Add an end to end regression test for the reporter's exact repro

A file that only imports a package subpath must resolve just like one
that imports the bare package, using the exact package.json plus two
file shape from the issue, instead of coming out fully disconnected
from the framework it depends on.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
(cherry picked from commit 5fb7fc34c1)

tests/test_phantom_external_import.py

@@ -136,3 +136,54 @@ def test_multiple_tsx_files_do_not_all_alias_onto_one_python_file(tmp_path: Path
         if d.get("relation") == "imports_from" and ({u, v} & py_ids)
     ]
     assert not phantom, f"phantom edges onto colors.py: {phantom}"
+
+
+def test_subpath_import_does_not_dangle_like_a_bare_import(tmp_path: Path):
+    """The reporter's exact repro for #3595: a package subpath import
+    ("next/image") produced no edge at all, while a bare import of the same
+    package ("next") resolved fine, so a file that only ever imports
+    subpaths came out fully disconnected from the framework it depends on."""
+    _write(
+        tmp_path / "package.json",
+        '{"name": "mre", "dependencies": {"next": "16.2.7"}}\n',
+    )
+    bare = _write(
+        tmp_path / "bare.ts",
+        'import type { Metadata } from "next";\n'
+        "export const meta: Metadata = {};\n",
+    )
+    subpath = _write(
+        tmp_path / "subpath.ts",
+        'import Image from "next/image";\n'
+        "export const i = Image;\n",
+    )
+
+    result = extract(
+        [tmp_path / "package.json", bare, subpath], cache_root=tmp_path / "graphify-out"
+    )
+    G = build_from_json(result, root=str(tmp_path))
+
+    def _imports_from(nid):
+        # The built graph may be undirected, which loses (u, v) edge-iteration
+        # order -- direction is preserved separately as _src/_tgt (build.py).
+        return {
+            d.get("_tgt") for u, v, d in G.edges(data=True)
+            if d.get("relation") == "imports_from" and d.get("_src") == nid
+        }
+
+    bare_id = next(
+        n for n, d in G.nodes(data=True)
+        if str(d.get("source_file", "")).endswith("bare.ts")
+    )
+    subpath_id = next(
+        n for n, d in G.nodes(data=True)
+        if str(d.get("source_file", "")).endswith("subpath.ts")
+    )
+    bare_targets = _imports_from(bare_id)
+    subpath_targets = _imports_from(subpath_id)
+    assert bare_targets, "the bare import must resolve"
+    assert subpath_targets, "the subpath import must resolve, not dangle"
+    assert subpath_targets == bare_targets, (
+        "a subpath import of a package must land on the same node as a bare "
+        "import of that package"
+    )