perf(tmdb): send catalog title matches in small requests (#1891)

CatalogTitleMatchService.matchTitles sent a caller's whole batch as one DB_MATCH_TITLES request, and the DB worker answers one request at a time: a recommendations batch held every other read for 95 s on a 3.9M-title library. The service now deduplicates the titles, keeps the 200-title cap, and sends requests of five titles one after another, concatenating the answers in order. The answer stays all-or-nothing: a failed request returns no matches, a lock that starts withholding everything stops the batch, and a batch starts over when ParentalLockService.version() changes between requests (no matches after three changing attempts).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture/tmdb-metadata-enrichment.md

@@ -208,7 +208,8 @@ component for detail→detail navigation.
 
 `CrossPortalSimilarService` (`libs/services`) extends the rail across
 portals: recommendations are matched against ALL imported Xtream
-playlists with one batched `DB_MATCH_TITLES` request (Electron only,
+playlists with one batched match (`DB_MATCH_TITLES`, sent in small
+requests, see "Sending a batched match"; Electron only,
 same two-tier + year rule). Stalker detail views — where the local
 catalog is server-paginated and unmatchable — get their "Similar" rail
 purely from these cross-portal matches (shared `VodDetailsComponent` for
@@ -353,7 +354,8 @@ Filmography has two scopes:
   rest open the portal search prefilled with the title (`?q=`). Stalker
   has no local catalog, so every title goes through the portal search.
 - **All portals** (Electron only, toggle hidden in the PWA): one batched
-  `DB_MATCH_TITLES` worker request runs a trigram-FTS lookup per title
+  match (`DB_MATCH_TITLES` worker requests of five titles, see "Sending a
+  batched match") runs a trigram-FTS lookup per title
   over ALL imported Xtream playlists
   (`operations/title-match.operations.ts`), confirming candidates with
   the same two-tier normalized-title matching the renderer uses
@@ -363,6 +365,24 @@ Filmography has two scopes:
   This also works from Stalker actor pages — the one place the Stalker
   catalog limitation is lifted.
 
+### Sending a batched match
+
+`CatalogTitleMatchService.matchTitles` deduplicates the titles, keeps the
+first `TITLE_MATCH_TITLE_LIMIT` (200, the worker's own cap) and sends them
+in `DB_MATCH_TITLES` requests of `TITLE_MATCH_REQUEST_SIZE` (5), one after
+another, concatenating the answers in order. The DB worker answers one
+request at a time, so a whole rail's batch in one request held every other
+read behind it: on a 3.9M-title library one recommendations batch took
+95 s cold and kept the dashboard's playback positions (and with them the
+Continue Watching rail) waiting; now other reads wait for five titles at
+most. The answer stays all-or-nothing: a failed
+request, or a parental lock that starts withholding everything midway,
+returns no matches, as one failed request did before. One request ran
+under one parental-lock state, so a batch does too: when
+`ParentalLockService.version()` changes between requests (a relock, an
+unlock, a changed lock list) the batch starts over, and after
+`TITLE_MATCH_LOCK_ATTEMPTS` (3) changing attempts it returns no matches.
+
 ### Resolving a batched match
 
 Every `DB_MATCH_TITLES` consumer — the Trending rail, the "Because you
@@ -645,7 +665,8 @@ since shipped.)
   toggle): `DashboardTrendingService`
   (`libs/workspace/dashboard/data-access`) pulls the weekly TMDB trending
   lists (cached one day per language) and runs ONE batched
-  `CatalogTitleMatchService.matchTitles` request against the imported
+  `CatalogTitleMatchService.matchTitles` call (worker requests of five
+  titles, see "Sending a batched match") against the imported
   Xtream playlists — matched cards navigate straight to their detail view
   and show the playlist name; unmatched cards open the global search
   prefilled. Requires both the TMDB opt-in and the Electron DB worker
@@ -665,7 +686,8 @@ since shipped.)
   interleaved round-robin, deduplicated by TMDB id, stripped of anything
   already watched or favorited, and matched against
   the imported libraries with ONE batched
-  `CatalogTitleMatchService.matchTitles` request. The watched/favorited
+  `CatalogTitleMatchService.matchTitles` call (worker requests of five
+  titles). The watched/favorited
   exclusion index is built through the same lookup-attempt builder the
   seeds use, so an activity row is indexed under more than its display
   title: under the media type the detail view enriched with (a Stalker
@@ -719,7 +741,7 @@ since shipped.)
   on its behalf would drop its recommendations for the session; a seed
   that has no TMDB match never resolves either, so that user's rail
   re-runs each visit, which is bounded work (cached enrichment misses
-  plus one batched worker call). Latched loads are keyed by the TMDB language
+  plus one batched title match). Latched loads are keyed by the TMDB language
   (payloads are localized; the facade exposes `language()` for this), the
   seed set, the watched/favorited exclusion set AND the imported-playlist
   id set — watching something new re-seeds on the next dashboard visit,