Add Suspend/Resume trading session button

- md_feeder: add _suspended flag; handle suspend/resume control messages
to pause/unpause order generation without ending the session
- dashboard: add suspended field to session_state; add POST /session/suspend
and POST /session/resume endpoints that publish to control topic
- dashboard template: Suspend button (blue-grey) between Start and End of Day;
toggles to Resume (green) when paused; session badge shows PAUSED (amber)
with pulsing dot when suspended; button disabled when session is idle

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dashboard/dashboard.py

@@ -20,7 +20,7 @@ sse_clients = []
 sse_clients_lock = threading.Lock()
 
 # Session state
-session_state = {"active": False, "start_time": None}
+session_state = {"active": False, "start_time": None, "suspended": False}
 
 # ── OHLCV History ──────────────────────────────────────────────────────────────
 HISTORY_DB = os.getenv("HISTORY_DB", "/app/data/dashboard_history.db")
@@ -305,6 +305,7 @@ def session_start():
         p.flush()
 
         session_state["active"] = True
+        session_state["suspended"] = False
         session_state["start_time"] = time.time()
         broadcast_event("session", {"status": "started", "time": session_state["start_time"]})
         return jsonify({"status": "ok", "message": "Day started"})
@@ -338,12 +339,43 @@ def session_end():
         p.flush()
 
         session_state["active"] = False
+        session_state["suspended"] = False
         broadcast_event("session", {"status": "ended", "time": time.time()})
         return jsonify({"status": "ok", "message": "Day ended, closing prices saved"})
     except Exception as e:
         return jsonify({"status": "error", "error": str(e)}), 500
 
 
+@app.route("/session/suspend", methods=["POST"])
+def session_suspend():
+    try:
+        if not session_state["active"]:
+            return jsonify({"status": "error", "error": "No active session"}), 400
+        p = get_producer()
+        p.send(Config.CONTROL_TOPIC, {"action": "suspend"})
+        p.flush()
+        session_state["suspended"] = True
+        broadcast_event("session", {"status": "suspended"})
+        return jsonify({"status": "ok", "message": "Session suspended"})
+    except Exception as e:
+        return jsonify({"status": "error", "error": str(e)}), 500
+
+
+@app.route("/session/resume", methods=["POST"])
+def session_resume():
+    try:
+        if not session_state["active"]:
+            return jsonify({"status": "error", "error": "No active session"}), 400
+        p = get_producer()
+        p.send(Config.CONTROL_TOPIC, {"action": "resume"})
+        p.flush()
+        session_state["suspended"] = False
+        broadcast_event("session", {"status": "active"})
+        return jsonify({"status": "ok", "message": "Session resumed"})
+    except Exception as e:
+        return jsonify({"status": "error", "error": str(e)}), 500
+
+
 @app.route("/session/status")
 def session_status():
     return jsonify(session_state)
@@ -404,7 +436,13 @@ def stream():
                     f"{json.dumps({'orders': list(orders), 'bbos': dict(bbos), 'trades': list(trades_cache)})}\n\n"
                 )
             # Also send current session state
-            yield f"event: session\ndata: {json.dumps({'status': 'started' if session_state['active'] else 'ended'})}\n\n"
+            if not session_state["active"]:
+                _sess_status = "ended"
+            elif session_state["suspended"]:
+                _sess_status = "suspended"
+            else:
+                _sess_status = "started"
+            yield f"event: session\ndata: {json.dumps({'status': _sess_status})}\n\n"
             while True:
                 try:
                     message = q.get(timeout=30)

dashboard/templates/index.html

@@ -140,10 +140,17 @@
     }
     .btn-start { background: #28a745; color: #fff; }
     .btn-start:hover { background: #218838; }
+    .btn-suspend { background: #607d8b; color: #fff; }
+    .btn-suspend:hover { background: #455a64; }
+    .btn-resume { background: #4caf50; color: #fff; }
+    .btn-resume:hover { background: #388e3c; }
     .btn-end { background: #ff9800; color: #fff; }
     .btn-end:hover { background: #e68900; }
+    .btn-day:disabled { background: #ccc !important; color: #999; cursor: not-allowed; }
     .status.active { background: #d4edda; color: #155724; }
     .status.active .dot { background: #28a745; }
+    .status.suspended { background: #fff3cd; color: #856404; }
+    .status.suspended .dot { background: #ffc107; animation: pulse 1s infinite; }
     .status.idle { background: #e8e8e8; color: #666; }
     .status.idle .dot { background: #9e9e9e; }
 
@@ -191,6 +198,7 @@
     <span id="status" class="status connecting"><span class="dot"></span><span id="status-text">Connecting...</span></span>
     <span id="session-badge" class="status idle"><span class="dot"></span><span id="session-text">IDLE</span></span>
     <button onclick="startDay()" class="btn-day btn-start">Start of Day</button>
+    <button id="suspend-btn" onclick="toggleSuspend()" class="btn-day btn-suspend" disabled>Suspend</button>
     <button onclick="endDay()" class="btn-day btn-end">End of Day</button>
     <a href="/fix/" style="margin-left:auto; padding:4px 14px; background:#6c757d; color:#fff; border-radius:20px; font-size:12px; font-weight:bold; text-decoration:none;">FIX UI</a>
   </h1>
@@ -1018,7 +1026,9 @@
 
       eventSource.addEventListener("session", (e) => {
         const data = JSON.parse(e.data);
-        updateSessionBadge(data.status === "started");
+        const active = data.status === "started" || data.status === "active" || data.status === "suspended";
+        const suspended = data.status === "suspended";
+        updateSessionBadge(active, suspended);
       });
 
       eventSource.onerror = () => {
@@ -1050,11 +1060,43 @@
 
     // ── Session control ────────────────────────────────────────────────────────
 
-    function updateSessionBadge(active) {
+    let _sessionSuspended = false;
+
+    function updateSessionBadge(active, suspended) {
       const badge = document.getElementById("session-badge");
       const text  = document.getElementById("session-text");
-      badge.className = "status " + (active ? "active" : "idle");
-      text.textContent = active ? "ACTIVE" : "IDLE";
+      const btn   = document.getElementById("suspend-btn");
+      _sessionSuspended = !!suspended;
+      if (!active) {
+        badge.className = "status idle";
+        text.textContent = "IDLE";
+        btn.disabled = true;
+        btn.textContent = "Suspend";
+        btn.className = "btn-day btn-suspend";
+      } else if (suspended) {
+        badge.className = "status suspended";
+        text.textContent = "PAUSED";
+        btn.disabled = false;
+        btn.textContent = "Resume";
+        btn.className = "btn-day btn-resume";
+      } else {
+        badge.className = "status active";
+        text.textContent = "ACTIVE";
+        btn.disabled = false;
+        btn.textContent = "Suspend";
+        btn.className = "btn-day btn-suspend";
+      }
+    }
+
+    async function toggleSuspend() {
+      try {
+        const url = _sessionSuspended ? "/session/resume" : "/session/suspend";
+        const r = await fetch(url, { method: "POST" });
+        const result = await r.json();
+        if (result.status !== "ok") alert("Error: " + (result.error || "Unknown error"));
+      } catch (e) {
+        alert("Error: " + e.message);
+      }
     }
 
     async function startDay() {
@@ -1063,7 +1105,7 @@
         const r = await fetch("/session/start", { method: "POST" });
         const result = await r.json();
         if (result.status === "ok") {
-          updateSessionBadge(true);
+          updateSessionBadge(true, false);
         } else {
           alert("Error: " + (result.error || "Unknown error"));
         }
@@ -1078,7 +1120,7 @@
         const r = await fetch("/session/end", { method: "POST" });
         const result = await r.json();
         if (result.status === "ok") {
-          updateSessionBadge(false);
+          updateSessionBadge(false, false);
           alert("Day ended. Closing prices saved.");
         } else {
           alert("Error: " + (result.error || "Unknown error"));

md_feeder/mdf_simulator.py

@@ -12,6 +12,7 @@ ORDER_INTERVAL = 60.0 / Config.ORDERS_PER_MIN
 # Module-level state (shared with control listener thread)
 _securities = {}
 _running = True
+_suspended = False
 
 
 def load_securities():
@@ -68,14 +69,15 @@ def make_snapshot(symbol, best_bid, best_ask, bid_size, ask_size):
 
 
 def listen_control(ctrl_consumer):
-    """Background thread: listen for start/stop control messages."""
-    global _running, _securities
+    """Background thread: listen for start/stop/suspend/resume control messages."""
+    global _running, _suspended, _securities
     print("[MDF] Control listener started")
     for msg in ctrl_consumer:
         action = (msg.value or {}).get("action")
         if action == "stop":
             _running = False
-            print("[MDF] STOP signal received – pausing simulation")
+            _suspended = False
+            print("[MDF] STOP signal received – simulation stopped")
         elif action == "start":
             try:
                 new_secs = load_securities()
@@ -84,8 +86,15 @@ def listen_control(ctrl_consumer):
                 print(f"[MDF] START signal – reloaded securities: {list(_securities.keys())}")
             except Exception as e:
                 print(f"[MDF] Error reloading securities on start: {e}")
+            _suspended = False
             _running = True
-            print("[MDF] Simulation resumed")
+            print("[MDF] Simulation started")
+        elif action == "suspend":
+            _suspended = True
+            print("[MDF] SUSPEND signal received – order generation paused")
+        elif action == "resume":
+            _suspended = False
+            print("[MDF] RESUME signal received – order generation resumed")
 
 
 if __name__ == "__main__":
@@ -112,12 +121,12 @@ if __name__ == "__main__":
 
     try:
         while True:
-            if not _running:
+            if not _running or _suspended:
                 time.sleep(0.5)
                 continue
 
             for sym, vals in list(_securities.items()):
-                if not _running:
+                if not _running or _suspended:
                     break
 
                 mid = vals["current"]