feat(translation): expose translated fields in post feed + provenance payloads (#143 step 4)

post_feed_service (card + detail) and provenance_service._post_dict now include
post_title_translated, description_translated (card-truncated / detail-uncapped)
and translated_source_lang, keeping the originals for the toggle. Feed
serialization test.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

backend/app/services/post_feed_service.py

@@ -200,6 +200,8 @@ class PostFeedService:
         atts_map = await self._attachments_for([post.id])
         item = self._to_dict(post, artist, source, thumbs_map, atts_map)
         item["description_full"] = html_to_plain(post.description)
+        # Full (uncapped) translated description for the detail view (#143).
+        item["description_translated_full"] = post.description_translated
         # Sanitized HTML body for faithful (semantic) rendering in the post view;
         # detail-only (the feed list stays lightweight plain text). None when the
         # post has no body. Inline `<img>` sources are remapped to locally-served
@@ -371,6 +373,12 @@ class PostFeedService:
             description_plain, truncated = None, False
         else:
             description_plain, truncated = truncate_at_word(plain_full, DESCRIPTION_LIMIT)
+        # Translation (#143): the stored translated description is already plain
+        # text; truncate it the same way for the card.
+        desc_trans = post.description_translated
+        desc_trans_short = (
+            truncate_at_word(desc_trans, DESCRIPTION_LIMIT)[0] if desc_trans else None
+        )
         thumbs_entry = thumbs_map.get(post.id, {"thumbs": [], "more": 0})
         # `source` is null for filesystem-imported posts with no live
         # subscription (alembic 0030). Frontend renders that as a
@@ -384,6 +392,11 @@ class PostFeedService:
             "downloaded_at": post.downloaded_at.isoformat(),
             "description_plain": description_plain,
             "description_truncated": truncated,
+            # Translation-forward fields (#143): shown by default when present;
+            # UI toggles back to the originals above. Source lang labels the toggle.
+            "post_title_translated": post.post_title_translated,
+            "description_translated": desc_trans_short,
+            "translated_source_lang": post.translated_source_lang,
             "artist": {"id": artist.id, "name": artist.name, "slug": artist.slug},
             "source": (
                 {"id": source.id, "platform": source.platform}

backend/app/services/provenance_service.py

@@ -29,6 +29,12 @@ def _post_dict(p: Post) -> dict:
         "date": p.post_date.isoformat() if p.post_date else None,
         "description_html": sanitize_post_html(p.description),
         "attachment_count": p.attachment_count,
+        # Translation (#143): the English title/description shown by default when
+        # a translation exists; the UI toggles to the original. Source lang labels
+        # the original.
+        "title_translated": p.post_title_translated,
+        "description_translated": p.description_translated,
+        "translated_source_lang": p.translated_source_lang,
     }