fix: clearCompleted must also delete from _knownSessions

Without this, _onSessionAdded never fires on reactivation because
isKnown=true short-circuits the new-session detection branch.

clearCompleted is called on lock file creation / ghost watch fire.
It clears _completedSessions cooldown but the session key stayed in
_knownSessions (isKnown=true), so poll() treated it as already tracked
and silently updated the entry instead of firing _onSessionAdded.

Fix: also delete from _knownSessions in clearCompleted() so next poll
sees the session as unknown and fires _onSessionAdded -> creates new
plugin status box.

Also: findExistingPost skipped in plugin mode on session-added to
prevent stale post reuse from REST search results.

src/session-monitor.js

@@ -106,6 +106,10 @@ class SessionMonitor extends EventEmitter {
    */
   clearCompleted(sessionKey) {
     this._completedSessions.delete(sessionKey);
+    // Also remove from _knownSessions so the next poll sees it as a new session
+    // and fires _onSessionAdded (which creates the new status box).
+    // Without this, isKnown=true suppresses _onSessionAdded even after clearCompleted.
+    this._knownSessions.delete(sessionKey);
   }
 
   /**

src/watcher-manager.js

@@ -287,8 +287,11 @@ async function startDaemon() {
       logger.info({ sessionKey }, 'Reactivating session — creating fresh status box');
     }
 
-    // Check for existing post (restart recovery)
-    if (!postId) {
+    // Check for existing post (restart recovery — REST mode only).
+    // In plugin mode we always create a fresh post: the plugin manages its own
+    // KV store and the old post is already marked done. Reusing it would make
+    // the status box appear stuck at the old position in the thread.
+    if (!postId && !(usePlugin && pluginClient)) {
       const saved = savedOffsets[sessionKey]; // eslint-disable-line security/detect-object-injection
       if (saved) {
         // Try to find existing post in channel history
@@ -300,7 +303,9 @@ async function startDaemon() {
     if (!postId) {
       try {
         if (usePlugin && pluginClient) {
-          // Plugin mode: create custom_livestatus post via plugin
+          // Plugin mode: always create a fresh custom_livestatus post.
+          // The plugin replaces any existing KV entry for this sessionKey so there
+          // is no risk of duplicate boxes.
           postId = await pluginClient.createSession(sessionKey, channelId, rootPostId, agentId);
           logger.info({ sessionKey, postId, channelId, mode: 'plugin' }, 'Created status box via plugin');
         } else {