feat: default ActivityPub syndication when force-syndicating from backend

When the backend Syndicate button is pressed on a post with no
mp-syndicate-to and no prior syndication URLs, fall back to targets
with checked:true (e.g. ActivityPub) instead of no-oping.

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

scripts/patch-syndicate-force-checked-default.mjs

@@ -0,0 +1,78 @@
+/**
+ * Patch: when the backend "Syndicate" button is pressed for a post that has
+ * no `mp-syndicate-to` and no existing syndication URLs, fall back to targets
+ * that have `checked: true` in their options (e.g. ActivityPub) instead of
+ * doing nothing.
+ *
+ * Without this patch, force-syndicating a post that was published without
+ * any syndication targets pre-selected would silently no-op.
+ */
+import { access, readFile, writeFile } from "node:fs/promises";
+
+const candidates = [
+  "node_modules/@indiekit/endpoint-syndicate/lib/utils.js",
+  "node_modules/@rmdes/indiekit-endpoint-syndicate/lib/utils.js",
+  "node_modules/@indiekit/indiekit/node_modules/@indiekit/endpoint-syndicate/lib/utils.js",
+  "node_modules/@indiekit/indiekit/node_modules/@rmdes/indiekit-endpoint-syndicate/lib/utils.js",
+];
+
+const marker = "// syndicate-force-checked-default patch";
+
+const oldSnippet = `    }
+    // If no existing syndication URLs, don't default to all — leave empty
+  }`;
+
+const newSnippet = `    } else {
+      // syndicate-force-checked-default patch
+      syndicateTo = syndicationTargets
+        .filter((t) => t?.options?.checked)
+        .map((t) => t.info.uid);
+    }
+  }`;
+
+async function exists(filePath) {
+  try {
+    await access(filePath);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+let checked = 0;
+let patched = 0;
+
+for (const filePath of candidates) {
+  if (!(await exists(filePath))) {
+    continue;
+  }
+
+  checked += 1;
+
+  const source = await readFile(filePath, "utf8");
+
+  if (source.includes(marker)) {
+    continue;
+  }
+
+  if (!source.includes(oldSnippet)) {
+    console.warn(
+      `[postinstall] Skipping syndicate-force-checked-default patch for ${filePath}: upstream format changed`,
+    );
+    continue;
+  }
+
+  const updated = source.replace(oldSnippet, newSnippet);
+  await writeFile(filePath, updated, "utf8");
+  patched += 1;
+}
+
+if (checked === 0) {
+  console.log("[postinstall] No endpoint-syndicate utils files found");
+} else if (patched === 0) {
+  console.log("[postinstall] syndicate-force-checked-default patch already applied");
+} else {
+  console.log(
+    `[postinstall] Patched syndicate-force-checked-default in ${patched} file(s)`,
+  );
+}