CDN probe: skip while idle, back off while degraded

The 3-min 64KB video download ran on a timer regardless of whether
anyone was using the app — wasteful upstream bandwidth, and pure churn
while the CDN 403s our IP. Now: no fetch while no stream has been
requested in 15 min (api_stream bumps _LAST_PLAY), and 30-min retry
while DEGRADED. Pill state goes stale while idle, which is fine — the
next viewer's own request is the true signal, and the probe resumes
within a minute of it.

server/app.py

@@ -49,8 +49,15 @@ VERSION = _version()
 # app.js uses the same value as these stats. Change here only.
 DONE_RATIO = 0.95
 
-# latest probe result + last 20 samples (~1h at 3-min spacing), for GET /api/cdn
+# latest probe result + last 20 samples, for GET /api/cdn
 _CDN = {"state": "unknown", "kbps": 0.0, "ts": 0.0, "hist": []}
+# ponytail: probe only when someone is around to care — skip the 64 KB video
+# download while the app has been idle (no stream requested in 15 min), and
+# back off to 30 min while DEGRADED (re-hitting a blocked CDN every 3 min is
+# just churn). api_stream() bumps _LAST_PLAY.
+_LAST_PLAY = 0.0
+_IDLE_SECS = 900
+_DEGRADED_RETRY = 1800
 # origin (primary provider pages/API) health — separate host, separate failure
 # mode (observed 2026-09-03: CDN fine while origin 503'd "Under Maintenance")
 _ORIGIN = {"state": "unknown", "msg": "", "ts": 0.0, "hist": []}
@@ -60,8 +67,9 @@ _CDN_THRESHOLD = float(os.environ.get("ANIWEB_CDN_KBPS", "40"))
 
 
 def _cdn_probe():
-    """Background probe: pull 64KB from the CDN every 3 min and log state
-    flips, so server.log shows when a degraded window ends (CDN RECOVERED).
+    """Background probe: pull 64KB from the CDN and log state flips, so
+    server.log shows when a degraded window ends (CDN RECOVERED). Skipped
+    while the app is idle and backed off while DEGRADED (see _LAST_PLAY).
     Probe target: ep_id 1 = One Piece E1 on the primary provider.
     ponytail: single fixed episode; if it ever disappears, the probe logs
     DEGRADED forever — swap the ID, don't build a picker."""
@@ -72,6 +80,9 @@ def _cdn_probe():
 
     state = None
     while True:
+        if time.time() - _LAST_PLAY > _IDLE_SECS:
+            time.sleep(60)  # nobody's watching: don't burn upstream bandwidth
+            continue
         try:
             m = upstream.master_m3u8(1, "jpn")
             if not m:
@@ -97,7 +108,7 @@ def _cdn_probe():
         _CDN["hist"].append({"t": time.time(), "kbps": round(kbps)})
         del _CDN["hist"][:-20]
         _origin_probe()
-        time.sleep(180)
+        time.sleep(_DEGRADED_RETRY if now == "DEGRADED" else 180)
 
 
 def _origin_probe():
@@ -559,6 +570,8 @@ def api_episodes(anime_id: int):
 
 @app.get("/api/episode/{ep_id}/stream")
 def api_stream(ep_id: int, lang: str = "jpn", request: Request = None):
+    global _LAST_PLAY
+    _LAST_PLAY = time.time()  # wakes the CDN probe: a viewer is here
     def go():
         master = _upstream(upstream.master_m3u8, ep_id, lang)
         if not master: