fix(node,client): query TMDB only once a language is chosen, in that languageHEADmain

TMDB fiches are fetched lazily, on browse, and the fetch used to run whatever
the moment it was first triggered — routinely before the operator had opened
settings and picked a language, so it queried in TMDB's English default. Then
the fiche was cached by tmdb_id alone, with no note of language and a 30-day
TTL, so switching to the intended language afterwards changed nothing: the
English fiche was served until it expired. The operator's only recourse was to
find and wipe the cache by hand (found live 2026-09-26: a whole library indexed
in English although "Français" had been chosen).

Two rules now, both there to make the first fetch the right language rather
than English-then-corrected, and to stop the doubled requests that eventually
get a node rate-limited:

- No language configured, no query. media_meta_req/season_meta_req answer
  confidence 0 and make no TMDB call while tmdb_language is unset; the fetch
  waits for the operator's choice, so the first (and only) query is in it.
  English is now a first-class choice (en-US), not the default of skipping the
  setting.
- Changing the language wipes the metadata cache (ops.set_tmdb_config), so the
  new language takes effect on an already-browsed library. The file->tmdb
  matches are language-independent and kept. The client refetches on the
  tmdb_config_ack that carries the new language, so the grid updates without a
  page reload.

docs/MESHBAY_DESIGN.md §9.7 states both rules; tests cover the gate and the
cache wipe, and two existing handler harnesses now declare a language.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/docs/MESHBAY_DESIGN.md b/docs/MESHBAY_DESIGN.md
index 4daa094..4541d64 100644
--- a/docs/MESHBAY_DESIGN.md
+++ b/docs/MESHBAY_DESIGN.md
@@ -2615,6 +2615,28 @@ its own bounded pool after a file is first seen: the file appears in the index
 immediately with size and hash, and an index delta fills in the technical and parsed
 fields once ready. **No scan is blocked waiting for enrichment.**
 
+**TMDB metadata is queried in one node-wide language, and not until one is chosen.**
+A cached fiche is keyed by TMDB id alone — it records no language, because there is
+only ever one. Two rules keep it honest, both there to make the very first fetch the
+right language rather than English-then-corrected:
+
+- **No language configured, no query.** While `tmdb_language` is unset the node
+  answers `media_meta_req`/`season_meta_req` with confidence 0 and makes no TMDB call
+  — it does *not* fall back to TMDB's English default. Browsing the library is what
+  triggers the lazy fetch, and it routinely happens before the operator has opened the
+  settings, so querying on an unset language would fetch the whole library in English
+  and then throw it all away the moment a language was picked — double the requests
+  against TMDB's rate limit, for a result nobody wanted. The fetch waits for the
+  choice, so the first (and only) query is in the chosen language. English is a
+  first-class choice like any other (`en-US`), not the accidental default of skipping
+  the setting.
+- **Changing the language wipes the cache.** A fiche fetched under the old language
+  would otherwise be served for its whole 30-day TTL. The file→TMDB matches are
+  language-independent and survive the wipe; only the localized fiches are dropped and
+  refetched, lazily, on the next request. The client refetches on its own when the
+  `tmdb_config_ack` carrying the new language arrives, so the grid switches language
+  (or fills in for the first time) without a page reload.
+
 ### 9.8 Music
 
 An album browser and a player over the audio files in the group's configured