feat(presets): Add upstream-default preset and enhance demo preset

- Add upstream-default preset matching upstream mainline behavior:
  - Terminal display (not pygame)
  - No message overlay
  - Classic effects: noise, fade, glitch, firehose
  - Mixed positioning mode

- Enhance demo preset to showcase sideline features:
  - Hotswappable effects via effect plugins
  - LFO sensor modulation (oscillator sensor)
  - Mixed positioning mode
  - Message overlay with ntfy integration
  - Includes hud effect for visual feedback

- Update all presets to use mixed positioning mode
- Update completion script for --positioning flag

Usage:
  python -m mainline --preset upstream-default --display terminal
  python -m mainline --preset demo --display pygame

engine/app/main.py

@@ -265,6 +265,12 @@ def run_pipeline_mode_direct():
         )
 
     display = DisplayRegistry.create(display_name)
+
+    # Set positioning mode
+    if "--positioning" in sys.argv:
+        idx = sys.argv.index("--positioning")
+        if idx + 1 < len(sys.argv):
+            params.positioning = sys.argv[idx + 1]
     if not display:
         print(f"  \033[38;5;196mFailed to create display: {display_name}\033[0m")
         sys.exit(1)

engine/app/pipeline_runner.py

@@ -139,6 +139,16 @@ def run_pipeline_mode(preset_name: str = "demo"):
                 print("Error: Invalid viewport format. Use WxH (e.g., 40x15)")
                 sys.exit(1)
 
+    # Set positioning mode from command line or config
+    if "--positioning" in sys.argv:
+        idx = sys.argv.index("--positioning")
+        if idx + 1 < len(sys.argv):
+            params.positioning = sys.argv[idx + 1]
+    else:
+        from engine import config as app_config
+
+        params.positioning = app_config.get_config().positioning
+
     pipeline = Pipeline(config=preset.to_config())
 
     print("  \033[38;5;245mFetching content...\033[0m")

engine/config.py

@@ -130,6 +130,7 @@ class Config:
     script_fonts: dict[str, str] = field(default_factory=_get_platform_font_paths)
 
     display: str = "pygame"
+    positioning: str = "mixed"
     websocket: bool = False
     websocket_port: int = 8765
     theme: str = "green"
@@ -174,6 +175,7 @@ class Config:
             kata_glyphs="ﾊﾐﾋｰｳｼﾅﾓﾆｻﾜﾂｵﾘｱﾎﾃﾏｹﾒｴｶｷﾑﾕﾗｾﾈｽﾀﾇﾍ",
             script_fonts=_get_platform_font_paths(),
             display=_arg_value("--display", argv) or "terminal",
+            positioning=_arg_value("--positioning", argv) or "mixed",
             websocket="--websocket" in argv,
             websocket_port=_arg_int("--websocket-port", 8765, argv),
             theme=_arg_value("--theme", argv) or "green",

engine/pipeline/presets.py

@@ -60,6 +60,7 @@ class PipelinePreset:
     source_items: list[dict[str, Any]] | None = None  # For ListDataSource
     enable_metrics: bool = True  # Enable performance metrics collection
     enable_message_overlay: bool = False  # Enable ntfy message overlay
+    positioning: str = "mixed"  # Positioning mode: "absolute", "relative", "mixed"
 
     def to_params(self) -> PipelineParams:
         """Convert to PipelineParams (runtime configuration)."""
@@ -68,6 +69,7 @@ class PipelinePreset:
         params = PipelineParams()
         params.source = self.source
         params.display = self.display
+        params.positioning = self.positioning
         params.border = (
             self.border
             if isinstance(self.border, bool)
@@ -115,18 +117,38 @@ class PipelinePreset:
             source_items=data.get("source_items"),
             enable_metrics=data.get("enable_metrics", True),
             enable_message_overlay=data.get("enable_message_overlay", False),
+            positioning=data.get("positioning", "mixed"),
         )
 
 
 # Built-in presets
+# Upstream-default preset: Matches the default upstream Mainline operation
+UPSTREAM_PRESET = PipelinePreset(
+    name="upstream-default",
+    description="Upstream default operation (terminal display, legacy behavior)",
+    source="headlines",
+    display="terminal",
+    camera="scroll",
+    effects=["noise", "fade", "glitch", "firehose"],
+    enable_message_overlay=False,
+    positioning="mixed",
+)
+
+# Demo preset: Showcases hotswappable effects and sensors
+# This preset demonstrates the sideline features:
+# - Hotswappable effects via effect plugins
+# - Sensor integration (oscillator LFO for modulation)
+# - Mixed positioning mode
+# - Message overlay with ntfy integration
 DEMO_PRESET = PipelinePreset(
     name="demo",
-    description="Demo mode with effect cycling and camera modes",
+    description="Demo: Hotswappable effects, LFO sensor modulation, mixed positioning",
     source="headlines",
     display="pygame",
     camera="scroll",
-    effects=["noise", "fade", "glitch", "firehose"],
+    effects=["noise", "fade", "glitch", "firehose", "hud"],
     enable_message_overlay=True,
+    positioning="mixed",
 )
 
 UI_PRESET = PipelinePreset(
@@ -201,6 +223,7 @@ def _build_presets() -> dict[str, PipelinePreset]:
     # Add built-in presets as fallback (if not in YAML)
     builtins = {
         "demo": DEMO_PRESET,
+        "upstream-default": UPSTREAM_PRESET,
         "poetry": POETRY_PRESET,
         "pipeline": PIPELINE_VIZ_PRESET,
         "websocket": WEBSOCKET_PRESET,