feat(export): prefer native save dialog over browser blob fallback

DictationPage + FilesPage handleExport() now use Tauri save() +
write_text_file_cmd when in the desktop runtime; browser blob path
remains as fallback when hasTauriRuntime() is false. saveMarkdown.ts
surfaces dialog errors via toasts. Adds txt to the extension map.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/pages/DictationPage.svelte

@@ -637,17 +637,38 @@
     activeTemplate = "";
   }
 
-  function handleExport(format) {
+  async function handleExport(format) {
     if (!transcript) return;
     showExportMenu = false;
     const content = exportTranscript(transcript, segments, format);
-    const extMap = { vtt: "vtt", srt: "srt", md: "md", csv: "csv", html: "html" };
+    const extMap = { txt: "txt", vtt: "vtt", srt: "srt", md: "md", csv: "csv", html: "html" };
     const ext = extMap[format] || "txt";
+    const defaultPath = `magnotia-${new Date().toISOString().slice(0, 10)}.${ext}`;
+
+    if (hasTauriRuntime()) {
+      try {
+        const { save } = await import("@tauri-apps/plugin-dialog");
+        const path = await save({
+          title: `Export ${format.toUpperCase()} transcript`,
+          defaultPath,
+          filters: [{ name: format.toUpperCase(), extensions: [ext] }],
+        });
+        if (!path) return;
+        await invoke("write_text_file_cmd", { path, contents: content });
+        toasts.success(`Exported ${format.toUpperCase()} transcript`);
+        return;
+      } catch (err) {
+        console.error("dictation export failed", err);
+        error = `Export failed: ${typeof err === "string" ? err : err.message || err}`;
+        return;
+      }
+    }
+
     const blob = new Blob([content], { type: "text/plain" });
     const url = URL.createObjectURL(blob);
     const a = document.createElement("a");
     a.href = url;
-    a.download = `magnotia-${new Date().toISOString().slice(0, 10)}.${ext}`;
+    a.download = defaultPath;
     a.click();
     URL.revokeObjectURL(url);
   }

src/lib/pages/FilesPage.svelte

@@ -8,6 +8,7 @@
   import Card from "$lib/components/Card.svelte";
   import EmptyState from "$lib/components/EmptyState.svelte";
   import { exportTranscript } from "$lib/utils/export.js";
+  import { hasTauriRuntime } from "$lib/utils/runtime";
   import { Upload } from 'lucide-svelte';
 
   let fileTranscript = $state("");
@@ -132,17 +133,37 @@
     }
   }
 
-  function handleExport(format) {
+  async function handleExport(format) {
     if (!fileTranscript) return;
     showExportMenu = false;
     const content = exportTranscript(fileTranscript, segments, format);
-    const extMap = { vtt: "vtt", srt: "srt", md: "md", csv: "csv", html: "html" };
+    const extMap = { txt: "txt", vtt: "vtt", srt: "srt", md: "md", csv: "csv", html: "html" };
     const ext = extMap[format] || "txt";
+    const defaultPath = `magnotia-file-${new Date().toISOString().slice(0, 10)}.${ext}`;
+
+    if (hasTauriRuntime()) {
+      try {
+        const { save } = await import("@tauri-apps/plugin-dialog");
+        const path = await save({
+          title: `Export ${format.toUpperCase()} transcript`,
+          defaultPath,
+          filters: [{ name: format.toUpperCase(), extensions: [ext] }],
+        });
+        if (!path) return;
+        await invoke("write_text_file_cmd", { path, contents: content });
+        return;
+      } catch (err) {
+        console.error("file transcript export failed", err);
+        error = `Export failed: ${typeof err === "string" ? err : err.message || err}`;
+        return;
+      }
+    }
+
     const blob = new Blob([content], { type: "text/plain" });
     const url = URL.createObjectURL(blob);
     const a = document.createElement("a");
     a.href = url;
-    a.download = `magnotia-file-${new Date().toISOString().slice(0, 10)}.${ext}`;
+    a.download = defaultPath;
     a.click();
     URL.revokeObjectURL(url);
   }

src/lib/utils/saveMarkdown.ts

@@ -33,14 +33,24 @@ export function suggestedFilename(item: TranscriptEntry): string {
 export async function saveTranscriptAsMarkdown(
   item: TranscriptEntry,
 ): Promise<string | null> {
-  if (!hasTauriRuntime()) return null;
+  if (!hasTauriRuntime()) {
+    toasts.error("Export unavailable", "Native save dialogs are only available in the desktop app.");
+    return null;
+  }
   const md = buildMarkdown(item);
   const defaultPath = suggestedFilename(item);
-  const path = await save({
+  let path: string | null = null;
+  try {
+    path = await save({
       title: "Save transcript as Markdown",
       defaultPath,
       filters: [{ name: "Markdown", extensions: ["md"] }],
     });
+  } catch (err) {
+    console.error("saveTranscriptAsMarkdown dialog failed", err);
+    toasts.error("Couldn't open save dialog", String(err));
+    return null;
+  }
   if (!path) return null;
   try {
     await invoke("write_text_file_cmd", { path, contents: md });
@@ -64,13 +74,24 @@ export async function saveTranscriptAsMarkdown(
 export async function exportTranscriptsToDir(
   items: TranscriptEntry[],
 ): Promise<number> {
-  if (!hasTauriRuntime() || items.length === 0) return 0;
+  if (items.length === 0) return 0;
+  if (!hasTauriRuntime()) {
+    toasts.error("Export unavailable", "Native folder dialogs are only available in the desktop app.");
+    return 0;
+  }
 
-  const dir = await open({
+  let dir: string | string[] | null = null;
+  try {
+    dir = await open({
       directory: true,
       multiple: false,
       title: "Choose export folder",
     });
+  } catch (err) {
+    console.error("exportTranscriptsToDir dialog failed", err);
+    toasts.error("Couldn't open export folder dialog", String(err));
+    return 0;
+  }
   if (!dir || typeof dir !== "string") return 0;
 
   const used = new Set<string>();