Typecheck tests/ in npm run check tests/ was in no tsconfig include path, so npm run check never looked at it. Vitest transpiles without typechecking, so a green npm test said nothing about whether the specs were type-correct — two type errors sat in tests/memory-leak.test.ts undetected until the previous commit. Adds tsconfig.tests.json, mirroring the existing tsconfig.scripts.json pattern: extends the root config and adds node types for process and globalThis.gc. Kept as a separate program rather than widening the root include so node types do not leak into the src build. Verified by planting a deliberate type error in tests/setup.ts and confirming npm run check fails on it. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011gaCkV6CD5uR1SJpq3BPss

CLAUDE.md

@@ -61,14 +61,21 @@ Fleet-standard Vitest layout:
 | `tests/setup.ts` | Canvas / AudioContext mocks + `init({ name: "…" })` before SceneryStack imports |
 | `tests/**/*.test.ts` | Model/physics unit tests — mirror `src/` under `tests/` |
 | `tests/memory-leak.test.ts` | WeakRef + `forceGC` dispose regression (fleet pattern) |
+| `tsconfig.tests.json` | Typecheck config for `tests/` (adds `node` types), run by `npm run check` |
 
 Actual specs:
 
 - `tests/track-lab/model/KinematicsComputer.test.ts`
+- `tests/track-lab/model/TrackingModel.test.ts`
 - `tests/memory-leak.test.ts`
 
 Run `npm test`. CI runs the suite when a `test` script is present.
 
+`npm run check` typechecks three programs — `src` (root `tsconfig.json`), `scripts`
+(`tsconfig.scripts.json`), and `tests` (`tsconfig.tests.json`). Vitest transpiles without
+typechecking, so a passing `npm test` does not imply the specs typecheck; `npm run check` is what
+catches that.
+
 ## Commands
 
 ```bash

package.json

@@ -29,7 +29,7 @@
     "lint": "biome check .",
     "format": "biome format --write .",
     "fix": "biome check --write .",
-    "check": "tsc --noEmit && tsc -p tsconfig.scripts.json --noEmit",
+    "check": "tsc --noEmit && tsc -p tsconfig.scripts.json --noEmit && tsc -p tsconfig.tests.json --noEmit",
     "test": "vitest run",
     "test:watch": "vitest",
     "release": "npm run check && npm run lint && npm run build && npm version patch && git push && git push --tags",

src/TrackLabColors.ts

@@ -253,6 +253,8 @@ const TrackLabColors = {
   tableEmptyTextProperty: profileColor("tableEmptyText", new Color(136, 136, 136), new Color(120, 120, 120)),
   tableSymbolShadowProperty: profileColor("tableSymbolShadow", new Color(0, 0, 0, 0.5), new Color(0, 0, 0, 0.3)),
   tableBackgroundProperty: profileColor("tableBackground", WHITE, new Color(250, 250, 250)),
+  // Outline marking the row for the frame the video is parked on.
+  tableCurrentRowProperty: profileColor("tableCurrentRow", new Color(232, 119, 34), new Color(214, 100, 20)),
   exportButtonProperty: profileColor("exportButton", new Color(76, 175, 80), new Color(60, 150, 65)),
 
   // Graph (ConfigurableGraph, GraphDataManager, GraphControlsPanel)

src/TrackLabIcons.ts

@@ -143,6 +143,76 @@ export function makeTrashIcon(): Node {
   return new Node({ children: [handle, lid, body, l1, l2, l3] });
 }
 
+/**
+ * Eraser icon: a tilted eraser block with a divider between the rubber and the
+ * sleeve.  Deliberately unlike makeTrashIcon() — the erase-point and
+ * remove-track actions must never be mistaken for one another.
+ */
+export function makeEraserIcon(): Node {
+  const w = 12; // eraser block length
+  const h = 6.5; // eraser block height
+  const lw = 1.2;
+  const sleeveX = 4.5; // divider between rubber tip and sleeve
+  const tilt = -Math.PI / 6; // block leans like a held eraser
+
+  const body = new Rectangle(0, 0, w, h, 1, 1, {
+    stroke: TrackLabColors.playbackButtonIconColorProperty,
+    lineWidth: lw,
+    fill: null,
+  });
+  const divider = new Line(sleeveX, 0, sleeveX, h, {
+    stroke: TrackLabColors.playbackButtonIconColorProperty,
+    lineWidth: lw,
+  });
+
+  const block = new Node({ children: [body, divider] });
+  block.rotation = tilt;
+  // Re-wrap so the caller receives an unrotated node whose origin is its centre.
+  return new Node({ children: [block] });
+}
+
+/**
+ * Restore icon: a counter-clockwise arrow looping back on itself ("undo the
+ * last delete").
+ */
+export function makeRestoreIcon(): Node {
+  const r = 5; // arc radius
+  const lw = 1.6;
+  const headLength = 5; // tip-to-base distance of the arrowhead
+  const headHalfWidth = 3; // half the arrowhead's base
+  // The glyph is only ~12px on screen, so the head has to be large relative to
+  // the arc — a subtle one just reads as a letter "C".
+  const headAngle = Math.PI * 0.4;
+  const tailAngle = Math.PI * 1.75;
+
+  const arc = new Path(new Shape().arc(0, 0, r, headAngle, tailAngle, false), {
+    stroke: TrackLabColors.playbackButtonIconColorProperty,
+    lineWidth: lw,
+    fill: null,
+  });
+
+  // Arrowhead at the arc's start, pointing back against the sweep so the loop
+  // reads as "go backwards". Tangent at headAngle is (-sin, cos); negate it.
+  const hx = r * Math.cos(headAngle);
+  const hy = r * Math.sin(headAngle);
+  const tipX = Math.sin(headAngle);
+  const tipY = -Math.cos(headAngle);
+  // Perpendicular to the tip direction, used to lay out the base corners.
+  const perpX = -tipY;
+  const perpY = tipX;
+
+  const head = new Path(
+    new Shape()
+      .moveTo(hx + tipX * headLength, hy + tipY * headLength)
+      .lineTo(hx + perpX * headHalfWidth, hy + perpY * headHalfWidth)
+      .lineTo(hx - perpX * headHalfWidth, hy - perpY * headHalfWidth)
+      .close(),
+    { fill: TrackLabColors.playbackButtonIconColorProperty },
+  );
+
+  return new Node({ children: [arc, head] });
+}
+
 /**
  * Two small XY arrows for the coordinate-system control / info-dialog row.
  */

src/i18n/StringManager.ts

@@ -88,11 +88,13 @@ export class StringManager {
     titleStringProperty: ReadOnlyProperty<string>;
     simulationControlsStringProperty: ReadOnlyProperty<string>;
     graphInteractionsStringProperty: ReadOnlyProperty<string>;
+    digitizingStringProperty: ReadOnlyProperty<string>;
     playPauseSimulationStringProperty: ReadOnlyProperty<string>;
     resetSimulationStringProperty: ReadOnlyProperty<string>;
     stepBackwardStringProperty: ReadOnlyProperty<string>;
     stepForwardStringProperty: ReadOnlyProperty<string>;
     rewindToStartStringProperty: ReadOnlyProperty<string>;
+    erasePointStringProperty: ReadOnlyProperty<string>;
     resetZoomStringProperty: ReadOnlyProperty<string>;
     zoomInOutStringProperty: ReadOnlyProperty<string>;
     panViewStringProperty: ReadOnlyProperty<string>;
@@ -101,11 +103,13 @@ export class StringManager {
       titleStringProperty: stringProperties.keyboardShortcuts.titleStringProperty,
       simulationControlsStringProperty: stringProperties.keyboardShortcuts.simulationControlsStringProperty,
       graphInteractionsStringProperty: stringProperties.keyboardShortcuts.graphInteractionsStringProperty,
+      digitizingStringProperty: stringProperties.keyboardShortcuts.digitizingStringProperty,
       playPauseSimulationStringProperty: stringProperties.keyboardShortcuts.playPauseSimulationStringProperty,
       resetSimulationStringProperty: stringProperties.keyboardShortcuts.resetSimulationStringProperty,
       stepBackwardStringProperty: stringProperties.keyboardShortcuts.stepBackwardStringProperty,
       stepForwardStringProperty: stringProperties.keyboardShortcuts.stepForwardStringProperty,
       rewindToStartStringProperty: stringProperties.keyboardShortcuts.rewindToStartStringProperty,
+      erasePointStringProperty: stringProperties.keyboardShortcuts.erasePointStringProperty,
       resetZoomStringProperty: stringProperties.keyboardShortcuts.resetZoomStringProperty,
       zoomInOutStringProperty: stringProperties.keyboardShortcuts.zoomInOutStringProperty,
       panViewStringProperty: stringProperties.keyboardShortcuts.panViewStringProperty,
@@ -441,6 +445,8 @@ export class StringManager {
     digitizingAreaStringProperty: ReadOnlyProperty<string>;
     digitizeTrackStringProperty: ReadOnlyProperty<string>;
     removeTrackStringProperty: ReadOnlyProperty<string>;
+    erasePointStringProperty: ReadOnlyProperty<string>;
+    restorePointStringProperty: ReadOnlyProperty<string>;
     dataTableStringProperty: ReadOnlyProperty<string>;
     exportCSVStringProperty: ReadOnlyProperty<string>;
     measuringTapeBaseStringProperty: ReadOnlyProperty<string>;
@@ -485,6 +491,8 @@ export class StringManager {
       digitizingAreaStringProperty: stringProperties.a11y.digitizingAreaStringProperty,
       digitizeTrackStringProperty: stringProperties.a11y.digitizeTrackStringProperty,
       removeTrackStringProperty: stringProperties.a11y.removeTrackStringProperty,
+      erasePointStringProperty: stringProperties.a11y.erasePointStringProperty,
+      restorePointStringProperty: stringProperties.a11y.restorePointStringProperty,
       dataTableStringProperty: stringProperties.a11y.dataTableStringProperty,
       exportCSVStringProperty: stringProperties.a11y.exportCSVStringProperty,
       measuringTapeBaseStringProperty: stringProperties.a11y.measuringTapeBaseStringProperty,

src/i18n/strings_en.json

@@ -42,11 +42,13 @@
     "title": "Keyboard Shortcuts",
     "simulationControls": "Simulation Controls",
     "graphInteractions": "Graph Interactions",
+    "digitizing": "Digitizing",
     "playPauseSimulation": "Play/Pause Simulation",
     "resetSimulation": "Reset Simulation",
     "stepBackward": "Step Backward",
     "stepForward": "Step Forward",
     "rewindToStart": "Rewind to Start",
+    "erasePoint": "Erase Point at Current Frame",
     "resetZoom": "Reset Zoom",
     "zoomInOut": "Zoom In/Out",
     "panView": "Pan View"
@@ -158,7 +160,7 @@
     "addTrackTitle": "4. Add a Track",
     "addTrackBody": "In the Tracks panel, click “+ Add Track” to create a new track (A, B, C…). Up to 4 tracks can be active at a time.",
     "digitizeTitle": "5. Digitize Frame by Frame",
-    "digitizeBody": "Select a track and click the object’s position in the video. Enable the Magnifier for precision. The video advances one frame after each click.",
+    "digitizeBody": "Select a track and click the object’s position in the video. Enable the Magnifier for precision. The video advances one frame after each click. Click the same frame again to move a point, or press Delete to erase it.",
     "autoTrackTitle": "Auto-Tracking",
     "autoTrackBody": "Enable Auto-Tracking in the control panel, then drag a selection box around the object. TrackLab will track it automatically across the remaining frames.",
     "measuringTapeTitle": "Measuring Tape",
@@ -176,9 +178,11 @@
     "videoPlayer": "Video player",
     "videoScrubber": "Video timeline — drag to seek",
     "rewindToStart": "Rewind to start",
-    "digitizingArea": "Video digitizing area — click to record the position of the active track",
+    "digitizingArea": "Video digitizing area — click to record the position of the active track, or press Delete to erase the point at this frame",
     "digitizeTrack": "Digitize track {{symbol}}",
     "removeTrack": "Remove track {{symbol}}",
+    "erasePoint": "Erase the digitized point at the current frame",
+    "restorePoint": "Restore the last erased point",
     "dataTable": "Track data",
     "exportCSV": "Export track data as CSV file",
     "measuringTapeBase": "Measuring tape base endpoint",

src/i18n/strings_es.json

@@ -42,11 +42,13 @@
     "title": "Atajos de teclado",
     "simulationControls": "Controles de simulación",
     "graphInteractions": "Interacciones con la gráfica",
+    "digitizing": "Digitalización",
     "playPauseSimulation": "Reproducir/Pausar la simulación",
     "resetSimulation": "Reiniciar la simulación",
     "stepBackward": "Retroceder un paso",
     "stepForward": "Avanzar un paso",
     "rewindToStart": "Rebobinar al inicio",
+    "erasePoint": "Borrar punto en el fotograma actual",
     "resetZoom": "Restablecer el zoom",
     "zoomInOut": "Acercar/Alejar",
     "panView": "Desplazar la vista"
@@ -158,7 +160,7 @@
     "addTrackTitle": "4. Añadir una pista",
     "addTrackBody": "En el panel de pistas, haz clic en «+ Añadir pista» para crear una nueva pista (A, B, C…). Pueden estar activas hasta 4 pistas a la vez.",
     "digitizeTitle": "5. Digitalizar fotograma a fotograma",
-    "digitizeBody": "Selecciona una pista y haz clic en la posición del objeto en el video. Activa la lupa para mayor precisión. El video avanza un fotograma después de cada clic.",
+    "digitizeBody": "Selecciona una pista y haz clic en la posición del objeto en el video. Activa la lupa para mayor precisión. El video avanza un fotograma después de cada clic. Vuelve a hacer clic en el mismo fotograma para mover un punto, o pulsa Supr para borrarlo.",
     "autoTrackTitle": "Seguimiento automático",
     "autoTrackBody": "Activa el seguimiento automático en el panel de control, luego arrastra un cuadro de selección alrededor del objeto. TrackLab lo seguirá automáticamente a lo largo de los fotogramas restantes.",
     "measuringTapeTitle": "Cinta métrica",
@@ -176,9 +178,11 @@
     "videoPlayer": "Reproductor de video",
     "videoScrubber": "Línea de tiempo del video — arrastra para buscar",
     "rewindToStart": "Rebobinar al inicio",
-    "digitizingArea": "Área de digitalización del video — haz clic para registrar la posición de la pista activa",
+    "digitizingArea": "Área de digitalización del video — haz clic para registrar la posición de la pista activa, o pulsa Supr para borrar el punto de este fotograma",
     "digitizeTrack": "Digitalizar la pista {{symbol}}",
     "removeTrack": "Eliminar la pista {{symbol}}",
+    "erasePoint": "Borrar el punto digitalizado en el fotograma actual",
+    "restorePoint": "Restaurar el último punto borrado",
     "dataTable": "Datos de la pista",
     "exportCSV": "Exportar los datos de la pista como archivo CSV",
     "measuringTapeBase": "Extremo base de la cinta métrica",

src/i18n/strings_fr.json

@@ -42,11 +42,13 @@
     "title": "Raccourcis clavier",
     "simulationControls": "Contrôles de simulation",
     "graphInteractions": "Interactions avec le graphique",
+    "digitizing": "Numérisation",
     "playPauseSimulation": "Lecture/Pause de la simulation",
     "resetSimulation": "Réinitialiser la simulation",
     "stepBackward": "Reculer d'un pas",
     "stepForward": "Avancer d'un pas",
     "rewindToStart": "Revenir au début",
+    "erasePoint": "Effacer le point à l'image actuelle",
     "resetZoom": "Réinitialiser le zoom",
     "zoomInOut": "Zoom avant/arrière",
     "panView": "Déplacer la vue"
@@ -158,7 +160,7 @@
     "addTrackTitle": "4. Ajouter une piste",
     "addTrackBody": "Dans le panneau Pistes, cliquez sur « + Ajouter une piste » pour créer une nouvelle piste étiquetée A, B, C, …",
     "digitizeTitle": "5. Numériser image par image",
-    "digitizeBody": "Sélectionnez une piste et cliquez sur la position de l’objet dans la vidéo. Activez la Loupe pour plus de précision. La vidéo avance automatiquement d’une image après chaque clic.",
+    "digitizeBody": "Sélectionnez une piste et cliquez sur la position de l’objet dans la vidéo. Activez la Loupe pour plus de précision. La vidéo avance automatiquement d’une image après chaque clic. Cliquez à nouveau sur la même image pour déplacer un point, ou appuyez sur Suppr pour l’effacer.",
     "autoTrackTitle": "Suivi automatique",
     "autoTrackBody": "Activez le Suivi automatique dans le panneau de contrôle, puis faites glisser un cadre de sélection autour de l’objet. TrackLab le suivra automatiquement sur les images restantes.",
     "measuringTapeTitle": "Ruban de mesure",
@@ -176,9 +178,11 @@
     "videoPlayer": "Lecteur vidéo",
     "videoScrubber": "Ligne de temps vidéo — glisser pour naviguer",
     "rewindToStart": "Revenir au début",
-    "digitizingArea": "Zone de numérisation vidéo — cliquer pour enregistrer la position de la piste active",
+    "digitizingArea": "Zone de numérisation vidéo — cliquer pour enregistrer la position de la piste active, ou appuyer sur Suppr pour effacer le point de cette image",
     "digitizeTrack": "Numériser la piste {{symbol}}",
     "removeTrack": "Supprimer la piste {{symbol}}",
+    "erasePoint": "Effacer le point numérisé à l'image actuelle",
+    "restorePoint": "Restaurer le dernier point effacé",
     "dataTable": "Données de piste",
     "exportCSV": "Exporter les données de piste en fichier CSV",
     "measuringTapeBase": "Extrémité de base du ruban de mesure",

src/track-lab/model/TrackLabModel.ts

@@ -61,12 +61,36 @@ export class TrackLabModel {
    * The view passes raw inputs (track id + pixel position); this method
    * coordinates all sub-model interactions so the view does not need to reach
    * into playback or overlayTools directly.
+   *
+   * Clicking a frame that already holds a point *replaces* it: re-clicking is
+   * how a user corrects a misclick, and silently ignoring the second click
+   * reads as the tool being broken.  Auto-tracking keeps the first-wins policy
+   * so it never clobbers a hand-placed point.
    */
   public recordTrackPoint(trackId: string, pixelPoint: Vector2): void {
     const time = this.playback.currentTimeProperty.value;
-    const frame = Math.round(time * this.playback.frameRateProperty.value);
+    // Same derivation as deleteTrackPointAtCurrentFrame(), so the frame a click
+    // writes is exactly the frame the erase button targets.
+    const frame = this.playback.currentFrameProperty.value;
     const modelPt = this.overlayTools.modelViewTransformProperty.value.inversePosition2(pixelPoint);
-    this.tracking.addPointToTrack(trackId, frame, time, modelPt.x, modelPt.y);
+    this.tracking.addOrReplacePointOnTrack(trackId, frame, time, modelPt.x, modelPt.y);
+  }
+
+  /**
+   * Delete the active track's point at the current playback frame, if any.
+   * Returns true when a point was actually removed.
+   */
+  public deleteTrackPointAtCurrentFrame(): boolean {
+    const trackId = this.tracking.activeTrackIdProperty.value;
+    if (trackId === null) {
+      return false;
+    }
+    const frame = this.playback.currentFrameProperty.value;
+    if (!this.tracking.hasPointAtFrame(trackId, frame)) {
+      return false;
+    }
+    this.tracking.removePointFromTrack(trackId, frame);
+    return true;
   }
 
   // ── Video source activation ─────────────────────────────────────────────