feat(demo): add HUD effect, resize handling, and tests

- Add HUD effect plugin showing FPS, effect name, intensity bar, pipeline
- Add pygame window resize handling (VIDEORESIZE event)
- Move HUD to end of chain so it renders on top
- Fix monitor stats API (returns dict, not object)
- Add tests/test_hud.py for HUD effect verification

effects_plugins/hud.py

@@ -14,9 +14,11 @@ class HudEffect(EffectPlugin):
         frame_time = 0.0
         if monitor:
             stats = monitor.get_stats()
-            if stats:
-                fps = stats.fps
-                frame_time = stats.avg_frame_time_ms
+            if stats and "pipeline" in stats:
+                frame_time = stats["pipeline"].get("avg_ms", 0.0)
+                frame_count = stats.get("frame_count", 0)
+                if frame_count > 0 and frame_time > 0:
+                    fps = 1000.0 / frame_time
 
         w = ctx.terminal_width
         h = ctx.terminal_height

engine/app.py

@@ -376,7 +376,7 @@ def run_demo_mode():
 
     registry = get_registry()
     chain = get_effect_chain()
-    chain.set_order(["hud", "noise", "fade", "glitch", "firehose"])
+    chain.set_order(["noise", "fade", "glitch", "firehose", "hud"])
 
     monitor = PerformanceMonitor()
     set_monitor(monitor)
@@ -512,6 +512,13 @@ def run_demo_mode():
             result = chain.process(buf, ctx)
             display.show(result)
 
+            new_w, new_h = display.get_dimensions()
+            if new_w != w or new_h != h:
+                w, h = new_w, new_h
+                scroll_step_interval = calculate_scroll_step(config.SCROLL_DUR, h)
+                active = []
+                noise_cache = {}
+
             frame_number += 1
             time.sleep(1 / 60)
 

engine/display/backends/pygame.py

@@ -36,6 +36,7 @@ class PygameDisplay:
         self._pygame = None
         self._screen = None
         self._font = None
+        self._resized = False
 
     def _get_font_path(self) -> str | None:
         """Get font path for rendering."""
@@ -110,7 +111,10 @@ class PygameDisplay:
         pygame.init()
         pygame.display.set_caption("Mainline")
 
-        self._screen = pygame.display.set_mode((self.window_width, self.window_height))
+        self._screen = pygame.display.set_mode(
+            (self.window_width, self.window_height),
+            pygame.RESIZABLE,
+        )
         self._pygame = pygame
         PygameDisplay._pygame_initialized = True
 
@@ -136,6 +140,12 @@ class PygameDisplay:
         for event in self._pygame.event.get():
             if event.type == self._pygame.QUIT:
                 sys.exit(0)
+            elif event.type == self._pygame.VIDEORESIZE:
+                self.window_width = event.w
+                self.window_height = event.h
+                self.width = max(1, self.window_width // self.cell_width)
+                self.height = max(1, self.window_height // self.cell_height)
+                self._resized = True
 
         self._screen.fill((0, 0, 0))
 
@@ -175,6 +185,16 @@ class PygameDisplay:
             self._screen.fill((0, 0, 0))
             self._pygame.display.flip()
 
+    def get_dimensions(self) -> tuple[int, int]:
+        """Get current terminal dimensions based on window size.
+
+        Returns:
+            (width, height) in character cells
+        """
+        if self._resized:
+            self._resized = False
+        return self.width, self.height
+
     def cleanup(self, quit_pygame: bool = True) -> None:
         """Cleanup display resources.
 

tests/test_hud.py

@@ -0,0 +1,107 @@
+
+from engine.effects.performance import PerformanceMonitor, set_monitor
+from engine.effects.types import EffectContext
+
+
+def test_hud_effect_adds_hud_lines():
+    """Test that HUD effect adds HUD lines to the buffer."""
+    from effects_plugins.hud import HudEffect
+
+    set_monitor(PerformanceMonitor())
+
+    hud = HudEffect()
+    hud.config.params["display_effect"] = "noise"
+    hud.config.params["display_intensity"] = 0.5
+
+    ctx = EffectContext(
+        terminal_width=80,
+        terminal_height=24,
+        scroll_cam=0,
+        ticker_height=24,
+        mic_excess=0.0,
+        grad_offset=0.0,
+        frame_number=0,
+        has_message=False,
+        items=[],
+    )
+
+    buf = [
+        "A" * 80,
+        "B" * 80,
+        "C" * 80,
+    ]
+
+    result = hud.process(buf, ctx)
+
+    assert len(result) >= 3, f"Expected at least 3 lines, got {len(result)}"
+
+    first_line = result[0]
+    assert "MAINLINE DEMO" in first_line, (
+        f"HUD not found in first line: {first_line[:50]}"
+    )
+
+    second_line = result[1]
+    assert "EFFECT:" in second_line, f"Effect line not found: {second_line[:50]}"
+
+    print("First line:", result[0])
+    print("Second line:", result[1])
+    if len(result) > 2:
+        print("Third line:", result[2])
+
+
+def test_hud_effect_shows_current_effect():
+    """Test that HUD displays the correct effect name."""
+    from effects_plugins.hud import HudEffect
+
+    set_monitor(PerformanceMonitor())
+
+    hud = HudEffect()
+    hud.config.params["display_effect"] = "fade"
+    hud.config.params["display_intensity"] = 0.75
+
+    ctx = EffectContext(
+        terminal_width=80,
+        terminal_height=24,
+        scroll_cam=0,
+        ticker_height=24,
+        mic_excess=0.0,
+        grad_offset=0.0,
+        frame_number=0,
+        has_message=False,
+        items=[],
+    )
+
+    buf = ["X" * 80]
+    result = hud.process(buf, ctx)
+
+    second_line = result[1]
+    assert "fade" in second_line, f"Effect name 'fade' not found in: {second_line}"
+
+
+def test_hud_effect_shows_intensity():
+    """Test that HUD displays intensity percentage."""
+    from effects_plugins.hud import HudEffect
+
+    set_monitor(PerformanceMonitor())
+
+    hud = HudEffect()
+    hud.config.params["display_effect"] = "glitch"
+    hud.config.params["display_intensity"] = 0.8
+
+    ctx = EffectContext(
+        terminal_width=80,
+        terminal_height=24,
+        scroll_cam=0,
+        ticker_height=24,
+        mic_excess=0.0,
+        grad_offset=0.0,
+        frame_number=0,
+        has_message=False,
+        items=[],
+    )
+
+    buf = ["Y" * 80]
+    result = hud.process(buf, ctx)
+
+    second_line = result[1]
+    assert "80%" in second_line, f"Intensity 80% not found in: {second_line}"