allow streams to marked as exhausted in more cases

At stream boundaries, we can mark streams as exhausted if there are no
groups active and there are no other ways to report matches. This allows us
to stop maintaining the history buffer on subsequent stream writes.
Previously, streams were only marked as exhausted if a pure highlander case
reported all patterns or the outfix in a sole outfix case died.

src/rose/rose_build_compile.cpp

@@ -1236,11 +1236,15 @@ void buildRoseSquashMasks(RoseBuildImpl &tbi) {
             }
         }
 
-        rose_group unsquashable = 0;
+        rose_group unsquashable = tbi.boundary_group_mask;
 
         for (u32 lit_id : lit_ids) {
             const rose_literal_info &info = tbi.literal_info[lit_id];
-            if (info.vertices.size() > 1 || !info.delayed_ids.empty()) {
+            if (!info.delayed_ids.empty()
+                || !all_of_in(info.vertices,
+                              [&](RoseVertex v) {
+                                  return left == tbi.g[v].left; })) {
+                DEBUG_PRINTF("group %llu is unsquashable\n", info.group_mask);
                 unsquashable |= info.group_mask;
             }
         }