From d03909c54108d11f8ace581ba1faf5bf7b50b92e Mon Sep 17 00:00:00 2001
From: AlanRockefeller <alanrockefeller@gmail.com>
Date: Mon, 4 May 2026 12:01:16 -0700
Subject: [PATCH] Tightened the backup-token regex so only hyphen-delimited
 trailing backups match, which prevents a bare backup.jpg stem from collapsing
 into an empty group key.

---
 faststack/io/variants.py               |  2 +-
 faststack/tests/test_variants_logic.py | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/faststack/io/variants.py b/faststack/io/variants.py
index af02b7a..8922ef7 100644
--- a/faststack/io/variants.py
+++ b/faststack/io/variants.py
@@ -17,7 +17,7 @@
 )
 
 # Trailing `-backup(\d+)?` token at end of (stripped) stem.
-_BACKUP_TRAILING_RE = re.compile(r"(?:^|-)([Bb][Aa][Cc][Kk][Uu][Pp])(\d+)?$")
+_BACKUP_TRAILING_RE = re.compile(r"-([Bb][Aa][Cc][Kk][Uu][Pp])(\d+)?$")
 
 
 @dataclass
diff --git a/faststack/tests/test_variants_logic.py b/faststack/tests/test_variants_logic.py
index 5870a8d..4cabdbe 100644
--- a/faststack/tests/test_variants_logic.py
+++ b/faststack/tests/test_variants_logic.py
@@ -66,6 +66,17 @@ def test_backup_sorting(self):
         self.assertEqual(group.backup_paths[2].name, "img-backup2.jpg")
         self.assertEqual(group.backup_paths[10].name, "img-backup10.jpg")
 
+    def test_plain_backup_filename_is_not_variant(self):
+        """A literal backup.jpg filename should not create an empty group key."""
+        groups = build_variant_map([Path("backup.jpg")])
+
+        self.assertIn("backup", groups)
+        self.assertNotIn("", groups)
+
+        group = groups["backup"]
+        self.assertEqual(group.main_path.name, "backup.jpg")
+        self.assertEqual(group.backup_paths, {})
+
     def test_developed_backup_handling(self):
         """Verify developed backups are handled correctly."""
         # Policy: developed-backup is "developed" candidate, AND "backup" candidate.