diff --git a/src/__tests__/scan.test.js b/src/__tests__/scan.test.js
index f25ddd1..bd0bde6 100644
--- a/src/__tests__/scan.test.js
+++ b/src/__tests__/scan.test.js
@@ -135,6 +135,22 @@ describe('runScan — missing blob reporting and cross-check', () => {
     expect(result.trustworthy).toBe(false);
     expect(result.errors.some((e) => e.step === 'listMissingBlobs')).toBe(true);
   });
+
+  test('listMissingBlobs is called WITHOUT a repo param (authenticated-session endpoint)', async () => {
+    const calls = [];
+    const api = makeApi({ held: [BLOB1], collections: [], pdsMissing: [] });
+    const orig = api.listMissingBlobs;
+    api.listMissingBlobs = async (params) => {
+      calls.push(params);
+      return orig(params);
+    };
+    await runScan({ did: DID, ...api });
+    expect(calls.length).toBeGreaterThan(0);
+    for (const c of calls) {
+      expect(c).not.toHaveProperty('repo');
+      expect(c).toHaveProperty('limit');
+    }
+  });
 });
 
 describe('runScan — fail-closed invariants', () => {
diff --git a/src/lib/scan.js b/src/lib/scan.js
index fd556c3..7c70b88 100644
--- a/src/lib/scan.js
+++ b/src/lib/scan.js
@@ -35,7 +35,8 @@ export const DEFAULT_LIST_RECORDS_LIMIT = 100;
  * @param {Function} opts.listBlobs     async ({did, limit, cursor}) => {data:{cids:[],cursor}}
  * @param {Function} opts.describeRepo  async ({repo}) => {data:{collections:[]}}
  * @param {Function} opts.listRecords   async ({repo, collection, limit, cursor}) => {data:{records:[],cursor}}
- * @param {Function} opts.listMissingBlobs async ({repo, limit, cursor}) => {data:{blobs:[],cursor}}
+ * @param {Function} opts.listMissingBlobs async ({limit, cursor}) => {data:{blobs:[],cursor}}
+ *              NOTE: takes only limit/cursor (operates on authenticated repo)
  * @param {string}   opts.did
  * @param {Object}   [opts.onProgress]  optional {onHeld, onCollection, onRecord, onMissing} callbacks
  * @returns {Promise<ScanResult>}
@@ -152,11 +153,13 @@ export async function runScan({
   missing.sort((a, b) => a.cid.localeCompare(b.cid));
 
   // 5. Cross-check missing against listMissingBlobs (PDS's own accounting)
+  // NOTE: listMissingBlobs takes ONLY limit/cursor — it operates on the
+  // authenticated session's repo. Passing `repo` is an invalid parameter.
   const pdsMissing = new Set();
   try {
     let cursor;
     do {
-      const res = await listMissingBlobs({ repo: did, limit: 500, cursor });
+      const res = await listMissingBlobs({ limit: 500, cursor });
       const blobs = res?.data?.blobs;
       if (Array.isArray(blobs)) {
         for (const b of blobs) {