Handle OS file association: open .md files passed as CLI args

src/App.tsx

@@ -3,6 +3,7 @@ import { open } from "@tauri-apps/plugin-dialog";
 import { readTextFile } from "@tauri-apps/plugin-fs";
 import { getCurrentWindow } from "@tauri-apps/api/window";
 import { getCurrentWebview } from "@tauri-apps/api/webview";
+import { listen } from "@tauri-apps/api/event";
 import MarkdownIt from "markdown-it";
 import hljs from "highlight.js";
 import { motion, AnimatePresence } from "framer-motion";
@@ -512,6 +513,31 @@ function App() {
     return () => { unlisten?.(); };
   }, [parseHeadings]);
 
+  // Handle file opened via OS file association (e.g. double-clicking a .md file)
+  useEffect(() => {
+    let unlisten: (() => void) | undefined;
+    listen<string>('open-file', async (event) => {
+      const filePath = event.payload;
+      try {
+        const existing = tabsRef.current.find(t => t.path === filePath);
+        if (existing) {
+          setActiveTabId(existing.id);
+          parseHeadings(existing.content);
+        } else {
+          const content = await readTextFile(filePath);
+          const title = filePath.split(/[/\\]/).pop() || 'Untitled';
+          const newTab: Tab = { id: Date.now().toString(), title, content, path: filePath };
+          setTabs(prev => [...prev, newTab]);
+          setActiveTabId(newTab.id);
+          parseHeadings(content);
+        }
+      } catch (err) {
+        console.error('Failed to open file from OS:', err);
+      }
+    }).then(fn => { unlisten = fn; });
+    return () => { unlisten?.(); };
+  }, [parseHeadings]);
+
   const handleOpenDialog = useCallback(async () => {
     try {
       const selected = await open({ multiple: false, filters: [{ name: 'Markdown', extensions: ['md', 'markdown', 'txt'] }] });