Test that co-wired Pipenv files are not contested

`vendor --check` and `vex` read lockfile discovery. With Pipfile.lock
and requirements.txt both pointing at the same vendored wheel, the
regression test now checks that discovery finds the patch in both
files and reports no contest between them.

Refs #612

Assisted-by: Claude Code:claude-opus-5-5

Author: claude

crates/socket-patch-core/src/vendor/pypi.rs

@@ -5695,6 +5695,21 @@ wheels = [
             warnings.iter().all(|w| w.code != "pypi_multiple_lockfiles"),
             "{warnings:?}"
         );
+        // What `vendor --check` and `vex` read: both files wire the same
+        // vendored wheel, so neither contests the other.
+        let discovery = crate::vex::discover::discover_patched_refs(&fx.root).await;
+        assert!(discovery.contested.is_empty(), "{:?}", discovery.contested);
+        let wired_in: std::collections::BTreeSet<String> = discovery
+            .refs
+            .iter()
+            .filter(|r| r.uuid == UUID)
+            .map(|r| r.source_file.to_string_lossy().replace('\\', "/"))
+            .collect();
+        assert!(
+            wired_in.contains("Pipfile.lock") && wired_in.contains("requirements.txt"),
+            "{:?}",
+            discovery.refs
+        );
 
         let outcome = revert_pypi(
             entry.as_ref().expect("a wet vendor records its entry"),