Dashboard: make LIVE not depend on the SSE stream

LIVE rendered ONLY from the EventSource snapshot handler — and that handler
swallowed render/parse errors (catch {}). If EventSource didn't establish in the
user's browser (proxy, extension, connection cap), LIVE stayed blank while the
date selector — a plain fetch — worked fine. Exactly the reported symptom.

- startStream() now does an immediate pollOnce() (the same fetch path the date
  selector uses) so LIVE shows data even if SSE never connects; SSE then layers
  on for low-latency pushes, with onerror -> interval polling as before.
- Surface render errors (console + conn status) instead of hiding them.
- Serve the dashboard HTML with no-store/no-cache so pushed fixes actually reach
  the browser (a stale cached shell was part of why "I see nothing" persisted).

Verified headless: with EventSource forcibly disabled, LIVE still populates
(10 armed rows, pnl, risk) via the polling fallback — stamp shows "polling ·".

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

api/main.py

@@ -257,6 +257,11 @@ class DashboardHandler(BaseHTTPRequestHandler):
         self.send_response(200)
         self.send_header("Content-Type", "text/html; charset=utf-8")
         self.send_header("Content-Length", str(len(body)))
+        # never cache the dashboard shell — a stale cached page was serving old
+        # JS/CSS, so pushed fixes (and live-vs-cached behaviour) didn't reach the
+        # browser. The page is tiny and the data is fetched separately anyway.
+        self.send_header("Cache-Control", "no-store, no-cache, must-revalidate")
+        self.send_header("Pragma", "no-cache")
         self.end_headers()
         self.wfile.write(body)
 

api/static/dashboard.html

@@ -793,13 +793,18 @@ function setConn(ok, msg) {
   $("stamp").textContent = msg;
 }
 function startStream() {
+  // Render immediately from a plain fetch (the same reliable path the date
+  // selector uses) so LIVE shows data even if EventSource never connects in
+  // this browser/proxy. SSE then layers on for low-latency pushes.
+  pollOnce();
+  if (typeof EventSource === "undefined") { startPolling(); return; }
   try {
     es = new EventSource("/api/stream");
     es.addEventListener("snapshot", (ev) => {
       try { render(JSON.parse(ev.data)); setConn(true, "live · " + new Date().toLocaleTimeString()); }
-      catch (e) {}
+      catch (e) { console.error("render failed:", e); setConn(false, "render error (see console)"); }
     });
-    es.onerror = () => { setConn(false, "stream lost — polling"); es.close(); es = null; startPolling(); };
+    es.onerror = () => { setConn(false, "stream lost — polling"); if (es) es.close(); es = null; startPolling(); };
   } catch (e) { startPolling(); }
 }
 async function pollOnce() {