fix(studio): a rule that plays nothing by design ends at its last block

Only a rule with no move yet ends in the placeholder; a rule that plays nothing on purpose,
which a later kind of block allows, keeps its last block as its end.

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

Author: sp00ktober

apps/studio/src/mhfu_studio/monster/panels/rows.py

@@ -142,6 +142,7 @@ def plan(
         links += [LinkSpec(a, graph.OUT, b, graph.IN) for a, b in zip(ids, ids[1:], strict=False)]
         if start is not None:
             links.append(LinkSpec(start.id, graph.WHILE, ids[0], graph.IN))
+        end: NodeSpec | None = None
         if p.play:
             by = played.get(p.play, ())
             end = NodeSpec(
@@ -155,7 +156,7 @@ def plan(
                 f"rule{'' if len(by) == 1 else 's'}: " + ", ".join(f"#{k}" for k in by),
                 ref=True,
             )
-        else:
+        elif rank is None:  # a rule that plays nothing by design ends at its last block
             end = NodeSpec(
                 f"{OPEN}{ids[-1]}",
                 PLACEHOLDER,
@@ -166,8 +167,9 @@ def plan(
                 " in the bar",
                 ref=True,
             )
-        nodes.append(end)
-        links.append(LinkSpec(ids[-1], graph.OUT, end.id, graph.PLAY))
+        if end is not None:
+            nodes.append(end)
+            links.append(LinkSpec(ids[-1], graph.OUT, end.id, graph.PLAY))
         if rank is None:
             news[p.blocks[0]] += 1
             frame, title = f"{FRAME}{NEW}:{p.blocks[0]}:{news[p.blocks[0]]}", UNFINISHED

apps/studio/tests/monster/ui/test_triggers.py

@@ -284,6 +284,12 @@ def test_a_rule_with_no_move_yet_ends_in_a_placeholder_after_the_others() -> Non
     assert plan.row_of("nope") is None
 
 
+def test_a_rule_that_plays_nothing_by_design_ends_at_its_last_block() -> None:
+    plan = rows.plan(trigger(Path(("b1", "b2"), "", None)), BLOCKS, NOTES, MOVES, {})
+    assert [n.id for n in plan.rows[0].nodes] == ["b1", "b2"] and len(plan.links) == 1
+    assert plan.rows[0].rank == 1
+
+
 def test_a_while_trigger_starts_from_its_move_once() -> None:
     t = trigger(Path(("b1",), "n", "m"), Path(("b3",), "n", "m"), section="move", name="m")
     plan = rows.plan(t, BLOCKS, NOTES, MOVES, {"n": (1, 2)})