hive-forge: test the two invariants dependency.rs documents but never checked

dep_meta's comment records a measured 404: leaving owner/repo as None
made every same-repo dependency fail, because forgejo resolves the
dependency's repo from the request BODY rather than the URL. Nothing
stopped a later tidy-up from simplifying them back to None.

index() promises "error instead of wrapping". A wrap would not fail
loudly -- it would hand the forge a negative index it looks up as some
other issue.

hive-forge/src/verbs/dependency.rs

@@ -186,3 +186,28 @@ fn dep_meta(owner: &str, repo: &str, dep: u64) -> Result<IssueMeta> {
         repo: Some(repo.to_owned()),
     })
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// The comment above `dep_meta` records a measured failure: leaving
+    /// `owner`/`repo` as `None` made every same-repo dependency 404,
+    /// because forgejo resolves the dependency's repo from the *body*
+    /// rather than falling back to the request URL. Nothing but a test
+    /// stops a future tidy-up from "simplifying" them back to `None`.
+    #[test]
+    fn dep_meta_populates_owner_and_repo_rather_than_leaving_them_none() {
+        let m = dep_meta("hyperhive", "hyperhive", 3950).expect("in range");
+        assert_eq!(m.owner.as_deref(), Some("hyperhive"));
+        assert_eq!(m.repo.as_deref(), Some("hyperhive"));
+        assert_eq!(m.index, Some(3950));
+    }
+
+    /// Out-of-range must be an error, not a wrapped negative index that
+    /// the forge would then look up as some other issue.
+    #[test]
+    fn dep_meta_refuses_a_number_no_forge_could_have() {
+        assert!(dep_meta("o", "r", u64::MAX).is_err());
+    }
+}