feat(effects): add plugin architecture for visual effects

- Extract effects as fully decoupled plugins in engine/effects/
- Add EffectConfig, EffectContext dataclasses and EffectPlugin protocol
- Add EffectRegistry for plugin discovery and management
- Add EffectChain for ordered pipeline execution
- Move built-in effects to effects_plugins/ directory
- Add interactive effects config picker during startup
- Add NTFY command handler for /effects commands
- Add tests for effects system (24 new tests)
- Update AGENTS.md with effects plugin documentation
- Add conventional commits section to AGENTS.md

chore: add coverage.xml to .gitignore

engine/app.py

@@ -249,6 +249,110 @@ def pick_font_face():
     print()
 
 
+def pick_effects_config():
+    """Interactive picker for configuring effects pipeline."""
+    import effects_plugins
+    from engine.effects import get_effect_chain, get_registry
+
+    effects_plugins.discover_plugins()
+
+    registry = get_registry()
+    chain = get_effect_chain()
+    chain.set_order(["noise", "fade", "glitch", "firehose"])
+
+    effects = list(registry.list_all().values())
+    if not effects:
+        return
+
+    selected = 0
+    editing_intensity = False
+    intensity_value = 1.0
+
+    def _draw_effects_picker():
+        w = tw()
+        print(CLR, end="")
+        print("\033[1;1H", end="")
+        print("  \033[1;38;5;231mEFFECTS CONFIG\033[0m")
+        print(f"  \033[2;38;5;37m{'─' * (w - 4)}\033[0m")
+        print()
+
+        for i, effect in enumerate(effects):
+            prefix = " > " if i == selected else "   "
+            marker = "[*]" if effect.config.enabled else "[ ]"
+            if editing_intensity and i == selected:
+                print(
+                    f"{prefix}{marker} \033[1;38;5;82m{effect.name}\033[0m: intensity={intensity_value:.2f} (use +/- to adjust, Enter to confirm)"
+                )
+            else:
+                print(
+                    f"{prefix}{marker} {effect.name}: intensity={effect.config.intensity:.2f}"
+                )
+
+        print()
+        print(f"  \033[2;38;5;37m{'─' * (w - 4)}\033[0m")
+        print(
+            "  \033[38;5;245mControls: space=toggle on/off | +/-=adjust intensity | arrows=move | Enter=next effect | q=done\033[0m"
+        )
+
+    def _read_effects_key():
+        ch = sys.stdin.read(1)
+        if ch == "\x03":
+            return "interrupt"
+        if ch in ("\r", "\n"):
+            return "enter"
+        if ch == " ":
+            return "toggle"
+        if ch == "q":
+            return "quit"
+        if ch == "+" or ch == "=":
+            return "up"
+        if ch == "-" or ch == "_":
+            return "down"
+        if ch == "\x1b":
+            c1 = sys.stdin.read(1)
+            if c1 != "[":
+                return None
+            c2 = sys.stdin.read(1)
+            if c2 == "A":
+                return "up"
+            if c2 == "B":
+                return "down"
+            return None
+        return None
+
+    if not sys.stdin.isatty():
+        return
+
+    fd = sys.stdin.fileno()
+    old_settings = termios.tcgetattr(fd)
+    try:
+        tty.setcbreak(fd)
+        while True:
+            _draw_effects_picker()
+            key = _read_effects_key()
+
+            if key == "quit" or key == "enter":
+                break
+            elif key == "up" and editing_intensity:
+                intensity_value = min(1.0, intensity_value + 0.1)
+                effects[selected].config.intensity = intensity_value
+            elif key == "down" and editing_intensity:
+                intensity_value = max(0.0, intensity_value - 0.1)
+                effects[selected].config.intensity = intensity_value
+            elif key == "up":
+                selected = max(0, selected - 1)
+                intensity_value = effects[selected].config.intensity
+            elif key == "down":
+                selected = min(len(effects) - 1, selected + 1)
+                intensity_value = effects[selected].config.intensity
+            elif key == "toggle":
+                effects[selected].config.enabled = not effects[selected].config.enabled
+            elif key == "interrupt":
+                raise KeyboardInterrupt
+    finally:
+        termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
+
+
 def main():
     atexit.register(lambda: print(CURSOR_ON, end="", flush=True))
 
@@ -263,6 +367,7 @@ def main():
     print(CLR, end="")
     print(CURSOR_OFF, end="")
     pick_font_face()
+    pick_effects_config()
     w = tw()
     print()
     time.sleep(0.4)

engine/effects/__init__.py

@@ -0,0 +1,38 @@
+from engine.effects.chain import EffectChain
+from engine.effects.controller import handle_effects_command, show_effects_menu
+from engine.effects.legacy import (
+    fade_line,
+    firehose_line,
+    glitch_bar,
+    next_headline,
+    noise,
+    vis_trunc,
+)
+from engine.effects.registry import EffectRegistry, get_registry, set_registry
+from engine.effects.types import EffectConfig, EffectContext, PipelineConfig
+
+
+def get_effect_chain():
+    from engine.layers import get_effect_chain as _chain
+
+    return _chain()
+
+
+__all__ = [
+    "EffectChain",
+    "EffectRegistry",
+    "EffectConfig",
+    "EffectContext",
+    "PipelineConfig",
+    "get_registry",
+    "set_registry",
+    "get_effect_chain",
+    "handle_effects_command",
+    "show_effects_menu",
+    "fade_line",
+    "firehose_line",
+    "glitch_bar",
+    "noise",
+    "next_headline",
+    "vis_trunc",
+]

engine/effects/chain.py

@@ -0,0 +1,47 @@
+from engine.effects.registry import EffectRegistry
+from engine.effects.types import EffectContext
+
+
+class EffectChain:
+    def __init__(self, registry: EffectRegistry):
+        self._registry = registry
+        self._order: list[str] = []
+
+    def set_order(self, names: list[str]) -> None:
+        self._order = list(names)
+
+    def get_order(self) -> list[str]:
+        return self._order.copy()
+
+    def add_effect(self, name: str, position: int | None = None) -> bool:
+        if name not in self._registry.list_all():
+            return False
+        if position is None:
+            self._order.append(name)
+        else:
+            self._order.insert(position, name)
+        return True
+
+    def remove_effect(self, name: str) -> bool:
+        if name in self._order:
+            self._order.remove(name)
+            return True
+        return False
+
+    def reorder(self, new_order: list[str]) -> bool:
+        all_plugins = set(self._registry.list_all().keys())
+        if not all(name in all_plugins for name in new_order):
+            return False
+        self._order = list(new_order)
+        return True
+
+    def process(self, buf: list[str], ctx: EffectContext) -> list[str]:
+        result = list(buf)
+        for name in self._order:
+            plugin = self._registry.get(name)
+            if plugin and plugin.config.enabled:
+                try:
+                    result = plugin.process(result, ctx)
+                except Exception:
+                    plugin.config.enabled = False
+        return result

engine/effects/controller.py

@@ -0,0 +1,102 @@
+from engine.effects.registry import get_registry
+
+
+def _get_effect_chain():
+    from engine.layers import get_effect_chain as _chain
+
+    return _chain()
+
+
+def handle_effects_command(cmd: str) -> str:
+    """Handle /effects command from NTFY message.
+
+    Commands:
+        /effects list - list all effects and their status
+        /effects <name> on - enable an effect
+        /effects <name> off - disable an effect
+        /effects <name> intensity <0.0-1.0> - set intensity
+        /effects reorder <name1>,<name2>,... - reorder pipeline
+    """
+    parts = cmd.strip().split()
+    if not parts or parts[0] != "/effects":
+        return "Unknown command"
+
+    registry = get_registry()
+    chain = _get_effect_chain()
+
+    if len(parts) == 1 or parts[1] == "list":
+        result = ["Effects:"]
+        for name, plugin in registry.list_all().items():
+            status = "ON" if plugin.config.enabled else "OFF"
+            intensity = plugin.config.intensity
+            result.append(f"  {name}: {status} (intensity={intensity})")
+        if chain:
+            result.append(f"Order: {chain.get_order()}")
+        return "\n".join(result)
+
+    if len(parts) < 3:
+        return "Usage: /effects <name> on|off|intensity <value>"
+
+    effect_name = parts[1]
+    action = parts[2]
+
+    if effect_name not in registry.list_all():
+        return f"Unknown effect: {effect_name}"
+
+    if action == "on":
+        registry.enable(effect_name)
+        return f"Enabled: {effect_name}"
+
+    if action == "off":
+        registry.disable(effect_name)
+        return f"Disabled: {effect_name}"
+
+    if action == "intensity" and len(parts) >= 4:
+        try:
+            value = float(parts[3])
+            if not 0.0 <= value <= 1.0:
+                return "Intensity must be between 0.0 and 1.0"
+            plugin = registry.get(effect_name)
+            if plugin:
+                plugin.config.intensity = value
+                return f"Set {effect_name} intensity to {value}"
+        except ValueError:
+            return "Invalid intensity value"
+
+    if action == "reorder" and len(parts) >= 3:
+        new_order = parts[2].split(",")
+        if chain and chain.reorder(new_order):
+            return f"Reordered pipeline: {new_order}"
+        return "Failed to reorder pipeline"
+
+    return f"Unknown action: {action}"
+
+
+def show_effects_menu() -> str:
+    """Generate effects menu text for display."""
+    registry = get_registry()
+    chain = _get_effect_chain()
+
+    lines = [
+        "\033[1;38;5;231m=== EFFECTS MENU ===\033[0m",
+        "",
+        "Effects:",
+    ]
+
+    for name, plugin in registry.list_all().items():
+        status = "ON" if plugin.config.enabled else "OFF"
+        intensity = plugin.config.intensity
+        lines.append(f"  [{status:3}] {name}: intensity={intensity:.2f}")
+
+    if chain:
+        lines.append("")
+        lines.append(f"Pipeline order: {' -> '.join(chain.get_order())}")
+
+    lines.append("")
+    lines.append("Controls:")
+    lines.append("  /effects <name> on|off")
+    lines.append("  /effects <name> intensity <0.0-1.0>")
+    lines.append("  /effects reorder name1,name2,...")
+    lines.append("")
+
+    return "\n".join(lines)

engine/effects/registry.py

@@ -0,0 +1,59 @@
+from engine.effects.types import EffectConfig, EffectPlugin
+
+
+class EffectRegistry:
+    def __init__(self):
+        self._plugins: dict[str, EffectPlugin] = {}
+        self._discovered: bool = False
+
+    def register(self, plugin: EffectPlugin) -> None:
+        self._plugins[plugin.name] = plugin
+
+    def get(self, name: str) -> EffectPlugin | None:
+        return self._plugins.get(name)
+
+    def list_all(self) -> dict[str, EffectPlugin]:
+        return self._plugins.copy()
+
+    def list_enabled(self) -> list[EffectPlugin]:
+        return [p for p in self._plugins.values() if p.config.enabled]
+
+    def enable(self, name: str) -> bool:
+        plugin = self._plugins.get(name)
+        if plugin:
+            plugin.config.enabled = True
+            return True
+        return False
+
+    def disable(self, name: str) -> bool:
+        plugin = self._plugins.get(name)
+        if plugin:
+            plugin.config.enabled = False
+            return True
+        return False
+
+    def configure(self, name: str, config: EffectConfig) -> bool:
+        plugin = self._plugins.get(name)
+        if plugin:
+            plugin.configure(config)
+            return True
+        return False
+
+    def is_enabled(self, name: str) -> bool:
+        plugin = self._plugins.get(name)
+        return plugin.config.enabled if plugin else False
+
+
+_registry: EffectRegistry | None = None
+
+
+def get_registry() -> EffectRegistry:
+    global _registry
+    if _registry is None:
+        _registry = EffectRegistry()
+    return _registry
+
+
+def set_registry(registry: EffectRegistry) -> None:
+    global _registry
+    _registry = registry

engine/effects/types.py

@@ -0,0 +1,39 @@
+from dataclasses import dataclass, field
+from typing import Any
+
+
+@dataclass
+class EffectContext:
+    terminal_width: int
+    terminal_height: int
+    scroll_cam: int
+    ticker_height: int
+    mic_excess: float
+    grad_offset: float
+    frame_number: int
+    has_message: bool
+    items: list = field(default_factory=list)
+
+
+@dataclass
+class EffectConfig:
+    enabled: bool = True
+    intensity: float = 1.0
+    params: dict[str, Any] = field(default_factory=dict)
+
+
+class EffectPlugin:
+    name: str
+    config: EffectConfig
+
+    def process(self, buf: list[str], ctx: EffectContext) -> list[str]:
+        raise NotImplementedError
+
+    def configure(self, config: EffectConfig) -> None:
+        raise NotImplementedError
+
+
+@dataclass
+class PipelineConfig:
+    order: list[str] = field(default_factory=list)
+    effects: dict[str, EffectConfig] = field(default_factory=dict)

engine/layers.py

@@ -10,6 +10,8 @@ from datetime import datetime
 
 from engine import config
 from engine.effects import (
+    EffectChain,
+    EffectContext,
     fade_line,
     firehose_line,
     glitch_bar,
@@ -199,3 +201,60 @@ def render_firehose(items: list, w: int, fh: int, h: int) -> list[str]:
             fline = firehose_line(items, w)
             buf.append(f"\033[{scr_row};1H{fline}\033[K")
     return buf
+
+
+_effect_chain = None
+
+
+def init_effects() -> None:
+    """Initialize effect plugins and chain."""
+    global _effect_chain
+    from engine.effects import EffectChain, get_registry
+
+    registry = get_registry()
+
+    import effects_plugins
+
+    effects_plugins.discover_plugins()
+
+    chain = EffectChain(registry)
+    chain.set_order(["noise", "fade", "glitch", "firehose"])
+    _effect_chain = chain
+
+
+def process_effects(
+    buf: list[str],
+    w: int,
+    h: int,
+    scroll_cam: int,
+    ticker_h: int,
+    mic_excess: float,
+    grad_offset: float,
+    frame_number: int,
+    has_message: bool,
+    items: list,
+) -> list[str]:
+    """Process buffer through effect chain."""
+    if _effect_chain is None:
+        init_effects()
+
+    ctx = EffectContext(
+        terminal_width=w,
+        terminal_height=h,
+        scroll_cam=scroll_cam,
+        ticker_height=ticker_h,
+        mic_excess=mic_excess,
+        grad_offset=grad_offset,
+        frame_number=frame_number,
+        has_message=has_message,
+        items=items,
+    )
+    return _effect_chain.process(buf, ctx)
+
+
+def get_effect_chain() -> EffectChain | None:
+    """Get the effect chain instance."""
+    global _effect_chain
+    if _effect_chain is None:
+        init_effects()
+    return _effect_chain

engine/scroll.py

@@ -11,6 +11,7 @@ from engine import config
 from engine.frame import calculate_scroll_step
 from engine.layers import (
     apply_glitch,
+    process_effects,
     render_firehose,
     render_message_overlay,
     render_ticker_zone,
@@ -18,6 +19,8 @@ from engine.layers import (
 from engine.terminal import CLR
 from engine.viewport import th, tw
 
+USE_EFFECT_CHAIN = True
+
 
 def stream(items, ntfy_poller, mic_monitor):
     """Main render loop with four layers: message, ticker, scroll motion, firehose."""
@@ -42,6 +45,7 @@ def stream(items, ntfy_poller, mic_monitor):
     noise_cache = {}
     scroll_motion_accum = 0.0
     msg_cache = (None, None)
+    frame_number = 0
 
     while True:
         if queued >= config.HEADLINE_LIMIT and not active:
@@ -93,10 +97,24 @@ def stream(items, ntfy_poller, mic_monitor):
         buf.extend(ticker_buf)
 
         mic_excess = mic_monitor.excess
-        buf = apply_glitch(buf, ticker_buf_start, mic_excess, w)
 
-        firehose_buf = render_firehose(items, w, fh, h)
-        buf.extend(firehose_buf)
+        if USE_EFFECT_CHAIN:
+            buf = process_effects(
+                buf,
+                w,
+                h,
+                scroll_cam,
+                ticker_h,
+                mic_excess,
+                grad_offset,
+                frame_number,
+                msg is not None,
+                items,
+            )
+        else:
+            buf = apply_glitch(buf, ticker_buf_start, mic_excess, w)
+            firehose_buf = render_firehose(items, w, fh, h)
+            buf.extend(firehose_buf)
 
         if msg_overlay:
             buf.extend(msg_overlay)
@@ -106,6 +124,7 @@ def stream(items, ntfy_poller, mic_monitor):
 
         elapsed = time.monotonic() - t0
         time.sleep(max(0, config.FRAME_DT - elapsed))
+        frame_number += 1
 
     sys.stdout.write(CLR)
     sys.stdout.flush()