Index measured label field overlap lookups with exact differential oracles

crates/oa-desktop/src/behavior/scenario_label.rs

@@ -26,7 +26,11 @@ use iced::advanced::{
     text::{Alignment, LineHeight, Shaping},
 };
 use iced::{Color, Font, Pixels, Point, Rectangle, Size, widget::canvas::Text};
-use std::{collections::VecDeque, ops::Range, sync::Arc};
+use std::{
+    collections::{HashSet, VecDeque},
+    ops::Range,
+    sync::Arc,
+};
 use unicode_segmentation::UnicodeSegmentation;
 
 const MAX_SOURCE_BYTES: usize = 64 * 1024;
@@ -102,6 +106,7 @@ pub(super) struct Label {
     clusters: Vec<FieldCluster>,
     source_spans: Vec<SourceSpan>,
     retained_normalized: usize,
+    field_index: FieldIndex,
 }
 
 #[derive(Clone, Debug, PartialEq)]
@@ -142,6 +147,69 @@ struct FieldCluster {
     missing: bool,
 }
 
+/// Immutable overlap membership, built from Normalized's ordered, disjoint
+/// scalar/separator spans. Clusters may overlap and need not be in visual order.
+/// Construction costs O(C log S + I), storage O(S + C + I), where I is the
+/// number of actual span/cluster overlaps, rather than the full S*C product.
+#[derive(Clone, Debug)]
+struct FieldIndex {
+    clusters_by_span: Vec<Vec<usize>>,
+    source_extents: Vec<Option<SourceExtents>>,
+}
+
+#[derive(Clone, Copy, Debug)]
+struct SourceExtents {
+    minimum_end: usize,
+    maximum_start: usize,
+}
+
+impl FieldIndex {
+    fn new(spans: &[SourceSpan], clusters: &[FieldCluster]) -> Self {
+        debug_assert!(
+            spans
+                .iter()
+                .all(|span| span.normalized.start < span.normalized.end)
+        );
+        debug_assert!(
+            spans
+                .windows(2)
+                .all(|pair| pair[0].normalized.end <= pair[1].normalized.start)
+        );
+        let mut result = Self {
+            clusters_by_span: vec![vec![]; spans.len()],
+            source_extents: vec![None; clusters.len()],
+        };
+        for (index, cluster) in clusters.iter().enumerate() {
+            if cluster.normalized.start >= cluster.normalized.end {
+                continue;
+            }
+            let first =
+                spans.partition_point(|span| span.normalized.end <= cluster.normalized.start);
+            for (offset, span) in spans[first..].iter().enumerate() {
+                if span.normalized.start >= cluster.normalized.end {
+                    break;
+                }
+                result.clusters_by_span[first + offset].push(index);
+                let extents = result.source_extents[index].get_or_insert(SourceExtents {
+                    minimum_end: span.source.end,
+                    maximum_start: span.source.start,
+                });
+                extents.minimum_end = extents.minimum_end.min(span.source.end);
+                extents.maximum_start = extents.maximum_start.max(span.source.start);
+            }
+        }
+        result
+    }
+}
+
+// Translation rejects nonfinite rectangle components before deduplication.
+// For finite f32 values, bit equality differs from `==` only at signed zero.
+// Normalize only the key: preserve the first rectangle and its original bits.
+fn rectangle_key(bounds: Rectangle) -> [u32; 4] {
+    [bounds.x, bounds.y, bounds.width, bounds.height]
+        .map(|value| if value == 0. { 0 } else { value.to_bits() })
+}
+
 impl Label {
     /// Geometry and coverage are separate: truncation is not missing-font
     /// coverage, and a positive .notdef advance is not represented field text.
@@ -168,7 +236,7 @@ impl Label {
             shared_cluster: false,
         };
         let mut selected = vec![false; self.clusters.len()];
-        for span in &self.source_spans {
+        for (span_index, span) in self.source_spans.iter().enumerate() {
             if span.whitespace || !overlaps(&span.source, &field) {
                 continue;
             }
@@ -178,27 +246,25 @@ impl Label {
                 append_range(&mut result.truncated, span.source.clone());
                 continue;
             }
-            let matching: Vec<_> = self
+            let matching = &self.field_index.clusters_by_span[span_index];
-                .clusters
+            result.shared_cluster |= matching.iter().any(|&index| {
-                .iter()
+                let cluster = &self.clusters[index];
-                .enumerate()
-                .filter(|(_, cluster)| overlaps(&cluster.normalized, &span.normalized))
-                .collect();
-            result.shared_cluster |= matching.iter().any(|(_, cluster)| {
                 cluster.normalized.end > self.retained_normalized
-                    || self.source_spans.iter().any(|other| {
+                    || self.field_index.source_extents[index].is_some_and(|extents| {
-                        overlaps(&other.normalized, &cluster.normalized)
+                        // Any overlapping source span outside the requested
-                            && !overlaps(&other.source, &field)
+                        // field is exactly either a too-small end or too-large
+                        // start. Include whitespace/nonpainting spans, as before.
+                        extents.minimum_end <= field.start || extents.maximum_start >= field.end
                     })
             });
             let issue = if span.non_painting {
                 Some(FieldIssue::NonPaintingScalar)
-            } else if matching.iter().any(|(_, cluster)| cluster.missing) {
+            } else if matching.iter().any(|&index| self.clusters[index].missing) {
                 Some(FieldIssue::MissingGlyph)
             } else if matching.is_empty()
                 || matching
                     .iter()
-                    .all(|(_, cluster)| cluster.rectangles.is_empty())
+                    .all(|&index| self.clusters[index].rectangles.is_empty())
             {
                 Some(FieldIssue::NoAdvanceGeometry)
             } else {
@@ -212,10 +278,11 @@ impl Label {
                 continue;
             }
             append_range(&mut result.covered, span.source.clone());
-            for (index, _) in matching {
+            for &index in matching {
                 selected[index] = true;
             }
         }
+        let mut seen = HashSet::new();
         for (cluster, selected) in self.clusters.iter().zip(selected) {
             if !selected {
                 continue;
@@ -225,7 +292,7 @@ impl Label {
                     Point::new(position.x + bounds.x, position.y + bounds.y),
                     bounds.size(),
                 )?;
-                if !result.rectangles.contains(&translated) {
+                if seen.insert(rectangle_key(translated)) {
                     result.rectangles.push(translated);
                 }
             }
@@ -502,6 +569,7 @@ impl Cache {
             );
             field_clusters(entry, zoom)?
         };
+        let field_index = FieldIndex::new(&normalized.spans, &clusters);
         let label = Arc::new(Label {
             source: source.into(),
             displayed,
@@ -513,6 +581,7 @@ impl Cache {
             clusters,
             source_spans: normalized.spans,
             retained_normalized: retained,
+            field_index,
         });
         if self.entries.len() == MAX_ENTRIES {
             self.entries.pop_front();
@@ -684,3 +753,7 @@ mod tests;
 #[cfg(test)]
 #[path = "scenario_label/field_tests.rs"]
 mod field_tests;
+
+#[cfg(test)]
+#[path = "scenario_label/lookup_tests.rs"]
+mod lookup_tests;

crates/oa-desktop/src/behavior/scenario_label/field_tests.rs

@@ -31,7 +31,10 @@ fn assert_ligature_fixture_face(oracle: &Paragraph) {
     let mut count = 0;
     for glyph in oracle.buffer().layout_runs().flat_map(|run| run.glyphs) {
         assert_eq!(
-            fonts.raw().db().with_face_data(glyph.font_id, |bytes, index| {
+            fonts
+                .raw()
+                .db()
+                .with_face_data(glyph.font_id, |bytes, index| {
                     index == 0 && bytes == LIGATURE_FONT
                 }),
             Some(true),
@@ -568,6 +571,13 @@ fn field_lookup_4096_scalars_and_combining_heavy_full_coverage() {
             .unwrap();
         let resolve_ns = start.elapsed().as_nanos();
         assert_eq!(label.displayed, source);
+        // The preserved 4c9 lookup runs on the exact same immutable shaped
+        // label. Its timing is separate from the optimized samples below.
+        let start = std::time::Instant::now();
+        let original = label
+            .original_field_layout(&session, 1., Point::ORIGIN, 0..source.len())
+            .unwrap();
+        let original_lookup_ns = start.elapsed().as_nanos();
         let mut lookup_ns = vec![];
         for _ in 0..3 {
             let start = std::time::Instant::now();
@@ -579,11 +589,33 @@ fn field_lookup_4096_scalars_and_combining_heavy_full_coverage() {
             assert!(field.truncated.is_empty() && field.unresolved.is_empty());
             assert!(!field.partially_retained && !field.shared_cluster);
             assert_complete_boxes(&field.rectangles, expected.clone());
+            super::lookup_tests::assert_exact(&field, &original);
+        }
+        // Fresh label construction plus lookup, not just a retained-index
+        // measurement: moving the old quadratic work into resolve cannot hide.
+        let mut fresh_resolve_lookup_ns = vec![];
+        for _ in 0..3 {
+            let mut fresh_cache = Cache::default();
+            let start = std::time::Instant::now();
+            let fresh = fresh_cache
+                .resolve(&session, &source, 1_000_000., 1., style)
+                .unwrap();
+            let field = fresh
+                .field_layout(&session, 1., Point::ORIGIN, 0..source.len())
+                .unwrap();
+            fresh_resolve_lookup_ns.push(start.elapsed().as_nanos());
+            super::lookup_tests::assert_exact(&field, &original);
+            assert_complete_boxes(&field.rectangles, expected.clone());
         }
         records.push(serde_json::json!({
             "case": name, "scalars": 4096, "graphemes": expected_graphemes,
             "source_bytes": source.len(), "expected_rectangles": expected.len(),
             "resolved_fonts": identities, "resolve_ns": resolve_ns, "lookup_ns": lookup_ns,
+            "original_lookup_ns": original_lookup_ns,
+            "fresh_resolve_lookup_ns": fresh_resolve_lookup_ns,
+            "source_spans": label.source_spans.len(), "clusters": label.clusters.len(),
+            "overlap_memberships": label.field_index.clusters_by_span.iter().map(Vec::len).sum::<usize>(),
+            "exact_original_result_including_rectangle_bits": "passed",
             "full_coverage_and_exact_geometry": "passed",
         }));
     }

crates/oa-desktop/src/behavior/scenario_label/lookup_tests.rs

@@ -0,0 +1,381 @@
+//! Exact differential oracle from 4c9bc87e4e66bba573dd63b23df5ea039f85d0ca.
+//! The old method body is retained verbatim; only its name/visibility changes.
+//! Its unchanged validation/translation helpers remain in the parent module.
+use super::*;
+
+pub(super) fn assert_exact(actual: &FieldLayout, expected: &FieldLayout) {
+    assert_eq!(actual, expected);
+    // PartialEq deliberately equates signed zero; the observable first box
+    // must nevertheless retain exactly the old representation and order.
+    for (actual, expected) in actual.rectangles.iter().zip(&expected.rectangles) {
+        let bits = |r: &Rectangle| [r.x, r.y, r.width, r.height].map(f32::to_bits);
+        assert_eq!(bits(actual), bits(expected));
+    }
+}
+
+fn compare(
+    label: &Label,
+    session: &RenderSession,
+    zoom: f32,
+    position: Point,
+    field: Range<usize>,
+) {
+    let old = label.original_field_layout(session, zoom, position, field.clone());
+    let new = label.field_layout(session, zoom, position, field);
+    match (new, old) {
+        (Ok(new), Ok(old)) => assert_exact(&new, &old),
+        (new, old) => assert_eq!(new, old),
+    }
+}
+
+fn all_fields(label: &Label, session: &RenderSession, position: Point) {
+    let boundaries: Vec<_> = label
+        .source
+        .char_indices()
+        .map(|(i, _)| i)
+        .chain(std::iter::once(label.source.len()))
+        .collect();
+    for &start in &boundaries {
+        for &end in &boundaries {
+            compare(label, session, label.measured_zoom, position, start..end);
+        }
+    }
+}
+
+fn synthetic(source: &str, retained: usize, clusters: Vec<FieldCluster>) -> (RenderSession, Label) {
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let normalized = Normalized::new(source);
+    let field_index = FieldIndex::new(&normalized.spans, &clusters);
+    let label = Label {
+        source: source.into(),
+        displayed: normalized.text,
+        retained_source: 0..source.len(),
+        bounds: Rectangle::with_size(Size::ZERO),
+        style: Style::default(),
+        measured_session: session.clone(),
+        measured_zoom: 1.,
+        clusters,
+        source_spans: normalized.spans,
+        retained_normalized: retained,
+        field_index,
+    };
+    (session, label)
+}
+
+fn cluster(range: Range<usize>, rectangles: Vec<Rectangle>, missing: bool) -> FieldCluster {
+    FieldCluster {
+        normalized: range,
+        rectangles,
+        missing,
+    }
+}
+
+#[test]
+fn indexed_lookup_matches_original_for_real_shaping_and_every_field_boundary() {
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let sources = [
+        "",
+        " \t\n ",
+        "ffi office",
+        " \talpha \r\n beta  ",
+        "a\u{301}\u{fe0f} b\u{2060}c",
+        "אבג abc דהו",
+        "A😀Z",
+    ];
+    let mut nonempty = 0;
+    for source in sources {
+        for shaping in [Shaping::Auto, Shaping::Advanced] {
+            for zoom in [0.5, 1.75] {
+                let mut cache = Cache::default();
+                for width in [0., 25., 500.] {
+                    let label = cache
+                        .resolve(
+                            &session,
+                            source,
+                            width,
+                            zoom,
+                            Style {
+                                shaping,
+                                ..Style::default()
+                            },
+                        )
+                        .unwrap();
+                    nonempty += usize::from(!label.clusters.is_empty());
+                    all_fields(&label, &session, Point::ORIGIN);
+                    all_fields(&label, &session, Point::new(-37.25, 16.125));
+                }
+            }
+        }
+    }
+    assert!(
+        nonempty >= sources.len(),
+        "must compare actual shaped geometry as well as empty labels"
+    );
+}
+
+#[test]
+fn indexed_lookup_matches_original_for_overlapping_and_reordered_clusters() {
+    // Normalization is "a + acute + VS16 + space + b + space + c".
+    // Cluster intervals overlap, nest, span separators, and occur in a
+    // deliberately non-source/non-visual order. This tests the join rather
+    // than assuming the simpler cluster partition of most actual fonts.
+    let source = "  a\u{301}\u{fe0f} b c  ";
+    assert_eq!(Normalized::new(source).text.len(), 10);
+    let a = Rectangle::new(Point::new(30., 3.), Size::new(4., 12.));
+    let b = Rectangle::new(Point::new(-20., -1.), Size::new(7., 11.));
+    let c = Rectangle::new(Point::new(9., 4.), Size::new(2., 10.));
+    let cases = vec![
+        cluster(7..10, vec![b, a], false),
+        cluster(0..6, vec![a, c, a], false),
+        cluster(1..3, vec![], false),
+        cluster(3..8, vec![c], true),
+        cluster(0..10, vec![b], false),
+        cluster(6..7, vec![c], false),
+        cluster(9..13, vec![a], false), // can extend into a synthetic ellipsis
+        cluster(3..3, vec![c], true),   // empty interval cannot match anything
+        cluster(8..7, vec![b], true),   // nor can a reversed interval
+    ];
+    for reverse in [false, true] {
+        let mut clusters = cases.clone();
+        if reverse {
+            clusters.reverse();
+        }
+        for retained in [0, 1, 3, 6, 7, 8, 10] {
+            let (session, label) = synthetic(source, retained, clusters.clone());
+            all_fields(&label, &session, Point::new(-0., -0.));
+            all_fields(&label, &session, Point::new(0.125, -64.));
+        }
+    }
+    let (session, priority) = synthetic(
+        "a\u{2060}b",
+        5,
+        vec![
+            cluster(0..1, vec![], false),
+            cluster(1..4, vec![a], true),
+            cluster(4..5, vec![b], true),
+        ],
+    );
+    all_fields(&priority, &session, Point::ORIGIN);
+    let result = priority
+        .field_layout(&session, 1., Point::ORIGIN, 0..5)
+        .unwrap();
+    assert_eq!(
+        result.unresolved,
+        vec![
+            UnresolvedField {
+                source: 0..1,
+                reason: FieldIssue::NoAdvanceGeometry
+            },
+            UnresolvedField {
+                source: 1..4,
+                reason: FieldIssue::NonPaintingScalar
+            },
+            UnresolvedField {
+                source: 4..5,
+                reason: FieldIssue::MissingGlyph
+            },
+        ]
+    );
+    assert!(result.covered.is_empty() && result.rectangles.is_empty());
+}
+
+#[test]
+fn indexed_lookup_preserves_first_rectangle_bits_and_shared_status() {
+    let negative = Rectangle::new(Point::new(-0., -0.), Size::new(6., 12.));
+    let positive = Rectangle::new(Point::ORIGIN, Size::new(6., 12.));
+    assert_eq!(negative, positive, "Rectangle equality merges signed zero");
+    let other = Rectangle::new(Point::new(-20., 4.), Size::new(3., 12.));
+    let (session, label) = synthetic(
+        "a b",
+        3,
+        vec![
+            cluster(2..3, vec![negative, other], false),
+            cluster(0..1, vec![positive, negative], false),
+        ],
+    );
+    let result = label
+        .field_layout(&session, 1., Point::new(-0., -0.), 0..3)
+        .unwrap();
+    assert_eq!(result.covered, vec![0..1, 2..3]);
+    assert!(!result.shared_cluster);
+    assert_eq!(result.rectangles.len(), 2);
+    assert_eq!(result.rectangles[0].x.to_bits(), (-0f32).to_bits());
+    assert_eq!(result.rectangles[0].y.to_bits(), (-0f32).to_bits());
+    assert_eq!(result.rectangles[1], other);
+    assert_exact(
+        &result,
+        &label
+            .original_field_layout(&session, 1., Point::new(-0., -0.), 0..3)
+            .unwrap(),
+    );
+
+    let (session, shared) = synthetic("a b", 3, vec![cluster(0..3, vec![other], false)]);
+    let partial = shared
+        .field_layout(&session, 1., Point::ORIGIN, 0..1)
+        .unwrap();
+    assert_eq!(partial.covered, vec![0..1]);
+    assert!(partial.shared_cluster);
+    let complete = shared
+        .field_layout(&session, 1., Point::ORIGIN, 0..3)
+        .unwrap();
+    assert!(!complete.shared_cluster);
+    all_fields(&shared, &session, Point::ORIGIN);
+
+    // The same logical cluster crosses the retained prefix: its box remains
+    // shared while the source scalar after that prefix remains truncated.
+    let (session, clipped) = synthetic("abc", 2, vec![cluster(0..3, vec![other], false)]);
+    let clipped = clipped
+        .field_layout(&session, 1., Point::ORIGIN, 0..3)
+        .unwrap();
+    assert_eq!(clipped.covered, vec![0..2]);
+    assert_eq!(clipped.truncated, vec![2..3]);
+    assert!(clipped.shared_cluster && clipped.partially_retained);
+}
+
+#[test]
+fn indexed_lookup_preserves_error_precedence_and_overflow_rejection() {
+    let (session, label) = synthetic(
+        "éa",
+        3,
+        vec![cluster(
+            0..3,
+            vec![Rectangle::new(
+                Point::new(f32::MAX, 0.),
+                Size::new(f32::MAX, 1.),
+            )],
+            false,
+        )],
+    );
+    let stale = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    assert_eq!(
+        label.field_layout(&stale, f32::NAN, Point::new(f32::NAN, 0.), 7..8),
+        Err(Error::StaleRenderSession)
+    );
+    assert_eq!(
+        label.field_layout(&session, 2., Point::new(f32::NAN, 0.), 7..8),
+        Err(Error::StaleZoom)
+    );
+    assert_eq!(
+        label.field_layout(&session, 1., Point::new(f32::NAN, 0.), 7..8),
+        Err(Error::InvalidPosition)
+    );
+    assert_eq!(
+        label.field_layout(&session, 1., Point::ORIGIN, 1..2),
+        Err(Error::InvalidFieldRange)
+    );
+    assert_eq!(
+        label.field_layout(&session, 1., Point::ORIGIN, 0..3),
+        Err(Error::InvalidPosition)
+    );
+    // An unselected overflowing box must not turn a valid empty query into an error.
+    assert!(
+        label
+            .field_layout(&session, 1., Point::ORIGIN, 0..0)
+            .unwrap()
+            .rectangles
+            .is_empty()
+    );
+    for guard in [&session, &stale] {
+        for zoom in [1., 2., f32::NAN] {
+            for position in [
+                Point::ORIGIN,
+                Point::new(f32::NAN, 0.),
+                Point::new(f32::MAX, 0.),
+            ] {
+                for range in [0..0, 0..3, 1..2, 3..2, 0..4] {
+                    compare(&label, guard, zoom, position, range);
+                }
+            }
+        }
+    }
+}
+
+impl Label {
+    pub(super) fn original_field_layout(
+        &self,
+        session: &RenderSession,
+        zoom: f32,
+        position: Point,
+        field: Range<usize>,
+    ) -> Result<FieldLayout, Error> {
+        self.check(session, zoom)?;
+        translated_bounds(position, Size::ZERO)?;
+        if field.start > field.end || self.source.get(field.clone()).is_none() {
+            return Err(Error::InvalidFieldRange);
+        }
+        let mut result = FieldLayout {
+            rectangles: vec![],
+            covered: vec![],
+            truncated: vec![],
+            unresolved: vec![],
+            partially_retained: false,
+            shared_cluster: false,
+        };
+        let mut selected = vec![false; self.clusters.len()];
+        for span in &self.source_spans {
+            if span.whitespace || !overlaps(&span.source, &field) {
+                continue;
+            }
+            // Source spans for text are exact UTF-8 scalars, not intervals
+            // between ends (which could assign trimmed whitespace to text).
+            if span.normalized.end > self.retained_normalized {
+                append_range(&mut result.truncated, span.source.clone());
+                continue;
+            }
+            let matching: Vec<_> = self
+                .clusters
+                .iter()
+                .enumerate()
+                .filter(|(_, cluster)| overlaps(&cluster.normalized, &span.normalized))
+                .collect();
+            result.shared_cluster |= matching.iter().any(|(_, cluster)| {
+                cluster.normalized.end > self.retained_normalized
+                    || self.source_spans.iter().any(|other| {
+                        overlaps(&other.normalized, &cluster.normalized)
+                            && !overlaps(&other.source, &field)
+                    })
+            });
+            let issue = if span.non_painting {
+                Some(FieldIssue::NonPaintingScalar)
+            } else if matching.iter().any(|(_, cluster)| cluster.missing) {
+                Some(FieldIssue::MissingGlyph)
+            } else if matching.is_empty()
+                || matching
+                    .iter()
+                    .all(|(_, cluster)| cluster.rectangles.is_empty())
+            {
+                Some(FieldIssue::NoAdvanceGeometry)
+            } else {
+                None
+            };
+            if let Some(reason) = issue {
+                result.unresolved.push(UnresolvedField {
+                    source: span.source.clone(),
+                    reason,
+                });
+                continue;
+            }
+            append_range(&mut result.covered, span.source.clone());
+            for (index, _) in matching {
+                selected[index] = true;
+            }
+        }
+        for (cluster, selected) in self.clusters.iter().zip(selected) {
+            if !selected {
+                continue;
+            }
+            for bounds in &cluster.rectangles {
+                let translated = translated_bounds(
+                    Point::new(position.x + bounds.x, position.y + bounds.y),
+                    bounds.size(),
+                )?;
+                if !result.rectangles.contains(&translated) {
+                    result.rectangles.push(translated);
+                }
+            }
+        }
+        result.partially_retained = !result.truncated.is_empty()
+            && (!result.covered.is_empty() || !result.unresolved.is_empty());
+        Ok(result)
+    }
+}

harness/experiments/scenario-label-lookup-20260913/README.md

@@ -0,0 +1,26 @@
+# Indexed field lookup experiment
+
+This unwired experiment extends source `4c9bc87e4e66bba573dd63b23df5ea039f85d0ca`. It does not adopt measured labels or field navigation in the renderer. This revision has **not been compiled or executed**. The baseline debug diagnostic reported roughly 2.4–6.6 seconds for a 4096-scalar plain field and 1.3–1.9 seconds for a 4096-scalar combining-heavy field; these are motivation, not results for this patch.
+
+`Label` now stores an overlap index built from the winning shaped buffer's clusters and the existing ordered, disjoint normalized scalar spans. For S spans, C clusters, and I actual span/cluster overlap memberships, index construction takes O(C log S + I) work and O(S + C + I) storage. A lookup visits the source spans and their indexed matches, then emits selected cluster rectangles in the original cluster/rectangle order. Hash membership replaces repeated linear rectangle searches. Signed zeros share a deduplication key, as with `Rectangle::PartialEq`, while the first original rectangle's bits remain unchanged. Hash iteration never determines output order.
+
+Per-cluster source end/start extrema preserve the old shared-cluster predicate, including whitespace and nonpainting spans. Source scalar overlap, truncation, missing-glyph and nonpainting precedence, partial/shared flags, invalid-range errors, session/font/zoom guards, and position/overflow rejection are unchanged. No new length limit is introduced. Index storage can be dense for intentionally overlapping synthetic clusters. Existing shaping and `field_clusters` extraction are unchanged, including that extractor's per-cluster linear rectangle deduplication; this is not a claim of globally linear shaping or preparation.
+
+The test-only `Label::original_field_layout` retains the baseline method body verbatim. Four new normal tests compare every `FieldLayout` field and every rectangle's exact component bits and position in the output:
+
+- Real Auto/Advanced shaping at two zooms and three widths, over every legal UTF-8 boundary pair, including scalar boundaries inside combining graphemes.
+- Overlapping, reordered, whitespace-spanning, missing, empty and reversed cluster ranges; partial retention and nonpainting/coverage precedence.
+- First-occurrence signed-zero bits, shared clusters and truncation.
+- Guard/error precedence, malformed fields, nonfinite positions and overflow.
+
+The existing ignored `field_lookup_4096_scalars_and_combining_heavy_full_coverage` diagnostic retains its two inputs and independent Paragraph coverage/rectangle oracle. It now times the original lookup separately, three indexed queries on the retained label, and three fresh-cache resolve-plus-lookup operations. Exact old/new results and independent complete rectangle sets are checked outside timed intervals. The original lookup precedes indexed samples; font caches are warm. These are debug experiment measurements, not a latency guarantee or a cold-process benchmark. Fresh resolution includes index construction so its cost cannot disappear into an unmeasured preprocessing step.
+
+The isolated harness should list 29 tests: 25 normal and four ignored. The production desktop does not register this module. Reuse the explicit dependency-bound harness recipe for the baseline, replacing its source binding with this revision and adding `scenario_label/lookup_tests.rs` to the input closure. Required execution is the normal suite plus these three ignored tests, each in a fresh process:
+
+```text
+scenario_label::field_tests::advanced_ligature_partial_field_uses_whole_shared_cluster_not_fraction
+scenario_label::field_tests::auto_ascii_to_ellipsis_advanced_transition_uses_final_buffer
+scenario_label::tests::actual_font_load_rejects_retained_label_and_old_session
+```
+
+Run the timing diagnostic separately with `--exact scenario_label::field_tests::field_lookup_4096_scalars_and_combining_heavy_full_coverage --ignored --nocapture --test-threads=1`. It remains optional functional-gate evidence; its exact full-coverage assertions are not waived. The new differential filter is `scenario_label::lookup_tests::` (four tests). The pinned-font checks retain their existing isolated-process contract. Other real-shaping differential cases use the current system default font and compare both methods on the same resolved buffer; they do not establish cross-machine glyph identity.