LRC-LIB-LIBFOLDERS: Synchronize Folder says it is listing the folder instead of sitting at "0 of N"

The scan lists the whole folder tree before it checks a photo. On a large
folder on a network share that takes minutes, and the scan's row showed
"0 of 64085" with an empty bar all that while: it looked frozen. ✕ did
not stop the listing either.

- engine: SyncProgress counts the folders and files the walk listed and
  says when the listing is over; a folder note (walk::NoteFolder) now
  answers whether to go on, and a cancelled scan answers no.
- ui: while the folder is listed, the row has an indeterminate bar and
  reads "Listing folders: N folders, M files · folder" (all 13
  catalogs); the dialog says the same; then the photos checked are
  counted as before.

Co-Authored-By: Claude <noreply@anthropic.com>

docs/parity-checklist.md

@@ -1,6 +1,6 @@
 # Lightroom parity checklist
 
-> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-20 · **Change:** minor (LR-VIEW-ZOOM: only a full-size drag within 20 ms clears a slow-drag verdict) · **Target:** Adobe Lightroom Classic 15.5 / Lightroom 9.6
+> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-20 · **Change:** minor (LR-VIEW-ZOOM: only a full-size drag within 20 ms clears a slow-drag verdict; LRC-LIB-LIBFOLDERS, LR-BEHAV-BG-TASKS: Synchronize Folder's scan shows its folder listing and stops it on ✕; earlier: LRC-PRINT-PAGE: Print Page Options) · **Target:** Adobe Lightroom Classic 15.5 / Lightroom 9.6
 
 The measured, row-by-row checklist: one row per Lightroom feature, menu item and shortcut, what we
 have and what is missing. It answers *does the feature exist?* (feature breadth). Whether it is good
@@ -896,3 +896,4 @@ Latin stays upright. Advanced Japanese composition remains open. Regression cove
 | 2026-10-14 | patch | LRC-LIB-CATALOG-IMPORT: reconciled with upstream phased progress, cancellation kinds, WAL-only import, translations and current progress tracking. Status and summary counts unchanged. |
 | 2026-10-13 | minor | KEYC-COMPARE: `=` / `-` (also `+`) increase / decrease the grid thumbnail size (`view.thumbSizeUp` / `view.thumbSizeDown`, View menu), grids only; status unchanged (🟡) |
 | 2026-10-16 | patch | LR-META-XMP: a TIFF or JPEG imported beside a raw of its stem reads its own `<file>.xmp` and takes nothing from the raw's `IMG_0001.xmp`, whether it arrives with the raw or after it (a stem sidecar belongs to one file: a raw first, then the first by name); status unchanged (✅) |
+| 2026-10-16 | minor | LRC-LIB-LIBFOLDERS, LR-BEHAV-BG-TASKS: Synchronize Folder's scan row says how many folders and files it has listed while it lists the folder (an indeterminate bar, not "0 of N"), and ✕ stops the listing; statuses unchanged |

docs/whats-new.md

@@ -24,6 +24,15 @@
   another ratio (4 × 5, 2 × 3…) keeps it portrait, as in Lightroom, and a Custom ratio taller than wide gives a
   portrait crop.
 
+## 2026-10-16
+
+### Synchronize Folder shows that it is listing the folder
+- A folder with tens of thousands of photos, above all on a network share, can take minutes to list before
+  Synchronize Folder checks a single photo. Its row in the activity stack used to sit at "0 of 64085" with an empty
+  bar all that time, as if it had stopped. It now says how many folders and files it has listed so far, with a bar
+  that moves on its own, and then counts the photos it checks. The dialog says the same.
+- ✕ on the row stops the listing too, not only the checks after it.
+
 ## 2026-10-15
 
 ### Constrain Crop tightens the crop you see