Added plugin/add-on system

Plugins live in plugins/<name>/ with a manifest.json and a LabPlugin
subclass. Enabled/disabled in Settings > Plugins tab; state persists in
plugins/enabled.json and in .labdaq profiles (loading a profile
enables/disables plugins to match). Plugins can contribute toolbar
buttons, BaseDevice instances (auto-wired into acquisition pipeline),
custom signal filter classes, a settings widget, and profile state via
get_save_state/apply_save_state. Load errors now report the exact
failing stage (file not found, class missing, on_load crash).
Includes example plugin skeleton and docs/plugin-development.md.

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

1 files changed, 133 insertions, 0 deletions

diff --git a/plugins/base_plugin.py b/plugins/base_plugin.py
new file mode 100644
index 0000000..0eeb25f
--- /dev/null
+++ b/plugins/base_plugin.py
@@ -0,0 +1,133 @@
+"""
+plugins/base_plugin.py
+
+Abstract base class for all LabDAQ plugins.
+
+To create a plugin:
+  1. Create a directory under plugins/  e.g. plugins/my_plugin/
+  2. Add manifest.json with plugin metadata
+  3. Add plugin.py with a class subclassing LabPlugin
+  4. Enable in Settings → Plugins
+
+manifest.json schema:
+  {
+    "plugin_id":   "my_plugin",          required — unique snake_case id
+    "name":        "My Plugin",          required
+    "version":     "1.0.0",
+    "description": "What this does.",
+    "author":      "Name",
+    "entry_point": "plugin.MyPlugin"     module.ClassName relative to plugin dir
+  }
+
+Integration points (all optional — override only what you need):
+
+  get_toolbar_actions()  → list of PluginAction   toolbar buttons in main window
+  get_devices()          → list of BaseDevice      auto-added to registry + engine
+  get_filter_classes()   → {name: FilterBase cls}  custom signal pipeline filters
+  get_settings_widget()  → QWidget | None          shown in Settings > Plugins
+  get_save_state()       → dict                    persisted in .labdaq profiles
+  apply_save_state(dict)                            restore from profile
+"""
+
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from dataclasses import dataclass, field
+from typing import Any, Callable, Dict, List, Optional, Type
+
+from PyQt6.QtWidgets import QWidget
+
+
+# ── Context ───────────────────────────────────────────────────────────────────
+
+@dataclass
+class PluginContext:
+    """Core app objects handed to each plugin on load."""
+    registry:    Any   # devices.device_registry.DeviceRegistry
+    engine:      Any   # core.acquisition.AcquisitionEngine
+    processor:   Any   # core.signal_processor.SignalProcessor
+    main_window: Any   # ui.main_window.MainWindow  (QMainWindow)
+
+
+# ── Toolbar action descriptor ─────────────────────────────────────────────────
+
+@dataclass
+class PluginAction:
+    """Describes one toolbar button contributed by a plugin."""
+    label:     str
+    callback:  Callable[[bool], None]   # receives checked state
+    icon:      str  = ""
+    tooltip:   str  = ""
+    checkable: bool = False
+
+
+# ── Base class ────────────────────────────────────────────────────────────────
+
+class LabPlugin(ABC):
+    """
+    Abstract base for all LabDAQ plugins.
+
+    Subclass this, set the metadata properties, and override whatever
+    integration hooks your plugin needs.
+    """
+
+    # ── Metadata ──────────────────────────────────────────────────────────
+
+    @property
+    @abstractmethod
+    def plugin_id(self) -> str:
+        """Unique identifier matching manifest plugin_id."""
+
+    @property
+    @abstractmethod
+    def name(self) -> str:
+        """Human-readable display name."""
+
+    @property
+    def version(self) -> str:
+        return "1.0.0"
+
+    @property
+    def description(self) -> str:
+        return ""
+
+    @property
+    def author(self) -> str:
+        return ""
+
+    # ── Lifecycle ─────────────────────────────────────────────────────────
+
+    def on_load(self, context: PluginContext) -> None:
+        """Called when the plugin is enabled. Store context for later use."""
+
+    def on_unload(self) -> None:
+        """Called when the plugin is disabled. Release all resources."""
+
+    # ── Integration hooks ─────────────────────────────────────────────────
+
+    def get_toolbar_actions(self) -> List[PluginAction]:
+        """Toolbar buttons added to the main window when plugin is enabled."""
+        return []
+
+    def get_devices(self) -> list:
+        """BaseDevice instances contributed by this plugin.
+        They are automatically added to the DeviceRegistry and AcquisitionEngine."""
+        return []
+
+    def get_filter_classes(self) -> Dict[str, Type]:
+        """Custom signal filters: {filter_type_name: FilterBase subclass}.
+        Registered in SignalProcessor.FILTER_CLASSES when plugin loads."""
+        return {}
+
+    def get_settings_widget(self) -> Optional[QWidget]:
+        """Plugin-specific settings panel shown in Settings > Plugins."""
+        return None
+
+    # ── Profile persistence ───────────────────────────────────────────────
+
+    def get_save_state(self) -> Dict[str, Any]:
+        """Return a JSON-serialisable dict, saved with the .labdaq profile."""
+        return {}
+
+    def apply_save_state(self, state: Dict[str, Any]) -> None:
+        """Restore plugin state when a profile is loaded."""