feat(extra-sheet) : add inline cell editing

lib/rich-text.test.ts

@@ -1,6 +1,7 @@
 import { describe, expect, it } from "vitest";
 
 import {
+  extraRichTextToPlainText,
   applyRichTextStylePatch,
   normalizeExtraRichText,
   richTextContentSignature,
@@ -34,6 +35,14 @@ describe("rich text sanitization", () => {
 });
 
 describe("legacy Extra rich text conversion", () => {
+  it("converts stored markup into safe multiline text for cell editing", () => {
+    expect(extraRichTextToPlainText(
+      "<p><strong>First</strong><br>line</p><p>Second &amp; safe<script>bad()</script></p>",
+    )).toBe("First\nline\nSecond & safe");
+    expect(normalizeExtraRichText(extraRichTextToPlainText("<p>A<br>B</p>")))
+      .toBe("<p>A<br>B</p>");
+  });
+
   it("escapes plain text, preserves newlines, and converts phrase colors", () => {
     expect(normalizeExtraRichText("<unsafe>\nMASSIVE damage", [
       { text: "MASSIVE", color: "#ff0000" },

lib/rich-text.ts

@@ -1,4 +1,5 @@
 import sanitizeHtml from "sanitize-html";
+import { decodeHTML } from "entities";
 
 import { highlightTextSegments, type TextHighlight } from "@/lib/guides/highlights";
 
@@ -112,6 +113,23 @@ export function normalizeExtraRichText(
   return content ? `<p>${content}</p>` : "";
 }
 
+/** Converts stored Extra Sheet rich text into editable plain text. */
+export function extraRichTextToPlainText(value: string): string {
+  const withLineBreaks = normalizeExtraRichText(value)
+    .replace(/<br\s*\/?>/gi, "\n")
+    .replace(/<\/(?:blockquote|li|ol|p|pre|ul)>/gi, "\n");
+  let text = "";
+  sanitizeHtml(withLineBreaks, {
+    allowedTags: [],
+    allowedAttributes: {},
+    textFilter: (chunk) => {
+      text += chunk;
+      return "";
+    },
+  });
+  return decodeHTML(text).replace(/\n$/, "");
+}
+
 const RICH_TEXT_MARK_TAGS = {
   bold: "strong",
   italic: "em",