🚧 Add better page browsing

api/app.py

@@ -1563,6 +1563,11 @@ def create_app(
         limit: int = Query(100, gt=0, description="Page size"),
         offset: int = Query(0, ge=0, description="Page offset"),
     ) -> dict[str, Any]:
+        """One page of messages. The response carries a filter-aware
+        "total" (the count over the SAME filters as the returned items)
+        next to limit/offset, so pagers can show "page X of Y" and support
+        jumping to the last page without a second request. GET
+        /messages/count stays the unfiltered total for the dashboard."""
         if from_time is not None and to_time is not None and from_time > to_time:
             raise HTTPException(
                 status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
@@ -1684,6 +1689,18 @@ def create_app(
             conn = psycopg.connect(config.dsn)
             try:
                 with conn.cursor() as cur:
+                    # Total matching the CURRENT filters, for the pager's
+                    # page count / jump-to-last. Counting plain mqtt_messages
+                    # (aliased m.) with the same WHERE is exact: the LEFT
+                    # JOINs of the page query never remove rows. Same
+                    # connection => same snapshot, so total and items can
+                    # never disagree.
+                    cur.execute(
+                        sql.SQL("SELECT count(*) FROM mqtt_messages m") + where,
+                        params,
+                    )
+                    row = cur.fetchone()
+                    total = row[0] if row is not None else 0
                     cur.execute(query, (*params, limit, offset))
                     rows = cur.fetchall()
             finally:
@@ -1692,6 +1709,7 @@ def create_app(
             raise _db_unavailable(exc) from exc
 
         return {
+            "total": total,
             "limit": limit,
             "offset": offset,
             "from": from_time.isoformat() if from_time is not None else None,