diff --git a/lib/federation-setup.js b/lib/federation-setup.js
index 04f3894..81ab27b 100644
--- a/lib/federation-setup.js
+++ b/lib/federation-setup.js
@@ -153,10 +153,10 @@ export function setupFederation(options) {
     // Mastodon retries failed deliveries with the original signature, which
     // can be hours old by the time the delivery succeeds.
     signatureTimeWindow: { hours: 12 },
-    // Allow fetching own-site URLs that resolve to private IPs (e.g. when
-    // the blog hostname resolves to a RFC-1918 address on the local LAN).
-    // Without this, Fedify's SSRF guard blocks lookupObject() and WebFinger
-    // calls for own-site posts, producing errors in the activity log.
+    // Required: the blog hostname (svemagie.net) resolves to a RFC-1918 address
+    // on the local LAN. Without this, Fedify blocks lookupObject() calls for
+    // own-site posts. SSRF from external input is mitigated at the input
+    // boundaries (profile.remote.js, followController) via scheme + host validation.
     allowPrivateAddress: true,
   });
 
diff --git a/lib/lookup-helpers.js b/lib/lookup-helpers.js
index c542fc5..3484e9e 100644
--- a/lib/lookup-helpers.js
+++ b/lib/lookup-helpers.js
@@ -35,8 +35,11 @@ export async function lookupWithSecurity(ctx, input, options = {}) {
   }
 
   // If signed lookup failed and we used a custom documentLoader,
-  // retry without it (unsigned GET)
+  // retry without it (unsigned GET). Log the downgrade so operators can detect
+  // key misconfigurations before they silently open unauth fetch paths.
   if (!result && options.documentLoader) {
+    const inputStr = typeof input === "string" ? input : input?.href || String(input);
+    console.debug(`[ActivityPub] Signed lookup failed for ${inputStr} — retrying unsigned`);
     try {
       const { documentLoader: _, ...unsignedOptions } = baseOptions;
       result = await ctx.lookupObject(input, unsignedOptions);
diff --git a/lib/mastodon/routes/statuses.js b/lib/mastodon/routes/statuses.js
index 1cb4dd3..23f6129 100644
--- a/lib/mastodon/routes/statuses.js
+++ b/lib/mastodon/routes/statuses.js
@@ -174,12 +174,14 @@ router.post("/api/v1/statuses", tokenRequired, scopeRequired("write", "write:sta
     const pluginOptions = req.app.locals.mastodonPluginOptions || {};
     const baseUrl = `${req.protocol}://${req.get("host")}`;
 
-    // Idempotency-Key support — prevent duplicate posts on client retry
+    // Idempotency-Key support — prevent duplicate posts on client retry.
+    // Scope key per token so two different authenticated users can't share responses.
     const idempotencyKey = req.headers["idempotency-key"];
+    const _tokenScope = (req.mastodonToken?.accessToken || req.mastodonToken?._id?.toString() || "").slice(0, 16);
     if (idempotencyKey && collections.ap_idempotency) {
       const { createHash } = await import("node:crypto");
       const key = createHash("sha256")
-        .update(`${baseUrl}:${idempotencyKey}`)
+        .update(`${_tokenScope}:${baseUrl}:${idempotencyKey}`)
         .digest("hex");
       const cached = await collections.ap_idempotency.findOne({ key });
       if (cached) {
@@ -305,7 +307,7 @@ router.post("/api/v1/statuses", tokenRequired, scopeRequired("write", "write:sta
 
       if (idempotencyKey && collections.ap_idempotency) {
         const { createHash } = await import("node:crypto");
-        const _spKey = createHash("sha256").update(`${baseUrl}:${idempotencyKey}`).digest("hex");
+        const _spKey = createHash("sha256").update(`${_tokenScope}:${baseUrl}:${idempotencyKey}`).digest("hex");
         await collections.ap_idempotency.insertOne({ key: _spKey, response: _spStatus, createdAt: new Date() }).catch(() => {});
       }
 
@@ -653,7 +655,7 @@ router.post("/api/v1/statuses", tokenRequired, scopeRequired("write", "write:sta
     if (idempotencyKey && collections.ap_idempotency) {
       const { createHash } = await import("node:crypto");
       const key = createHash("sha256")
-        .update(`${baseUrl}:${idempotencyKey}`)
+        .update(`${_tokenScope}:${baseUrl}:${idempotencyKey}`)
         .digest("hex");
       await collections.ap_idempotency
         .insertOne({ key, response: statusResponse, createdAt: new Date() })
diff --git a/lib/outbox-backfill.js b/lib/outbox-backfill.js
index c6e3fda..c0379c2 100644
--- a/lib/outbox-backfill.js
+++ b/lib/outbox-backfill.js
@@ -26,25 +26,33 @@ import { addTimelineItem } from "./storage/timeline.js";
 export async function backfillFromOutbox({ actorUrl, remoteActor, ctx, handle, collections, limit = 20 }) {
   if (!collections?.ap_timeline) return;
 
-  try {
-    const documentLoader = await ctx.getDocumentLoader({ identifier: handle });
+  const withTimeout = (p, ms = 8000) =>
+    Promise.race([p, new Promise((_, rej) => setTimeout(() => rej(new Error("timeout")), ms))]);
 
-    // Fetch outbox collection
-    const outbox = await remoteActor.getOutbox({ documentLoader }).catch(() => null);
+  try {
+    const documentLoader = await withTimeout(ctx.getDocumentLoader({ identifier: handle }));
+
+    // Fetch outbox collection — cap at 8 s
+    const outbox = await withTimeout(remoteActor.getOutbox({ documentLoader })).catch(() => null);
     if (!outbox) return;
 
-    // Collect activity items — try direct items first, then first-page
+    // Guard: if outbox reports more than 500 items without pagination, skip the direct-items path
+    // to avoid materialising a huge in-memory array from a hostile server.
+    const totalItems = typeof outbox.totalItems === "number" ? outbox.totalItems : null;
+
+    // Collect activity items — try direct items first (only for small collections), then first-page
     const activities = [];
     let itemSource = null;
-    try {
-      // Some servers return a directly-iterable collection without pagination
-      const direct = outbox.getItems?.({ documentLoader });
-      if (direct) itemSource = direct;
-    } catch { /* not directly iterable */ }
+    if (totalItems === null || totalItems <= 100) {
+      try {
+        const direct = outbox.getItems?.({ documentLoader });
+        if (direct) itemSource = direct;
+      } catch { /* not directly iterable */ }
+    }
 
     if (!itemSource) {
       // Paginated — navigate to first page
-      const firstPage = await outbox.getFirst({ documentLoader }).catch(() => null);
+      const firstPage = await withTimeout(outbox.getFirst({ documentLoader })).catch(() => null);
       if (firstPage?.getItems) itemSource = firstPage.getItems({ documentLoader });
     }
 
@@ -55,8 +63,8 @@ export async function backfillFromOutbox({ actorUrl, remoteActor, ctx, handle, c
         activities.push(item);
         if (activities.length >= limit) break;
       }
-    } catch {
-      // Partial read is fine — use what we got
+    } catch (iterErr) {
+      console.debug(`[ActivityPub] Outbox backfill iterator stopped for ${actorUrl}: ${iterErr?.message}`);
     }
 
     if (activities.length === 0) return;
@@ -69,9 +77,9 @@ export async function backfillFromOutbox({ actorUrl, remoteActor, ctx, handle, c
         let boostedBy = null;
 
         if (activity instanceof Create) {
-          object = await activity.getObject({ documentLoader }).catch(() => null);
+          object = await withTimeout(activity.getObject({ documentLoader }), 5000).catch(() => null);
         } else if (activity instanceof Announce) {
-          object = await activity.getObject({ documentLoader }).catch(() => null);
+          object = await withTimeout(activity.getObject({ documentLoader }), 5000).catch(() => null);
           if (object) {
             const _username = remoteActor.preferredUsername?.toString() || "";
             const _domain = (() => { try { return new URL(actorUrl).hostname; } catch { return ""; } })();
@@ -107,8 +115,8 @@ export async function backfillFromOutbox({ actorUrl, remoteActor, ctx, handle, c
 
         await addTimelineItem({ ap_timeline: collections.ap_timeline }, item);
         stored++;
-      } catch {
-        // Skip individual item errors — keep going
+      } catch (itemErr) {
+        console.debug(`[ActivityPub] Outbox backfill skipped item from ${actorUrl}: ${itemErr?.message}`);
       }
     }
 
diff --git a/lib/timeline-store.js b/lib/timeline-store.js
index 962c1e9..0e1f3d1 100644
--- a/lib/timeline-store.js
+++ b/lib/timeline-store.js
@@ -235,7 +235,16 @@ export async function extractObjectData(object, options = {}) {
   try {
     if (typeof object.getAttributedTo === "function") {
       const attr = await object.getAttributedTo(loaderOpts);
-      authorObj = Array.isArray(attr) ? attr[0] : attr;
+      const candidate = Array.isArray(attr) ? attr[0] : attr;
+      // If a trusted actorFallback is provided, only accept the resolved author
+      // if it shares the same origin — prevents forged attributedTo impersonation.
+      if (candidate && options.actorFallback) {
+        const candidateHost = (() => { try { return new URL(candidate.id?.href || "").hostname; } catch { return null; } })();
+        const fallbackHost = (() => { try { return new URL(options.actorFallback.id?.href || "").hostname; } catch { return null; } })();
+        authorObj = (candidateHost && fallbackHost && candidateHost === fallbackHost) ? candidate : options.actorFallback;
+      } else {
+        authorObj = candidate;
+      }
     }
   } catch {
     // getAttributedTo() failed (unreachable, deleted, etc.)