fix(markdown): preserve literal image fallback labels

packages/app/src/components/markdown/renderer.test.ts

@@ -335,3 +335,16 @@ it("normalizes images following HTML code in the same HTML block", () => {
   expect(prepared.render(new Map([["shot.png", "blob:shot"]]))).toContain("![](<blob:shot>)");
   expect(prepared.render()).toContain("`\nx\n`");
 });
+
+it("preserves literal Markdown punctuation in unsupported and failed image labels", () => {
+  const label = String.raw`\*literal\* \[label\]`;
+  expect(
+    prepareMarkdownSource(`![${label}](badge.svg)`, undefined, { supportsSvg: false }).render(),
+  ).toBe(label);
+  expect(
+    prepareMarkdownSource(`![${label}](https://example.com/badge.png)`).render(
+      new Map(),
+      new Set(["https://example.com/badge.png"]),
+    ),
+  ).toBe(label);
+});

packages/app/src/components/markdown/source.ts

@@ -90,7 +90,7 @@ export function prepareMarkdownSource(
       options.supportsSvg === false &&
       /(?:\.svg(?:[?#]|$)|^data:image\/svg\+xml)/i.test(target.url)
     ) {
-      edits.push({ start, end, text: node.alt ?? "" });
+      edits.push({ start, end, text: escapeMarkdownText(node.alt ?? "") });
       return;
     }
     if (target)
@@ -153,7 +153,7 @@ export function prepareMarkdownSource(
           end: image.end,
           text: url
             ? `![${image.alt.replace(/[[\]\\]/g, "\\$&")}](<${url}>${image.title ? ` ${JSON.stringify(image.title)}` : ""})`
-            : image.alt,
+            : escapeMarkdownText(image.alt),
         });
       }
       let result = source;
@@ -164,3 +164,7 @@ export function prepareMarkdownSource(
     },
   };
 }
+
+function escapeMarkdownText(text: string): string {
+  return text.replace(/[!-/:-@[-`{-~]/g, "\\$&");
+}