fix(aihr): recover stalled media processing

scripts/release-preflight.sh

@@ -766,7 +766,36 @@ REMOTE
 
   [[ -z "$missing_work_assistant_columns" ]] \
     || fail "remote work-assistant schema missing required columns: $(printf '%s' "$missing_work_assistant_columns" | tr '\n' ', ' | sed 's/, $//')"
+
+  local media_reprocess_contract
+  media_reprocess_contract="$(ssh -o BatchMode=yes -o ConnectTimeout=10 "$remote_ssh" bash -s -- "$remote_db" <<'REMOTE'
+set -euo pipefail
+db="$1"
+mysql --batch --skip-column-names --connect-timeout=5 "$db" <<'SQL'
+SELECT CONCAT(
+  COALESCE((
+    SELECT column_name
+      FROM information_schema.columns
+     WHERE table_schema = DATABASE()
+       AND table_name = 'aihr_knowledge_upload_item'
+       AND column_name = 'source_attach_id'
+  ), 'missing'), '|',
+  COALESCE((
+    SELECT GROUP_CONCAT(column_name ORDER BY seq_in_index)
+      FROM information_schema.statistics
+     WHERE table_schema = DATABASE()
+       AND table_name = 'aihr_knowledge_upload_item'
+       AND index_name = 'idx_aihr_upload_item_source'
+  ), 'missing')
+);
+SQL
+REMOTE
+  )" || fail "remote media-reprocess schema check failed: $remote_ssh:$remote_db"
+
+  [[ "$media_reprocess_contract" = "source_attach_id|tenant_id,source_attach_id,id" ]] \
+    || fail "remote media-reprocess schema is invalid: got ${media_reprocess_contract:-missing}"
   echo "remote_schema=64/64 $remote_ssh:$remote_db"
+  echo "remote_media_reprocess_contract=1/1 $remote_ssh:$remote_db"
   echo "remote_work_report_idempotency=3/3 $remote_ssh:$remote_db"
   echo "remote_practice_curriculum_columns=13/13 $remote_ssh:$remote_db"
   echo "remote_knowledge_category_columns=7/7 $remote_ssh:$remote_db"