ADS-B map: altitude-colored aircraft icons + click-to-show flight trail

Icons were 16px accent-colored glyphs, indistinguishable from OSM's own
airport symbols. Now a 30px outlined airliner silhouette filled on
tar1090/ADS-B Exchange's altitude hue ramp, with a callsign/altitude
hover tooltip; the selected aircraft grows and gets a white outline.

Clicking an aircraft draws the path heard so far, segment-colored by
altitude. c2-core writes one point per position change to
aircraft/{icao}/positions (deduped in-process, writes now concurrent);
points carry expire_at and a TTL fieldOverride deletes them after ~24h.
Trail reads are gated on the parent aircraft doc's org via get(), so the
query needs no org filter or composite index. The latest stretch without
a 20-min gap counts as the current flight.

Verified: c2-core pytest 479 passed; frontend tsc --noEmit clean (node:20
container on radio-box).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-c2-core/app/routers/telemetry.py

@@ -1,5 +1,6 @@
-from datetime import datetime, timezone
-from typing import List, Optional
+import asyncio
+from datetime import datetime, timedelta, timezone
+from typing import Dict, List, Optional, Tuple
 
 from fastapi import APIRouter, Depends, HTTPException
 from pydantic import BaseModel
@@ -10,6 +11,20 @@ from app.internal.logger import logger
 
 router = APIRouter(prefix="/telemetry", tags=["telemetry"])
 
+# Flight trail: every position change is also written to
+# aircraft/{icao}/positions/{epoch_ms}, so clicking an aircraft on the map can
+# draw the path heard so far. Points expire via a Firestore TTL policy on
+# expire_at (infra/firestore/firestore.indexes.json fieldOverrides).
+POSITIONS_SUBCOLLECTION = "positions"
+POSITION_TTL = timedelta(hours=24)
+
+# Last position written per icao, so an aircraft reported unchanged across
+# several 10s uploads (readsb holds a position until a new one decodes)
+# doesn't get a duplicate point each time. Process-local and lossy by design:
+# after a restart the worst case is one duplicate point per aircraft.
+_last_position: Dict[str, Tuple[float, float]] = {}
+_LAST_POSITION_MAX = 5000
+
 
 class AircraftReport(BaseModel):
     icao: str
@@ -32,8 +47,8 @@ async def upload_adsb(
 ):
     """
     Node-initiated: a second-SDR ADS-B decoder (node-26#9) periodically posts
-    its current aircraft snapshot here. One doc per icao, last-seen-wins —
-    this is a live-map overlay, not a flight history.
+    its current aircraft snapshot here. One doc per icao, last-seen-wins,
+    plus one trail point per position change (see POSITIONS_SUBCOLLECTION).
     """
     node_id = decoded.get("node_id")
     if not node_id:
@@ -43,7 +58,11 @@ async def upload_adsb(
     org_id = node.get("org_id") if node else None
     now = datetime.now(timezone.utc).isoformat()
 
+    expire_at = datetime.now(timezone.utc) + POSITION_TTL
+    epoch_ms = int(datetime.now(timezone.utc).timestamp() * 1000)
+
     writes = []
+    trail = []
     for ac in body.aircraft:
         if not ac.icao:
             continue
@@ -62,12 +81,33 @@ async def upload_adsb(
             doc["org_id"] = org_id
         writes.append(("aircraft", ac.icao, doc))
 
-    for collection, doc_id, doc in writes:
+        if ac.lat is None or ac.lon is None:
+            continue
+        pos = (ac.lat, ac.lon)
+        if _last_position.get(ac.icao) == pos:
+            continue
+        _last_position[ac.icao] = pos
+        point = {
+            "lat": ac.lat,
+            "lon": ac.lon,
+            "altitude_ft": ac.altitude_ft,
+            "t": now,
+            "expire_at": expire_at,
+        }
+        trail.append((f"aircraft/{ac.icao}/{POSITIONS_SUBCOLLECTION}", str(epoch_ms), point))
+
+    if len(_last_position) > _LAST_POSITION_MAX:
+        _last_position.clear()
+
+    async def _write(collection: str, doc_id: str, doc: dict) -> None:
         try:
             await fstore.doc_set(collection, doc_id, doc, merge=True)
         except Exception as e:
             logger.warning(f"Failed to upsert {collection}/{doc_id} from node {node_id}: {e}")
 
+    # Concurrent: a busy sky is dozens of aircraft, two writes each, every 10s.
+    await asyncio.gather(*(_write(*w) for w in writes + trail))
+
     return {"ok": True, "count": len(writes)}