diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
new file mode 100644
index 0000000..a93e070
--- /dev/null
+++ b/.github/pull_request_template.md
@@ -0,0 +1,13 @@
+## Summary
+
+<!-- What changed and why (1–3 bullets). -->
+
+## Test plan
+
+- [ ] <!-- How you verified the change -->
+
+## Production hardening (data path / fetchers / unattended deploys only)
+
+If this PR touches the data path, fetchers, or live-data APIs, walk through [docs/production-hardening.md](../docs/production-hardening.md) and note any N/A items here.
+
+- [ ] Checklist reviewed (or N/A — explain why)
diff --git a/backend/main.py b/backend/main.py
index 8695b54..96ed16e 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -3848,426 +3848,6 @@ async def update_layers(update: LayerUpdate, request: Request):
     return {"status": "ok"}
 
 
-def _etag_response(request: Request, payload: dict, prefix: str = "", default=None):
-    """Serialize once, use data version for ETag, return 304 or full response.
-
-    Uses a monotonic version counter instead of MD5-hashing the full payload.
-    The 304 fast path avoids serialization entirely.
-    """
-    etag = _current_etag(prefix)
-    if request.headers.get("if-none-match") == etag:
-        return Response(status_code=304, headers={"ETag": etag, "Cache-Control": "no-cache"})
-    content = json_mod.dumps(_json_safe(payload), default=default, allow_nan=False)
-    return Response(
-        content=content,
-        media_type="application/json",
-        headers={"ETag": etag, "Cache-Control": "no-cache"},
-    )
-
-
-def _current_etag(prefix: str = "") -> str:
-    from services.fetchers._store import get_active_layers_version, get_data_version
-
-    return f"{prefix}v{get_data_version()}-l{get_active_layers_version()}"
-
-
-def _json_safe(value):
-    """Recursively replace non-finite floats with None so responses stay valid JSON."""
-    if isinstance(value, float):
-        return value if math.isfinite(value) else None
-    if isinstance(value, dict):
-        # Snapshot mutable mappings first so background fetcher updates do not
-        # invalidate iteration while we serialize a response.
-        return {k: _json_safe(v) for k, v in list(value.items())}
-    if isinstance(value, list):
-        return [_json_safe(v) for v in list(value)]
-    if isinstance(value, tuple):
-        return [_json_safe(v) for v in list(value)]
-    return value
-
-
-def _sanitize_payload(value):
-    """Thread-safe snapshot with NaN→None. Cheaper than _json_safe: only deep-
-    copies dicts (for thread safety) and replaces non-finite floats. Lists are
-    shallow-copied — orjson handles the leaf serialisation natively."""
-    if isinstance(value, float):
-        return value if math.isfinite(value) else None
-    if isinstance(value, dict):
-        return {k: _sanitize_payload(v) for k, v in list(value.items())}
-    if isinstance(value, (list, tuple)):
-        return list(value)
-    return value
-
-
-def _bbox_filter(
-    items: list, s: float, w: float, n: float, e: float, lat_key: str = "lat", lng_key: str = "lng"
-) -> list:
-    """Filter a list of dicts to those within the bounding box (with 20% padding).
-    Handles antimeridian crossing (e.g. w=170, e=-170)."""
-    pad_lat = (n - s) * 0.2
-    pad_lng = (e - w) * 0.2 if e > w else ((e + 360 - w) * 0.2)
-    s2, n2 = s - pad_lat, n + pad_lat
-    w2, e2 = w - pad_lng, e + pad_lng
-    crosses_antimeridian = w2 > e2
-    out = []
-    for item in items:
-        lat = item.get(lat_key)
-        lng = item.get(lng_key)
-        if lat is None or lng is None:
-            out.append(item)  # Keep items without coords (don't filter them out)
-            continue
-        if not (s2 <= lat <= n2):
-            continue
-        if crosses_antimeridian:
-            if lng >= w2 or lng <= e2:
-                out.append(item)
-        else:
-            if w2 <= lng <= e2:
-                out.append(item)
-    return out
-
-
-def _bbox_filter_geojson_points(items: list, s: float, w: float, n: float, e: float) -> list:
-    """Filter GeoJSON Point features to a padded bounding box."""
-    pad_lat = (n - s) * 0.2
-    pad_lng = (e - w) * 0.2 if e > w else ((e + 360 - w) * 0.2)
-    s2, n2 = s - pad_lat, n + pad_lat
-    w2, e2 = w - pad_lng, e + pad_lng
-    crosses_antimeridian = w2 > e2
-    out = []
-    for item in items:
-        geometry = item.get("geometry") if isinstance(item, dict) else None
-        coords = geometry.get("coordinates") if isinstance(geometry, dict) else None
-        if not isinstance(coords, (list, tuple)) or len(coords) < 2:
-            out.append(item)
-            continue
-        lng, lat = coords[0], coords[1]
-        if lat is None or lng is None:
-            out.append(item)
-            continue
-        if not (s2 <= lat <= n2):
-            continue
-        if crosses_antimeridian:
-            if lng >= w2 or lng <= e2:
-                out.append(item)
-        else:
-            if w2 <= lng <= e2:
-                out.append(item)
-    return out
-
-
-def _bbox_spans(s: float | None, w: float | None, n: float | None, e: float | None) -> tuple[float, float]:
-    if None in (s, w, n, e):
-        return 180.0, 360.0
-    lat_span = max(0.0, float(n) - float(s))
-    lng_span = float(e) - float(w)
-    if lng_span < 0:
-        lng_span += 360.0
-    if lng_span == 0 and w == -180 and e == 180:
-        lng_span = 360.0
-    return lat_span, max(0.0, lng_span)
-
-
-def _downsample_points(items: list, max_items: int) -> list:
-    if max_items <= 0 or len(items) <= max_items:
-        return items
-    step = len(items) / float(max_items)
-    return [items[min(len(items) - 1, int(i * step))] for i in range(max_items)]
-
-
-def _world_and_continental_scale(
-    has_bbox: bool, s: float | None, w: float | None, n: float | None, e: float | None
-) -> tuple[bool, bool]:
-    lat_span, lng_span = _bbox_spans(s, w, n, e)
-    world_scale = (not has_bbox) or lng_span >= 300 or lat_span >= 120
-    continental_scale = has_bbox and not world_scale and (lng_span >= 120 or lat_span >= 55)
-    return world_scale, continental_scale
-
-
-def _filter_sigint_by_layers(items: list, active_layers: dict[str, bool]) -> list:
-    allow_aprs = bool(active_layers.get("sigint_aprs", True))
-    allow_mesh = bool(active_layers.get("sigint_meshtastic", True))
-    if allow_aprs and allow_mesh:
-        return items
-
-    allowed_sources: set[str] = {"js8call"}
-    if allow_aprs:
-        allowed_sources.add("aprs")
-    if allow_mesh:
-        allowed_sources.update({"meshtastic", "meshtastic-map"})
-    return [item for item in items if str(item.get("source") or "").lower() in allowed_sources]
-
-
-def _sigint_totals_for_items(items: list) -> dict[str, int]:
-    totals = {
-        "total": len(items),
-        "meshtastic": 0,
-        "meshtastic_live": 0,
-        "meshtastic_map": 0,
-        "aprs": 0,
-        "js8call": 0,
-    }
-    for item in items:
-        source = str(item.get("source") or "").lower()
-        if source == "meshtastic":
-            totals["meshtastic"] += 1
-            if bool(item.get("from_api")):
-                totals["meshtastic_map"] += 1
-            else:
-                totals["meshtastic_live"] += 1
-        elif source == "aprs":
-            totals["aprs"] += 1
-        elif source == "js8call":
-            totals["js8call"] += 1
-    return totals
-
-
-def _cap_startup_items(items: list | None, max_items: int) -> list:
-    if not items:
-        return []
-    if len(items) <= max_items:
-        return items
-    return items[:max_items]
-
-
-def _cap_fast_startup_payload(payload: dict) -> dict:
-    """Trim high-volume layers for the first dashboard paint.
-
-    The full fast payload can legitimately contain tens of thousands of AIS,
-    ADS-B, SIGINT, and CCTV records. Returning all of that during app startup
-    blocks the first map render behind serialization/proxy/network pressure.
-    This startup payload paints representative live data immediately; the next
-    normal poll replaces it with the full dataset.
-    """
-    capped = dict(payload)
-    capped["commercial_flights"] = _cap_startup_items(capped.get("commercial_flights"), 800)
-    capped["private_flights"] = _cap_startup_items(capped.get("private_flights"), 300)
-    capped["private_jets"] = _cap_startup_items(capped.get("private_jets"), 150)
-    capped["ships"] = _cap_startup_items(capped.get("ships"), 1500)
-    capped["cctv"] = []
-    capped["sigint"] = _cap_startup_items(capped.get("sigint"), 500)
-    capped["trains"] = _cap_startup_items(capped.get("trains"), 100)
-    capped["startup_payload"] = True
-    return capped
-
-
-def _cap_fast_dashboard_payload(payload: dict) -> dict:
-    capped = dict(payload)
-    capped["commercial_flights"] = _downsample_points(capped.get("commercial_flights") or [], 6000)
-    capped["private_flights"] = _downsample_points(capped.get("private_flights") or [], 1500)
-    capped["private_jets"] = _downsample_points(capped.get("private_jets") or [], 1500)
-    capped["ships"] = _downsample_points(capped.get("ships") or [], 8000)
-    capped["cctv"] = _downsample_points(capped.get("cctv") or [], 2500)
-    capped["sigint"] = _downsample_points(capped.get("sigint") or [], 5000)
-    return capped
-
-
-@app.get("/api/live-data/fast")
-@limiter.limit("120/minute")
-async def live_data_fast(
-    request: Request,
-    # bbox params accepted for backward compat but no longer used for filtering —
-    # all cached data is returned and the frontend culls off-screen entities via MapLibre.
-    s: float = Query(None, description="South bound (ignored)", ge=-90, le=90),
-    w: float = Query(None, description="West bound (ignored)", ge=-180, le=180),
-    n: float = Query(None, description="North bound (ignored)", ge=-90, le=90),
-    e: float = Query(None, description="East bound (ignored)", ge=-180, le=180),
-    initial: bool = Query(False, description="Return a capped startup payload for first paint"),
-):
-    etag = _current_etag(prefix="fast|initial|" if initial else "fast|full|")
-    if request.headers.get("if-none-match") == etag:
-        return Response(status_code=304, headers={"ETag": etag, "Cache-Control": "no-cache"})
-
-    from services.fetchers._store import (
-        active_layers,
-        get_latest_data_subset_refs,
-        get_source_timestamps_snapshot,
-    )
-
-    d = get_latest_data_subset_refs(
-        "last_updated",
-        "commercial_flights",
-        "military_flights",
-        "private_flights",
-        "private_jets",
-        "tracked_flights",
-        "ships",
-        "cctv",
-        "uavs",
-        "liveuamap",
-        "gps_jamming",
-        "satellites",
-        "satellite_source",
-        "sigint",
-        "sigint_totals",
-        "trains",
-    )
-    freshness = get_source_timestamps_snapshot()
-
-    ships_enabled = any(
-        active_layers.get(key, True)
-        for key in (
-            "ships_military",
-            "ships_cargo",
-            "ships_civilian",
-            "ships_passenger",
-            "ships_tracked_yachts",
-        )
-    )
-    cctv_total = len(d.get("cctv") or [])
-    sigint_items = _filter_sigint_by_layers(d.get("sigint") or [], active_layers)
-    sigint_totals = _sigint_totals_for_items(sigint_items)
-
-    payload = {
-        "commercial_flights": (d.get("commercial_flights") or []) if active_layers.get("flights", True) else [],
-        "military_flights": (d.get("military_flights") or []) if active_layers.get("military", True) else [],
-        "private_flights": (d.get("private_flights") or []) if active_layers.get("private", True) else [],
-        "private_jets": (d.get("private_jets") or []) if active_layers.get("jets", True) else [],
-        "tracked_flights": (d.get("tracked_flights") or []) if active_layers.get("tracked", True) else [],
-        "ships": (d.get("ships") or []) if ships_enabled else [],
-        "cctv": (d.get("cctv") or []) if active_layers.get("cctv", True) else [],
-        "uavs": (d.get("uavs") or []) if active_layers.get("military", True) else [],
-        "liveuamap": (d.get("liveuamap") or []) if active_layers.get("global_incidents", True) else [],
-        "gps_jamming": (d.get("gps_jamming") or []) if active_layers.get("gps_jamming", True) else [],
-        "satellites": (d.get("satellites") or []) if active_layers.get("satellites", True) else [],
-        "satellite_source": d.get("satellite_source", "none"),
-        "sigint": sigint_items
-        if (active_layers.get("sigint_meshtastic", True) or active_layers.get("sigint_aprs", True))
-        else [],
-        "sigint_totals": sigint_totals,
-        "cctv_total": cctv_total,
-        "trains": (d.get("trains") or []) if active_layers.get("trains", True) else [],
-        "freshness": freshness,
-    }
-    if initial:
-        payload = _cap_fast_startup_payload(payload)
-    else:
-        payload = _cap_fast_dashboard_payload(payload)
-    return Response(
-        content=orjson.dumps(_sanitize_payload(payload)),
-        media_type="application/json",
-        headers={"ETag": etag, "Cache-Control": "no-cache"},
-    )
-
-
-@app.get("/api/live-data/slow")
-@limiter.limit("60/minute")
-async def live_data_slow(
-    request: Request,
-    # bbox params accepted for backward compat but no longer used for filtering.
-    s: float = Query(None, description="South bound (ignored)", ge=-90, le=90),
-    w: float = Query(None, description="West bound (ignored)", ge=-180, le=180),
-    n: float = Query(None, description="North bound (ignored)", ge=-90, le=90),
-    e: float = Query(None, description="East bound (ignored)", ge=-180, le=180),
-):
-    etag = _current_etag(prefix="slow|full|")
-    if request.headers.get("if-none-match") == etag:
-        return Response(status_code=304, headers={"ETag": etag, "Cache-Control": "no-cache"})
-
-    from services.fetchers._store import (
-        active_layers,
-        get_latest_data_subset_refs,
-        get_source_timestamps_snapshot,
-    )
-
-    d = get_latest_data_subset_refs(
-        "last_updated",
-        "news",
-        "stocks",
-        "financial_source",
-        "oil",
-        "weather",
-        "traffic",
-        "earthquakes",
-        "frontlines",
-        "gdelt",
-        "airports",
-        "kiwisdr",
-        "satnogs_stations",
-        "satnogs_observations",
-        "tinygs_satellites",
-        "space_weather",
-        "internet_outages",
-        "firms_fires",
-        "datacenters",
-        "military_bases",
-        "power_plants",
-        "viirs_change_nodes",
-        "scanners",
-        "weather_alerts",
-        "ukraine_alerts",
-        "air_quality",
-        "volcanoes",
-        "fishing_activity",
-        "psk_reporter",
-        "crowdthreat",
-        "correlations",
-        "threat_level",
-        "trending_markets",
-        "fimi",
-        "uap_sightings",
-        "wastewater",
-        "sar_scenes",
-        "sar_anomalies",
-        "sar_aoi_coverage",
-    )
-    freshness = get_source_timestamps_snapshot()
-
-    payload = {
-        "last_updated": d.get("last_updated"),
-        "threat_level": d.get("threat_level"),
-        "trending_markets": d.get("trending_markets", []),
-        "fimi": d.get("fimi", {}),
-        "news": d.get("news", []),
-        "stocks": d.get("stocks", {}),
-        "financial_source": d.get("financial_source", ""),
-        "oil": d.get("oil", {}),
-        "weather": d.get("weather"),
-        "traffic": d.get("traffic", []),
-        "earthquakes": (d.get("earthquakes") or []) if active_layers.get("earthquakes", True) else [],
-        "frontlines": d.get("frontlines") if active_layers.get("ukraine_frontline", True) else None,
-        "gdelt": (d.get("gdelt") or []) if active_layers.get("global_incidents", True) else [],
-        "airports": d.get("airports") or [],
-        "kiwisdr": (d.get("kiwisdr") or []) if active_layers.get("kiwisdr", True) else [],
-        "satnogs_stations": (d.get("satnogs_stations") or []) if active_layers.get("satnogs", True) else [],
-        "satnogs_total": len(d.get("satnogs_stations") or []),
-        "satnogs_observations": (d.get("satnogs_observations") or []) if active_layers.get("satnogs", True) else [],
-        "tinygs_satellites": (d.get("tinygs_satellites") or []) if active_layers.get("tinygs", True) else [],
-        "tinygs_total": len(d.get("tinygs_satellites") or []),
-        "psk_reporter": (d.get("psk_reporter") or []) if active_layers.get("psk_reporter", True) else [],
-        "space_weather": d.get("space_weather"),
-        "internet_outages": (d.get("internet_outages") or []) if active_layers.get("internet_outages", True) else [],
-        "firms_fires": (d.get("firms_fires") or []) if active_layers.get("firms", True) else [],
-        "datacenters": (d.get("datacenters") or []) if active_layers.get("datacenters", True) else [],
-        "military_bases": (d.get("military_bases") or []) if active_layers.get("military_bases", True) else [],
-        "power_plants": (d.get("power_plants") or []) if active_layers.get("power_plants", True) else [],
-        "viirs_change_nodes": (d.get("viirs_change_nodes") or []) if active_layers.get("viirs_nightlights", True) else [],
-        "scanners": (d.get("scanners") or []) if active_layers.get("scanners", True) else [],
-        "weather_alerts": d.get("weather_alerts", []) if active_layers.get("weather_alerts", True) else [],
-        "ukraine_alerts": d.get("ukraine_alerts", []) if active_layers.get("ukraine_alerts", True) else [],
-        "air_quality": (d.get("air_quality") or []) if active_layers.get("air_quality", True) else [],
-        "volcanoes": (d.get("volcanoes") or []) if active_layers.get("volcanoes", True) else [],
-        "fishing_activity": (d.get("fishing_activity") or []) if active_layers.get("fishing_activity", True) else [],
-        "crowdthreat": (d.get("crowdthreat") or []) if active_layers.get("crowdthreat", True) else [],
-        "correlations": (d.get("correlations") or []) if active_layers.get("correlations", True) else [],
-        "uap_sightings": (d.get("uap_sightings") or []) if active_layers.get("uap_sightings", True) else [],
-        "wastewater": (d.get("wastewater") or []) if active_layers.get("wastewater", True) else [],
-        "sar_scenes": (d.get("sar_scenes") or []) if active_layers.get("sar", True) else [],
-        "sar_anomalies": (d.get("sar_anomalies") or []) if active_layers.get("sar", True) else [],
-        "sar_aoi_coverage": (d.get("sar_aoi_coverage") or []) if active_layers.get("sar", True) else [],
-        "freshness": freshness,
-    }
-    return Response(
-        content=orjson.dumps(
-            _sanitize_payload(payload),
-            default=str,
-            option=orjson.OPT_NON_STR_KEYS,
-        ),
-        media_type="application/json",
-        headers={"ETag": etag, "Cache-Control": "no-cache"},
-    )
-
-
 @app.get("/api/oracle/region-intel")
 @limiter.limit("30/minute")
 async def oracle_region_intel(
diff --git a/backend/routers/data.py b/backend/routers/data.py
index 06fbece..92e10ae 100644
--- a/backend/routers/data.py
+++ b/backend/routers/data.py
@@ -211,6 +211,15 @@ def _sanitize_payload(value):
     return value
 
 
+def _live_data_json_bytes(payload: dict) -> bytes:
+    """Serialize dashboard payloads with the same defensive orjson options everywhere."""
+    return orjson.dumps(
+        _sanitize_payload(payload),
+        default=str,
+        option=orjson.OPT_NON_STR_KEYS,
+    )
+
+
 def _bbox_filter(items: list, s: float, w: float, n: float, e: float,
                  lat_key: str = "lat", lng_key: str = "lng") -> list:
     pad_lat = (n - s) * 0.2
@@ -561,11 +570,7 @@ async def live_data(request: Request):
 
     payload = get_latest_data_deepcopy_snapshot()
     return Response(
-        content=orjson.dumps(
-            _sanitize_payload(payload),
-            default=str,
-            option=orjson.OPT_NON_STR_KEYS,
-        ),
+        content=_live_data_json_bytes(payload),
         media_type="application/json",
         headers={"ETag": etag, "Cache-Control": "no-cache"},
     )
@@ -663,7 +668,7 @@ async def bootstrap_critical(request: Request):
         "bootstrap_payload": True,
     }
     return Response(
-        content=orjson.dumps(_sanitize_payload(payload), default=str, option=orjson.OPT_NON_STR_KEYS),
+        content=_live_data_json_bytes(payload),
         media_type="application/json",
         headers={"ETag": etag, "Cache-Control": "no-cache"},
     )
@@ -725,8 +730,11 @@ async def live_data_fast(
     # to the pre-#288 implementation.
     if _has_full_bbox(s, w, n, e):
         payload = _apply_bbox_to_payload(payload, _FAST_BBOX_HEAVY_KEYS, s, w, n, e)
-    return Response(content=orjson.dumps(_sanitize_payload(payload)), media_type="application/json",
-        headers={"ETag": etag, "Cache-Control": "no-cache"})
+    return Response(
+        content=_live_data_json_bytes(payload),
+        media_type="application/json",
+        headers={"ETag": etag, "Cache-Control": "no-cache"},
+    )
 
 
 @router.get("/api/live-data/slow")
@@ -800,7 +808,7 @@ async def live_data_slow(
     if _has_full_bbox(s, w, n, e):
         payload = _apply_bbox_to_payload(payload, _SLOW_BBOX_HEAVY_KEYS, s, w, n, e)
     return Response(
-        content=orjson.dumps(_sanitize_payload(payload), default=str, option=orjson.OPT_NON_STR_KEYS),
+        content=_live_data_json_bytes(payload),
         media_type="application/json",
         headers={"ETag": etag, "Cache-Control": "no-cache"},
     )
diff --git a/backend/services/liveuamap_scraper.py b/backend/services/liveuamap_scraper.py
index 541061b..2d408bb 100644
--- a/backend/services/liveuamap_scraper.py
+++ b/backend/services/liveuamap_scraper.py
@@ -39,6 +39,9 @@ def fetch_liveuamap():
             viewport={"width": 1920, "height": 1080},
             color_scheme="dark",
         )
+        # Bound navigation and script evaluation so a stuck region cannot hang the slow pool.
+        context.set_default_navigation_timeout(60_000)
+        context.set_default_timeout(30_000)
         page = context.new_page()
         stealth_sync(page)
 
diff --git a/backend/tests/data/duplicate_routes_baseline.json b/backend/tests/data/duplicate_routes_baseline.json
index fe0d732..17ff17d 100644
--- a/backend/tests/data/duplicate_routes_baseline.json
+++ b/backend/tests/data/duplicate_routes_baseline.json
@@ -38,14 +38,6 @@
       "main",
       "routers.health"
     ],
-    "GET /api/live-data/fast": [
-      "main",
-      "routers.data"
-    ],
-    "GET /api/live-data/slow": [
-      "main",
-      "routers.data"
-    ],
     "GET /api/mesh/channels": [
       "main",
       "routers.mesh_public"
diff --git a/backend/tests/test_issue_375_production_hardening.py b/backend/tests/test_issue_375_production_hardening.py
index 47574a6..8d655ec 100644
--- a/backend/tests/test_issue_375_production_hardening.py
+++ b/backend/tests/test_issue_375_production_hardening.py
@@ -66,6 +66,24 @@ class TestLiveDataFullEndpoint:
         assert r2.status_code == 304
         assert r2.headers.get("etag") == etag
 
+    def test_live_data_fast_serializes_non_json_native_values(self, client):
+        from datetime import datetime, timezone
+
+        from services.fetchers import _store
+
+        with _store._data_lock:
+            prior = _store.latest_data.get("sigint")
+            _store.latest_data["sigint"] = [
+                {"source": "aprs", "observed": datetime(2026, 1, 1, tzinfo=timezone.utc)},
+            ]
+        try:
+            r = client.get("/api/live-data/fast")
+            assert r.status_code == 200
+            assert "2026-01-01" in r.text
+        finally:
+            with _store._data_lock:
+                _store.latest_data["sigint"] = prior
+
     def test_live_data_serializes_non_json_native_values(self, client):
         from datetime import datetime, timezone