feat(flights): cumulative fuel burned + CO2 emitted per flight

Pre-fix the emissions tooltip only showed the per-hour *rate* — what most
users actually want is the cumulative *amount* burned. This adds running
totals computed by multiplying the model-based rate by the elapsed
observation time since we first saw the airframe.

New module ``flight_observations.py``:
* Tracks first_seen_at + last_seen_at per icao24 hex.
* Re-opens a fresh session when an aircraft is unseen for > 15 min
  (treated as a new flight — landed and took off, or transited a dead
  zone). Prevents the cumulative counter from resetting mid-flight if
  the trail-rendering cache prunes the trail.
* Clamps elapsed time to 24h max so clock skew can't produce comically
  large numbers.
* Pruned every 5 min via a new scheduler job (mirrors ais_prune cadence).

flights.py + military.py emission enrichment now also attaches:
* observed_seconds — how long we've been tracking this airframe.
* fuel_gallons_burned — rate * elapsed_h.
* co2_kg_emitted — rate * elapsed_h.

The existing per-hour rate fields stay in the dict for backward compat
and are shown as small secondary context in the tooltip.

Frontend EmissionsEstimateBlock (NewsFeed.tsx) now prominently shows
the cumulative totals with the rate as smaller context underneath plus
"Observed in flight for Xh Ym". When observed_seconds is 0 (first refresh)
it renders "Just observed · totals will appear on next refresh" instead
of a misleading "0 gal".

12 backend tests cover record/accumulate/reset, the 24h clamp, prune,
case-insensitive key normalization, and end-to-end emission integration
in _classify_and_publish.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/services/data_fetcher.py

@@ -777,6 +777,19 @@ def start_scheduler():
         misfire_grace_time=60,
     )
 
+    # Flight observation pruning — drops icao24 → first_seen_at entries we
+    # haven't seen in an hour. Same cadence as AIS prune for symmetry; the
+    # per-tick scan is O(in-flight aircraft) so it's cheap.
+    from services.fetchers.flight_observations import prune as _prune_flight_observations
+    _scheduler.add_job(
+        lambda: _run_task_with_health(_prune_flight_observations, "prune_flight_observations"),
+        "interval",
+        minutes=5,
+        id="flight_observation_prune",
+        max_instances=1,
+        misfire_grace_time=60,
+    )
+
     # AISHub REST fallback — slow polling when the AISStream WebSocket
     # primary is offline. Configurable interval via
     # AISHUB_POLL_INTERVAL_MINUTES env (default 20 min). Operator must

backend/services/fetchers/flight_observations.py

@@ -0,0 +1,148 @@
+"""Per-aircraft observation tracking for cumulative fuel/CO2 estimates.
+
+Background
+----------
+The pre-existing emissions enrichment attached a *rate* to each flight
+(GPH and kg/hr) based on aircraft model. Users — reasonably — wanted the
+running total: how much fuel HAS this plane burned since we started
+seeing it? Multiplying the rate by elapsed observation time gets us
+there, but it requires somewhere to remember "when did this icao24
+first appear on our radar?"
+
+Why this lives outside ``flight_trails``
+----------------------------------------
+``flight_trails`` is sized and pruned aggressively for map rendering
+(5-minute TTL for untracked aircraft, 200 trail points max). That's
+wrong for cumulative burn: if a plane has been airborne 2 hours but
+its trail was pruned 30 min in, the "first trail point" timestamp is
+30 min ago, not 2h ago. Worse, when the trail expires and re-creates,
+the cumulative counter would reset mid-flight.
+
+This module tracks observation lifecycle separately:
+
+* When a hex is first observed: start a new flight session.
+* While observed regularly (gap < ``REOPEN_GAP_S``): keep accumulating.
+* When unseen for longer than ``REOPEN_GAP_S``: treat next sighting as
+  a new session (the plane landed and took off again, or it's a
+  different leg). Reset ``first_seen_at``.
+* Stale sessions are pruned every ``PRUNE_INTERVAL_S`` so memory stays
+  bounded.
+
+The user explicitly asked for this counting semantic: "as soon as a
+plane appears there should be a counter that keeps a running count of
+the fuel being burned... If there is no estimate take off time then it
+can just be from the time the server starts to keep a log of whats in
+the air."
+"""
+
+from __future__ import annotations
+
+import threading
+import time
+
+
+# Gap between sightings that resets the session. ADS-B refreshes the
+# whole aircraft list every minute or two, so anything over a few
+# minutes means the plane left our coverage window (landed, transit
+# through dead zone, etc). 15 minutes is conservative.
+REOPEN_GAP_S = 15 * 60
+
+# Don't accumulate runaway memory: drop entries unseen for an hour.
+PRUNE_AFTER_S = 60 * 60
+
+# Cap on accumulated airtime per session so a single bug elsewhere
+# (e.g. ts clock skew) can't produce comically large numbers.
+MAX_SESSION_SECONDS = 24 * 3600  # 24h — longest realistic civilian leg
+
+
+_observations: dict[str, dict[str, float]] = {}
+_lock = threading.Lock()
+_last_prune_at = 0.0
+
+
+def record_observation(icao_hex: str, *, now: float | None = None) -> int:
+    """Record a sighting of ``icao_hex`` and return airtime so far (seconds).
+
+    Returns 0 for the first-ever sighting (no elapsed time yet) or when
+    ``icao_hex`` is falsy. The caller can multiply the returned seconds
+    by ``rate_per_hour / 3600`` to get cumulative consumption.
+    """
+    if not icao_hex:
+        return 0
+    key = str(icao_hex).strip().lower()
+    if not key:
+        return 0
+    current = float(now if now is not None else time.time())
+
+    with _lock:
+        entry = _observations.get(key)
+        if entry is None:
+            _observations[key] = {"first_seen_at": current, "last_seen_at": current}
+            return 0
+        # Use explicit ``is None`` checks instead of ``or`` short-circuit:
+        # ``0.0`` is a legitimate timestamp value (e.g. test fixtures
+        # seeding a far-past first_seen_at to exercise the clamp) but
+        # ``0.0 or fallback`` collapses to ``fallback`` because 0.0 is
+        # falsy. Bit me on my own test — leaving the safer form here.
+        last_raw = entry.get("last_seen_at")
+        last_seen = float(last_raw) if last_raw is not None else current
+        gap = current - last_seen
+        if gap > REOPEN_GAP_S:
+            # Treat as a new flight session — the plane landed/disappeared
+            # long enough that the prior cumulative count is no longer
+            # the same flight.
+            _observations[key] = {"first_seen_at": current, "last_seen_at": current}
+            return 0
+        first_raw = entry.get("first_seen_at")
+        first = float(first_raw) if first_raw is not None else current
+        # Clamp absurd values from clock skew or bad input.
+        elapsed = max(0, min(int(current - first), MAX_SESSION_SECONDS))
+        entry["last_seen_at"] = current
+        return elapsed
+
+
+def prune(*, now: float | None = None) -> int:
+    """Drop entries we haven't seen in ``PRUNE_AFTER_S`` seconds.
+
+    Returns number of entries dropped. Safe to call from a scheduler tick;
+    cheap (single dict scan) so cadence doesn't matter much.
+    """
+    current = float(now if now is not None else time.time())
+    dropped = 0
+    with _lock:
+        stale_keys = []
+        for k, v in _observations.items():
+            last_raw = v.get("last_seen_at")
+            last = float(last_raw) if last_raw is not None else 0.0
+            if current - last > PRUNE_AFTER_S:
+                stale_keys.append(k)
+        for k in stale_keys:
+            del _observations[k]
+            dropped += 1
+    return dropped
+
+
+def get_session_seconds(icao_hex: str, *, now: float | None = None) -> int:
+    """Read-only accessor: airtime for a known icao without bumping last-seen.
+
+    Used by tests and external consumers (e.g. when rendering a snapshot
+    of all in-flight aircraft, you want the current value, not to update
+    last_seen_at as a side effect).
+    """
+    if not icao_hex:
+        return 0
+    key = str(icao_hex).strip().lower()
+    with _lock:
+        entry = _observations.get(key)
+        if entry is None:
+            return 0
+        current = float(now if now is not None else time.time())
+        first_raw = entry.get("first_seen_at")
+        first = float(first_raw) if first_raw is not None else current
+        return max(0, min(int(current - first), MAX_SESSION_SECONDS))
+
+
+def _reset_for_tests() -> None:
+    """Drop all observations. Test helper only."""
+    with _lock:
+        _observations.clear()

backend/services/fetchers/flights.py

@@ -17,6 +17,7 @@ from services.network_utils import fetch_with_curl
 from services.fetchers._store import latest_data, _data_lock, _mark_fresh
 from services.fetchers.plane_alert import enrich_with_plane_alert, enrich_with_tracked_names
 from services.fetchers.emissions import get_emissions_info
+from services.fetchers.flight_observations import record_observation as _record_flight_observation
 from services.fetchers.retry import with_retry
 from services.fetchers.route_database import lookup_route
 from services.fetchers.aircraft_database import lookup_aircraft_type
@@ -601,6 +602,22 @@ def _classify_and_publish(all_adsb_flights):
         if model:
             emi = get_emissions_info(model)
             if emi:
+                # Cumulative fuel/CO2: multiply the per-hour rate by how
+                # long we've been observing this airframe. Users want to
+                # see the *amount* burned, not just the rate. If we've
+                # never seen this hex before, observed_seconds is 0 and
+                # the cumulative values are 0 until the next refresh —
+                # the rate is still useful info on its own.
+                observed_seconds = _record_flight_observation(
+                    f.get("icao24") or ""
+                )
+                elapsed_h = observed_seconds / 3600.0
+                emi = {
+                    **emi,
+                    "observed_seconds": observed_seconds,
+                    "fuel_gallons_burned": round(emi["fuel_gph"] * elapsed_h, 1),
+                    "co2_kg_emitted": round(emi["co2_kg_per_hour"] * elapsed_h, 1),
+                }
                 f["emissions"] = emi
 
         callsign = f.get("callsign", "").strip().upper()

backend/services/fetchers/military.py

@@ -7,6 +7,7 @@ import requests
 from services.network_utils import fetch_with_curl
 from services.fetchers._store import latest_data, _data_lock, _mark_fresh
 from services.fetchers.emissions import get_emissions_info
+from services.fetchers.flight_observations import record_observation as _record_flight_observation
 from services.fetchers.plane_alert import enrich_with_plane_alert
 
 logger = logging.getLogger("services.data_fetcher")
@@ -300,6 +301,18 @@ def fetch_military_flights():
         if model:
             emissions = get_emissions_info(model)
             if emissions:
+                # Cumulative fuel/CO2 since first observation — mirrors
+                # the civilian path in flights._classify_and_publish.
+                observed_seconds = _record_flight_observation(
+                    mf.get("icao24") or ""
+                )
+                elapsed_h = observed_seconds / 3600.0
+                emissions = {
+                    **emissions,
+                    "observed_seconds": observed_seconds,
+                    "fuel_gallons_burned": round(emissions["fuel_gph"] * elapsed_h, 1),
+                    "co2_kg_emitted": round(emissions["co2_kg_per_hour"] * elapsed_h, 1),
+                }
                 mf["emissions"] = emissions
         if mf.get("alert_category"):
             mf["type"] = "tracked_flight"