fix(media): a tvdb episode page is not the episode list

Tvdb's default episode query answers at most 500 rows and states no total.
One Piece (1999), Crayon Shin-chan (1992) and Detective Conan (1996) each
answer exactly 500 while holding over a thousand, so the contradiction rule
added in the previous commit read every long-running show as contradicted:
the pack books more episodes than "the authority holds", and the rule that
exists to stop a wrong anime title would have stripped the right one from
every file of the season.

A capped list now records that it is capped (`tvdb:capped:<id>`, so a warm
cache answers the same question a cold one did) and contradicts nothing;
titles for the episodes the page does hold still ride.

Test: a 500-row page with a 501-episode pack keeps ` - Episode 1` and lists
no contradiction. Red before the change, proved in a copy of the tree with
the cap raised past the fixture.

scripts/media-shows.py

@@ -404,20 +404,37 @@ def tvdb_search(name):
     return None
 
 
+# Tvdb's default episode query answers AT MOST this many rows and states no
+# total: One Piece (1999), Crayon Shin-chan (1992) and Detective Conan (1996)
+# each answer exactly 500 while holding over a thousand. A list that long bounds
+# nothing above itself, so it must never be read as "the series holds 500".
+EPISODE_PAGE_CAP = 500
+
+
 def tvdb_episodes(sid):
-    """`season/episode` -> title for one series, in the one call tvdb answers."""
+    """`season/episode` -> title for one series, in the one call tvdb answers.
+    Whether that call came back a cut-off page is recorded in the cache beside
+    it, so a warm cache answers the same question a cold one did."""
     ck = f"tvdb:episodes:{sid}"
-    if ck in CACHE:
-        return CACHE[ck]
-    data = tvdb(f"/series/{sid}/episodes/default")
-    if not data:
-        return None
-    CACHE[ck] = {f"{e.get('seasonNumber')}/{e.get('number')}":
-                 (e.get("name") or "").strip()
-                 for e in data.get("episodes") or []}
+    if ck not in CACHE:
+        data = tvdb(f"/series/{sid}/episodes/default")
+        if not data:
+            return None
+        rows = data.get("episodes") or []
+        CACHE[ck] = {f"{e.get('seasonNumber')}/{e.get('number')}":
+                     (e.get("name") or "").strip() for e in rows}
+        CACHE[f"tvdb:capped:{sid}"] = len(rows) >= EPISODE_PAGE_CAP
     return CACHE[ck]
 
 
+def tvdb_list_capped(sid):
+    """True when tvdb's episode answer for this series is a page, not a list."""
+    rows = tvdb_episodes(sid)
+    if not rows:
+        return False
+    return CACHE.get(f"tvdb:capped:{sid}", len(rows) >= EPISODE_PAGE_CAP)
+
+
 
 # tvdb's titles read backwards, for the rows that carry a title and no numbering.
 _TITLE_IDX = {}
@@ -757,14 +774,17 @@ def label_of(s):
 
 def contradicted_seasons(s):
     """Seasons whose numbering tvdb's own episode list contradicts — the one place
-    a tvdb title can be a confident lie. An anime pack numbered by its release group
-    books S05E01 in a season tvdb does not hold, or books more episodes there than
-    tvdb lists, and the slot its number points at is a DIFFERENT episode. Books <=
-    tvdb's count stays plausible: a partial pack is the normal shape."""
+        a tvdb title can be a confident lie. An anime pack numbered by its release group
+        books S05E01 in a season tvdb does not hold, or books more episodes there than
+        tvdb lists, and the slot its number points at is a DIFFERENT episode. Books <=
+        tvdb's count stays plausible: a partial pack is the normal shape. A list the
+        authority cut off at its page limit (EPISODE_PAGE_CAP) contradicts nothing —
+        it says nothing about the episodes it never sent."""
     if "contradicted" in s:
         return s["contradicted"]
     bad = set()
-    eps = tvdb_episodes(s["tvdb"]) if s["tvdb"] else None
+    eps = None if not s["tvdb"] or tvdb_list_capped(s["tvdb"]) \
+            else tvdb_episodes(s["tvdb"])
     if eps:
         have = collections.Counter()
         for k in eps: