diff --git a/static/sessions.js b/static/sessions.js
index 98ee6252..e4527a95 100644
--- a/static/sessions.js
+++ b/static/sessions.js
@@ -2023,6 +2023,31 @@ function _isOptimisticFirstTurnSessionRow(s){
   );
 }
 
+function _shouldKeepLocalOnlyOptimisticSessionRow(local){
+  if(!_isOptimisticFirstTurnSessionRow(local)) return false;
+  const sid=local.session_id;
+  if(typeof _sendInProgress!=='undefined'&&_sendInProgress&&sid===_sendInProgressSid) return true;
+  const activeSid=S&&S.session&&S.session.session_id;
+  const isActive=Boolean(activeSid&&activeSid===sid);
+  const hasRuntimeConfirmation=Boolean(local.active_stream_id||local.pending_user_message||local.pending_started_at);
+  if(isActive&&S.busy&&hasRuntimeConfirmation) return true;
+  const localTs=Number(local.last_message_at||local.updated_at||0);
+  const ageMs=localTs>0?Date.now()-(localTs*1000):Infinity;
+  return Boolean(isActive&&S.busy&&ageMs>=0&&ageMs<5000);
+}
+
+function _dropStaleOptimisticSessionRow(sid){
+  if(!sid) return;
+  if(INFLIGHT&&INFLIGHT[sid]){
+    delete INFLIGHT[sid];
+    if(typeof clearInflightState==='function') clearInflightState(sid);
+  }
+  if(typeof _sessionStreamingById!=='undefined'&&_sessionStreamingById&&typeof _sessionStreamingById.set==='function'){
+    _sessionStreamingById.set(sid,false);
+  }
+  if(typeof _forgetObservedStreamingSession==='function') _forgetObservedStreamingSession(sid);
+}
+
 function _mergeOptimisticFirstTurnSessions(fetchedSessions){
   const merged=Array.isArray(fetchedSessions)?[...fetchedSessions]:[];
   const bySid=new Map();
@@ -2034,24 +2059,31 @@ function _mergeOptimisticFirstTurnSessions(fetchedSessions){
     if(idx>=0){
       const fetched=merged[idx]||{};
       const fetchedIsServerIdle=_isServerIdleSessionRow(fetched);
+      const keepLocalOptimistic=!fetchedIsServerIdle||_shouldKeepLocalOnlyOptimisticSessionRow(local);
       const localCount=Number(local.message_count||0);
       const fetchedCount=Number(fetched.message_count||0);
       const localTs=Number(local.last_message_at||local.updated_at||0);
       const fetchedTs=Number(fetched.last_message_at||fetched.updated_at||0);
+      if(!keepLocalOptimistic) _dropStaleOptimisticSessionRow(sid);
       merged[idx]={
         ...local,
         ...fetched,
-        message_count:Math.max(localCount,fetchedCount),
-        last_message_at:Math.max(localTs,fetchedTs),
-        updated_at:Math.max(Number(local.updated_at||0),Number(fetched.updated_at||0),localTs,fetchedTs),
-        active_stream_id:fetchedIsServerIdle?null:(fetched.active_stream_id||local.active_stream_id||null),
-        pending_user_message:fetchedIsServerIdle?null:(fetched.pending_user_message||local.pending_user_message||null),
-        pending_started_at:fetchedIsServerIdle?null:(fetched.pending_started_at||local.pending_started_at||null),
-        is_streaming:fetchedIsServerIdle?false:Boolean(fetched.is_streaming||local.is_streaming||_isSessionLocallyStreaming(local)),
+        title:keepLocalOptimistic?(local.title||fetched.title):fetched.title,
+        message_count:keepLocalOptimistic?Math.max(localCount,fetchedCount):fetchedCount,
+        last_message_at:keepLocalOptimistic?Math.max(localTs,fetchedTs):fetchedTs,
+        updated_at:keepLocalOptimistic?Math.max(Number(local.updated_at||0),Number(fetched.updated_at||0),localTs,fetchedTs):Number(fetched.updated_at||fetchedTs||0),
+        active_stream_id:keepLocalOptimistic?(fetched.active_stream_id||local.active_stream_id||null):null,
+        pending_user_message:keepLocalOptimistic?(fetched.pending_user_message||local.pending_user_message||null):null,
+        pending_started_at:keepLocalOptimistic?(fetched.pending_started_at||local.pending_started_at||null):null,
+        is_streaming:keepLocalOptimistic&&Boolean(fetched.is_streaming||local.is_streaming||_isSessionLocallyStreaming(local)),
       };
     }else{
-      merged.push({...local,is_streaming:true});
-      bySid.set(sid,merged.length-1);
+      if(_shouldKeepLocalOnlyOptimisticSessionRow(local)){
+        merged.push({...local,is_streaming:true});
+        bySid.set(sid,merged.length-1);
+      }else{
+        _dropStaleOptimisticSessionRow(sid);
+      }
     }
   }
   return merged;
diff --git a/tests/test_inflight_send_start_race.py b/tests/test_inflight_send_start_race.py
index 933e62a4..1908acad 100644
--- a/tests/test_inflight_send_start_race.py
+++ b/tests/test_inflight_send_start_race.py
@@ -49,3 +49,35 @@ def test_stale_inflight_purge_preserves_current_send_before_stream_id_exists():
     skip_idx = body.index("_sendInProgress")
     delete_idx = body.index("delete INFLIGHT[sid];")
     assert skip_idx < delete_idx, "the current-send skip must run before any purge deletion"
+
+
+def test_server_absent_optimistic_first_turn_rows_are_not_kept_forever():
+    """A local first-turn sidebar row must expire when /api/chat/start never persisted it."""
+    body = _function_body(SESSIONS_JS, "_mergeOptimisticFirstTurnSessions")
+
+    assert "_shouldKeepLocalOnlyOptimisticSessionRow(local)" in body, (
+        "server-absent optimistic rows need an explicit keep/drop gate"
+    )
+    keep_idx = body.index("if(_shouldKeepLocalOnlyOptimisticSessionRow(local))")
+    append_idx = body.index("merged.push({...local,is_streaming:true});")
+    drop_idx = body.index("_dropStaleOptimisticSessionRow(sid);", append_idx)
+    assert keep_idx < append_idx < drop_idx, (
+        "local optimistic rows may only be appended inside the explicit keep gate"
+    )
+    drop_body = _function_body(SESSIONS_JS, "_dropStaleOptimisticSessionRow")
+    assert "clearInflightState(sid)" in drop_body, (
+        "dropping a phantom row should also clear persisted browser recovery state"
+    )
+
+
+def test_server_idle_row_wins_over_stale_optimistic_count():
+    """If the server says the row is idle, stale local message_count/title must not win."""
+    body = _function_body(SESSIONS_JS, "_mergeOptimisticFirstTurnSessions")
+
+    assert "const keepLocalOptimistic=" in body
+    assert "message_count:keepLocalOptimistic?Math.max(localCount,fetchedCount):fetchedCount" in body, (
+        "stale optimistic message_count must not override a confirmed idle server row"
+    )
+    assert "title:keepLocalOptimistic?(local.title||fetched.title):fetched.title" in body, (
+        "stale optimistic provisional title must not override a confirmed idle server row"
+    )