Copy progress: format sub-1 files/s readouts instead of rounding to 0

Previously the dialog used `Math.round(filesPerSecond)`, so any rate below 0.5 displayed as "0 files/s" — misleading whenever an MTP→SMB copy was streaming a big file at ~0.3 actual files/s. New `formatFilesPerSecond(rate)`:

- `< 3`: 1 decimal (`0.4 files/s`, `1.8 files/s`)
- Rounds to exactly 1: `1 file/s` (singular)
- `>= 3`: integer (`27 files/s`)
- Returns `null` when the rate rounds to 0.0 so the readout hides instead of lying

15 unit tests cover all cases including the singular boundary (0.95/1.04 round to 1, 1.05 flips to plural) and the 0.05 floor.

Author: vdavid

apps/desktop/src/lib/file-operations/transfer/TransferProgressDialog.svelte

@@ -20,6 +20,7 @@
         onScanPreviewError,
         onScanPreviewCancelled,
         formatDuration,
+        formatFilesPerSecond,
         DEFAULT_VOLUME_ID,
         type WriteProgressEvent,
         type WriteCompleteEvent,
@@ -1027,8 +1028,11 @@
                         {#if bytesPerSecond !== null && bytesPerSecond > 0}
                             <span class="progress-speed"><Size bytes={bytesPerSecond} />/s</span>
                         {/if}
-                        {#if filesPerSecond !== null && filesPerSecond > 0}
-                            <span class="progress-speed">{formatNumber(Math.round(filesPerSecond))} files/s</span>
+                        {#if filesPerSecond !== null}
+                            {@const filesPerSecLabel = formatFilesPerSecond(filesPerSecond)}
+                            {#if filesPerSecLabel !== null}
+                                <span class="progress-speed">{filesPerSecLabel}</span>
+                            {/if}
                         {/if}
                     </span>
                     {#if etaSecondsDisplay !== null}

apps/desktop/src/lib/tauri-commands/index.ts

@@ -169,6 +169,7 @@ export {
   onWriteConflict,
   formatBytes,
   formatDuration,
+  formatFilesPerSecond,
 } from './write-operations'
 export type { Event, UnlistenFn } from './write-operations'
 

apps/desktop/src/lib/tauri-commands/write-operations.test.ts

@@ -0,0 +1,74 @@
+import { describe, it, expect } from 'vitest'
+import { formatFilesPerSecond } from './write-operations'
+
+describe('formatFilesPerSecond', () => {
+  describe('rates below 3 (1 decimal)', () => {
+    it('formats sub-1 rates with 1 decimal', () => {
+      expect(formatFilesPerSecond(0.4)).toBe('0.4 files/s')
+    })
+
+    it('formats 1.x rates with 1 decimal (plural)', () => {
+      expect(formatFilesPerSecond(1.8)).toBe('1.8 files/s')
+    })
+
+    it('formats 2.x rates with 1 decimal', () => {
+      expect(formatFilesPerSecond(2.5)).toBe('2.5 files/s')
+    })
+
+    it('rounds to 1 decimal', () => {
+      expect(formatFilesPerSecond(0.44)).toBe('0.4 files/s')
+      expect(formatFilesPerSecond(0.45)).toBe('0.5 files/s')
+    })
+  })
+
+  describe('singular ("1 file/s")', () => {
+    it('uses singular when rate is exactly 1', () => {
+      expect(formatFilesPerSecond(1)).toBe('1 file/s')
+    })
+
+    it('uses singular when rate rounds to 1.0 from below', () => {
+      expect(formatFilesPerSecond(0.97)).toBe('1 file/s')
+    })
+
+    it('uses singular when rate rounds to 1.0 from above', () => {
+      expect(formatFilesPerSecond(1.04)).toBe('1 file/s')
+    })
+
+    it('switches to plural at 1.05', () => {
+      expect(formatFilesPerSecond(1.05)).toBe('1.1 files/s')
+    })
+  })
+
+  describe('rates at or above 3 (integer)', () => {
+    it('rounds to integer at exactly 3', () => {
+      expect(formatFilesPerSecond(3)).toBe('3 files/s')
+    })
+
+    it('rounds 27.4 down to 27', () => {
+      expect(formatFilesPerSecond(27.4)).toBe('27 files/s')
+    })
+
+    it('rounds 27.5 up to 28', () => {
+      expect(formatFilesPerSecond(27.5)).toBe('28 files/s')
+    })
+
+    it('handles large rates', () => {
+      expect(formatFilesPerSecond(1500)).toBe('1500 files/s')
+    })
+  })
+
+  describe('returns null when rate rounds to 0', () => {
+    it('returns null for exactly 0', () => {
+      expect(formatFilesPerSecond(0)).toBe(null)
+    })
+
+    it('returns null for rates < 0.05 (round to 0.0)', () => {
+      expect(formatFilesPerSecond(0.04)).toBe(null)
+      expect(formatFilesPerSecond(0.0001)).toBe(null)
+    })
+
+    it('returns "0.1 files/s" at the 0.05 boundary', () => {
+      expect(formatFilesPerSecond(0.05)).toBe('0.1 files/s')
+    })
+  })
+})

apps/desktop/src/lib/tauri-commands/write-operations.ts

@@ -216,6 +216,27 @@ export function formatBytes(bytes: number): string {
   return `${(bytes / (1024 * 1024 * 1024)).toFixed(1)} GB`
 }
 
+/**
+ * Formats a files-per-second rate for the progress dialog.
+ *
+ * - `< 3`: 1 decimal (`"0.4 files/s"`, `"1.8 files/s"`). Small values aren't useful as integers.
+ * - Rounds to exactly `1`: `"1 file/s"` (singular).
+ * - `>= 3`: integer (`"27 files/s"`). Decimal precision adds nothing at high rates.
+ *
+ * Returns `null` for rates that round to `0.0` so the caller can hide the readout
+ * entirely. The previous "0 files/s" display masked the real (sub-1) rates that
+ * heterogeneous-size copies produce.
+ */
+export function formatFilesPerSecond(rate: number): string | null {
+  if (rate < 3) {
+    const oneDecimal = Math.round(rate * 10) / 10
+    if (oneDecimal === 0) return null
+    if (oneDecimal === 1) return '1 file/s'
+    return `${oneDecimal.toFixed(1)} files/s`
+  }
+  return `${String(Math.round(rate))} files/s`
+}
+
 /**
  * Formats seconds as human-readable duration (like "2m 30s").
  */