diff --git a/lib/solvers/RectDiffSolver.ts b/lib/solvers/RectDiffSolver.ts
index 34bda41..ad85b69 100644
--- a/lib/solvers/RectDiffSolver.ts
+++ b/lib/solvers/RectDiffSolver.ts
@@ -14,11 +14,6 @@ import {
 } from "./rectdiff/engine"
 import { rectsToMeshNodes } from "./rectdiff/rectsToMeshNodes"
 import { overlaps } from "./rectdiff/geometry"
-import type { GapFillOptions } from "./rectdiff/gapfill/types"
-import {
-  findUncoveredPoints,
-  calculateCoverage,
-} from "./rectdiff/gapfill/engine"
 
 /**
  * A streaming, one-step-per-iteration solver for capacity mesh generation.
@@ -82,34 +77,6 @@ export class RectDiffSolver extends BaseSolver {
     return { meshNodes: this._meshNodes }
   }
 
-  /** Get coverage percentage (0-1). */
-  getCoverage(sampleResolution: number = 0.05): number {
-    return calculateCoverage(
-      { sampleResolution },
-      {
-        bounds: this.state.bounds,
-        layerCount: this.state.layerCount,
-        obstaclesByLayer: this.state.obstaclesByLayer,
-        placedByLayer: this.state.placedByLayer,
-      },
-    )
-  }
-
-  /** Find uncovered points for debugging gaps. */
-  getUncoveredPoints(
-    sampleResolution: number = 0.05,
-  ): Array<{ x: number; y: number; z: number }> {
-    return findUncoveredPoints(
-      { sampleResolution },
-      {
-        bounds: this.state.bounds,
-        layerCount: this.state.layerCount,
-        obstaclesByLayer: this.state.obstaclesByLayer,
-        placedByLayer: this.state.placedByLayer,
-      },
-    )
-  }
-
   /** Get color based on z layer for visualization. */
   private getColorForZLayer(zLayers: number[]): {
     fill: string
diff --git a/lib/solvers/rectdiff/gapfill/detection.ts b/lib/solvers/rectdiff/gapfill/detection.ts
deleted file mode 100644
index 7126d89..0000000
--- a/lib/solvers/rectdiff/gapfill/detection.ts
+++ /dev/null
@@ -1,3 +0,0 @@
-// lib/solvers/rectdiff/gapfill/detection.ts
-export * from "./detection/findAllGaps"
-// findGapsOnLayer is not exported as it's only used by findAllGaps
diff --git a/lib/solvers/rectdiff/gapfill/detection/deduplicateGaps.ts b/lib/solvers/rectdiff/gapfill/detection/deduplicateGaps.ts
deleted file mode 100644
index 0f45164..0000000
--- a/lib/solvers/rectdiff/gapfill/detection/deduplicateGaps.ts
+++ /dev/null
@@ -1,28 +0,0 @@
-// lib/solvers/rectdiff/gapfill/detection/deduplicateGaps.ts
-import { rectsEqual } from "../../../../../utils/rectsEqual"
-import { rectsOverlap } from "../../../../../utils/rectsOverlap"
-import type { GapRegion } from "../types"
-
-export function deduplicateGaps(gaps: GapRegion[]): GapRegion[] {
-  const result: GapRegion[] = []
-
-  for (const gap of gaps) {
-    // Check if we already have a gap at the same location with overlapping layers
-    const existing = result.find(
-      (g) =>
-        rectsEqual(g.rect, gap.rect) ||
-        (rectsOverlap(g.rect, gap.rect) &&
-          gap.zLayers.some((z) => g.zLayers.includes(z))),
-    )
-
-    if (!existing) {
-      result.push(gap)
-    } else if (gap.zLayers.length > existing.zLayers.length) {
-      // Replace with the one that has more layers
-      const idx = result.indexOf(existing)
-      result[idx] = gap
-    }
-  }
-
-  return result
-}
diff --git a/lib/solvers/rectdiff/gapfill/detection/findAllGaps.ts b/lib/solvers/rectdiff/gapfill/detection/findAllGaps.ts
deleted file mode 100644
index d4cc9ec..0000000
--- a/lib/solvers/rectdiff/gapfill/detection/findAllGaps.ts
+++ /dev/null
@@ -1,83 +0,0 @@
-// lib/solvers/rectdiff/gapfill/detection/findAllGaps.ts
-import type { XYRect } from "../../types"
-import type { GapRegion, LayerContext } from "../types"
-import { EPS } from "../../geometry"
-import { findGapsOnLayer } from "./findGapsOnLayer"
-import { rectsOverlap } from "../../../../../utils/rectsOverlap"
-import { deduplicateGaps } from "./deduplicateGaps"
-
-/**
- * Find gaps across all layers and return GapRegions with z-layer info.
- */
-export function findAllGaps(
-  {
-    scanResolution,
-    minWidth,
-    minHeight,
-  }: {
-    scanResolution: number
-    minWidth: number
-    minHeight: number
-  },
-  ctx: LayerContext,
-): GapRegion[] {
-  const { bounds, layerCount, obstaclesByLayer, placedByLayer } = ctx
-
-  // Find gaps on each layer
-  const gapsByLayer: XYRect[][] = []
-  for (let z = 0; z < layerCount; z++) {
-    const obstacles = obstaclesByLayer[z] ?? []
-    const placed = placedByLayer[z] ?? []
-    const gaps = findGapsOnLayer({ bounds, obstacles, placed, scanResolution })
-    gapsByLayer.push(gaps)
-  }
-
-  // Convert to GapRegions with z-layer info
-  const allGaps: GapRegion[] = []
-
-  for (let z = 0; z < layerCount; z++) {
-    for (const gap of gapsByLayer[z]!) {
-      // Filter out gaps that are too small
-      if (gap.width < minWidth - EPS || gap.height < minHeight - EPS) continue
-
-      // Check if this gap exists on adjacent layers too
-      const zLayers = [z]
-
-      // Look up
-      for (let zu = z + 1; zu < layerCount; zu++) {
-        const hasOverlap = gapsByLayer[zu]!.some((g) => rectsOverlap(g, gap))
-        if (hasOverlap) zLayers.push(zu)
-        else break
-      }
-
-      // Look down (if z > 0 and not already counted)
-      for (let zd = z - 1; zd >= 0; zd--) {
-        const hasOverlap = gapsByLayer[zd]!.some((g) => rectsOverlap(g, gap))
-        if (hasOverlap && !zLayers.includes(zd)) zLayers.unshift(zd)
-        else break
-      }
-
-      allGaps.push({
-        rect: gap,
-        zLayers: zLayers.sort((a, b) => a - b),
-        centerX: gap.x + gap.width / 2,
-        centerY: gap.y + gap.height / 2,
-        area: gap.width * gap.height,
-      })
-    }
-  }
-
-  // Deduplicate gaps that are essentially the same across layers
-  const deduped = deduplicateGaps(allGaps)
-
-  // Sort by priority: prefer larger gaps and multi-layer gaps
-  deduped.sort((a, b) => {
-    // Prefer multi-layer gaps
-    const layerDiff = b.zLayers.length - a.zLayers.length
-    if (layerDiff !== 0) return layerDiff
-    // Then prefer larger area
-    return b.area - a.area
-  })
-
-  return deduped
-}
diff --git a/lib/solvers/rectdiff/gapfill/detection/findGapsOnLayer.ts b/lib/solvers/rectdiff/gapfill/detection/findGapsOnLayer.ts
deleted file mode 100644
index 895ed9d..0000000
--- a/lib/solvers/rectdiff/gapfill/detection/findGapsOnLayer.ts
+++ /dev/null
@@ -1,100 +0,0 @@
-// lib/solvers/rectdiff/gapfill/detection/findGapsOnLayer.ts
-import type { XYRect } from "../../types"
-import { EPS } from "../../geometry"
-
-import { mergeUncoveredCells } from "./mergeUncoveredCells"
-
-/**
- * Sweep-line algorithm to find maximal uncovered rectangles on a single layer.
- */
-export function findGapsOnLayer({
-  bounds,
-  obstacles,
-  placed,
-  scanResolution,
-}: {
-  bounds: XYRect
-  obstacles: XYRect[]
-  placed: XYRect[]
-  scanResolution: number
-}): XYRect[] {
-  const blockers = [...obstacles, ...placed]
-
-  // Collect all unique x-coordinates
-  const xCoords = new Set<number>()
-  xCoords.add(bounds.x)
-  xCoords.add(bounds.x + bounds.width)
-
-  for (const b of blockers) {
-    if (b.x > bounds.x && b.x < bounds.x + bounds.width) {
-      xCoords.add(b.x)
-    }
-    if (b.x + b.width > bounds.x && b.x + b.width < bounds.x + bounds.width) {
-      xCoords.add(b.x + b.width)
-    }
-  }
-
-  // Also add intermediate points based on scan resolution
-  for (let x = bounds.x; x <= bounds.x + bounds.width; x += scanResolution) {
-    xCoords.add(x)
-  }
-
-  const sortedX = Array.from(xCoords).sort((a, b) => a - b)
-
-  // Similarly for y-coordinates
-  const yCoords = new Set<number>()
-  yCoords.add(bounds.y)
-  yCoords.add(bounds.y + bounds.height)
-
-  for (const b of blockers) {
-    if (b.y > bounds.y && b.y < bounds.y + bounds.height) {
-      yCoords.add(b.y)
-    }
-    if (
-      b.y + b.height > bounds.y &&
-      b.y + b.height < bounds.y + bounds.height
-    ) {
-      yCoords.add(b.y + b.height)
-    }
-  }
-
-  for (let y = bounds.y; y <= bounds.y + bounds.height; y += scanResolution) {
-    yCoords.add(y)
-  }
-
-  const sortedY = Array.from(yCoords).sort((a, b) => a - b)
-
-  // Build a grid of cells and mark which are uncovered
-  const uncoveredCells: Array<{ x: number; y: number; w: number; h: number }> =
-    []
-
-  for (let i = 0; i < sortedX.length - 1; i++) {
-    for (let j = 0; j < sortedY.length - 1; j++) {
-      const cellX = sortedX[i]!
-      const cellY = sortedY[j]!
-      const cellW = sortedX[i + 1]! - cellX
-      const cellH = sortedY[j + 1]! - cellY
-
-      if (cellW <= EPS || cellH <= EPS) continue
-
-      // Check if this cell is covered by any blocker
-      const cellCenterX = cellX + cellW / 2
-      const cellCenterY = cellY + cellH / 2
-
-      const isCovered = blockers.some(
-        (b) =>
-          cellCenterX >= b.x - EPS &&
-          cellCenterX <= b.x + b.width + EPS &&
-          cellCenterY >= b.y - EPS &&
-          cellCenterY <= b.y + b.height + EPS,
-      )
-
-      if (!isCovered) {
-        uncoveredCells.push({ x: cellX, y: cellY, w: cellW, h: cellH })
-      }
-    }
-  }
-
-  // Merge adjacent uncovered cells into maximal rectangles
-  return mergeUncoveredCells(uncoveredCells)
-}
diff --git a/lib/solvers/rectdiff/gapfill/detection/mergeUncoveredCells.ts b/lib/solvers/rectdiff/gapfill/detection/mergeUncoveredCells.ts
deleted file mode 100644
index 940c75c..0000000
--- a/lib/solvers/rectdiff/gapfill/detection/mergeUncoveredCells.ts
+++ /dev/null
@@ -1,75 +0,0 @@
-// lib/solvers/rectdiff/gapfill/detection/mergeUncoveredCells.ts
-import type { XYRect } from "../../types"
-import { EPS } from "../../geometry"
-
-/**
- * Merge adjacent uncovered cells into larger rectangles using a greedy approach.
- */
-export function mergeUncoveredCells(
-  cells: Array<{ x: number; y: number; w: number; h: number }>,
-): XYRect[] {
-  if (cells.length === 0) return []
-
-  // Group cells by their left edge and width
-  const byXW = new Map<string, typeof cells>()
-  for (const c of cells) {
-    const key = `${c.x.toFixed(9)}|${c.w.toFixed(9)}`
-    const arr = byXW.get(key) ?? []
-    arr.push(c)
-    byXW.set(key, arr)
-  }
-
-  // Within each vertical strip, merge adjacent cells
-  const verticalStrips: XYRect[] = []
-  for (const stripCells of byXW.values()) {
-    // Sort by y
-    stripCells.sort((a, b) => a.y - b.y)
-
-    let current: XYRect | null = null
-    for (const c of stripCells) {
-      if (!current) {
-        current = { x: c.x, y: c.y, width: c.w, height: c.h }
-      } else if (Math.abs(current.y + current.height - c.y) < EPS) {
-        // Adjacent vertically, merge
-        current.height += c.h
-      } else {
-        // Gap, save current and start new
-        verticalStrips.push(current)
-        current = { x: c.x, y: c.y, width: c.w, height: c.h }
-      }
-    }
-    if (current) verticalStrips.push(current)
-  }
-
-  // Now try to merge horizontal strips with same y and height
-  const byYH = new Map<string, XYRect[]>()
-  for (const r of verticalStrips) {
-    const key = `${r.y.toFixed(9)}|${r.height.toFixed(9)}`
-    const arr = byYH.get(key) ?? []
-    arr.push(r)
-    byYH.set(key, arr)
-  }
-
-  const merged: XYRect[] = []
-  for (const rowRects of byYH.values()) {
-    // Sort by x
-    rowRects.sort((a, b) => a.x - b.x)
-
-    let current: XYRect | null = null
-    for (const r of rowRects) {
-      if (!current) {
-        current = { ...r }
-      } else if (Math.abs(current.x + current.width - r.x) < EPS) {
-        // Adjacent horizontally, merge
-        current.width += r.width
-      } else {
-        // Gap, save current and start new
-        merged.push(current)
-        current = { ...r }
-      }
-    }
-    if (current) merged.push(current)
-  }
-
-  return merged
-}
diff --git a/lib/solvers/rectdiff/gapfill/engine.ts b/lib/solvers/rectdiff/gapfill/engine.ts
deleted file mode 100644
index a440663..0000000
--- a/lib/solvers/rectdiff/gapfill/engine.ts
+++ /dev/null
@@ -1,7 +0,0 @@
-// lib/solvers/rectdiff/gapfill/engine.ts
-export * from "./engine/calculateCoverage"
-export * from "./engine/findUncoveredPoints"
-export * from "./engine/getGapFillProgress"
-export * from "./engine/initGapFillState"
-
-export * from "./engine/stepGapFill"
diff --git a/lib/solvers/rectdiff/gapfill/engine/addPlacement.ts b/lib/solvers/rectdiff/gapfill/engine/addPlacement.ts
deleted file mode 100644
index 9c7bda7..0000000
--- a/lib/solvers/rectdiff/gapfill/engine/addPlacement.ts
+++ /dev/null
@@ -1,27 +0,0 @@
-// lib/solvers/rectdiff/gapfill/engine/addPlacement.ts
-import type { Placed3D, XYRect } from "../../types"
-import type { GapFillState } from "../types"
-
-/**
- * Add a new placement to the state.
- */
-export function addPlacement(
-  state: GapFillState,
-  {
-    rect,
-    zLayers,
-  }: {
-    rect: XYRect
-    zLayers: number[]
-  },
-): void {
-  const placed: Placed3D = { rect, zLayers: [...zLayers] }
-  state.placed.push(placed)
-
-  for (const z of zLayers) {
-    if (!state.placedByLayer[z]) {
-      state.placedByLayer[z] = []
-    }
-    state.placedByLayer[z]!.push(rect)
-  }
-}
diff --git a/lib/solvers/rectdiff/gapfill/engine/calculateCoverage.ts b/lib/solvers/rectdiff/gapfill/engine/calculateCoverage.ts
deleted file mode 100644
index d9de4b3..0000000
--- a/lib/solvers/rectdiff/gapfill/engine/calculateCoverage.ts
+++ /dev/null
@@ -1,44 +0,0 @@
-// lib/solvers/rectdiff/gapfill/engine/calculateCoverage.ts
-import type { LayerContext } from "../types"
-
-/**
- * Calculate coverage percentage (0-1).
- */
-export function calculateCoverage(
-  { sampleResolution = 0.1 }: { sampleResolution?: number },
-  ctx: LayerContext,
-): number {
-  const { bounds, layerCount, obstaclesByLayer, placedByLayer } = ctx
-
-  let totalPoints = 0
-  let coveredPoints = 0
-
-  for (let z = 0; z < layerCount; z++) {
-    const obstacles = obstaclesByLayer[z] ?? []
-    const placed = placedByLayer[z] ?? []
-    const allRects = [...obstacles, ...placed]
-
-    for (
-      let x = bounds.x;
-      x <= bounds.x + bounds.width;
-      x += sampleResolution
-    ) {
-      for (
-        let y = bounds.y;
-        y <= bounds.y + bounds.height;
-        y += sampleResolution
-      ) {
-        totalPoints++
-
-        const isCovered = allRects.some(
-          (r) =>
-            x >= r.x && x <= r.x + r.width && y >= r.y && y <= r.y + r.height,
-        )
-
-        if (isCovered) coveredPoints++
-      }
-    }
-  }
-
-  return totalPoints > 0 ? coveredPoints / totalPoints : 1
-}
diff --git a/lib/solvers/rectdiff/gapfill/engine/findUncoveredPoints.ts b/lib/solvers/rectdiff/gapfill/engine/findUncoveredPoints.ts
deleted file mode 100644
index c0a09b6..0000000
--- a/lib/solvers/rectdiff/gapfill/engine/findUncoveredPoints.ts
+++ /dev/null
@@ -1,43 +0,0 @@
-// lib/solvers/rectdiff/gapfill/engine/findUncoveredPoints.ts
-import type { LayerContext } from "../types"
-
-/**
- * Find uncovered points for debugging gaps.
- */
-export function findUncoveredPoints(
-  { sampleResolution = 0.05 }: { sampleResolution?: number },
-  ctx: LayerContext,
-): Array<{ x: number; y: number; z: number }> {
-  const { bounds, layerCount, obstaclesByLayer, placedByLayer } = ctx
-
-  const uncovered: Array<{ x: number; y: number; z: number }> = []
-
-  for (let z = 0; z < layerCount; z++) {
-    const obstacles = obstaclesByLayer[z] ?? []
-    const placed = placedByLayer[z] ?? []
-    const allRects = [...obstacles, ...placed]
-
-    for (
-      let x = bounds.x;
-      x <= bounds.x + bounds.width;
-      x += sampleResolution
-    ) {
-      for (
-        let y = bounds.y;
-        y <= bounds.y + bounds.height;
-        y += sampleResolution
-      ) {
-        const isCovered = allRects.some(
-          (r) =>
-            x >= r.x && x <= r.x + r.width && y >= r.y && y <= r.y + r.height,
-        )
-
-        if (!isCovered) {
-          uncovered.push({ x, y, z })
-        }
-      }
-    }
-  }
-
-  return uncovered
-}
diff --git a/lib/solvers/rectdiff/gapfill/engine/getGapFillProgress.ts b/lib/solvers/rectdiff/gapfill/engine/getGapFillProgress.ts
deleted file mode 100644
index 6d4d65a..0000000
--- a/lib/solvers/rectdiff/gapfill/engine/getGapFillProgress.ts
+++ /dev/null
@@ -1,42 +0,0 @@
-// lib/solvers/rectdiff/gapfill/engine/getGapFillProgress.ts
-import type { GapFillState } from "../types"
-
-/**
- * Get progress as a number between 0 and 1.
- * Accounts for four-stage processing (scan → select → expand → place for each gap).
- */
-export function getGapFillProgress(state: GapFillState): number {
-  if (state.done) return 1
-
-  const iterationProgress = state.iteration / state.options.maxIterations
-  const gapProgress =
-    state.gapsFound.length > 0 ? state.gapIndex / state.gapsFound.length : 0
-
-  // Add sub-progress within current gap based on stage
-  let stageProgress = 0
-  switch (state.stage) {
-    case "scan":
-      stageProgress = 0
-      break
-    case "select":
-      stageProgress = 0.25
-      break
-    case "expand":
-      stageProgress = 0.5
-      break
-    case "place":
-      stageProgress = 0.75
-      break
-  }
-
-  const gapStageProgress =
-    state.gapsFound.length > 0
-      ? stageProgress / (state.gapsFound.length * 4) // 4 stages per gap
-      : 0
-
-  return Math.min(
-    0.999,
-    iterationProgress +
-      (gapProgress + gapStageProgress) / state.options.maxIterations,
-  )
-}
diff --git a/lib/solvers/rectdiff/gapfill/engine/initGapFillState.ts b/lib/solvers/rectdiff/gapfill/engine/initGapFillState.ts
deleted file mode 100644
index 8f5d886..0000000
--- a/lib/solvers/rectdiff/gapfill/engine/initGapFillState.ts
+++ /dev/null
@@ -1,57 +0,0 @@
-// lib/solvers/rectdiff/gapfill/engine/initGapFillState.ts
-import type { Placed3D } from "../../types"
-import type { GapFillState, GapFillOptions, LayerContext } from "../types"
-
-const DEFAULT_OPTIONS: GapFillOptions = {
-  minWidth: 0.1,
-  minHeight: 0.1,
-  maxIterations: 10,
-  targetCoverage: 0.999,
-  scanResolution: 0.5,
-}
-
-/**
- * Initialize the gap fill state from existing rectdiff state.
- */
-export function initGapFillState(
-  {
-    placed,
-    options,
-  }: {
-    placed: Placed3D[]
-    options?: Partial<GapFillOptions>
-  },
-  ctx: LayerContext,
-): GapFillState {
-  const opts = { ...DEFAULT_OPTIONS, ...options }
-
-  // Deep copy placed arrays to avoid mutation issues
-  const placedCopy = placed.map((p) => ({
-    rect: { ...p.rect },
-    zLayers: [...p.zLayers],
-  }))
-
-  const placedByLayerCopy = ctx.placedByLayer.map((layer) =>
-    layer.map((r) => ({ ...r })),
-  )
-
-  return {
-    bounds: { ...ctx.bounds },
-    layerCount: ctx.layerCount,
-    obstaclesByLayer: ctx.obstaclesByLayer,
-    placed: placedCopy,
-    placedByLayer: placedByLayerCopy,
-    options: opts,
-    iteration: 0,
-    gapsFound: [],
-    gapIndex: 0,
-    done: false,
-    initialGapCount: 0,
-    filledCount: 0,
-    // Four-stage visualization state
-    stage: "scan",
-    currentGap: null,
-    currentSeed: null,
-    expandedRect: null,
-  }
-}
diff --git a/lib/solvers/rectdiff/gapfill/engine/stepGapFill.ts b/lib/solvers/rectdiff/gapfill/engine/stepGapFill.ts
deleted file mode 100644
index ad143c8..0000000
--- a/lib/solvers/rectdiff/gapfill/engine/stepGapFill.ts
+++ /dev/null
@@ -1,128 +0,0 @@
-// lib/solvers/rectdiff/gapfill/engine/stepGapFill.ts
-import type { GapFillState } from "../types"
-import { findAllGaps } from "../detection"
-import { tryExpandGap } from "./tryExpandGap"
-import { addPlacement } from "./addPlacement"
-
-/**
- * Perform one step of gap filling with four-stage visualization.
- * Stages: scan → select → expand → place
- * Returns true if still working, false if done.
- */
-export function stepGapFill(state: GapFillState): boolean {
-  if (state.done) return false
-
-  switch (state.stage) {
-    case "scan": {
-      // Stage 1: Gap detection/scanning
-
-      // Check if we need to find new gaps
-      if (
-        state.gapsFound.length === 0 ||
-        state.gapIndex >= state.gapsFound.length
-      ) {
-        // Check if we've hit max iterations
-        if (state.iteration >= state.options.maxIterations) {
-          state.done = true
-          return false
-        }
-
-        // Find new gaps
-        state.gapsFound = findAllGaps(
-          {
-            scanResolution: state.options.scanResolution,
-            minWidth: state.options.minWidth,
-            minHeight: state.options.minHeight,
-          },
-          {
-            bounds: state.bounds,
-            layerCount: state.layerCount,
-            obstaclesByLayer: state.obstaclesByLayer,
-            placedByLayer: state.placedByLayer,
-          },
-        )
-
-        if (state.iteration === 0) {
-          state.initialGapCount = state.gapsFound.length
-        }
-
-        state.gapIndex = 0
-        state.iteration++
-
-        // If no gaps found, we're done
-        if (state.gapsFound.length === 0) {
-          state.done = true
-          return false
-        }
-      }
-
-      // Move to select stage
-      state.stage = "select"
-      return true
-    }
-
-    case "select": {
-      // Stage 2: Show the gap being targeted
-      if (state.gapIndex >= state.gapsFound.length) {
-        // No more gaps in this iteration, go back to scan
-        state.stage = "scan"
-        return true
-      }
-
-      state.currentGap = state.gapsFound[state.gapIndex]!
-      state.currentSeed = {
-        x: state.currentGap.centerX,
-        y: state.currentGap.centerY,
-      }
-      state.expandedRect = null
-
-      // Move to expand stage
-      state.stage = "expand"
-      return true
-    }
-
-    case "expand": {
-      // Stage 3: Show expansion attempt
-      if (!state.currentGap) {
-        // Shouldn't happen, but handle gracefully
-        state.stage = "select"
-        return true
-      }
-
-      // Try to expand from the current seed
-      const expandedRect = tryExpandGap(state, {
-        gap: state.currentGap,
-        seed: state.currentSeed!,
-      })
-      state.expandedRect = expandedRect
-
-      // Move to place stage
-      state.stage = "place"
-      return true
-    }
-
-    case "place": {
-      // Stage 4: Show the placed result
-      if (state.expandedRect && state.currentGap) {
-        // Actually place the rectangle
-        addPlacement(state, {
-          rect: state.expandedRect,
-          zLayers: state.currentGap.zLayers,
-        })
-        state.filledCount++
-      }
-
-      // Move to next gap and reset to select stage
-      state.gapIndex++
-      state.currentGap = null
-      state.currentSeed = null
-      state.expandedRect = null
-      state.stage = "select"
-      return true
-    }
-
-    default:
-      state.stage = "scan"
-      return true
-  }
-}
diff --git a/lib/solvers/rectdiff/gapfill/engine/tryExpandGap.ts b/lib/solvers/rectdiff/gapfill/engine/tryExpandGap.ts
deleted file mode 100644
index d3ae73c..0000000
--- a/lib/solvers/rectdiff/gapfill/engine/tryExpandGap.ts
+++ /dev/null
@@ -1,78 +0,0 @@
-// lib/solvers/rectdiff/gapfill/engine/tryExpandGap.ts
-import type { XYRect } from "../../types"
-import type { GapFillState, GapRegion } from "../types"
-import { expandRectFromSeed } from "../../geometry"
-
-/**
- * Try to expand a rectangle from a seed point within the gap.
- * Returns the expanded rectangle or null if expansion fails.
- */
-export function tryExpandGap(
-  state: GapFillState,
-  {
-    gap,
-    seed,
-  }: {
-    gap: GapRegion
-    seed: { x: number; y: number }
-  },
-): XYRect | null {
-  // Build blockers for the gap's z-layers
-  const blockers: XYRect[] = []
-  for (const z of gap.zLayers) {
-    blockers.push(...(state.obstaclesByLayer[z] ?? []))
-    blockers.push(...(state.placedByLayer[z] ?? []))
-  }
-
-  // Try to expand from the seed point
-  const rect = expandRectFromSeed({
-    startX: seed.x,
-    startY: seed.y,
-    gridSize: Math.min(gap.rect.width, gap.rect.height),
-    bounds: state.bounds,
-    blockers,
-    initialCellRatio: 0,
-    maxAspectRatio: null,
-    minReq: { width: state.options.minWidth, height: state.options.minHeight },
-  })
-
-  if (!rect) {
-    // Try additional seed points within the gap
-    const seeds = [
-      { x: gap.rect.x + state.options.minWidth / 2, y: gap.centerY },
-      {
-        x: gap.rect.x + gap.rect.width - state.options.minWidth / 2,
-        y: gap.centerY,
-      },
-      { x: gap.centerX, y: gap.rect.y + state.options.minHeight / 2 },
-      {
-        x: gap.centerX,
-        y: gap.rect.y + gap.rect.height - state.options.minHeight / 2,
-      },
-    ]
-
-    for (const altSeed of seeds) {
-      const altRect = expandRectFromSeed({
-        startX: altSeed.x,
-        startY: altSeed.y,
-        gridSize: Math.min(gap.rect.width, gap.rect.height),
-        bounds: state.bounds,
-        blockers,
-        initialCellRatio: 0,
-        maxAspectRatio: null,
-        minReq: {
-          width: state.options.minWidth,
-          height: state.options.minHeight,
-        },
-      })
-
-      if (altRect) {
-        return altRect
-      }
-    }
-
-    return null
-  }
-
-  return rect
-}
diff --git a/lib/solvers/rectdiff/gapfill/types.ts b/lib/solvers/rectdiff/gapfill/types.ts
deleted file mode 100644
index 59bdbf6..0000000
--- a/lib/solvers/rectdiff/gapfill/types.ts
+++ /dev/null
@@ -1,60 +0,0 @@
-// lib/solvers/rectdiff/gapfill/types.ts
-import type { XYRect, Placed3D } from "../types"
-
-export interface GapFillOptions {
-  /** Minimum width for gap-fill rectangles (can be smaller than main solver) */
-  minWidth: number
-  /** Minimum height for gap-fill rectangles */
-  minHeight: number
-  /** Maximum iterations to prevent infinite loops */
-  maxIterations: number
-  /** Target coverage percentage (0-1) to stop early */
-  targetCoverage: number
-  /** Grid resolution for gap detection */
-  scanResolution: number
-}
-
-export interface GapRegion {
-  /** Bounding box of the gap */
-  rect: XYRect
-  /** Z-layers where this gap exists */
-  zLayers: number[]
-  /** Center point for seeding */
-  centerX: number
-  centerY: number
-  /** Approximate area of the gap */
-  area: number
-}
-
-export interface GapFillState {
-  bounds: XYRect
-  layerCount: number
-  obstaclesByLayer: XYRect[][]
-  placed: Placed3D[]
-  placedByLayer: XYRect[][]
-  options: GapFillOptions
-
-  // Progress tracking
-  iteration: number
-  gapsFound: GapRegion[]
-  gapIndex: number
-  done: boolean
-
-  // Stats
-  initialGapCount: number
-  filledCount: number
-
-  // Four-stage visualization state
-  stage: "scan" | "select" | "expand" | "place"
-  currentGap: GapRegion | null
-  currentSeed: { x: number; y: number } | null
-  expandedRect: XYRect | null
-}
-
-/** Context for layer-based operations shared across gap fill functions */
-export interface LayerContext {
-  bounds: XYRect
-  layerCount: number
-  obstaclesByLayer: XYRect[][]
-  placedByLayer: XYRect[][]
-}
diff --git a/lib/solvers/rectdiff/subsolvers/GapFillSubSolver.ts b/lib/solvers/rectdiff/subsolvers/GapFillSubSolver.ts
deleted file mode 100644
index ecc6cdc..0000000
--- a/lib/solvers/rectdiff/subsolvers/GapFillSubSolver.ts
+++ /dev/null
@@ -1,253 +0,0 @@
-// lib/solvers/rectdiff/subsolvers/GapFillSubSolver.ts
-import { BaseSolver } from "@tscircuit/solver-utils"
-import type { GraphicsObject } from "graphics-debug"
-import type { XYRect, Placed3D } from "../types"
-import type {
-  GapFillState,
-  GapFillOptions,
-  LayerContext,
-} from "../gapfill/types"
-import {
-  initGapFillState,
-  stepGapFill,
-  getGapFillProgress,
-} from "../gapfill/engine"
-
-/**
- * A sub-solver that fills empty spaces (gaps) left by the main grid-based
- * placement algorithm.
- *
- * The preceding grid-based placement is fast but can leave irregular un-placed
- * areas. This solver maximizes board coverage by finding and filling these
- * gaps, which is critical for producing a high-quality capacity mesh.
- *
- * The core of the algorithm is its gap-detection phase. It works by first
- * collecting all unique x and y-coordinates from the edges of existing
- * obstacles and placed rectangles. This set of coordinates is supplemented by a
- * uniform grid based on the `scanResolution` parameter. Together, these form a
- * non-uniform grid of cells. The solver then tests the center of each cell for
- * coverage. Contiguous uncovered cells are merged into larger, maximal
- * rectangles, which become the candidate gaps to be filled.
- *
- * Once a prioritized list of gaps is generated (favoring larger, multi-layer
- * gaps), the solver iteratively attempts to fill each one by expanding a new
- * rectangle from a seed point until it collides with an existing boundary.
- *
- * The time complexity is dominated by the gap detection, which is approximately
- * O((N+1/R)^2 * B), where N is the number of objects, R is the scan
- * resolution, and B is the number of blockers. The algorithm's performance is
- * therefore highly dependent on the `scanResolution`. It is a heuristic
- * designed to be "fast enough" by avoiding a brute-force search, instead
- * relying on this grid-based cell checking to find significant gaps.
- */
-export class GapFillSubSolver extends BaseSolver {
-  private state: GapFillState
-  private layerCtx: LayerContext
-
-  constructor(params: {
-    placed: Placed3D[]
-    options?: Partial<GapFillOptions>
-    layerCtx: LayerContext
-  }) {
-    super()
-    this.layerCtx = params.layerCtx
-    this.state = initGapFillState(
-      {
-        placed: params.placed,
-        options: params.options,
-      },
-      params.layerCtx,
-    )
-  }
-
-  /**
-   * Execute one step of the gap fill algorithm.
-   * Each gap goes through four stages: scan for gaps, select a target gap,
-   * expand a rectangle from seed point, then place the final result.
-   */
-  override _step() {
-    const stillWorking = stepGapFill(this.state)
-    if (!stillWorking) {
-      this.solved = true
-    }
-  }
-
-  /**
-   * Calculate progress as a value between 0 and 1.
-   * Accounts for iterations, gaps processed, and current stage within each gap.
-   */
-  computeProgress(): number {
-    return getGapFillProgress(this.state)
-  }
-
-  /**
-   * Get all placed rectangles including original ones plus newly created gap-fill rectangles.
-   */
-  getPlaced(): Placed3D[] {
-    return this.state.placed
-  }
-
-  /**
-   * Get placed rectangles organized by Z-layer for efficient layer-based operations.
-   */
-  getPlacedByLayer(): XYRect[][] {
-    return this.state.placedByLayer
-  }
-
-  override getOutput() {
-    return {
-      placed: this.state.placed,
-      placedByLayer: this.state.placedByLayer,
-      filledCount: this.state.filledCount,
-    }
-  }
-
-  /** Zen visualization: show four-stage gap filling process. */
-  override visualize(): GraphicsObject {
-    const rects: NonNullable<GraphicsObject["rects"]> = []
-    const points: NonNullable<GraphicsObject["points"]> = []
-
-    // Board bounds (subtle)
-    rects.push({
-      center: {
-        x: this.layerCtx.bounds.x + this.layerCtx.bounds.width / 2,
-        y: this.layerCtx.bounds.y + this.layerCtx.bounds.height / 2,
-      },
-      width: this.layerCtx.bounds.width,
-      height: this.layerCtx.bounds.height,
-      fill: "none",
-      stroke: "#e5e7eb",
-      label: "",
-    })
-
-    switch (this.state.stage) {
-      case "scan": {
-        // Stage 1: Show scanning/detection phase with light blue overlay
-        rects.push({
-          center: {
-            x: this.layerCtx.bounds.x + this.layerCtx.bounds.width / 2,
-            y: this.layerCtx.bounds.y + this.layerCtx.bounds.height / 2,
-          },
-          width: this.layerCtx.bounds.width,
-          height: this.layerCtx.bounds.height,
-          fill: "#dbeafe",
-          stroke: "#3b82f6",
-          label: "scanning",
-        })
-        break
-      }
-
-      case "select": {
-        // Stage 2: Show the gap being targeted (red outline)
-        if (this.state.currentGap) {
-          rects.push({
-            center: {
-              x:
-                this.state.currentGap.rect.x +
-                this.state.currentGap.rect.width / 2,
-              y:
-                this.state.currentGap.rect.y +
-                this.state.currentGap.rect.height / 2,
-            },
-            width: this.state.currentGap.rect.width,
-            height: this.state.currentGap.rect.height,
-            fill: "#fecaca",
-            stroke: "#ef4444",
-            label: "target gap",
-          })
-
-          // Show the seed point
-          if (this.state.currentSeed) {
-            points.push({
-              x: this.state.currentSeed.x,
-              y: this.state.currentSeed.y,
-              color: "#dc2626",
-              label: "seed",
-            })
-          }
-        }
-        break
-      }
-
-      case "expand": {
-        // Stage 3: Show expansion attempt (yellow growing rectangle + seed)
-        if (this.state.currentGap) {
-          // Show gap outline (faded)
-          rects.push({
-            center: {
-              x:
-                this.state.currentGap.rect.x +
-                this.state.currentGap.rect.width / 2,
-              y:
-                this.state.currentGap.rect.y +
-                this.state.currentGap.rect.height / 2,
-            },
-            width: this.state.currentGap.rect.width,
-            height: this.state.currentGap.rect.height,
-            fill: "none",
-            stroke: "#f87171",
-            label: "",
-          })
-        }
-
-        if (this.state.currentSeed) {
-          // Show seed point
-          points.push({
-            x: this.state.currentSeed.x,
-            y: this.state.currentSeed.y,
-            color: "#f59e0b",
-            label: "expanding",
-          })
-        }
-
-        if (this.state.expandedRect) {
-          // Show expanded rectangle
-          rects.push({
-            center: {
-              x: this.state.expandedRect.x + this.state.expandedRect.width / 2,
-              y: this.state.expandedRect.y + this.state.expandedRect.height / 2,
-            },
-            width: this.state.expandedRect.width,
-            height: this.state.expandedRect.height,
-            fill: "#fef3c7",
-            stroke: "#f59e0b",
-            label: "expanding",
-          })
-        }
-        break
-      }
-
-      case "place": {
-        // Stage 4: Show final placed rectangle (green)
-        if (this.state.expandedRect) {
-          rects.push({
-            center: {
-              x: this.state.expandedRect.x + this.state.expandedRect.width / 2,
-              y: this.state.expandedRect.y + this.state.expandedRect.height / 2,
-            },
-            width: this.state.expandedRect.width,
-            height: this.state.expandedRect.height,
-            fill: "#bbf7d0",
-            stroke: "#22c55e",
-            label: "placed",
-          })
-        }
-        break
-      }
-    }
-
-    const stageNames = {
-      scan: "scanning",
-      select: "selecting",
-      expand: "expanding",
-      place: "placing",
-    }
-
-    return {
-      title: `GapFill (${stageNames[this.state.stage]}): ${this.state.filledCount} filled`,
-      coordinateSystem: "cartesian",
-      rects,
-      points,
-    }
-  }
-}