[eric] WS resilience: per-session seq + ring buffer + resume protocol so agent runs survive transient disconnects (wifi flap, sleep, NAT

drop) instead of flipping to completed. Adds heartbeat (25s ping/10s pong), reconnect with infinite jittered backoff, outbound queue gated
   on resume_ack, gap_detected fallback for long offlines, on-disk persistence of terminal events for post-restart recovery, and a
  reconnecting connection state decoupled from session.status. 1089 backend tests covering 500 randomized disconnect scenarios + concurrent
  broadcast races. Backend/WS handler does not cancel agent task on disconnect

frontend/src/shared/state/agentsSlice.ts

@@ -83,6 +83,12 @@ export interface AgentSession {
   mcp_suggestions_is_vague?: boolean;
   active_outputs?: string[];
   compacted_through_msg_id?: string | null;
+  // Transient frontend-only WS connection state. Independent of
+  // `status` (which describes the agent run itself). When the WS
+  // drops we set this to 'reconnecting' so the UI can render a
+  // subtle indicator without faking a terminal status. Cleared back
+  // to 'live' on resume_ack. Never persisted to the backend.
+  connection_state?: 'live' | 'reconnecting';
 }
 
 export interface AgentConfig {
@@ -602,6 +608,19 @@ const agentsSlice = createSlice({
       }
     },
 
+    setSessionConnState(
+      state,
+      action: PayloadAction<{ sessionId: string; state: 'live' | 'reconnecting' }>
+    ) {
+      // Transient WS-layer indicator. Decoupled from session.status
+      // so a network blip never masquerades as a run terminating —
+      // status keeps reflecting the agent's actual lifecycle.
+      const session = state.sessions[action.payload.sessionId];
+      if (session) {
+        session.connection_state = action.payload.state;
+      }
+    },
+
     addMessage(state, action: PayloadAction<{ sessionId: string; message: AgentMessage }>) {
       const session = state.sessions[action.payload.sessionId];
       if (session) {
@@ -1129,6 +1148,7 @@ export const {
   setDraftSystemPrompt,
   updateSession,
   updateSessionStatus,
+  setSessionConnState,
   addMessage,
   streamStart,
   streamDelta,