feat(images): duplicate cleanup keeps images' own categories (#332)

The kept copy's own category wins; a kept copy without one receives the
removed copy's, keyed by the deepest output source holding each file.
The removed copy's row is never deleted, so a give-back or a failed
delete loses nothing. The job log reports how many were kept.

py/api/duplicate_files.py

@@ -589,6 +589,7 @@ class DuplicateFilesMixin:
         spellings = await self._run_in_executor(self._source_spellings)
         removed, failure, keepers = 0, None, {}
         totals = dict.fromkeys(("moved", "merged", "favorites", "tags", "review"), 0)
+        totals["categories"] = 0  # image categories kept on the kept copies (#332)
         for done, target in enumerate(targets, start=1):
             if failure is not None:
                 self._record_target(job, "kept", target, NOT_ATTEMPTED)
@@ -635,6 +636,9 @@ class DuplicateFilesMixin:
             job.log_line(
                 f"Added {_plural(totals['tags'], 'image tag')} to the kept copies"
             )
+        if totals.get("categories"):
+            kept = _plural(totals["categories"], "image category", "image categories")
+            job.log_line(f"Kept {kept} on the kept copies")
         if totals["review"]:
             job.log_line(
                 f"Settled {_plural(totals['review'], 'Needs review item')} "

py/api/duplicate_spellings.py

@@ -18,7 +18,7 @@ Blocking: each lookup stats the file's folders once (cached).
 import os
 from pathlib import Path
 
-from .images import _favorite_relative_key, _favorite_root_key
+from .images import _favorite_relative_key, _favorite_root_key, image_category_key
 
 
 def _identity(path):
@@ -78,6 +78,15 @@ class Spellings:
                 )
         return spelled
 
+    @property
+    def listed_roots(self):
+        """The listed roots (the output sources), in order."""
+        return [root for root, _identity in self._listed]
+
+    def category_key(self, path):
+        """*path*'s image category file key (#332), or None outside every source."""
+        return image_category_key(self.listed_roots, path)
+
     def favorites(self, path):
         """``{listed root: path below it (POSIX)}`` for each listed root holding it."""
         path = os.path.abspath(str(path))
@@ -125,9 +134,23 @@ def copy_move(target, kept_stat, spellings):
         "targets": targets,
         "kept_path": target["keeper_abs"],
         "favorites": favorites,
+        "categories": _category_pairs(target, spellings),
         "removed_locator": target["locator"],
         "kept_locator": target["keeper_locator"],
         "sha256": target["hash"],
         "kept_size": kept_stat.st_size,
         "kept_mtime_ns": kept_stat.st_mtime_ns,
     }
+
+
+def _category_pairs(target, spellings):
+    """``[(removed file key, kept file key)]`` for the image category (#332).
+
+    From the two absolute paths, not the favorites tuples: those follow the
+    listed root, which differs from the file key when sources nest.
+    """
+    removed = spellings.category_key(target["abs"])
+    kept = spellings.category_key(target["keeper_abs"])
+    if removed is None or kept is None:
+        return []
+    return [(removed, kept)]