Added rule and logic to detect if accounts are abusing faceting by pushing multiple facets in same byte space

src/main.ts

···
 import { checkPosts } from "./checkPosts.js";
 import { checkHandle } from "./checkHandles.js";
 import { checkDescription, checkDisplayName } from "./checkProfiles.js";
+import { checkFacetSpam } from "./rules/embeds/facets.js";
 
 let cursor = 0;
 let cursorUpdateInterval: NodeJS.Timeout;
···
 
     // Check if the record has facets
     if (hasFacets) {
+      // Check for facet spam (hidden mentions with duplicate byte positions)
+      tasks.push(
+        checkFacetSpam(event.did, event.time_us, atURI, event.commit.record.facets!),
+      );
+
       const hasLinkType = event.commit.record.facets!.some((facet) =>
         facet.features.some(
           (feature) => feature.$type === "app.bsky.richtext.facet#link",

src/rules/embeds/facets.ts

···
+import { createAccountLabel } from "../../moderation.js";
+import { logger } from "../../logger.js";
+import { Facet } from "../../types.js";
+
+// Threshold for duplicate facet positions before flagging as spam
+export const FACET_SPAM_THRESHOLD = 1;
+
+// Label configuration
+export const FACET_SPAM_LABEL = "suspect-inauthentic";
+export const FACET_SPAM_COMMENT =
+  "Abusive facet usage detected (hidden mentions)";
+
+/**
+ * Checks if a post contains facet spam by detecting multiple facets
+ * with identical byte positions (indicating hidden/abusive mentions)
+ */
+export const checkFacetSpam = async (
+  did: string,
+  time: number,
+  atURI: string,
+  facets: Facet[],
+): Promise<void> => {
+  if (!facets || facets.length === 0) {
+    return;
+  }
+
+  // Group facets by their byte position (byteStart:byteEnd)
+  const positionMap = new Map<string, number>();
+
+  for (const facet of facets) {
+    const key = `${facet.index.byteStart}:${facet.index.byteEnd}`;
+    positionMap.set(key, (positionMap.get(key) || 0) + 1);
+  }
+
+  // Check if any position has more than the threshold
+  for (const [position, count] of positionMap.entries()) {
+    if (count > FACET_SPAM_THRESHOLD) {
+      logger.info(
+        {
+          process: "FACET_SPAM",
+          did,
+          atURI,
+          position,
+          count,
+        },
+        "Facet spam detected",
+      );
+
+      await createAccountLabel(
+        did,
+        FACET_SPAM_LABEL,
+        `${time}: ${FACET_SPAM_COMMENT} - ${count} facets at position ${position} in ${atURI}`,
+      );
+
+      // Only label once per post even if multiple positions are suspicious
+      return;
+    }
+  }
+};

src/types.ts

···
   label: string;
   rkey: string;
 }
+
+export interface FacetIndex {
+  byteStart: number;
+  byteEnd: number;
+}
+
+export interface Facet {
+  index: FacetIndex;
+  features: Array<{ $type: string; [key: string]: any }>;
+}