perf: UX-safe fetch trimming and instant layer-enable refresh.

Drop duplicate slow-tier weather/ukraine jobs, gate correlations when off, slim health probes, keyed layer-panel subscriptions, align backend layer defaults with the dashboard, and fetch CCTV/FIRMS/PSK/etc. synchronously on enable so toggles stay responsive without background prefetch waste.

backend/services/data_fetcher.py

@@ -479,24 +479,27 @@ def update_slow_data():
         fetch_military_bases,
         fetch_scanners,
         fetch_psk_reporter,
-        fetch_weather_alerts,
+        # weather_alerts + ukraine_alerts: owned by dedicated scheduler jobs
+        # (5 min and 2 min) — keep off slow tier to avoid duplicate upstream work.
         fetch_air_quality,
         fetch_fishing_activity,
         fetch_power_plants,
-        fetch_ukraine_air_raid_alerts,
         fetch_malware_threats,
         fetch_cyber_threats,
         fetch_scm_suppliers,
     ]
     _run_tasks("slow-tier", slow_funcs)
-    # Run correlation engine after all data is fresh
+    # Run correlation engine after all data is fresh (skip when overlay is off).
     try:
+        from services.fetchers._store import is_any_active
         from services.correlation_engine import compute_correlations
-        with _data_lock:
-            snapshot = dict(latest_data)
-        correlations = compute_correlations(snapshot)
-        with _data_lock:
-            latest_data["correlations"] = correlations
+
+        if is_any_active("correlations"):
+            with _data_lock:
+                snapshot = dict(latest_data)
+            correlations = compute_correlations(snapshot)
+            with _data_lock:
+                latest_data["correlations"] = correlations
     except Exception as e:
         logger.error("Correlation engine failed: %s", e)
     try:

backend/services/fetchers/_store.py

@@ -334,15 +334,15 @@ active_layers: dict[str, bool] = {
     "ships_passenger": True,
     "ships_tracked_yachts": True,
     "earthquakes": True,
-    "cctv": True,
+    "cctv": False,
     "ukraine_frontline": True,
     "global_incidents": True,
     "gps_jamming": True,
     "kiwisdr": True,
     "scanners": True,
-    "firms": True,
+    "firms": False,
     "internet_outages": True,
-    "datacenters": True,
+    "datacenters": False,
     "military_bases": True,
     "sigint_meshtastic": True,
     "sigint_aprs": True,
@@ -353,9 +353,9 @@ active_layers: dict[str, bool] = {
     "satnogs": True,
     "tinygs": True,
     "ukraine_alerts": True,
-    "power_plants": True,
+    "power_plants": False,
     "viirs_nightlights": False,
-    "psk_reporter": True,
+    "psk_reporter": False,
     "correlations": True,
     "contradictions": True,
     "uap_sightings": True,

backend/services/layer_enable_refresh.py

@@ -0,0 +1,78 @@
+"""Immediate data refresh when the operator enables a map layer.
+
+Runs synchronously inside POST /api/layers so the frontend's post-toggle
+live-data refetch sees populated payloads (T_toggle_visible guardrail).
+"""
+from __future__ import annotations
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+def snapshot_active_layers() -> dict[str, bool]:
+    from services.fetchers._store import active_layers
+
+    return dict(active_layers)
+
+
+def refresh_newly_enabled_layers(before: dict[str, bool]) -> None:
+    """Fetch any layers that transitioned off → on."""
+    from services.fetchers._store import active_layers, bump_data_version
+
+    refreshed = False
+
+    def _enabled(key: str) -> bool:
+        return bool(active_layers.get(key, False))
+
+    def _was_off_now_on(key: str) -> bool:
+        return not bool(before.get(key, False)) and _enabled(key)
+
+    if _was_off_now_on("cctv"):
+        from services.fetchers.infrastructure import fetch_cctv
+
+        fetch_cctv()
+        refreshed = True
+        logger.info("CCTV loaded (layer enabled)")
+
+    if _was_off_now_on("firms"):
+        from services.fetchers.earth_observation import (
+            fetch_firms_country_fires,
+            fetch_firms_fires,
+        )
+
+        fetch_firms_fires()
+        fetch_firms_country_fires()
+        refreshed = True
+        logger.info("FIRMS fires loaded (layer enabled)")
+
+    if _was_off_now_on("power_plants"):
+        from services.fetchers.infrastructure import fetch_power_plants
+
+        fetch_power_plants()
+        refreshed = True
+        logger.info("Power plants loaded (layer enabled)")
+
+    if _was_off_now_on("psk_reporter"):
+        from services.fetchers.infrastructure import fetch_psk_reporter
+
+        fetch_psk_reporter()
+        refreshed = True
+        logger.info("PSK Reporter loaded (layer enabled)")
+
+    if _was_off_now_on("datacenters"):
+        from services.fetchers.infrastructure import fetch_datacenters
+
+        fetch_datacenters()
+        refreshed = True
+        logger.info("Datacenters loaded (layer enabled)")
+
+    if _was_off_now_on("fishing_activity"):
+        from services.fetchers.geo import fetch_fishing_activity
+
+        fetch_fishing_activity()
+        refreshed = True
+        logger.info("Fishing activity loaded (layer enabled)")
+
+    if refreshed:
+        bump_data_version()