feat: Hollo-inspired federation patterns — outbox failure handling, reply chains, forwarding, visibility

- Add outbox permanent failure handling with smart cleanup:
  - 410 Gone: immediate full cleanup (follower + timeline + notifications)
  - 404: strike system (3 failures over 7+ days triggers cleanup)
  - Strike reset on inbound activity (proves actor is alive)
- Add recursive reply chain fetching (depth 5) with isContext flag
- Add reply forwarding to followers for public replies to our posts
- Add write-time visibility classification (public/unlisted/private/direct)

Confab-Link: http://localhost:8080/sessions/af5f8b45-6b8d-442d-8f25-78c326190709

lib/inbox-handlers.js

@@ -152,6 +152,73 @@ function isDirectMessage(object, ourActorUrl, followersUrl) {
   return true;
 }
 
+/**
+ * Compute post visibility from to/cc addressing fields.
+ * Matches Hollo's write-time visibility classification.
+ *
+ * @param {object} object - Fedify object (Note, Article, etc.)
+ * @returns {"public"|"unlisted"|"private"|"direct"}
+ */
+function computeVisibility(object) {
+  const to = new Set((object.toIds || []).map((u) => u.href));
+  const cc = new Set((object.ccIds || []).map((u) => u.href));
+
+  if (to.has(PUBLIC)) return "public";
+  if (cc.has(PUBLIC)) return "unlisted";
+  // Without knowing the remote actor's followers URL, we can't distinguish
+  // "private" (followers-only) from "direct". Both are non-public.
+  if (to.size > 0 || cc.size > 0) return "private";
+  return "direct";
+}
+
+/**
+ * Recursively fetch and store ancestor posts for a reply chain.
+ * Each ancestor is stored with isContext: true so it can be filtered
+ * from the main timeline while being available for thread views.
+ *
+ * @param {object} object - Fedify object (Note, Article, etc.)
+ * @param {object} collections - MongoDB collections
+ * @param {object} authLoader - Authenticated document loader
+ * @param {number} maxDepth - Maximum recursion depth
+ */
+async function fetchReplyChain(object, collections, authLoader, maxDepth) {
+  if (maxDepth <= 0) return;
+  const parentUrl = object.replyTargetId?.href;
+  if (!parentUrl) return;
+
+  // Skip if we already have this post
+  if (collections.ap_timeline) {
+    const existing = await collections.ap_timeline.findOne({ uid: parentUrl });
+    if (existing) return;
+  }
+
+  // Fetch the parent post
+  let parent;
+  try {
+    parent = await object.getReplyTarget({ documentLoader: authLoader });
+  } catch {
+    // Remote server unreachable — stop climbing
+    return;
+  }
+  if (!parent || !parent.id) return;
+
+  // Store as context item
+  try {
+    const timelineItem = await extractObjectData(parent, {
+      documentLoader: authLoader,
+    });
+    timelineItem.isContext = true;
+    timelineItem.visibility = computeVisibility(parent);
+    await addTimelineItem(collections, timelineItem);
+  } catch {
+    // Extraction failed — stop climbing
+    return;
+  }
+
+  // Recurse for the parent's parent
+  await fetchReplyChain(parent, collections, authLoader, maxDepth - 1);
+}
+
 // ---------------------------------------------------------------------------
 // Individual handlers
 // ---------------------------------------------------------------------------
@@ -515,7 +582,7 @@ export async function handleAnnounce(item, collections, ctx, handle) {
         boostedAt: announce.published ? String(announce.published) : new Date().toISOString(),
         documentLoader: authLoader,
       });
-
+      timelineItem.visibility = computeVisibility(object);
       await addTimelineItem(collections, timelineItem);
 
       // Fire-and-forget quote enrichment for boosted posts
@@ -688,6 +755,18 @@ export async function handleCreate(item, collections, ctx, handle) {
     }
   }
 
+  // --- Recursive reply chain fetching ---
+  // Fetch and store ancestor posts so conversation threads have context.
+  // Each ancestor is stored with isContext: true to distinguish from organic timeline items.
+  if (inReplyTo) {
+    try {
+      await fetchReplyChain(object, collections, authLoader, 5);
+    } catch (error) {
+      // Non-critical — incomplete context is acceptable
+      console.warn("[inbox-handlers] Reply chain fetch failed:", error.message);
+    }
+  }
+
   // Check for mentions of our actor
   if (object.tag) {
     const tags = Array.isArray(object.tag) ? object.tag : [object.tag];
@@ -728,6 +807,7 @@ export async function handleCreate(item, collections, ctx, handle) {
         actorFallback: actorObj,
         documentLoader: authLoader,
       });
+      timelineItem.visibility = computeVisibility(object);
       await addTimelineItem(collections, timelineItem);
 
       // Fire-and-forget OG unfurling for notes and articles (not boosts)
@@ -768,6 +848,7 @@ export async function handleCreate(item, collections, ctx, handle) {
             actorFallback: actorObj,
             documentLoader: authLoader,
           });
+          timelineItem.visibility = computeVisibility(object);
           await addTimelineItem(collections, timelineItem);
         }
       }