Add regression tests for Frame.children mutation and parent=None removal

frame_children_mutation_test: validates remove(), property mutation via
stored refs, fill_color persistence, iteration mutation, pop(), and
while-loop clearing — with visual screenshot verification.

parent_none_removal_test: validates that setting .parent = None removes
children from Frame.children and scene.children, Entity.grid = None
removal, and Grid overlay children removal.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/regression/parent_none_removal_test.py

@@ -0,0 +1,172 @@
+"""Test that setting .parent = None removes child from parent's children.
+
+Verifies consistency between:
+- Frame.children.remove(child)
+- child.parent = None
+- Entity.grid = None
+"""
+import mcrfpy
+from mcrfpy import automation
+import sys
+
+PASS = True
+results = []
+
+def check(name, condition):
+    global PASS
+    if not condition:
+        PASS = False
+        results.append(f"  FAIL: {name}")
+    else:
+        results.append(f"  pass: {name}")
+
+# ============================================================
+# Test 1: child.parent = None removes from Frame.children
+# ============================================================
+
+scene = mcrfpy.Scene("test")
+mcrfpy.current_scene = scene
+
+box = mcrfpy.Frame(pos=(10,10), size=(200,200),
+                    fill_color=mcrfpy.Color(40,40,40))
+scene.children.append(box)
+
+cap1 = mcrfpy.Caption(text="child1", pos=(5,5))
+cap2 = mcrfpy.Caption(text="child2", pos=(5,25))
+cap3 = mcrfpy.Caption(text="child3", pos=(5,45))
+box.children.append(cap1)
+box.children.append(cap2)
+box.children.append(cap3)
+
+check("1a: initial count is 3", len(box.children) == 3)
+check("1b: cap2 parent is box", cap2.parent is not None)
+
+# Remove via parent = None
+cap2.parent = None
+check("1c: count after cap2.parent=None is 2", len(box.children) == 2)
+check("1d: cap2.parent is now None", cap2.parent is None)
+check("1e: remaining children are cap1,cap3",
+      box.children[0].text == "child1" and box.children[1].text == "child3")
+
+# ============================================================
+# Test 2: child.parent = None on Frame child (not Caption)
+# ============================================================
+
+inner = mcrfpy.Frame(pos=(10,100), size=(50,50),
+                      fill_color=mcrfpy.Color(255,0,0))
+box.children.append(inner)
+check("2a: count after adding inner frame is 3", len(box.children) == 3)
+
+inner.parent = None
+check("2b: count after inner.parent=None is 2", len(box.children) == 2)
+check("2c: inner.parent is None", inner.parent is None)
+
+# ============================================================
+# Test 3: child.parent = None on scene-level element
+# ============================================================
+
+top_frame = mcrfpy.Frame(pos=(300,10), size=(100,100),
+                          fill_color=mcrfpy.Color(0,255,0))
+scene.children.append(top_frame)
+initial_scene_count = len(scene.children)
+check("3a: top_frame added to scene", initial_scene_count >= 2)
+
+top_frame.parent = None
+check("3b: scene count decreased", len(scene.children) == initial_scene_count - 1)
+check("3c: top_frame.parent is None", top_frame.parent is None)
+
+# ============================================================
+# Test 4: while-loop clearing via parent = None
+# ============================================================
+
+container = mcrfpy.Frame(pos=(10,10), size=(200,200))
+scene.children.append(container)
+
+for i in range(5):
+    container.children.append(
+        mcrfpy.Caption(text=f"item{i}", pos=(0, i*20)))
+check("4a: container has 5 children", len(container.children) == 5)
+
+# Clear by setting parent = None on each child
+while len(container.children):
+    container.children[0].parent = None
+check("4b: container cleared via parent=None loop", len(container.children) == 0)
+
+# ============================================================
+# Test 5: Entity.grid = None removes from grid
+# ============================================================
+
+tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+grid = mcrfpy.Grid(grid_size=(10,10), texture=tex,
+                    pos=(0,0), size=(200,200))
+scene.children.append(grid)
+
+e1 = mcrfpy.Entity(grid_pos=(1,1), texture=tex, sprite_index=0)
+e2 = mcrfpy.Entity(grid_pos=(2,2), texture=tex, sprite_index=1)
+e3 = mcrfpy.Entity(grid_pos=(3,3), texture=tex, sprite_index=2)
+grid.entities.append(e1)
+grid.entities.append(e2)
+grid.entities.append(e3)
+
+check("5a: grid has 3 entities", len(grid.entities) == 3)
+
+e2.grid = None
+check("5b: grid has 2 entities after e2.grid=None", len(grid.entities) == 2)
+check("5c: e2.grid is None", e2.grid is None)
+
+# ============================================================
+# Test 6: Grid.children (overlay drawables) - parent = None
+# ============================================================
+
+overlay_cap = mcrfpy.Caption(text="overlay", pos=(5,5))
+grid.children.append(overlay_cap)
+check("6a: grid.children has 1 overlay", len(grid.children) == 1)
+
+overlay_cap.parent = None
+check("6b: grid.children empty after parent=None", len(grid.children) == 0)
+
+# ============================================================
+# Test 7: Visual verification with screenshots
+# ============================================================
+
+scene2 = mcrfpy.Scene("visual")
+parent = mcrfpy.Frame(pos=(10,10), size=(400,300),
+                       fill_color=mcrfpy.Color(40,40,40))
+scene2.children.append(parent)
+
+red = mcrfpy.Frame(pos=(10,10), size=(80,80),
+                    fill_color=mcrfpy.Color(255,0,0))
+green = mcrfpy.Frame(pos=(100,10), size=(80,80),
+                      fill_color=mcrfpy.Color(0,255,0))
+blue = mcrfpy.Frame(pos=(190,10), size=(80,80),
+                     fill_color=mcrfpy.Color(0,0,255))
+
+parent.children.append(red)
+parent.children.append(green)
+parent.children.append(blue)
+
+mcrfpy.current_scene = scene2
+mcrfpy.step(0.05)
+automation.screenshot("parent_none_7a_before.png")
+
+# Remove green via parent = None
+green.parent = None
+mcrfpy.step(0.05)
+automation.screenshot("parent_none_7b_after.png")
+
+check("7a: visual - green removed from children", len(parent.children) == 2)
+
+# ============================================================
+# Report
+# ============================================================
+
+print("=" * 50)
+print("parent=None removal test results:")
+for r in results:
+    print(r)
+print("=" * 50)
+if PASS:
+    print("PASS")
+else:
+    print("FAIL")
+sys.exit(0 if PASS else 1)