diff --git a/graphify/build.py b/graphify/build.py
index d9b5e768f..29acd2526 100644
--- a/graphify/build.py
+++ b/graphify/build.py
@@ -1649,6 +1649,9 @@ def build_merge(
     graph to inherit from. An explicit True/False always overrides the on-disk
     flag.
     """
+    # Iterated more than once below (source sets, the hyperedge carry, the
+    # build itself), so a one-shot iterator must be materialised first.
+    new_chunks = list(new_chunks)
     graph_path = Path(graph_path if graph_path is not None else _default_graph_json())
     _loaded = _load_existing_graph(graph_path)
     if _loaded is not None:
@@ -1726,11 +1729,6 @@ def _kept(item: dict) -> bool:
                 file=sys.stderr,
             )
 
-    base = [{"nodes": existing_nodes, "edges": existing_edges}] if had_graph else []
-
-    all_chunks = base + list(new_chunks)
-    G = build(all_chunks, directed=directed, dedup=dedup, dedup_llm_backend=dedup_llm_backend, root=root)
-
     # Prune set for deleted source files — both the raw form (matches nodes that
     # kept absolute source_file) and the normalised relative form (matches nodes
     # relativised by _norm_source_file at build time). .resolve() (via _eff_root)
@@ -1797,12 +1795,25 @@ def _prune_match(sf: "str | None") -> bool:
     # deleted (#1574). build() only sees the new chunks' hyperedges, so without
     # this every --update collapses the graph's hyperedge set down to just the
     # changed files'. Re-extracted files' prior hyperedges are dropped (their new
-    # version is already in G — replace-per-source, like nodes/edges); deleted
-    # files' are dropped via prune_set. id-dedup (attach_hyperedges) so a carried
-    # hyperedge never duplicates one the new chunks re-emitted. Mirrors watch.py,
-    # which already preserves existing hyperedges across a rebuild.
+    # version is already in the new chunks — replace-per-source, like
+    # nodes/edges); deleted files' are dropped via prune_set; id-dedup so a
+    # carried hyperedge never duplicates one the new chunks re-emitted. Mirrors
+    # watch.py, which already preserves existing hyperedges across a rebuild.
+    #
+    # The carried set rides INTO build() on the base chunk rather than being
+    # attached to G afterwards (#3102): entity dedup rewires every edge endpoint
+    # and every hyperedge member it sees onto the survivor (#2805), but a
+    # hyperedge attached after the fact kept naming the merged-away node — a
+    # dangling member with no backing node in the written graph.
+    carried_hyperedges: list[dict] = []
     if existing_hyperedges:
-        carried = []
+        carried = carried_hyperedges
+        _new_hyperedge_ids = {
+            he.get("id")
+            for chunk in new_chunks
+            for he in (chunk.get("hyperedges") or [])
+            if isinstance(he, dict) and he.get("id")
+        }
         for he in existing_hyperedges:
             if not isinstance(he, dict):
                 continue
@@ -1815,10 +1826,17 @@ def _prune_match(sf: "str | None") -> bool:
                 continue  # semantically re-extracted — replaced by the new chunk's version
             if _prune_match(sf):
                 continue  # deleted — pruned
+            if he.get("id") and he.get("id") in _new_hyperedge_ids:
+                continue  # the new chunks re-emitted it — theirs wins
             carried.append(he)
-        if carried:
-            from graphify.export import attach_hyperedges
-            attach_hyperedges(G, carried)
+
+    base = (
+        [{"nodes": existing_nodes, "edges": existing_edges, "hyperedges": carried_hyperedges}]
+        if had_graph else []
+    )
+
+    all_chunks = base + list(new_chunks)
+    G = build(all_chunks, directed=directed, dedup=dedup, dedup_llm_backend=dedup_llm_backend, root=root)
 
     # Prune nodes and edges from deleted source files
     if prune_sources:
diff --git a/tests/test_carried_hyperedge_remap.py b/tests/test_carried_hyperedge_remap.py
new file mode 100644
index 000000000..d5b4d1047
--- /dev/null
+++ b/tests/test_carried_hyperedge_remap.py
@@ -0,0 +1,103 @@
+"""Carried-forward hyperedges must follow the dedup survivor remap (#3102).
+
+build_merge() carries hyperedges from unchanged files across an incremental
+rebuild (#1574). They used to be attached to G AFTER build() and entity
+dedup had finished, so while every edge endpoint was rewired onto the dedup
+survivor (#2805), a carried hyperedge kept naming the merged-away node — a
+dangling member in graph.json with no backing node.
+"""
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+from graphify.build import build_from_json, build_merge
+from graphify.export import to_json
+
+# `alpha_a` and `alpha_concept_long_variant_id` label-dedup into one node.
+NODES = [
+    {"id": "alpha_a", "label": "Alpha Concept", "file_type": "concept", "source_file": "notes/a.md"},
+    {"id": "alpha_concept_long_variant_id", "label": "alpha_concept", "file_type": "concept",
+     "source_file": "notes/b.md"},
+    {"id": "beta_node", "label": "Beta", "file_type": "concept", "source_file": "notes/group.md"},
+    {"id": "gamma_node", "label": "Gamma", "file_type": "concept", "source_file": "notes/group.md"},
+]
+EDGES = [{"source": "alpha_concept_long_variant_id", "target": "beta_node", "relation": "references",
+          "confidence": "EXTRACTED", "confidence_score": 1.0, "source_file": "notes/b.md"}]
+HYPEREDGE = {"id": "the_group", "label": "The Group",
+             "nodes": ["alpha_concept_long_variant_id", "beta_node", "gamma_node"],
+             "relation": "participate_in", "confidence": "EXTRACTED", "confidence_score": 1.0,
+             "source_file": "notes/group.md"}
+UNRELATED_CHUNK = {
+    "nodes": [{"id": "delta_node", "label": "Delta", "file_type": "concept", "source_file": "notes/d.md"}],
+    "edges": [], "hyperedges": [],
+}
+
+
+def _baseline(tmp_path: Path) -> Path:
+    """A graph written WITHOUT dedup, so the pair is still two nodes on disk
+    and the hyperedge names the variant — the shape an older build leaves."""
+    G = build_from_json({"nodes": NODES, "edges": EDGES, "hyperedges": [HYPEREDGE]})
+    p = tmp_path / "graph.json"
+    to_json(G, {0: list(G.nodes)}, str(p))
+    return p
+
+
+def _hyperedges(G):
+    return {he["id"]: he for he in G.graph.get("hyperedges", [])}
+
+
+def test_a_carried_hyperedge_is_remapped_onto_the_dedup_survivor(tmp_path):
+    G = build_merge([UNRELATED_CHUNK], _baseline(tmp_path))
+    survivors = set(G.nodes)
+    assert "alpha_concept_long_variant_id" not in survivors  # merged away
+    he = _hyperedges(G)["the_group"]
+    assert set(he["nodes"]) <= survivors, f"dangling members: {set(he['nodes']) - survivors}"
+    assert "alpha_a" in he["nodes"]  # onto the survivor, not just dropped
+    assert {"beta_node", "gamma_node"} <= set(he["nodes"])
+
+
+def test_the_written_graph_has_no_dangling_hyperedge_member(tmp_path):
+    G = build_merge([UNRELATED_CHUNK], _baseline(tmp_path))
+    out = tmp_path / "merged.json"
+    to_json(G, {0: list(G.nodes)}, str(out), force=True)
+    data = json.loads(out.read_text(encoding="utf-8"))
+    ids = {n["id"] for n in data["nodes"]}
+    for he in data.get("hyperedges", []):
+        assert set(he["nodes"]) <= ids, f"{he['id']} names a node that is not in the graph"
+
+
+def test_edges_and_hyperedges_agree_on_the_survivor(tmp_path):
+    """The edge endpoint and the hyperedge member came from the same
+    merged-away node; both must now name the same survivor."""
+    G = build_merge([UNRELATED_CHUNK], _baseline(tmp_path))
+    edge_ends = {u for u, v in G.edges} | {v for u, v in G.edges}
+    assert "alpha_a" in edge_ends
+    assert "alpha_a" in _hyperedges(G)["the_group"]["nodes"]
+
+
+def test_a_hyperedge_re_emitted_by_the_new_chunk_is_not_duplicated(tmp_path):
+    fresh = {"nodes": [{"id": "beta_node", "label": "Beta", "file_type": "concept",
+                        "source_file": "notes/group.md"},
+                       {"id": "gamma_node", "label": "Gamma", "file_type": "concept",
+                        "source_file": "notes/group.md"}],
+             "edges": [],
+             "hyperedges": [{**HYPEREDGE, "nodes": ["beta_node", "gamma_node"], "label": "The Group v2"}]}
+    G = build_merge([fresh], _baseline(tmp_path))
+    hes = [he for he in G.graph.get("hyperedges", []) if he["id"] == "the_group"]
+    assert len(hes) == 1
+    assert hes[0]["label"] == "The Group v2"  # the re-extracted version wins
+
+
+def test_a_pruned_sources_hyperedge_is_still_dropped(tmp_path):
+    G = build_merge([UNRELATED_CHUNK], _baseline(tmp_path), prune_sources=["notes/group.md"])
+    assert "the_group" not in _hyperedges(G)
+
+
+def test_an_unchanged_hyperedge_with_no_dedup_involved_is_carried_verbatim(tmp_path):
+    nodes = [n for n in NODES if n["id"] != "alpha_a"]  # nothing to dedup now
+    G0 = build_from_json({"nodes": nodes, "edges": EDGES, "hyperedges": [HYPEREDGE]})
+    p = tmp_path / "g.json"
+    to_json(G0, {0: list(G0.nodes)}, str(p))
+    G = build_merge([UNRELATED_CHUNK], p)
+    assert set(_hyperedges(G)["the_group"]["nodes"]) == set(HYPEREDGE["nodes"])