feat(plex): full-library cast backfill via a batched rich re-sync (S1b)

Lazy enrichment only covers viewed titles, so an actor's count/results were
partial. Add a background backfill: each plex_sync rich-fetches a bounded batch
(60) of not-yet-enriched movies/shows and persists their FULL cast, stamping
people_enriched_at so each is fetched once — the whole library is covered over
successive runs (migration 0057 adds the marker). Extracted the enrichment into a
shared app/plex/people.py (cast_from_meta / enrich_row_people / prune_orphan_people
+ the person-image host/proxy) so the info-page lazy path and the batch share ONE
implementation — no duplication; the info page also stamps the marker so the batch
skips it. Verified: an 8-item batch grows those movies' cast_names 3->24 and fills
plex_people (32->224); the info-page cast is intact after the _rich_meta refactor.
(Plex cast-explore S1b)

backend/app/routes/plex.py

@@ -17,7 +17,6 @@ from concurrent.futures import ThreadPoolExecutor
 from dataclasses import dataclass
 from datetime import datetime, timedelta, timezone
 from pathlib import Path
-from urllib.parse import quote
 
 import httpx
 from fastapi import APIRouter, BackgroundTasks, Depends, HTTPException, Query, Request, Response
@@ -43,6 +42,7 @@ from app.models import (
     User,
 )
 from app.plex import paths as plex_paths
+from app.plex import people as plex_people
 from app.plex import stream as plex_stream
 from app.plex import sync as plex_sync
 from app.plex import watch_sync as plex_watch
@@ -1227,8 +1227,11 @@ def show_detail(
         pass
 
     # Lazy enrichment: persist the show's full cast so its cast members become filterable (same as the
-    # movie info page — the sync only stored the listing's top ~3). Best-effort.
-    if _enrich_people_from_rich(db, sh, rich):
+    # movie info page — the sync only stored the listing's top ~3), and stamp people_enriched_at so the
+    # backfill skips it. Best-effort.
+    if rich.get("cast"):
+        plex_people.enrich_row_people(db, sh, rich["cast"])
+        sh.people_enriched_at = datetime.now(timezone.utc)
         try:
             db.commit()
         except Exception:
@@ -1582,11 +1585,6 @@ _PROGRESS_MIN_S = 5
 _FINISH_MARGIN_S = 30
 
 
-# Cast/crew photos come from Plex's PUBLIC metadata CDN (no token). We proxy them (host-whitelisted)
-# so the user's browser makes no third-party request (privacy + self-host CSP friendliness).
-_PERSON_IMG_HOST = "https://metadata-static.plex.tv/"
-
-
 def _rich_meta(meta: dict) -> dict:
     """Pull the "info page" extras out of a full Plex metadata dict: an IMDb score + link, content
     rating, genres, director(s), studio, tagline, and cast (name/role/photo). Best-effort — any
@@ -1612,21 +1610,6 @@ def _rich_meta(meta: dict) -> dict:
         if gid.startswith("imdb://"):
             imdb_id = gid.split("imdb://", 1)[1]
             break
-    cast = []
-    for role in (meta.get("Role") or [])[:24]:
-        name = role.get("tag")
-        if not name:
-            continue
-        thumb = str(role.get("thumb") or "")
-        cast.append(
-            {
-                "name": name,
-                "role": role.get("role"),
-                "thumb": f"/api/plex/person-image?u={quote(thumb, safe='')}"
-                if thumb.startswith(_PERSON_IMG_HOST)
-                else None,
-            }
-        )
     return {
         "imdb_rating": imdb_rating,
         "imdb_id": imdb_id,
@@ -1636,47 +1619,10 @@ def _rich_meta(meta: dict) -> dict:
         "directors": [d.get("tag") for d in (meta.get("Director") or []) if d.get("tag")][:4],
         "studio": meta.get("studio"),
         "tagline": meta.get("tagline"),
-        "cast": cast,
+        "cast": plex_people.cast_from_meta(meta),
     }
 
 
-def _enrich_people_from_rich(db: Session, row, rich: dict) -> bool:
-    """Persist the FULLER cast (from an item's rich metadata) onto the row's `cast_names` + the
-    `people_text` search blob, and cache each cast member's headshot in plex_people. The cheap section
-    listing that drives the main sync only carries the top ~3 cast, so this — run when a rich fetch
-    happens (info-page view + the rich re-sync) — is what makes the full displayed cast filterable.
-    Returns True if anything was written (the caller commits). Best-effort: never the reason a read
-    500s (the caller wraps the commit)."""
-    cast = rich.get("cast") or []
-    names = list(dict.fromkeys(c["name"] for c in cast if c.get("name")))[:24]
-    if not names:
-        return False
-    dirty = False
-    # Grow/refresh cast_names only when the rich set adds names the stored (listing top-3) set lacks —
-    # avoid churn and never downgrade a fuller set back to the thin listing.
-    if set(names) - set(row.cast_names or []):
-        row.cast_names = names
-        row.people_text = " ".join(dict.fromkeys(list(row.directors or []) + names)) or None
-        dirty = True
-    # Headshot cache: upsert name -> proxied thumb (a later fetch fills a prior NULL; names without a
-    # whitelisted photo still get a row so a card can show a placeholder).
-    existing = {p.name: p for p in db.query(PlexPerson).filter(PlexPerson.name.in_(names))}
-    for c in cast:
-        nm, th = c.get("name"), c.get("thumb")
-        if not nm:
-            continue
-        p = existing.get(nm)
-        if p is None:
-            p = PlexPerson(name=nm, photo_thumb=th)
-            db.add(p)
-            existing[nm] = p
-            dirty = True
-        elif th and not p.photo_thumb:
-            p.photo_thumb = th
-            dirty = True
-    return dirty
-
-
 @router.get("/people/cards")
 def people_cards(
     names: str,
@@ -1727,7 +1673,7 @@ def person_image(u: str, request: Request) -> Response:
     """Proxy a cast/crew photo from Plex's public metadata CDN (host-whitelisted; no token needed).
     Signed-session auth (no DB) so it, like /image, never holds a pool connection during the fetch."""
     _require_session(request)
-    if not u.startswith(_PERSON_IMG_HOST):
+    if not u.startswith(plex_people.PERSON_IMG_HOST):
         raise HTTPException(status_code=400, detail="Unsupported image host")
     cache_key = "person_" + hashlib.sha1(u.encode()).hexdigest()
     hit = _img_cache_read(cache_key)
@@ -1875,9 +1821,12 @@ def item_detail(
         pass  # metadata extras are best-effort; any live-Plex failure must degrade, not 500 — playback works without them
 
     # Lazy enrichment: the rich fetch above carries the FULL cast (the sync only stored the listing's
-    # top ~3), so persist it onto this movie so every cast member shown here becomes filterable. A
-    # movie only — episodes aren't in the grid; their show's cast is enriched from /show. Best-effort.
-    if it.kind == "movie" and _enrich_people_from_rich(db, it, rich):
+    # top ~3), so persist it onto this movie so every cast member shown here becomes filterable, and
+    # stamp people_enriched_at so the backfill skips it. Movie only — episodes aren't in the grid; a
+    # show's cast is enriched from /show. Best-effort.
+    if it.kind == "movie" and rich.get("cast"):
+        plex_people.enrich_row_people(db, it, rich["cast"])
+        it.people_enriched_at = datetime.now(timezone.utc)
         try:
             db.commit()
         except Exception: