Release v0.51.343 — Release LG (Phase-1 batch: #3883 + #3878 + #3880) (#3891)

Phase-1 low-risk batch, each rebased onto fresh master + gated fresh:

- #3883 (@rodboev, #3740): sidebar refreshes a stale message_count:0 index row
  from its sidecar when user_message_count>0 + sidecar mtime newer than index,
  self-healing the interrupted-stream stale-count case beyond compression lineage.
- #3878 (@rodboev, #3833): manual workspace refresh clears the dir cache and
  re-fetches expanded descendants so background-written files become visible.
- #3880 (@koshikai): translate the 11 remaining English strings in the ja locale.

greptile flags evaluated: #3878 P1 relative-path + P2 stale-comment already fixed
in PR head; #3883 P2 missing-snapshot-test already covered by the PR's own
test_all_sessions_refreshes_stale_zero_count_snapshot_row_from_sidecar, P2
double-stat is a bounded cheap micro-opt (FOLD); #3880 'needs screenshots'
rejected (in-place translation of existing keys, no UI shape change).

Co-authored-by: nesquena-hermes <[email protected]>
Co-authored-by: rodboev <rodboev@users.noreply.github.com>
Co-authored-by: koshikai <koshikai@users.noreply.github.com>

api/models.py

@@ -2654,6 +2654,14 @@ def _strip_sidebar_internal_flags(sessions: list[dict]) -> None:
         session.pop('_show_pre_compression_snapshot', None)
 
 
+def _looks_like_stale_zero_message_row(session: dict) -> bool:
+    """Return True for indexed rows that likely need sidecar metadata repair."""
+    return bool(
+        int(session.get('message_count') or 0) == 0
+        and int(session.get('user_message_count') or 0) > 0
+    )
+
+
 def _row_may_need_sidecar_metadata_refresh(
     session: dict,
     *,
@@ -2693,7 +2701,19 @@ def _row_may_need_sidecar_metadata_refresh(
             or session.get('_lineage_root_id')
             or session.get('_compression_segment_count')
         )
-        return bool(lineage_shaped and sid and _sidecar_mtime_after_index_timestamp(session))
+        needs_mtime_check = lineage_shaped or (
+            sid and _looks_like_stale_zero_message_row(session)
+        )
+        if needs_mtime_check and _sidecar_mtime_after_index_timestamp(session):
+            return True
+        return False
+    if (
+        sid
+        and _looks_like_stale_zero_message_row(session)
+        and str(session.get('session_source') or '').strip().lower() != 'fork'
+        and _sidecar_mtime_after_index_timestamp(session)
+    ):
+        return True
     if session.get('message_count') is None or session.get('last_message_at') is None:
         return True
     return bool(sid and stale_snapshot_ids and sid in stale_snapshot_ids)