tests: the display-title tests still passed the argument that went away

Three of them called derive_display_title(body, first_item). I updated the call
sites in src/ and not these — the integration lane and the linter both passed,
because a stale keyword argument is only a TypeError at the moment it runs.

Rewritten rather than deleted. The property the fallback existed to protect is
still real — a note that is only a checklist has to have a name — it is just
reached differently now: an item IS a body line, so the first one is simply the
first line with its marker stripped. The new cases pin the two edges that rule
introduces: an empty item must not name a note "", and a list of nothing but empty
items still has no name.

tests/test_notes.py

@@ -139,27 +139,32 @@ def test_derive_display_title_is_the_first_body_line():
     assert derive_display_title("\n   \nreal line\nmore") == "real line"
 
 
-def test_derive_display_title_falls_back_to_the_first_item():
-    # What step 2 bought: a note that is only a checklist still has a name. Without
-    # this it would have none at all, which is why the title could not go first.
-    assert derive_display_title("", "milk") == "milk"
-    assert derive_display_title("   \n  ", "  eggs  ") == "eggs"
-    # The body still wins when it has anything to say.
-    assert derive_display_title("shopping", "milk") == "shopping"
+def test_derive_display_title_names_a_list_only_note():
+    # The same property the old `first_item` fallback protected — a note that is only
+    # a checklist still has a name — reached a different way. Items ARE body lines now
+    # (M304), so the first one is simply the first line, with its marker stripped:
+    # calling the note "- [ ] milk" would show someone the storage instead of the note.
+    assert derive_display_title("- [ ] milk\n- [ ] eggs") == "milk"
+    assert derive_display_title("  * [x]   eggs  ") == "eggs"
+    # Prose still wins when it comes first, because it IS the first line.
+    assert derive_display_title("shopping\n\n- [ ] milk") == "shopping"
+    # An EMPTY item does not name the note "" — a half-typed list still has a name.
+    assert derive_display_title("- [ ]\n- [ ] eggs") == "eggs"
 
 
 def test_derive_display_title_empty():
     assert derive_display_title(None) == ""
     assert derive_display_title("") == ""
-    assert derive_display_title("   \n  ", None) == ""
-    assert derive_display_title("   \n  ", "   ") == ""
+    assert derive_display_title("   \n  ") == ""
+    # A list of nothing but empty items is still a note with no name.
+    assert derive_display_title("- [ ]\n- [ ]") == ""
 
 
 def test_derive_display_title_caps_length():
     long = "x" * 300
     assert derive_display_title(long) == "x" * 200
-    # the item fallback is capped on the same rule
-    assert derive_display_title("", long) == "x" * 200
+    # A first line that happens to be an item is capped on the same rule.
+    assert derive_display_title(f"- [ ] {long}") == "x" * 200
 
 
 def test_parse_tags():
@@ -502,13 +507,10 @@ def test_append_item_spacing():
     assert append_item("", "done", True) == "- [x] done"
 
 
-def test_strip_marker_and_display_title():
+def test_strip_marker():
     assert strip_marker("- [x] milk") == "milk"
     assert strip_marker("just prose") == "just prose"
-    # A list-only note is named by its first item, without the marker.
-    assert derive_display_title("- [ ] milk\n- [ ] eggs") == "milk"
-    # An EMPTY item does not name the note "" — a half-typed list still has a name.
-    assert derive_display_title("- [ ]\n- [ ] eggs") == "eggs"
+    assert strip_marker("- [ ]") == ""
 
 
 def test_the_migration_folds_exactly_like_the_app():