fix(fts): deterministic top-k tiebreak (score DESC, row_id ASC)

rust/lance-index/src/scalar/inverted/builder.rs

@@ -1756,8 +1756,15 @@ impl PartialOrd for ScoredDoc {
 }
 
 impl Ord for ScoredDoc {
+    // Total order for the FTS top-k: score first, ties broken by ascending row_id (a lower row_id ranks
+    // higher, so it compares as "greater" here). A total tiebreak makes top-k a stable prefix across `k`
+    // (top-k1 is an ordered prefix of top-k2), which tied-score pagination needs. This orientation makes a
+    // min-heap's `peek` the worst candidate (lowest score, highest row_id) to evict first, and
+    // `into_sorted_vec` over `Reverse<ScoredDoc>` yield (score DESC, row_id ASC).
     fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-        self.score.cmp(&other.score)
+        self.score
+            .cmp(&other.score)
+            .then_with(|| other.row_id.cmp(&self.row_id))
     }
 }