diff --git a/config/scripts/trim-windows-icon-source.mjs b/config/scripts/trim-windows-icon-source.mjs
new file mode 100644
index 00000000000..90a1914e733
--- /dev/null
+++ b/config/scripts/trim-windows-icon-source.mjs
@@ -0,0 +1,219 @@
+#!/usr/bin/env node
+// Build the Windows multi-size ICO from the macOS 1024px render, trimming the
+// transparent Icon Composer "safe-area" inset so the glyph fills the canvas the
+// way other Windows taskbar/"Open with" icons do. Without this the glyph is only
+// ~83% of the frame and looks visibly small next to native apps (issue #5357).
+import { existsSync, readFileSync, writeFileSync } from 'node:fs'
+import { dirname, join } from 'node:path'
+import { fileURLToPath } from 'node:url'
+import { PNG } from 'pngjs'
+
+// Why: Windows renders the largest ICO frame at small sizes too, so the glyph
+// must fill nearly the whole canvas (~96%) to match native apps. A small uniform
+// margin keeps anti-aliased edges and the soft shadow from clipping at the border.
+export const ICON_CANVAS_MARGIN_RATIO = 0.02
+// Why: alpha below this is treated as background; the macOS render fades the
+// safe-area shadow to a few percent opacity, which must not count as glyph.
+const ALPHA_BACKGROUND_THRESHOLD = 16
+// Standard Windows ICO sizes, largest first (matches the prior ImageMagick set).
+export const ICO_FRAME_SIZES = [256, 128, 64, 48, 32, 16]
+
+export function decodePng(buffer) {
+  const png = PNG.sync.read(buffer)
+  return { width: png.width, height: png.height, data: png.data }
+}
+
+export function encodePng({ width, height, data }) {
+  const png = new PNG({ width, height })
+  data.copy(png.data)
+  return PNG.sync.write(png)
+}
+
+// Tightest box containing every pixel whose alpha exceeds the background
+// threshold. Returns null when the image is fully transparent.
+export function findOpaqueBounds({ width, height, data }, threshold = ALPHA_BACKGROUND_THRESHOLD) {
+  let minX = width
+  let minY = height
+  let maxX = -1
+  let maxY = -1
+  for (let y = 0; y < height; y++) {
+    for (let x = 0; x < width; x++) {
+      const alpha = data[(y * width + x) * 4 + 3]
+      if (alpha > threshold) {
+        if (x < minX) {
+          minX = x
+        }
+        if (x > maxX) {
+          maxX = x
+        }
+        if (y < minY) {
+          minY = y
+        }
+        if (y > maxY) {
+          maxY = y
+        }
+      }
+    }
+  }
+  if (maxX < 0) {
+    return null
+  }
+  return { minX, minY, maxX, maxY, width: maxX - minX + 1, height: maxY - minY + 1 }
+}
+
+// Crop an RGBA image to the given inclusive bounds.
+export function cropImage({ width, data }, bounds) {
+  const cropWidth = bounds.width
+  const cropHeight = bounds.height
+  const out = Buffer.alloc(cropWidth * cropHeight * 4)
+  for (let y = 0; y < cropHeight; y++) {
+    const srcRow = (bounds.minY + y) * width + bounds.minX
+    const srcStart = srcRow * 4
+    out.set(data.subarray(srcStart, srcStart + cropWidth * 4), y * cropWidth * 4)
+  }
+  return { width: cropWidth, height: cropHeight, data: out }
+}
+
+// Center the (already-trimmed) glyph on a transparent square canvas, leaving a
+// small uniform margin so edges/shadow do not clip. The square side is the
+// glyph's longer dimension grown by the margin so the glyph keeps its shape.
+export function squareWithMargin(image, marginRatio = ICON_CANVAS_MARGIN_RATIO) {
+  const longSide = Math.max(image.width, image.height)
+  const side = Math.round(longSide / (1 - 2 * marginRatio))
+  const data = Buffer.alloc(side * side * 4)
+  const offsetX = Math.floor((side - image.width) / 2)
+  const offsetY = Math.floor((side - image.height) / 2)
+  for (let y = 0; y < image.height; y++) {
+    const srcStart = y * image.width * 4
+    const dstStart = ((offsetY + y) * side + offsetX) * 4
+    data.set(image.data.subarray(srcStart, srcStart + image.width * 4), dstStart)
+  }
+  return { width: side, height: side, data }
+}
+
+// Area-averaging (box filter) resize with premultiplied alpha so transparent
+// edges do not bleed dark fringes. Used to downscale to each ICO frame size.
+export function resizeImage(image, targetWidth, targetHeight) {
+  const { width: srcW, height: srcH, data: src } = image
+  const out = Buffer.alloc(targetWidth * targetHeight * 4)
+  const scaleX = srcW / targetWidth
+  const scaleY = srcH / targetHeight
+  for (let ty = 0; ty < targetHeight; ty++) {
+    const sy0 = ty * scaleY
+    const sy1 = (ty + 1) * scaleY
+    const y0 = Math.floor(sy0)
+    const y1 = Math.min(srcH, Math.ceil(sy1))
+    for (let tx = 0; tx < targetWidth; tx++) {
+      const sx0 = tx * scaleX
+      const sx1 = (tx + 1) * scaleX
+      const x0 = Math.floor(sx0)
+      const x1 = Math.min(srcW, Math.ceil(sx1))
+      let rSum = 0
+      let gSum = 0
+      let bSum = 0
+      let aSum = 0
+      let weightSum = 0
+      for (let sy = y0; sy < y1; sy++) {
+        const wy = Math.min(sy1, sy + 1) - Math.max(sy0, sy)
+        for (let sx = x0; sx < x1; sx++) {
+          const wx = Math.min(sx1, sx + 1) - Math.max(sx0, sx)
+          const weight = wx * wy
+          if (weight <= 0) {
+            continue
+          }
+          const idx = (sy * srcW + sx) * 4
+          const alpha = src[idx + 3]
+          const premul = (alpha / 255) * weight
+          rSum += src[idx] * premul
+          gSum += src[idx + 1] * premul
+          bSum += src[idx + 2] * premul
+          aSum += alpha * weight
+          weightSum += weight
+        }
+      }
+      const dst = (ty * targetWidth + tx) * 4
+      if (weightSum === 0 || aSum === 0) {
+        out[dst] = 0
+        out[dst + 1] = 0
+        out[dst + 2] = 0
+        out[dst + 3] = 0
+        continue
+      }
+      const alphaAvg = aSum / weightSum
+      const colorDivisor = alphaAvg / 255
+      out[dst] = Math.round(rSum / weightSum / colorDivisor)
+      out[dst + 1] = Math.round(gSum / weightSum / colorDivisor)
+      out[dst + 2] = Math.round(bSum / weightSum / colorDivisor)
+      out[dst + 3] = Math.round(alphaAvg)
+    }
+  }
+  return { width: targetWidth, height: targetHeight, data: out }
+}
+
+// Encode a Windows .ico holding PNG-compressed frames (supported since Vista,
+// the format ImageMagick's auto-resize also emits for the larger sizes).
+export function encodeIco(frames) {
+  const header = Buffer.alloc(6)
+  header.writeUInt16LE(0, 0) // reserved
+  header.writeUInt16LE(1, 2) // type 1 = icon
+  header.writeUInt16LE(frames.length, 4)
+
+  const directory = Buffer.alloc(frames.length * 16)
+  let dataOffset = 6 + frames.length * 16
+  const payloads = []
+  frames.forEach((frame, index) => {
+    const png = encodePng(frame)
+    payloads.push(png)
+    const entry = index * 16
+    // Width/height of 256 are stored as 0 per the ICO spec.
+    directory.writeUInt8(frame.width >= 256 ? 0 : frame.width, entry)
+    directory.writeUInt8(frame.height >= 256 ? 0 : frame.height, entry + 1)
+    directory.writeUInt8(0, entry + 2) // color count (0 = truecolor)
+    directory.writeUInt8(0, entry + 3) // reserved
+    directory.writeUInt16LE(1, entry + 4) // color planes
+    directory.writeUInt16LE(32, entry + 6) // bits per pixel
+    directory.writeUInt32LE(png.length, entry + 8)
+    directory.writeUInt32LE(dataOffset, entry + 12)
+    dataOffset += png.length
+  })
+
+  return Buffer.concat([header, directory, ...payloads])
+}
+
+// Trim the safe-area inset from a 1024px source render and produce a filled
+// multi-size ICO buffer. Exported so the regression test can drive it directly.
+export function buildWindowsIcoFromPng(sourcePngBuffer, sizes = ICO_FRAME_SIZES) {
+  const source = decodePng(sourcePngBuffer)
+  const bounds = findOpaqueBounds(source)
+  if (!bounds) {
+    throw new Error('Source icon is fully transparent; cannot trim safe-area inset.')
+  }
+  const trimmed = cropImage(source, bounds)
+  const filled = squareWithMargin(trimmed)
+  const frames = sizes.map((size) => resizeImage(filled, size, size))
+  return encodeIco(frames)
+}
+
+function resolveDefaultPaths() {
+  const scriptDir = dirname(fileURLToPath(import.meta.url))
+  const projectDir = dirname(dirname(scriptDir))
+  return {
+    sourcePng: join(projectDir, 'resources', 'build', 'icon.png'),
+    outputIco: join(projectDir, 'resources', 'build', 'icon.ico')
+  }
+}
+
+function main() {
+  const { sourcePng, outputIco } = resolveDefaultPaths()
+  if (!existsSync(sourcePng)) {
+    console.error(`Error: source PNG not found at ${sourcePng}`)
+    process.exit(1)
+  }
+  const ico = buildWindowsIcoFromPng(readFileSync(sourcePng))
+  writeFileSync(outputIco, ico)
+  console.log(`  -> ${outputIco} (filled multi-size ICO, safe-area inset trimmed)`)
+}
+
+if (import.meta.url === `file://${process.argv[1]}` || process.argv[1]?.endsWith('trim-windows-icon-source.mjs')) {
+  main()
+}
diff --git a/config/scripts/trim-windows-icon-source.test.mjs b/config/scripts/trim-windows-icon-source.test.mjs
new file mode 100644
index 00000000000..a52f0c49f2c
--- /dev/null
+++ b/config/scripts/trim-windows-icon-source.test.mjs
@@ -0,0 +1,114 @@
+import { readFileSync } from 'node:fs'
+import { dirname, join } from 'node:path'
+import { fileURLToPath } from 'node:url'
+import { describe, expect, it } from 'vitest'
+import { PNG } from 'pngjs'
+import {
+  buildWindowsIcoFromPng,
+  cropImage,
+  findOpaqueBounds,
+  resizeImage,
+  squareWithMargin
+} from './trim-windows-icon-source.mjs'
+
+const scriptDir = dirname(fileURLToPath(import.meta.url))
+const projectDir = dirname(dirname(scriptDir))
+const buildDir = join(projectDir, 'resources', 'build')
+
+// Why: Windows scales the largest ICO frame down for the taskbar/"Open with"
+// list, so the glyph must fill most of that frame to match native apps. The
+// macOS safe-area inset left it at ~83%, which is the visible defect (#5357).
+const MIN_GLYPH_FILL_FRACTION = 0.92
+
+function largestIcoFrame(icoBuffer) {
+  const count = icoBuffer.readUInt16LE(4)
+  let best = null
+  for (let i = 0; i < count; i++) {
+    const entry = 6 + i * 16
+    let width = icoBuffer.readUInt8(entry)
+    if (width === 0) {
+      width = 256
+    }
+    const byteLength = icoBuffer.readUInt32LE(entry + 8)
+    const imageOffset = icoBuffer.readUInt32LE(entry + 12)
+    if (!best || width > best.width) {
+      best = { width, byteLength, imageOffset }
+    }
+  }
+  return best
+}
+
+function decodeIcoFrame(icoBuffer, frame) {
+  const payload = icoBuffer.subarray(frame.imageOffset, frame.imageOffset + frame.byteLength)
+  const isPng =
+    payload[0] === 0x89 && payload[1] === 0x50 && payload[2] === 0x4e && payload[3] === 0x47
+  if (!isPng) {
+    throw new Error('Expected PNG-compressed ICO frame')
+  }
+  const png = PNG.sync.read(Buffer.from(payload))
+  return { width: png.width, height: png.height, data: png.data }
+}
+
+function glyphFillFraction(image) {
+  const bounds = findOpaqueBounds(image)
+  if (!bounds) {
+    return 0
+  }
+  return Math.max(bounds.width, bounds.height) / Math.max(image.width, image.height)
+}
+
+describe('Windows ICO glyph fill', () => {
+  it('committed resources/build/icon.ico fills the canvas', () => {
+    const ico = readFileSync(join(buildDir, 'icon.ico'))
+    const frame = decodeIcoFrame(ico, largestIcoFrame(ico))
+    expect(glyphFillFraction(frame)).toBeGreaterThanOrEqual(MIN_GLYPH_FILL_FRACTION)
+  })
+
+  it('regenerating from the macOS render fills the canvas', () => {
+    const sourcePng = readFileSync(join(buildDir, 'icon.png'))
+    const ico = buildWindowsIcoFromPng(sourcePng)
+    const frame = decodeIcoFrame(ico, largestIcoFrame(ico))
+    expect(glyphFillFraction(frame)).toBeGreaterThanOrEqual(MIN_GLYPH_FILL_FRACTION)
+  })
+})
+
+describe('trim pipeline', () => {
+  function solidSquareWithInset(canvas, glyph) {
+    const data = Buffer.alloc(canvas * canvas * 4)
+    const offset = Math.floor((canvas - glyph) / 2)
+    for (let y = 0; y < glyph; y++) {
+      for (let x = 0; x < glyph; x++) {
+        const idx = ((offset + y) * canvas + (offset + x)) * 4
+        data[idx] = 200
+        data[idx + 1] = 100
+        data[idx + 2] = 50
+        data[idx + 3] = 255
+      }
+    }
+    return { width: canvas, height: canvas, data }
+  }
+
+  it('finds the opaque glyph bounds and ignores transparent inset', () => {
+    const image = solidSquareWithInset(100, 60)
+    const bounds = findOpaqueBounds(image)
+    expect(bounds).toEqual({ minX: 20, minY: 20, maxX: 79, maxY: 79, width: 60, height: 60 })
+  })
+
+  it('crops to the glyph then re-squares with a small margin', () => {
+    const image = solidSquareWithInset(100, 60)
+    const cropped = cropImage(image, findOpaqueBounds(image))
+    expect(cropped.width).toBe(60)
+    const squared = squareWithMargin(cropped, 0.04)
+    // Glyph (60) plus ~4% margin per side keeps it near-full-bleed.
+    expect(glyphFillFraction(squared)).toBeGreaterThanOrEqual(0.9)
+    expect(squared.width).toBe(squared.height)
+  })
+
+  it('downscales without leaving the glyph undersized', () => {
+    const image = solidSquareWithInset(256, 200)
+    const filled = squareWithMargin(cropImage(image, findOpaqueBounds(image)))
+    const small = resizeImage(filled, 32, 32)
+    expect(small.width).toBe(32)
+    expect(glyphFillFraction(small)).toBeGreaterThanOrEqual(0.9)
+  })
+})
diff --git a/resources/build/icon.ico b/resources/build/icon.ico
index 88093983a0d..d73c40f4af3 100644
Binary files a/resources/build/icon.ico and b/resources/build/icon.ico differ
diff --git a/resources/icon-source/generate.sh b/resources/icon-source/generate.sh
index d8377345a51..3ea4d72c78e 100755
--- a/resources/icon-source/generate.sh
+++ b/resources/icon-source/generate.sh
@@ -70,8 +70,14 @@ echo "  -> resources/build/icon.png (1024x1024)"
 sips -s format png --resampleWidth 256 "$TMP_DIR/icon.icns" --out "$RESOURCES_DIR/icon.png" >/dev/null 2>&1
 echo "  -> resources/icon.png (256x256)"
 
-# Generate .ico for Windows (proper ICO format with multiple sizes)
-"$MAGICK_BIN" "$BUILD_DIR/icon.png" -define icon:auto-resize=256,128,64,48,32,16 "$BUILD_DIR/icon.ico"
-echo "  -> resources/build/icon.ico (multi-size ICO via ImageMagick)"
+# Generate .ico for Windows. Icon Composer keeps the macOS safe-area inset in
+# the 1024px render, but Windows scales the largest ICO frame down for the
+# taskbar/"Open with" list without compensating, so the glyph looks small next
+# to native apps (issue #5357). Delegate to the pngjs trim script so the
+# committed ICO always matches it: it trims the transparent inset, re-squares
+# with a small 2% margin, and emits the filled multi-size ICO. Node + pngjs are
+# already repo dependencies, so this also works where ImageMagick is unavailable.
+node "$PROJECT_DIR/config/scripts/trim-windows-icon-source.mjs"
+echo "  -> resources/build/icon.ico (trimmed, filled multi-size ICO)"
 
 echo "Done! Icons generated in resources/build/ and resources/"