fix(thumbnails): report removals that fail and explain the quiet excepts (#320)

An old thumbnail the finishing move cannot remove (held open on Windows)
is now an error row of the job with its path, and logged; a failed copy's
temp that cannot go is logged with its path. Every except that only
passes says why, and the thread runners say their caller re-raises.

py/api/preview_location.py

@@ -531,7 +531,7 @@ def _timed(func, timeout):
     def run():
         try:
             result["value"] = func()
-        except BaseException as error:  # handed to the caller
+        except BaseException as error:  # _timed() re-raises it in the caller
             result["error"] = error
         finally:
             done.set()

py/api/preview_store.py

@@ -288,7 +288,7 @@ class _Probe:
         def run():
             try:
                 result["value"] = preview_location.folder_state(path, expected_id)
-            except BaseException as error:  # handed to the caller
+            except BaseException as error:  # check() re-raises it in the caller
                 result["error"] = error
             finally:
                 done.set()
@@ -428,7 +428,7 @@ def ensure_store(root, location=None, *, create=False):
             with store_io():
                 os.mkdir(store)
         except FileExistsError:
-            pass
+            pass  # already there: another writer made the key folder
         except OSError:
             return None
     return store
@@ -528,7 +528,7 @@ def make_parent(dst, location=None):
             try:
                 os.mkdir(current_folder)
             except FileExistsError:
-                pass
+                pass  # already there: another writer made this folder
             if preview_location.is_link_like(current_folder):
                 raise PermissionError(errno.EACCES, "a link in the thumbnail folder")
 

py/api/thumbnail_location.py

@@ -82,7 +82,7 @@ class ThumbnailLocationMixin:
                 if folder:
                     contained.append(str(folder))
         except ImportError:
-            pass
+            pass  # folder_paths exists only inside ComfyUI (tests run without it)
         try:
             contained.append(library_location.config_location()[1])
         except Exception:  # no data folder can be decided

py/api/thumbnail_move.py

@@ -529,10 +529,23 @@ class ThumbnailMoveMixin:
                         removed += 1
                     else:
                         complete = False
+                        relative = path.relative_to(store).as_posix()
+                        self.logger.warning(
+                            f"Could not remove the old thumbnail {path}; it is "
+                            "removed at the next start"
+                        )
                         if job is not None:
-                            job.log_line(
-                                "In use by another program; removed at the next "
-                                f"start: {name}"
+                            # D10A: a removal that failed is an error the job lists.
+                            job.record(
+                                "errors",
+                                {
+                                    "path": relative,
+                                    "root": store.name,
+                                    "detail": "In use by another program; removed "
+                                    "at the next start",
+                                },
+                                f"In use by another program; removed at the next "
+                                f"start: {store.name}/{relative}",
                             )
         files.remove_empty_folders(store)
         if job is not None and removed:

py/api/thumbnail_move_files.py

@@ -24,6 +24,7 @@ unlink (Windows).
 """
 
 import errno
+import logging
 import os
 import re
 import secrets
@@ -41,6 +42,8 @@ try:
 except ImportError:  # tests import the package top-level
     from utils.media_folders import in_trash_folder
 
+logger = logging.getLogger("prompt_manager.thumbnails")
+
 MOVE_TEMP = re.compile(r"\.pm-move-[0-9a-f]{8}\.tmp$")
 MOVE_TEMP_SUFFIX = ".pm-move-{token}.tmp"
 # The temp name adds this much to a destination path (".pm-move-xxxxxxxx.tmp").
@@ -206,7 +209,7 @@ def _make_folders(base, relative_dir, created):
             os.mkdir(current)
             created.append(str(current))
         except FileExistsError:
-            pass
+            pass  # already there: made by an earlier copy into this folder
         except OSError as error:
             if error.errno in (errno.ENOSPC, errno.EDQUOT, errno.EROFS):
                 raise FolderGone(str(error)) from error
@@ -263,10 +266,18 @@ def copy_one(source, destination, size, mtime_ns, created, *, long_paths=None):
 
 
 def _unlink(path):
+    """Remove a copy's temp file after a failed copy; True when it is gone.
+
+    One that cannot go (a Windows lock, permissions) is logged with its path;
+    the next start's temp sweep removes it (``.pm-move-*.tmp``)."""
     try:
         os.unlink(path)
-    except OSError:
-        pass
+        return True
+    except FileNotFoundError:
+        return True  # never written, or already renamed into place
+    except OSError as error:
+        logger.warning(f"Could not remove the move's temp file {path}: {error}")
+        return False
 
 
 # ── removing ─────────────────────────────────────────────────────────

py/api/thumbnail_move_plan.py

@@ -94,7 +94,7 @@ def _remove(path):
     try:
         os.unlink(path)
     except FileNotFoundError:
-        pass
+        pass  # already gone: removing it is the goal
 
 
 def _is_network(path):

tests/test_thumbnail_move.py

@@ -165,8 +165,10 @@ class TestMoveToAFolder(MoveCase):
         make_png(self.folder / "old-0123abcd" / "x_thumb.webp", size=(4, 4))
         preview_store.refresh()
         status, plan = await self.plan({"mode": "source"})
+        self.assertEqual(status, 200)
         self.assertEqual(plan["totals"]["unlisted_sources"], 1)
-        _plan, job = await self.move({"mode": "source"})
+        _, job = await self.move({"mode": "source"})
+        self.assertEqual(job.state, "finished", job.log)
         self.assertFalse(self.folder.exists())
 
     async def test_confirmation_and_a_stale_token(self):
@@ -296,6 +298,11 @@ class TestRestart(MoveCase):
             _plan, job = await self.move({"mode": "folder", "path": str(self.folder)})
         self.assertTrue(preview_store.setting().cleanup)
         self.assertTrue((self.old_store / "a_thumb.webp").exists())
+        # Each removal that failed is an error the job counts and lists by path.
+        rows = job.outcomes["errors"]
+        self.assertEqual(job.counters["errors"], len(rows))
+        self.assertIn("sub/b_thumb.webp", {row["path"] for row in rows})
+        self.assertTrue(all("next start" in row["detail"] for row in rows))
         job = await self.api.finish_thumbnail_move()
         await job.task
         self.assertEqual(job.title, "Move thumbnails (finishing)")
@@ -401,6 +408,14 @@ class TestFiles(unittest.TestCase):
         self.assertTrue(files.too_long("D:\\" + "x" * 240, long_paths=False))
         self.assertFalse(files.too_long("D:\\x", long_paths=False))
 
+    def test_a_failed_copys_temp_that_cannot_go_is_logged(self):
+        with patch.object(files.os, "unlink", side_effect=PermissionError("held")):
+            with self.assertLogs("prompt_manager.thumbnails", "WARNING") as logs:
+                self.assertFalse(files._unlink("D:/thumbs/.pm-move-1.tmp"))
+        self.assertIn(".pm-move-1.tmp", logs.output[0])
+        with patch.object(files.os, "unlink", side_effect=FileNotFoundError()):
+            self.assertTrue(files._unlink("gone"))
+
     def test_a_held_open_file_is_retried_then_left(self):
         waits = []
         error = OSError("in use")