fix(markdown): retry transient image decode failures

packages/app/src/components/markdown/image-decoding.ts

@@ -0,0 +1,18 @@
+type ImageDecoder = (
+  uri: string,
+  success: (width: number, height: number) => void,
+  failure: (error: unknown) => void,
+) => void;
+
+export function decodeMarkdownImage(uri: string, decode: ImageDecoder): Promise<true> {
+  return new Promise((resolve, reject) => {
+    decode(
+      uri,
+      (width, height) => {
+        if (width > 0 && height > 0) resolve(true);
+        else reject(new Error("Image has no decodable dimensions"));
+      },
+      reject,
+    );
+  });
+}