Tag names have leading and trailing whitespace stripped

A padded name now finds the existing Tag instead of creating a
near-duplicate, and a whitespace-only name is rejected.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

wrolpi/tags.py

@@ -166,7 +166,9 @@ class Tag(ModelHelper, Base):
 
         # Replace forward-slash (linux directories) with Unicode Big Solidus (U+29F8)
         name = name.replace('/', '⧸')
-        name = INVALID_FILE_CHARS.sub('', name)
+        name = INVALID_FILE_CHARS.sub('', name).strip()
+        if not name:
+            raise InvalidTag('Tag name cannot be empty')
 
         if (other := self.get_by_name(session, name)) and other.id != self.id:
             raise InvalidTag('Tag name already taken')
@@ -266,6 +268,7 @@ class Tag(ModelHelper, Base):
         @warning: does not commit"""
         if name and id_:
             raise RuntimeError('Tag name and id cannot be used together')
+        name = name.strip() if name else name
 
         if tag := session.query(Tag).filter(Tag.id == id_).one_or_none():
             return tag

wrolpi/test/test_tags.py

@@ -406,6 +406,32 @@ async def test_invalid_tag(async_client, test_session, test_directory):
     with pytest.raises(UnknownTag):
         await tags.upsert_tag(test_session, 'Tag ID does not exist', '#fff', 1)
 
+    with pytest.raises(InvalidTag):
+        await tags.upsert_tag(test_session, '   ', '#fff')
+    with pytest.raises(InvalidTag):
+        tags.Tag.get_or_create_tag(test_session, ' \t')
+
+
+@pytest.mark.asyncio
+async def test_tag_name_whitespace_stripped(test_session, test_directory, tag_factory):
+    """Leading and trailing whitespace is never part of a Tag's name."""
+    await tags.upsert_tag(test_session, ' one  ', '#fff')
+    tag = tags.Tag.find_by_name(test_session, 'one')
+    assert tag.name == 'one'
+
+    # Renaming strips too.
+    await tags.upsert_tag(test_session, '\ttwo\n', '#fff', tag.id)
+    assert tag.name == 'two'
+
+    # A padded name finds the existing Tag rather than creating a near-duplicate.
+    assert tags.Tag.get_or_create_tag(test_session, 'two ').id == tag.id
+    assert tags.Tag.get_or_create_tag(test_session, ' three ').name == 'three'
+    assert {i.name for i in test_session.query(tags.Tag)} == {'two', 'three'}
+
+    # A padded name conflicts with an existing Tag.
+    with pytest.raises(InvalidTag):
+        await tags.upsert_tag(test_session, 'three ', '#fff', tag.id)
+
 
 @pytest.mark.asyncio
 async def test_tags_directory(test_session, test_directory, tag_factory, video_factory, example_pdf, await_switches,