fix(meshing): mirror the v1 manifest response in v2

v2 emits each fragment identical to v1 (seg id prepended when asked) and honors return_seg_ids, differing only by grouping fragments under their bucket key, so the client reuses its v1 handling unchanged.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: akhileshh

pychunkedgraph/app/meshing/common.py

@@ -138,10 +138,10 @@ def manifest_response(cg, args):
 
     if manifest_version >= 2:
         mm = MeshMeta(cg)
-        initial, dynamic = v2.to_v2_groups(
-            seg_ids, fragments, seg_id_in_fragment=not verify
-        )
+        initial, dynamic = v2.to_v2_groups(seg_ids, fragments, prepend_seg_ids)
         resp = v2.assemble(mm.initial_path, mm.dynamic_path, initial, dynamic)
+        if return_seg_ids:
+            resp["seg_ids"] = seg_ids
     else:
         resp = {"fragments": fragments}
         if prepend_seg_ids:

pychunkedgraph/meshing/manifest/v2.py

@@ -31,23 +31,17 @@ def requested_manifest_version(accept_header, default: int = 1) -> int:
     return default
 
 
-def to_v2_groups(node_ids, fragments, seg_id_in_fragment: bool):
-    """Split the v1 ``(node_ids, fragments)`` output into
-    ``(initial_frags, dynamic_frags)`` for the v2 format.
+def to_v2_groups(node_ids, fragments, prepend_seg_ids):
+    """Group v1 fragments into ``(initial, dynamic)`` by the leading ``~`` marker.
 
-    Initial (sharded) fragments are marked by a leading ``~``; the marker is
-    dropped and the seg id ensured as the leading field. Dynamic fragments carry
-    no marker and already lead with the seg id. ``seg_id_in_fragment`` is True
-    when the initial fragments already embed the seg id (speculative), False when
-    it must be prepended (verified).
+    Each fragment is emitted exactly as the v1 manifest would (seg id prepended
+    when requested); only the initial-vs-dynamic grouping is added. The raw ``~``
+    selects the group, matching v1's ``~<segid>:<fragment>``.
     """
     initial, dynamic = [], []
     for node_id, frag in zip(node_ids, fragments):
-        if frag.startswith("~"):
-            body = frag[1:]
-            initial.append(body if seg_id_in_fragment else f"{node_id}:{body}")
-        else:
-            dynamic.append(frag)
+        out = f"~{node_id}:{frag}" if prepend_seg_ids else frag
+        (initial if frag.startswith("~") else dynamic).append(out)
     return initial, dynamic
 
 

pychunkedgraph/tests/meshing/test_manifest_v2.py

@@ -0,0 +1,28 @@
+"""Tests for pychunkedgraph.meshing.manifest.v2."""
+
+from pychunkedgraph.meshing.manifest.v2 import assemble, to_v2_groups
+
+
+class TestToV2Groups:
+    def test_prepend_matches_v1_grouped_by_type(self):
+        """With prepend_seg_ids each fragment is v1's ``~<segid>:<frag>``; grouping
+        is by the raw ~ (initial/sharded) vs no-~ (dynamic/whole-file)."""
+        node_ids = [386, 529]
+        frags = ["~5/774017-0.shard:74809813:4532", "529:0:90112-98304"]
+        ini, dyn = to_v2_groups(node_ids, frags, prepend_seg_ids=True)
+        assert ini == ["~386:~5/774017-0.shard:74809813:4532"]
+        assert dyn == ["~529:529:0:90112-98304"]
+
+    def test_no_prepend_keeps_raw(self):
+        ini, dyn = to_v2_groups(
+            [386, 529], ["~a.shard:1:2", "529:0:bbox"], prepend_seg_ids=False
+        )
+        assert ini == ["~a.shard:1:2"]
+        assert dyn == ["529:0:bbox"]
+
+    def test_assemble_groups_under_bucket(self):
+        resp = assemble(
+            "gs://b/initial", "gs://b/dynamic", ["~386:~a.shard:1:2"], ["~529:529:0:y"]
+        )
+        assert resp["fragments"]["gs://b/initial"]["fragments"] == ["~386:~a.shard:1:2"]
+        assert resp["manifest_version"] == 2