Filter candidates defined after the the current page

Previously when both prev and last candidates were none hydra would show
candidates defined on later pages. I believe that candidates defined on
pages after the current page should never be displayed.

src/core.typ

@@ -118,6 +118,7 @@
     next-targets = next-targets.filter(x => (ctx.primary.filter)(ctx, x))
     last-targets = last-targets.filter(x => (ctx.primary.filter)(ctx, x))
   }
+  next-targets = next-targets.filter(x => x.location().page() == ctx.anchor-loc.page())
   last-targets = last-targets.filter(x => x.location().page() == ctx.anchor-loc.page())
 
   let prev = if prev-targets != () { prev-targets.last() }

tests/regressions/fallback-to-future/test.typ

@@ -0,0 +1,19 @@
+// Synopsis:
+// - When both last and prev candidates where none hydra would fall back to a heading defined on a future page.
+//   Headings defined after the current page should never be displayed.
+
+#import "/src/lib.typ": hydra
+
+#set page(
+  paper: "a7",
+  header: context hydra(),
+)
+#set heading(numbering: "1.1")
+#show heading.where(level: 1): it => pagebreak(weak: true) + it
+#set par(justify: true)
+
+#lorem(100)
+
+= Introduction
+#lorem(100)
+