fix(explorer): read SSE stream until event and data lines arrive

The health check stopped after two non-empty lines and missed the data line that follows event: ping on mission-control streams.

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/check-explorer-health.sh

@@ -7,6 +7,7 @@ BASE_URL="${1:-https://explorer.d-bis.org}"
 python3 - "$BASE_URL" <<'PY'
 import re
 import sys
+import time
 
 import requests
 
@@ -158,15 +159,22 @@ try:
         if resp.status_code >= 400:
             failed = True
         else:
-            lines = []
+            saw_event = False
+            saw_data = False
+            deadline = time.time() + 25
             for raw in resp.iter_lines(decode_unicode=True):
                 if raw:
-                    lines.append(raw)
-                if len(lines) >= 2:
+                    if raw.startswith("event:"):
+                        saw_event = True
+                    if raw.startswith("data:"):
+                        saw_data = True
+                if saw_event and saw_data:
                     break
-            if not any(line.startswith("event:") for line in lines):
+                if time.time() > deadline:
+                    break
+            if not saw_event:
                 mark_failure("     mission-control stream did not emit an event line")
-            if not any(line.startswith("data:") for line in lines):
+            if not saw_data:
                 mark_failure("     mission-control stream did not emit a data line")
 except Exception as exc:
     mark_failure(f"ERR  /explorer-api/v1/mission-control/stream  [{exc}]")