
    #[test]
    fn merge_overlapping_regulars_collapses_a_block_over_its_lines() {
        let mut regions = vec![
            region("text", 0.84, 60.0, 186.0, 270.0, 198.0),
            region("text", 0.80, 60.0, 160.0, 294.0, 172.0),
            region("text", 0.79, 59.0, 107.0, 272.0, 119.0),
            // The paragraph box, lower score, containing all three lines.
            region("text", 0.52, 59.0, 107.0, 295.0, 200.0),
            // Elsewhere on the page: stays as is.
            region("section_header", 0.77, 60.0, 71.0, 253.0, 86.0),
            // A picture the block overlaps is not a regular — never grouped.
            region("picture", 0.9, 50.0, 100.0, 300.0, 210.0),
        ];
        merge_overlapping_regulars(&mut regions);
        assert_eq!(regions.len(), 3, "{regions:?}");
        let block = regions
            .iter()
            .find(|r| r.label == "text")
            .expect("one text");
        // docling keeps the largest passing candidate unless a rival is both
        // comparable in size and > 0.05 more confident; the 16× larger block
        // passes, and a smaller line never replaces a larger current best.
        // Either way the survivor spans the whole group.
        assert_eq!(
            (block.l, block.t, block.r, block.b),
            (59.0, 107.0, 295.0, 200.0)
        );
        assert!(regions.iter().any(|r| r.label == "section_header"));
        assert!(regions.iter().any(|r| r.label == "picture"));
    }

    /// The pairwise rules, each in the arrangement where it decides the
    /// outcome: docling seeds the survivor with the group's first passing
    /// cluster and a later one replaces it only when larger *and* within
    /// 0.05 confidence, so a rule that merely lets a cluster pass matters
    /// exactly when that cluster comes first — a same-sized list item ahead
    /// of a far more confident text box, a code box ahead of the text it
    /// contains. Without the rule either would be rejected outright (similar
    /// size, rival > 0.05 more confident) and the text box would win.
    #[test]
    fn merge_overlapping_regulars_follows_the_preference_rules() {
        let mut regions = vec![
            region("list_item", 0.6, 0.0, 0.0, 102.0, 20.0),
            region("text", 0.9, 0.0, 0.0, 100.0, 20.0),
        ];
        merge_overlapping_regulars(&mut regions);
        assert_eq!(regions.len(), 1);
        assert_eq!(regions[0].label, "list_item");

        let mut regions = vec![
            region("code", 0.6, 0.0, 0.0, 100.0, 100.0),
            region("text", 0.9, 2.0, 2.0, 98.0, 98.0),
        ];
        merge_overlapping_regulars(&mut regions);
        assert_eq!(regions.len(), 1);
        assert_eq!(regions[0].label, "code");

        // No rule applies: a near-identical rival that is > 0.05 more
        // confident rejects the candidate whatever the order.
        for order in [[0.9, 0.6], [0.6, 0.9]] {
            let mut regions = vec![
                region("text", order[0], 0.0, 0.0, 100.0, 20.0),
                region("text", order[1], 0.0, 0.0, 105.0, 21.0),
            ];
            merge_overlapping_regulars(&mut regions);
            assert_eq!(regions.len(), 1);
            assert_eq!(regions[0].score, 0.9, "the confident twin wins");
            assert_eq!(
                (regions[0].r, regions[0].b),
                (105.0, 21.0),
                "on the union box"
            );
        }

        // Side by side (no containment, IoU 0): nothing to merge.
        let mut regions = vec![
            region("text", 0.9, 0.0, 0.0, 100.0, 20.0),
            region("text", 0.9, 0.0, 22.0, 100.0, 42.0),
        ];
        merge_overlapping_regulars(&mut regions);
        assert_eq!(regions.len(), 2);
    }

    fn region(label: &'static str, score: f32, l: f32, t: f32, r: f32, b: f32) -> Region {
        Region {
            label,
            score,
            l,
            t,
            r,
            b,
        }
    }

    #[test]
    fn resolve_collapses_nested_code_keeping_the_larger_box() {
        // A tight high-score `code` box and a taller lower-score near-duplicate that
        // contains it must collapse to one — the *larger* box, so every cell stays
        // covered and nothing leaks out as orphan text.
        let tight = region("code", 0.95, 78.0, 292.0, 300.0, 330.0);
        let wide = region("code", 0.66, 63.0, 260.0, 320.0, 346.0);
        let kept = super::resolve(vec![tight, wide]);
        assert_eq!(kept.len(), 1, "nested code boxes must collapse to one");
        assert!(
            kept[0].l == 63.0 && kept[0].b == 346.0,
            "the larger containing box is kept"
        );
    }

    #[test]
    fn resolve_keeps_distinct_and_differently_typed_regions() {
        // A text box fully inside a lower-score *table* must NOT be collapsed (the
        // code dedup is code-only), and two separate code blocks stay separate.
        let text = region("text", 0.95, 90.0, 210.0, 200.0, 230.0);
        let table = region("table", 0.60, 80.0, 200.0, 400.0, 500.0);
        assert_eq!(super::resolve(vec![text, table]).len(), 2);

        let code_a = region("code", 0.9, 78.0, 100.0, 300.0, 140.0);
        let code_b = region("code", 0.9, 78.0, 300.0, 300.0, 360.0); // far below, no overlap
        assert_eq!(super::resolve(vec![code_a, code_b]).len(), 2);
    }

    /// A two-column glossary page came out as three column
    /// tables *and* one low-score whole-page table over them. docling's wrapper
    /// `_remove_overlapping_clusters` keeps one table per overlapping group
    /// (here the whole-page one: > 2× every rival's area and ≤ 0.2 less
    /// confident than the running best); `greedy` alone kept all four and
    /// emitted every cell twice.
    #[test]
    fn resolve_keeps_one_table_per_nested_group() {
        let kept = super::resolve(vec![
            region("table", 0.71, 26.0, 203.0, 183.0, 558.0),
            region("table", 0.67, 26.0, 55.0, 183.0, 196.0),
            region("table", 0.66, 196.0, 56.0, 354.0, 561.0),
            region("table", 0.53, 25.0, 53.0, 354.0, 561.0),
        ]);
        assert_eq!(kept.len(), 1, "one survivor per overlapping group");
        assert_eq!((kept[0].l, kept[0].b), (25.0, 561.0));
        // Side-by-side tables that don't overlap stay separate.
        let kept = super::resolve(vec![
            region("table", 0.9, 26.0, 55.0, 183.0, 558.0),
            region("table", 0.9, 196.0, 56.0, 354.0, 561.0),
        ]);
        assert_eq!(kept.len(), 2);
    }

    /// A dense data table detected as both picture (0.80) and table (0.62) on one box.
    /// The picture is ≥ 0.1 more confident, so `_handle_cross_type_overlaps`
    /// keeps both, and the dense table text passed the text-panel gates: the
    /// demoted paragraph repeated every cell the table grid renders. A
    /// paragraph > 80 % inside a surviving table is the table's child and is
    /// not emitted; a panel with no table under it still demotes.
    #[test]
    fn text_panel_over_a_table_does_not_repeat_its_cells() {
        let lines = |t0: f32| -> Vec<TextCell> {
            (0..4)
                .map(|i| {
                    let t = t0 + 10.0 * i as f32;
                    cell("1 2 3 4 5 6 7 8 9 10 11 12", 5.0, t, 95.0, t + 8.0)
                })
                .collect()
        };
        let mut cells = lines(0.0);
        cells.extend(lines(200.0));
        let mut regions = vec![
            region("picture", 0.80, 0.0, 0.0, 100.0, 45.0),
            region("table", 0.62, 0.0, 0.0, 100.0, 45.0),
            region("picture", 0.80, 0.0, 200.0, 100.0, 245.0),
        ];
        super::recover_text_panels(&mut regions, &cells);
        assert_eq!(
            regions.iter().map(|r| r.label).collect::<Vec<_>>(),
            ["table", "text"]
        );
        assert_eq!(regions[1].t, 200.0, "the table-free panel still demotes");
    }

    #[test]
    fn code_language_label_above_code_is_detected() {
        // A bare "XML" token directly above a code box is a language label; a real
        // heading above the same code is not; a language word with no code below is
        // left alone.
        let label = region("section_header", 0.9, 76.0, 540.0, 96.0, 549.0);
        let code = region("code", 0.7, 77.0, 552.0, 290.0, 640.0);
        let heading = region("section_header", 0.9, 76.0, 500.0, 260.0, 512.0);
        let cells = vec![
            cell("XML", 78.0, 541.0, 94.0, 548.0),       // inside `label`
            cell("Overview", 78.0, 501.0, 250.0, 511.0), // inside `heading`
        ];
        let drop = super::code_language_labels(&[label, code, heading], &cells);
        assert_eq!(drop, vec![true, false, false], "only the label is consumed");

        // Same label with no code region present → not consumed.
        let label2 = region("section_header", 0.9, 76.0, 540.0, 96.0, 549.0);
        let only = vec![cell("XML", 78.0, 541.0, 94.0, 548.0)];
        assert_eq!(super::code_language_labels(&[label2], &only), vec![false]);

        // A label swallowed into the top of a wider code box (negative gap) is still
        // recognized.
        let inside_lbl = region("text", 0.9, 76.0, 540.0, 96.0, 549.0);
        let wide_code = region("code", 0.7, 63.0, 531.0, 320.0, 654.0);
        let cells2 = vec![cell("XML", 78.0, 541.0, 94.0, 548.0)];
        assert_eq!(
            super::code_language_labels(&[inside_lbl, wide_code], &cells2),
            vec![true, false]
        );

        assert!(super::is_code_language("XML") && super::is_code_language("c#"));
        assert!(!super::is_code_language("Configure") && !super::is_code_language("XML schema"));
    }

    #[test]
    fn code_region_text_keeps_lines_and_indentation() {
        // Three source lines; each glyph is 6 units wide (width / chars = 6), so the
        // `int X;` line indented to x=22 is (22-10)/6 = 2 spaces in.
        let region = Region {
            label: "code",
            score: 1.0,
            l: 0.0,
            t: -5.0,
            r: 100.0,
            b: 40.0,
        };
        let cells = vec![
            cell("struct P {", 10.0, 0.0, 70.0, 10.0),
            cell("int X;", 22.0, 12.0, 58.0, 22.0),
            cell("}", 10.0, 24.0, 16.0, 34.0),
        ];
        assert_eq!(code_region_text(&region, &cells), "struct P {\n  int X;\n}");
    }

    #[test]
    fn code_region_text_tightens_punctuation_without_eating_indentation() {
        // A fluent `.Foo()` line at x=22 (2 chars in). Per-line tightening must not
        // consume the leading indent space by matching " ." across it.
        let region = Region {
            label: "code",
            score: 1.0,
            l: 0.0,
            t: -5.0,
            r: 100.0,
            b: 40.0,
        };
        let cells = vec![
            cell("builder", 10.0, 0.0, 52.0, 10.0),
            // pdfium spaced the call: ".Foo (x)" tightens to ".Foo(x)", still 2-indented.
            cell(".Foo (x)", 22.0, 12.0, 70.0, 22.0),
        ];
        assert_eq!(code_region_text(&region, &cells), "builder\n  .Foo(x)");
    }

    #[test]
    fn code_region_text_orders_out_of_order_cells_and_ignores_blank_lines() {
        let region = Region {
            label: "code",
            score: 1.0,
            l: 0.0,
            t: -5.0,
            r: 100.0,
            b: 60.0,
        };
        // Fed bottom-up and with a whitespace-only cell; output is top-down, no blank.
        let cells = vec![
            cell("b();", 10.0, 24.0, 34.0, 34.0),
            cell("   ", 10.0, 12.0, 20.0, 22.0),
            cell("a();", 10.0, 0.0, 34.0, 10.0),
        ];
        assert_eq!(code_region_text(&region, &cells), "a();\nb();");
        // No code cells → empty, so the caller falls back to the prose text.
        assert_eq!(code_region_text(&region, &[]), "");
    }

    fn para(text: &str) -> Node {
        Node::Paragraph { text: text.into() }
    }

    /// Run a node sequence through [`StreamAssembler`] with the given page splits
    /// and assert the flushed result equals one-shot [`merge_continuations`].
    fn assert_stream_eq(nodes: &[Node], splits: &[usize]) {
        let mut want = nodes.to_vec();
        merge_continuations(&mut want);

        let mut asm = StreamAssembler::new();
        let mut got = Vec::new();
        let mut start = 0;
        for &end in splits {
            got.extend(asm.push(nodes[start..end].to_vec()));
            start = end;
        }
        got.extend(asm.push(nodes[start..].to_vec()));
        got.extend(asm.finish());
        assert_eq!(got, want, "stream assembly diverged (splits={splits:?})");
    }

    #[test]
    fn stream_assembler_matches_merge_continuations() {
        // Open fragment + lowercase continuation split across a page boundary.
        let cross = [para("the definition of"), para("lists in scope")];
        assert_stream_eq(&cross, &[1]);
        assert_stream_eq(&cross, &[]);

        // Continuation that wraps around a figure (+ its caption) on the boundary.
        let wrap = [
            para("the wing type that is"),
            Node::Picture {
                caption: None,
                caption_href: None,
                image: None,
                classification: None,
                caption_parent: Default::default(),
            },
            para("Fig. 1. a diagram"),
            para("the most common kind"),
        ];
        for splits in [&[][..], &[1][..], &[2][..], &[3][..], &[1, 3][..]] {
            assert_stream_eq(&wrap, splits);
        }

        // A heading between fragments blocks the merge (must still flush correctly).
        let blocked = [
            para("ends mid word and"),
            Node::Heading {
                level: 2,
                text: "New Section".into(),
            },
            para("more body here"),
        ];
        for splits in [&[][..], &[1][..], &[2][..]] {
            assert_stream_eq(&blocked, splits);
        }

        // A chain across three pages: each page is one open lowercase fragment.
        let chain = [
            para("alpha beta"),
            para("gamma delta"),
            para("epsilon zeta"),
        ];
        assert_stream_eq(&chain, &[1, 2]);
    }

    #[test]
    fn clean_text_dehyphenates_and_normalizes_typography() {
        // U+0002 line-wrap hyphen + the join space → merged word (like docling).
        assert_eq!(clean_text("com\u{2} pact"), "compact");
        assert_eq!(clean_text("end-to\u{2} end deep"), "end-toend deep");
        // A stray wrap hyphen (no following join) is dropped.
        assert_eq!(clean_text("word\u{2}"), "word");
        // Typographic punctuation → ASCII: every curly quote becomes `'`
        // (docling-parse's sanitizer table), a literal `"` stays.
        assert_eq!(
            clean_text("Graph\u{2019}s \u{201c}x\u{201d} \"y\""),
            "Graph's 'x' \"y\""
        );
        assert_eq!(clean_text("a\u{2026}"), "a...");
        // The dp default (the docling-parse sanitizer) preserves internal spacing
        // it placed deliberately; line breaks/tabs normalize to a space, ends trim.
        assert_eq!(clean_text("a   b\nc"), "a   b c");
    }

    /// docling#4064: a form's children are emitted together where the form
    /// sits in the top-level order, not interleaved with surrounding text.
    #[test]
    fn form_children_stay_together_in_reading_order() {
        let reg = |label: &'static str, l: f32, t: f32, r: f32, b: f32| Region {
            label,
            score: 0.9,
            l,
            t,
            r,
            b,
        };
        // Page: intro text, then a form spanning the left column with two
        // fields and a table inside, while a right-column paragraph sits
        // level with the form's first field (it would otherwise be read
        // between the form's children).
        let mut items = vec![
            reg("text", 50.0, 50.0, 550.0, 70.0),    // 0 intro
            reg("form", 50.0, 100.0, 300.0, 400.0),  // 1 container
            reg("text", 60.0, 110.0, 290.0, 130.0),  // 2 field A (child)
            reg("text", 320.0, 110.0, 550.0, 130.0), // 3 right column paragraph
            reg("table", 60.0, 150.0, 290.0, 300.0), // 4 table (child)
            reg("text", 60.0, 320.0, 290.0, 340.0),  // 5 field B (child)
            reg("text", 50.0, 450.0, 550.0, 470.0),  // 6 outro
        ];
        let cids = super::cluster_cids(&items, &[]);
        super::order_with_containers(&mut items, &cids, 600.0, 800.0, |r| r);
        let order: Vec<(&str, f32)> = items.iter().map(|r| (r.label, r.t)).collect();
        // The form block (container, then its children top-down) is one unit.
        let form_pos = order.iter().position(|(l, _)| *l == "form").unwrap();
        assert_eq!(
            &order[form_pos..form_pos + 4],
            &[
                ("form", 100.0),
                ("text", 110.0),
                ("table", 150.0),
                ("text", 320.0)
            ]
        );
        assert_eq!(order[0], ("text", 50.0));
        assert_eq!(order[order.len() - 1], ("text", 450.0));
        // Without a container the plain order interleaves by geometry.
        let mut flat: Vec<Region> = items
            .iter()
            .filter(|r| r.label != "form")
            .cloned()
            .collect();
        let cids = super::cluster_cids(&flat, &[]);
        super::order_regions(&mut flat, &cids, 600.0, 800.0, |r| r);
        assert_ne!(
            flat.iter().map(|r| r.t).collect::<Vec<_>>(),
            order
                .iter()
                .filter(|(l, _)| *l != "form")
                .map(|(_, t)| *t)
                .collect::<Vec<_>>()
        );
    }

    /// docling#3906: a picture inside a table lands in the covering cell,
    /// chosen by the picture's inferred grid position when cell boxes overlap.
    #[test]
    fn picture_matches_the_cell_at_its_grid_position() {
        let cell = |r: usize, c: usize, bbox: [f32; 4]| docling_core::TableCell {
            text: format!("r{r}c{c}"),
            bbox: Some(bbox),
            start_row: r,
            start_col: c,
            row_span: 1,
            col_span: 1,
            column_header: false,
            row_header: false,
            row_section: false,
        };
        // 2×2 grid; the (1,0) cell box is generous and also covers the picture.
        let cells = vec![
            cell(0, 0, [0.0, 0.0, 100.0, 50.0]),
            cell(0, 1, [100.0, 0.0, 200.0, 50.0]),
            cell(1, 0, [0.0, 50.0, 100.0, 100.0]),
            cell(1, 1, [100.0, 50.0, 200.0, 100.0]),
        ];
        let pic = Region {
            label: "picture",
            score: 0.9,
            l: 110.0,
            t: 60.0,
            r: 190.0,
            b: 95.0,
        };
        assert_eq!(super::match_picture_to_cell(&pic, &cells), Some((1.0, 3)));
        // A picture only half inside any cell is not nested.
        let straddling = Region {
            label: "picture",
            score: 0.9,
            l: 60.0,
            t: 60.0,
            r: 160.0,
            b: 95.0,
        };
        assert_eq!(super::match_picture_to_cell(&straddling, &cells), None);
    }

    /// docling#4052 (2.122): a line-final dash fuses the wrapped word only
    /// when attached to it; a detached dash is a literal and the lines join
    /// with a space.
    #[test]
    fn line_final_hyphen_fuses_only_when_attached_to_a_word() {
        let line = |text: &str, t: f32| TextCell {
            text: text.to_string(),
            l: 0.0,
            t,
            r: 100.0,
            b: t + 10.0,
        };
        // `algo-` / `rithms`: attached hyphen, alnum on both sides → fused.
        assert_eq!(
            cells_text(vec![&line("algo-", 0.0), &line("rithms", 12.0)]),
            "algorithms"
        );
        // `pp. 545-` / `561`: attached, digits count as alnum → `545561` (upstream).
        assert_eq!(
            cells_text(vec![&line("pp. 545-", 0.0), &line("561", 12.0)]),
            "pp. 545561"
        );
        // A dash after whitespace — a separator or a lone `-` cell — is kept and
        // the lines take the ordinary joining space.
        assert_eq!(
            cells_text(vec![&line("range -", 0.0), &line("wide", 12.0)]),
            "range - wide"
        );
        assert_eq!(
            cells_text(vec![&line("-", 0.0), &line("item", 12.0)]),
            "- item"
        );
        // Attached but the next line opens with no word (`x-` / `...`): dash
        // kept and, as before, no separating space.
        assert_eq!(
            cells_text(vec![&line("x-", 0.0), &line("...", 12.0)]),
            "x-..."
        );
    }

    #[test]
    fn lam_alef_only_swaps_a_genuinely_reversed_ligature() {
        // A mid-word `alef-variant + lam` is pdfium's reversed lam-alef ligature and
        // is swapped back to logical `lam + alef-variant` (`ب أ ل` → `ب ل أ`).
        assert_eq!(
            clean_text("\u{0628}\u{0623}\u{0644}"),
            "\u{0628}\u{0644}\u{0623}"
        );
        // But when the alef-variant is *already* preceded by a lam it is the logical
        // ligature `لآ`; the following lam is the next syllable's letter and must not
        // move. `التعلم الآلي` must stay `الآلي`, not become `اللآي`.
        assert_eq!(
            clean_text("\u{0627}\u{0644}\u{0622}\u{0644}\u{064a}"),
            "\u{0627}\u{0644}\u{0622}\u{0644}\u{064a}"
        );
    }

    /// The #419 page, in points: three layout boxes over one paragraph, two of
    /// them ending partway through a line. The sliced lines miss the 0.2 claim
    /// and become orphans; the third model box starts above the second orphan,
    /// so unfitted the reading order emits that box first and strands the line.
    fn sliced_paragraph() -> (Vec<Region>, Vec<TextCell>) {
        let line = |text: &str, t: f32, r: f32| cell(text, 60.0, t, r, t + 11.0);
        let cells = vec![
            line("The mission of this series is to improve", 135.0, 458.0),
            line("The books in this series are technical,", 147.0, 458.0),
            line("substantial. The authors are", 159.0, 458.0),
            line("highly experienced craftsmen and", 171.5, 458.0), // sliced: 1.5/11 under box A
            line("actually works in practice, as opposed", 185.0, 458.0),
            line("about what the author has done, not", 197.0, 458.0),
            line("about programming, there will be lots", 210.5, 458.0), // sliced: 1.5/11 under box B
            line("will be lots of case studies from real", 223.0, 206.0), // C's line
        ];
        let regions = vec![
            region("text", 0.9, 60.0, 132.0, 458.0, 173.0), // A: three lines + a sliver of the 4th
            region("text", 0.9, 60.0, 184.0, 458.0, 212.0), // B: two lines + a sliver of the 7th
            region("text", 0.9, 60.0, 216.0, 206.0, 227.0), // C: last line, box opening 5.5pt too early
        ];
        (regions, cells)
    }

    fn ordered_texts(regions: &[Region], cells: &[TextCell]) -> Vec<String> {
        let mut items: Vec<Region> = regions.to_vec();
        let cids = super::cluster_cids(&items, cells);
        super::order_regions(&mut items, &cids, 500.0, 700.0, |r| r);
        super::region_texts_exclusive(&items, cells)
            .into_iter()
            .map(|t| t.chars().take(9).collect())
            .collect()
    }

    /// #419: fitted to its cells, a model box that cut a line in half no longer
    /// overlaps the orphan that line became, so the orphan orders where it
    /// reads; unfitted, the same page strands the line after the paragraph.
    #[test]
    fn fitting_boxes_to_cells_puts_a_sliced_line_back_in_order() {
        let (mut regions, cells) = sliced_paragraph();
        super::add_orphan_regions(&mut regions, &cells);
        assert_eq!(regions.len(), 5, "two orphan lines");
        // The defect, for the record: C (top 216) is not strictly below the
        // orphan at 210.5–221.5, so the graph orders C first.
        assert_eq!(
            ordered_texts(&regions, &cells).last().map(String::as_str),
            Some("about pro")
        );

        super::fit_regions_to_cells(&mut regions, &cells);
        assert_eq!(regions.len(), 5);
        // A ends on its last claimed line, C starts on its only one.
        assert_eq!((regions[0].t, regions[0].b), (135.0, 170.0));
        assert_eq!((regions[2].t, regions[2].b), (223.0, 234.0));
        assert_eq!(
            ordered_texts(&regions, &cells),
            [
                "The missi",
                "highly ex",
                "actually ",
                "about pro",
                "will be l"
            ]
        );
    }

    /// An orphan the fitted paragraph box surrounds (a short middle line the
    /// narrow model box missed while claiming the lines around it) is folded
    /// into the paragraph; an empty regular box goes away, a formula stays, a
    /// picture is never refitted, and a page with no cells is left untouched.
    #[test]
    fn fitting_folds_surrounded_orphans_and_drops_empty_regulars() {
        let wide = |text: &str, t: f32| cell(text, 60.0, t, 400.0, t + 11.0);
        let cells = vec![
            wide("first line of the paragraph", 100.0),
            cell("stray", 250.0, 112.0, 400.0, 123.0), // clear of the narrow box
            wide("third line of the paragraph", 124.0),
        ];
        let mut regions = vec![
            // Narrow box: claims the wide lines at 0.41, misses the short one.
            region("text", 0.9, 60.0, 98.0, 200.0, 136.0),
            region("section_header", 0.8, 60.0, 300.0, 200.0, 320.0), // no cells
            region("formula", 0.8, 60.0, 340.0, 200.0, 360.0),        // no cells, kept
            region("picture", 0.8, 0.0, 400.0, 500.0, 600.0),
        ];
        super::add_orphan_regions(&mut regions, &cells);
        assert_eq!(regions.len(), 5, "the short line became an orphan");
        super::fit_regions_to_cells(&mut regions, &cells);
        let labels: Vec<&str> = regions.iter().map(|r| r.label).collect();
        assert_eq!(labels, ["text", "formula", "picture"]);
        let para = &regions[0];
        assert_eq!(
            (para.l, para.t, para.r, para.b),
            (60.0, 100.0, 400.0, 135.0)
        );
        assert_eq!(
            super::region_texts_exclusive(&regions, &cells)[0],
            "first line of the paragraph stray third line of the paragraph"
        );
        assert_eq!(
            (regions[2].t, regions[2].b),
            (400.0, 600.0),
            "picture untouched"
        );

        let mut untouched = vec![region("text", 0.9, 0.0, 0.0, 10.0, 10.0)];
        super::fit_regions_to_cells(&mut untouched, &[]);
        assert_eq!(untouched.len(), 1, "no cells yet: nothing dropped");
    }
}