feat(web): notes render as markdown — markdown-it+DOMPurify pipeline, rich paste

Objective 6 (web half). Storage/sync stay raw markdown (KOReader shows
literal source, accepted). Notes-grade syntax: headings, emphasis/
strikethrough, code, links, lists, blockquotes, GFM tables, reference
links, footnotes (markdown-it-footnote); images/raw HTML/math excluded
(html:false posture + FORBID img/style/form + default safe-scheme URI
check). Display sites: annotations-drawer note rows and highlight note
lines render pre-sanitized HTML (x-html); render-time sanitize only.

Rich paste: both note textareas intercept paste; a text/html clipboard
flavor converts via turndown (gfm tables incl. a headingless-table rule
emitting pipe syntax; images blanked) and inserts at the caret; plain
pastics fall through to the default paste unchanged.

Verified live in Brave: bold/italic/strike/code/lists/quote/table/
footnote-ref/reference-link render; <script> renders inert literal
text with no alert; javascript: hrefs absent from the DOM; paste of
rich HTML lands markdown at the caret; plain pastes untouched.

web/src/markdown.ts

@@ -0,0 +1,102 @@
+// Notes render as markdown: storage and every sync payload carry the raw
+// source string (KOReader devices show it literally — accepted), and every
+// DISPLAY site renders it through this pipeline. Raw HTML is disabled at the
+// parser level (markdown-it's default) and DOMPurify strips whatever the
+// enabled syntax still produced (link hrefs are scheme-whitelisted below),
+// so a malicious note can render nothing more than styled text.
+import MarkdownIt from "markdown-it";
+import footnote from "markdown-it-footnote";
+import DOMPurify from "dompurify";
+import TurndownService from "turndown";
+import { gfm, tables } from "turndown-plugin-gfm";
+
+const md = new MarkdownIt({ html: false, linkify: false });
+md.use(footnote);
+
+export function renderNoteHtml(source: string): string {
+    if (!source) return "";
+    const raw = md.render(source);
+    // Disallowing img/input/style/form by tag and keeping DOMPurify's default
+    // safe-URI scheme check (http/https/mailto + same-page anchors only)
+    // closes the link-injection hole, which is the one markdown pivot into
+    // script execution.
+    const clean = DOMPurify.sanitize(raw, {
+        ALLOWED_ATTR: ["href", "class", "id", "role"],
+        FORBID_TAGS: ["img", "input", "style", "form"],
+    });
+    return clean;
+}
+
+// Compact rows may show a plain line instead of rich markup.
+export function stripNote(source: string): string {
+    if (!source) return "";
+    const holder = document.createElement("div");
+    holder.innerHTML = renderNoteHtml(source);
+    return (holder.textContent || "").replace(/\s+/g, " ").trim();
+}
+
+// ----- rich paste: HTML flavor -> markdown source -----
+const turndown = new TurndownService({
+    // Keep the converted output inside our supported syntax: headings,
+    // emphasis, lists, code, quotes, links, tables. Everything else degrades.
+    headingStyle: "atx",
+    codeBlockStyle: "fenced",
+    bulletListMarker: "-",
+    hr: "---",
+});
+turndown.use(gfm);
+turndown.use(tables);
+// Images are explicitly out of scope for notes: blank them at convert time
+// (remove() alone can leave the node's alt-text shape behind).
+turndown.addRule("noImages", { filter: "img", replacement: () => "" });
+// The gfm tables service only converts tables with a heading row and keeps
+// headingless ones as raw HTML — which our no-raw-HTML parser would then
+// show as literal tags. Convert those to pipe syntax with a blank header.
+turndown.addRule("tablesNoHeading", {
+    filter: (node: Node) => {
+        const el = node as HTMLElement;
+        if (el.nodeName !== "TABLE" || !el.querySelector) return false;
+        return !el.querySelector("th") && el.querySelectorAll("tr").length > 0;
+    },
+    replacement: (_content: string, node: Node) => {
+        const table = node as HTMLTableElement;
+        const rows = Array.from(table.querySelectorAll("tr")).map((tr) =>
+            Array.from(tr.querySelectorAll("td, th")).map((cell) =>
+                (cell.textContent ?? "").replace(/\s+/g, " ").trim().replace(/\|/g, "\\|"),
+            ),
+        );
+        const cols = Math.max(1, ...rows.map((r) => r.length));
+        const pad = (r: string[]) => {
+            const copy = [...r];
+            while (copy.length < cols) copy.push("");
+            return copy.map((c) => c || " ");
+        };
+        const head = pad(rows[0] ?? []);
+        const lines = [
+            "| " + head.join(" | ") + " |",
+            "|" + Array.from({ length: cols }, () => " --- ").join("|") + "|",
+            ...rows.slice(1).map((r) => "| " + pad(r).join(" | ") + " |"),
+        ];
+        return "\n\n" + lines.join("\n") + "\n\n";
+    },
+});
+
+export function htmlToMarkdown(html: string): string {
+    return turndown.turndown(html);
+}
+
+/** Reads the paste event's clipboard and returns markdown converted from the
+ *  rich (text/html) flavor, or null when the clipboard holds no usable rich
+ *  content (plain pastes must fall through to the browser default). */
+export function richPasteToMarkdown(event: ClipboardEvent): string | null {
+    const data = event.clipboardData;
+    if (!data) return null;
+    const html = data.getData("text/html");
+    if (!html || !html.trim()) return null;
+    // A rich flavor that is just an HTML wrapper of plain text (some apps
+    // emit <p>...</p> wrappers for everything Chrome copies) still converts
+    // harmlessly to the same text, so no content sniffing is needed here.
+    const markdown = htmlToMarkdown(html);
+    if (!markdown || !markdown.trim()) return null;
+    return markdown;
+}

web/src/reader/reader.ts

@@ -5,6 +5,7 @@ import { Alpine } from "../alpine";
 import { loadSettings, saveSettings } from "./settings-manager";
 import { getToken } from "../storage";
 import { showToast } from "../toast";
+import { renderNoteHtml, richPasteToMarkdown } from "../markdown";
 import {
   extractPdfPages,
   searchPdfPages,
@@ -435,6 +436,7 @@ document.addEventListener("alpine:init", () => {
       id: string;
       text: string;
       note: string;
+      noteHtml: string;
       color: string;
       cfi: string;
       cfiEnd: string;
@@ -443,7 +445,7 @@ document.addEventListener("alpine:init", () => {
       pdfPage: number;
       pdfRects: number[][];
     }[],
-    noteItems: [] as { id: string; content: string; positionLabel: string }[],
+    noteItems: [] as { id: string; content: string; contentHtml: string; positionLabel: string }[],
     annotationsTab: "highlights" as string,
     newNoteText: "",
     // Mirrors the server-side validator cap on note content
@@ -1556,6 +1558,7 @@ document.addEventListener("alpine:init", () => {
         id: r.id,
         text: r.selection_text ?? "",
         note: r.note_text ?? "",
+        noteHtml: renderNoteHtml(r.note_text ?? ""),
         color: r.color ?? "#ffff00",
         cfi,
         cfiEnd,
@@ -1642,6 +1645,7 @@ document.addEventListener("alpine:init", () => {
           this.noteItems = (rows as any[]).map((r) => ({
             id: r.id,
             content: r.content ?? "",
+            contentHtml: renderNoteHtml(r.content ?? ""),
             positionLabel: r.position ?? "",
           }));
         }
@@ -2021,6 +2025,21 @@ document.addEventListener("alpine:init", () => {
     noteCountLabel(text: string): string {
       return `${text.length.toLocaleString()}/${this.noteMaxLength.toLocaleString()}`;
     },
+    // Rich clipboard (text/html) converts to markdown source at the caret;
+    // plain-only clipboards fall through to the browser default paste.
+    richNotePaste(event: ClipboardEvent) {
+      const markdown = richPasteToMarkdown(event);
+      if (markdown === null) return;
+      event.preventDefault();
+      const el = event.target as HTMLTextAreaElement | null;
+      if (!el) return;
+      const start = el.selectionStart ?? el.value.length;
+      const end = el.selectionEnd ?? start;
+      el.value = el.value.slice(0, start) + markdown + el.value.slice(end);
+      const caret = start + markdown.length;
+      el.setSelectionRange(caret, caret);
+      el.dispatchEvent(new Event("input", { bubbles: true }));
+    },
     async addNote(content: string) {
       const token = getToken();
       if (!token || !this.mediaItemId || !content.trim()) return;

web/src/shims.d.ts

@@ -0,0 +1,2 @@
+declare module "markdown-it-footnote";
+declare module "turndown-plugin-gfm";