fix(shared): preserve image blocks during markdown/html round-trip

AGENTS.md

@@ -406,6 +406,7 @@ When reviewing code (or writing code that will be reviewed):
 - **Do not hide accessible data using presentation heuristics** - In UI lists, avoid masking content based on flags like `source.public`; rely on backend access controls and render the data returned by the query.
 - **Keep scope tight in design iterations** - When adjusting UI, avoid unrelated behavioral/SEO changes in the same commit unless explicitly requested.
 - **Keep action spacing consistent in control headers** - When adding icon/action buttons near search fields or other controls, match existing horizontal gaps on both sides to avoid controls touching each other.
+- **Protect generated HTML from markdown regex passes** - In markdown conversion utilities, never run formatting regexes across already-generated HTML tags/attributes (for example, image `src` URLs with `_`); add regression tests for URL edge cases.
 
 ## Node.js Version Upgrade Checklist
 

packages/shared/src/lib/markdownConversion.spec.ts

@@ -40,11 +40,53 @@ describe('markdownConversion', () => {
 
     const convertedHtml = markdownToHtmlBasic(markdown);
 
-    expect(convertedHtml).toContain(
+    expect(convertedHtml).toBe(
       '<img src="https://cdn.daily.dev/image.png" alt="Preview" />',
     );
   });
 
+  it('should keep standalone image in markdown round-trip', () => {
+    const initialMarkdown = '![Preview](https://cdn.daily.dev/image.png)';
+    const html = markdownToHtmlBasic(initialMarkdown);
+
+    expect(html).toBe(
+      '<img src="https://cdn.daily.dev/image.png" alt="Preview" />',
+    );
+
+    const markdown = htmlToMarkdownBasic(html);
+
+    expect(markdown).toBe(initialMarkdown);
+  });
+
+  it('should handle image between paragraphs', () => {
+    const md = 'hello\n\n![img](https://cdn.daily.dev/a.png)\n\nworld';
+    const html = markdownToHtmlBasic(md);
+
+    expect(html).toBe(
+      '<p>hello</p><img src="https://cdn.daily.dev/a.png" alt="img" /><p>world</p>',
+    );
+  });
+
+  it('should keep inline image within paragraph', () => {
+    const md = 'text ![img](https://cdn.daily.dev/a.png) more';
+    const html = markdownToHtmlBasic(md);
+
+    expect(html).toBe(
+      '<p>text <img src="https://cdn.daily.dev/a.png" alt="img" /> more</p>',
+    );
+  });
+
+  it('should not parse underscore characters inside image url attributes', () => {
+    const markdown =
+      '![Block words feature](https://media.daily.dev/image/upload/s--A9t0KF3Y--/f_auto/v1741689017/ugc/content_b24c703e-ca99-4feb-b19b-349a502afa66)';
+    const html = markdownToHtmlBasic(markdown);
+
+    expect(html).toBe(
+      '<img src="https://media.daily.dev/image/upload/s--A9t0KF3Y--/f_auto/v1741689017/ugc/content_b24c703e-ca99-4feb-b19b-349a502afa66" alt="Block words feature" />',
+    );
+    expect(html).not.toContain('<em>');
+  });
+
   it('should preserve bold text across line breaks', () => {
     const markdown = htmlToMarkdownBasic(
       '<p><strong>line1<br>line2</strong></p>',

packages/shared/src/lib/markdownConversion.ts

@@ -6,6 +6,17 @@ const escapeAttribute = (value: string): string =>
 
 const normalizeText = (value: string): string => value.replace(/\u00a0/g, ' ');
 
+const applyInlineTextFormatting = (value: string): string => {
+  let result = value;
+
+  result = result.replace(/\*\*(.+?)\*\*/g, '<strong>$1</strong>');
+  result = result.replace(/\*(?!\*)([^*]+)\*(?!\*)/g, '<em>$1</em>');
+  result = result.replace(/_(.+?)_/g, '<em>$1</em>');
+  result = result.replace(/`([^`]+)`/g, '<code>$1</code>');
+
+  return result;
+};
+
 const inlineMarkdownToHtml = (value: string): string => {
   let result = escapeHtml(value);
 
@@ -21,12 +32,12 @@ const inlineMarkdownToHtml = (value: string): string => {
       `<a href="${escapeAttribute(url)}">${label}</a>`,
   );
 
-  result = result.replace(/\*\*(.+?)\*\*/g, '<strong>$1</strong>');
-  result = result.replace(/\*(?!\*)([^*]+)\*(?!\*)/g, '<em>$1</em>');
-  result = result.replace(/_(.+?)_/g, '<em>$1</em>');
-  result = result.replace(/`([^`]+)`/g, '<code>$1</code>');
-
-  return result;
+  return result
+    .split(/(<[^>]+>)/g)
+    .map((part) =>
+      part.startsWith('<') ? part : applyInlineTextFormatting(part),
+    )
+    .join('');
 };
 
 /**
@@ -147,6 +158,14 @@ export const markdownToHtmlBasic = (markdown: string): string => {
       return;
     }
 
+    if (/^!\[[^\]]*\]\([^)]+\)$/.test(trimmed)) {
+      flushList();
+      flushPendingEmptyParagraphs();
+      htmlParts.push(inlineMarkdownToHtml(trimmed));
+      hasRenderedBlock = true;
+      return;
+    }
+
     flushList();
     flushPendingEmptyParagraphs();
     htmlParts.push(`<p>${inlineMarkdownToHtml(line)}</p>`);