fix(bluesky): guard uploadMedia() against non-image HTTP responses

uploadMedia() had no content-type check, so an HTML login-redirect response
from an auth-protected internal endpoint was uploaded to Bluesky as a blob
with encoding "text/html". uploadBlob() accepts it, but record validation
rejects the post with 'Expected "image/*" (got "text/html")'.

The patch mirrors the guard already present in uploadImageFromUrl() and also
wraps per-photo uploads in try/catch so one bad photo doesn't abort the
entire syndication — other photos and the post text are still published.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/patch-bluesky-syndicator-media-type-guard.mjs

@@ -0,0 +1,119 @@
+/**
+ * Patch: guard uploadMedia() against non-image HTTP responses.
+ *
+ * Root cause:
+ *   uploadMedia() fetches a photo URL and uploads whatever it receives to Bluesky
+ *   without checking the Content-Type. If the internal fetch returns an HTML page
+ *   (e.g. a login redirect from an auth-protected endpoint), the blob is uploaded
+ *   with encoding "text/html". uploadBlob() accepts it, but app.bsky.feed.post
+ *   record validation then rejects the post:
+ *     "Expected 'image/*' (got 'text/html') at $.record.embed.images[0].image.mimeType"
+ *
+ *   uploadImageFromUrl() has this guard already (it returns null for non-image
+ *   responses) but uploadMedia() does not.
+ *
+ * Fix:
+ *   1. Add a content-type guard to uploadMedia() — throw if response is not image/*.
+ *   2. Wrap per-photo uploads in post() with try/catch and filter out failures,
+ *      so one bad photo doesn't block the entire syndication.
+ */
+
+import { access, readFile, writeFile } from "node:fs/promises";
+
+const TARGET =
+  "node_modules/@rmdes/indiekit-syndicator-bluesky/lib/bluesky.js";
+
+const MARKER = "// bsky-media-type-guard patch";
+
+// ---------------------------------------------------------------------------
+// 1. Guard in uploadMedia(): reject non-image content types
+// ---------------------------------------------------------------------------
+const OLD_ENCODING = `      let blob = await mediaResponse.blob();
+      let encoding = mediaResponse.headers.get("Content-Type");
+
+      if (encoding?.startsWith("image/")) {`;
+
+const NEW_ENCODING = `      let blob = await mediaResponse.blob();
+      let encoding = mediaResponse.headers.get("Content-Type");
+
+      // Reject non-image responses (e.g. HTML login redirects) ${MARKER}
+      if (!encoding || !encoding.startsWith("image/")) {
+        throw new Error(\`uploadMedia: non-image content-type "\${encoding}" for \${mediaUrl}\`); ${MARKER}
+      }
+
+      if (encoding?.startsWith("image/")) {`;
+
+// ---------------------------------------------------------------------------
+// 2. Per-photo error handling in post(): skip failed uploads instead of
+//    propagating a broken blob into the images array.
+// ---------------------------------------------------------------------------
+const OLD_UPLOADS = `      if (properties.photo) {
+        const photos = properties.photo.slice(0, 4);
+        const uploads = photos.map(async (photo) => ({
+          alt: photo.alt || "",
+          image: await this.uploadMedia(photo, me),
+        }));
+        images = await Promise.all(uploads);
+      }`;
+
+const NEW_UPLOADS = `      if (properties.photo) {
+        const photos = properties.photo.slice(0, 4);
+        const uploads = photos.map(async (photo) => { ${MARKER}
+          try {
+            const image = await this.uploadMedia(photo, me);
+            return image ? { alt: photo.alt || "", image } : null; ${MARKER}
+          } catch (err) {
+            console.error(\`[Bluesky] uploadMedia failed for \${photo.url}: \${err.message}\`); ${MARKER}
+            return null; ${MARKER}
+          }
+        });
+        images = (await Promise.all(uploads)).filter(Boolean); ${MARKER}
+      }`;
+
+// ---------------------------------------------------------------------------
+
+async function exists(filePath) {
+  try {
+    await access(filePath);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+if (!(await exists(TARGET))) {
+  console.log("[postinstall] patch-bluesky-syndicator-media-type-guard: target not found");
+  process.exit(0);
+}
+
+const source = await readFile(TARGET, "utf8");
+
+if (source.includes(MARKER)) {
+  console.log("[postinstall] patch-bluesky-syndicator-media-type-guard: already applied");
+  process.exit(0);
+}
+
+let updated = source;
+let changed = false;
+
+if (updated.includes(OLD_ENCODING)) {
+  updated = updated.replace(OLD_ENCODING, NEW_ENCODING);
+  changed = true;
+} else {
+  console.warn("[postinstall] patch-bluesky-syndicator-media-type-guard: encoding block not found — skipping");
+}
+
+if (updated.includes(OLD_UPLOADS)) {
+  updated = updated.replace(OLD_UPLOADS, NEW_UPLOADS);
+  changed = true;
+} else {
+  console.warn("[postinstall] patch-bluesky-syndicator-media-type-guard: uploads block not found — skipping");
+}
+
+if (!changed || updated === source) {
+  console.log("[postinstall] patch-bluesky-syndicator-media-type-guard: no changes applied");
+  process.exit(0);
+}
+
+await writeFile(TARGET, updated, "utf8");
+console.log(`[postinstall] Applied patch-bluesky-syndicator-media-type-guard to ${TARGET}`);