feat: add filesystem watcher for automatic user plugin hot-reload

Watch ~/.config/owlry/plugins/ for changes using notify-debouncer-mini
(500ms debounce) and trigger a full runtime reload on file modifications.
Respects OWLRY_SKIP_RUNTIMES=1 to skip watcher in tests.

crates/owlry-core/src/plugins/mod.rs

@@ -26,6 +26,7 @@ pub mod manifest;
 pub mod native_loader;
 pub mod registry;
 pub mod runtime_loader;
+pub mod watcher;
 
 // Lua-specific modules (require mlua)
 #[cfg(feature = "lua")]

crates/owlry-core/src/plugins/watcher.rs

@@ -0,0 +1,96 @@
+//! Filesystem watcher for user plugin hot-reload
+//!
+//! Watches `~/.config/owlry/plugins/` for changes and triggers
+//! runtime reload when plugin files are modified.
+
+use std::path::PathBuf;
+use std::sync::{Arc, RwLock};
+use std::thread;
+use std::time::Duration;
+
+use log::{info, warn};
+use notify_debouncer_mini::{new_debouncer, DebouncedEventKind};
+
+use crate::providers::ProviderManager;
+
+/// Start watching the user plugins directory for changes.
+///
+/// Spawns a background thread that monitors the directory and triggers
+/// a full runtime reload on any file change. Returns immediately.
+///
+/// Respects `OWLRY_SKIP_RUNTIMES=1` — returns early if set.
+pub fn start_watching(pm: Arc<RwLock<ProviderManager>>) {
+    if std::env::var("OWLRY_SKIP_RUNTIMES").is_ok() {
+        info!("OWLRY_SKIP_RUNTIMES set, skipping file watcher");
+        return;
+    }
+
+    let plugins_dir = match crate::paths::plugins_dir() {
+        Some(d) => d,
+        None => {
+            info!("No plugins directory configured, skipping file watcher");
+            return;
+        }
+    };
+
+    if !plugins_dir.exists()
+        && std::fs::create_dir_all(&plugins_dir).is_err()
+    {
+        warn!(
+            "Failed to create plugins directory: {}",
+            plugins_dir.display()
+        );
+        return;
+    }
+
+    info!(
+        "Plugin file watcher started for {}",
+        plugins_dir.display()
+    );
+
+    thread::spawn(move || {
+        if let Err(e) = watch_loop(&plugins_dir, &pm) {
+            warn!("Plugin watcher stopped: {}", e);
+        }
+    });
+}
+
+fn watch_loop(
+    plugins_dir: &PathBuf,
+    pm: &Arc<RwLock<ProviderManager>>,
+) -> Result<(), Box<dyn std::error::Error>> {
+    let (tx, rx) = std::sync::mpsc::channel();
+
+    let mut debouncer = new_debouncer(Duration::from_millis(500), tx)?;
+
+    debouncer
+        .watcher()
+        .watch(plugins_dir.as_ref(), notify::RecursiveMode::Recursive)?;
+
+    info!("Watching {} for plugin changes", plugins_dir.display());
+
+    loop {
+        match rx.recv() {
+            Ok(Ok(events)) => {
+                let has_relevant_change = events.iter().any(|e| {
+                    matches!(
+                        e.kind,
+                        DebouncedEventKind::Any | DebouncedEventKind::AnyContinuous
+                    )
+                });
+
+                if has_relevant_change {
+                    info!("Plugin file change detected, reloading runtimes...");
+                    let mut pm_guard = pm.write().unwrap_or_else(|e| e.into_inner());
+                    pm_guard.reload_runtimes();
+                }
+            }
+            Ok(Err(error)) => {
+                warn!("File watcher error: {}", error);
+            }
+            Err(e) => {
+                return Err(Box::new(e));
+            }
+        }
+    }
+}