feat(renderer): add Save As button to chapter header

- Add 'Save As' button next to Save in the chapter writing view
- Exports current chapter as Markdown to a user-chosen file location
- New IPC handler folio:saveChapterAs shows OS save dialog

src/main/index.ts

@@ -550,6 +550,22 @@ handleIpc("folio:saveChapter", (_e, id: string, content: string) => {
   return { ok: true };
 });
 
+handleIpc("folio:saveChapterAs", async (_e, id: string) => {
+  const bp = requireBook();
+  const meta = loadBook(bp);
+  const entry = meta.chapters[id];
+  if (!entry) return { error: "Chapter not found" };
+  const { canceled, filePath } = await showSaveDialog({
+    title: "Save Chapter As",
+    defaultPath: `${entry.title}.md`,
+    filters: [{ name: "Markdown", extensions: ["md"] }],
+  });
+  if (canceled || !filePath) return { canceled: true } as const;
+  const content = getChapterContent(bp, id);
+  fs.writeFileSync(filePath, content, "utf-8");
+  return { ok: true, filePath };
+});
+
 // Explicit, opt-in migration of a single chapter (or the whole book) to the
 // native Folio document format. Never automatic — the UI triggers this. The
 // migration pipeline makes a recovery backup and keeps the original .md files.

src/main/preload.ts

@@ -42,6 +42,8 @@ contextBridge.exposeInMainWorld("folio", {
     ipcRenderer.invoke("folio:loadChapterDoc", id),
   saveChapterDoc: (id: string, doc: unknown) =>
     ipcRenderer.invoke("folio:saveChapterDoc", id, doc),
+  saveChapterAs: (id: string) =>
+    ipcRenderer.invoke("folio:saveChapterAs", id),
   importImageAsset: () => ipcRenderer.invoke("folio:importImageAsset"),
   exportMarkdown: () => ipcRenderer.invoke("folio:exportMarkdown"),
   exportZip: () => ipcRenderer.invoke("folio:exportZip"),

src/renderer/book/editor.ts

@@ -11,6 +11,7 @@ import type { BookCtx } from "./types.js";
 import { alertMessage } from "../dialog.js";
 import {
   $,
+  basename,
   closeEl,
   countWords,
   formatWordCount,
@@ -230,6 +231,19 @@ export function createEditorFeature(ctx: BookCtx): EditorFeature {
   const saveBtn = $("saveBtn");
   saveBtn?.addEventListener("click", () => void saveAndNotify());
 
+  // Save As button — exports the current chapter as a Markdown file to a
+  // user-chosen location via the OS save dialog.
+  const saveAsBtn = $("saveAsBtn");
+  saveAsBtn?.addEventListener("click", async () => {
+    if (!state.selectedId) return;
+    const res = await api.saveChapterAs(state.selectedId);
+    if (res && "error" in res) {
+      showToast("Save As failed");
+    } else if (res && "filePath" in res) {
+      showToast(`Saved to ${basename(res.filePath as string)}`);
+    }
+  });
+
   // Flush any pending auto-save when the window is hidden or loses focus, so the
   // last stretch of typing is persisted even if the app closes within the
   // debounce window.

src/renderer/book/types.ts

@@ -56,6 +56,7 @@ export type FolioAPI = {
   migrateBook: () => Promise<any>;
   loadChapterDoc: (id: string) => Promise<any>;
   saveChapterDoc: (id: string, doc: unknown) => Promise<any>;
+  saveChapterAs: (id: string) => Promise<any>;
   importImageAsset: () => Promise<any>;
   exportMarkdown: () => Promise<any>;
   exportZip: () => Promise<any>;

src/renderer/index.html

@@ -70,6 +70,7 @@
             <div class="editor-actions">
               <span class="save-state" id="saveState">Saved</span>
               <button class="button button-ghost" id="saveBtn" title="Save chapter (Ctrl+S)">Save</button>
+              <button class="button button-ghost" id="saveAsBtn" title="Save chapter as Markdown file">Save As</button>
               <span class="word-count" id="wordCount">words: 0</span>
               <button class="icon-button" id="statsBtn" title="Writing statistics">📊</button>
               <button class="icon-button" id="commentsBtn" title="Comments">💬</button>