feat: visibility/CW compose controls, @mention support (v2.11.0)

Add visibility and content warning controls to the reply compose form.
Add @user@domain mention parsing, WebFinger resolution, Mention tags,
inbox delivery, and content linkification for outbound posts.

Confab-Link: http://localhost:8080/sessions/cc343b15-8d10-43cd-a48f-ca912eb79b83

index.js

@@ -8,6 +8,7 @@ import {
 import {
   jf2ToActivityStreams,
   jf2ToAS2Activity,
+  parseMentions,
 } from "./lib/jf2-to-as2.js";
 import { dashboardController } from "./lib/controllers/dashboard.js";
 import {
@@ -467,6 +468,40 @@ export default class ActivityPubEndpoint {
             }
           }
 
+          // Resolve @user@domain mentions in content via WebFinger
+          const contentText = properties.content?.html || properties.content || "";
+          const mentionHandles = parseMentions(contentText);
+          const resolvedMentions = [];
+          const mentionRecipients = [];
+
+          for (const { handle } of mentionHandles) {
+            try {
+              const mentionedActor = await ctx.lookupObject(
+                new URL(`acct:${handle}`),
+              );
+              if (mentionedActor?.id) {
+                resolvedMentions.push({
+                  handle,
+                  actorUrl: mentionedActor.id.href,
+                });
+                mentionRecipients.push({
+                  handle,
+                  actorUrl: mentionedActor.id.href,
+                  actor: mentionedActor,
+                });
+                console.info(
+                  `[ActivityPub] Resolved mention @${handle} → ${mentionedActor.id.href}`,
+                );
+              }
+            } catch (error) {
+              console.warn(
+                `[ActivityPub] Could not resolve mention @${handle}: ${error.message}`,
+              );
+              // Still add with no actorUrl so it gets a fallback link
+              resolvedMentions.push({ handle, actorUrl: null });
+            }
+          }
+
           const activity = jf2ToAS2Activity(
             properties,
             actorUrl,
@@ -475,6 +510,7 @@ export default class ActivityPubEndpoint {
               replyToActorUrl: replyToActor?.url,
               replyToActorHandle: replyToActor?.handle,
               visibility: self.options.defaultVisibility,
+              mentions: resolvedMentions,
             },
           );
 
@@ -529,12 +565,35 @@ export default class ActivityPubEndpoint {
             }
           }
 
+          // Deliver to mentioned actors' inboxes (skip reply-to author, already delivered above)
+          for (const { handle: mHandle, actorUrl: mUrl, actor: mActor } of mentionRecipients) {
+            if (replyToActor?.url === mUrl) continue;
+            try {
+              await ctx.sendActivity(
+                { identifier: handle },
+                mActor,
+                activity,
+                { orderingKey: properties.url },
+              );
+              console.info(
+                `[ActivityPub] Mention delivered to @${mHandle}: ${mUrl}`,
+              );
+            } catch (error) {
+              console.warn(
+                `[ActivityPub] Failed to deliver mention to @${mHandle}: ${error.message}`,
+              );
+            }
+          }
+
           // Determine activity type name
           const typeName =
             activity.constructor?.name || "Create";
           const replyNote = replyToActor
             ? ` (reply to ${replyToActor.url})`
             : "";
+          const mentionNote = mentionRecipients.length > 0
+            ? ` (mentions: ${mentionRecipients.map(m => `@${m.handle}`).join(", ")})`
+            : "";
 
           await logActivity(self._collections.ap_activities, {
             direction: "outbound",
@@ -542,7 +601,7 @@ export default class ActivityPubEndpoint {
             actorUrl: self._publicationUrl,
             objectUrl: properties.url,
             targetUrl: properties["in-reply-to"] || undefined,
-            summary: `Sent ${typeName} for ${properties.url} to ${followerCount} followers${replyNote}`,
+            summary: `Sent ${typeName} for ${properties.url} to ${followerCount} followers${replyNote}${mentionNote}`,
           });
 
           console.info(