diff --git a/graphify/export.py b/graphify/export.py
index 50ed388a..7ff216bd 100644
--- a/graphify/export.py
+++ b/graphify/export.py
@@ -163,7 +163,13 @@ _CONFIDENCE_SCORE_DEFAULTS = {"EXTRACTED": 1.0, "INFERRED": 0.5, "AMBIGUOUS": 0.
 def attach_hyperedges(G: nx.Graph, hyperedges: list) -> None:
     """Store hyperedges in the graph's metadata dict."""
     existing = G.graph.get("hyperedges", [])
-    seen_ids = {h["id"] for h in existing}
+    # Skip id-less persisted entries when seeding the dedup set (#2775): the
+    # semantic extractor emits hyperedges with no `id` and build.py persists them
+    # verbatim, so a prior graph.json can contain id-less hyperedges. A hard
+    # `h["id"]` here raised `KeyError: 'id'` on every incremental re-extract,
+    # symmetric with the `.get("id")` guard the loop below already applies to the
+    # incoming set.
+    seen_ids = {h["id"] for h in existing if h.get("id")}
     for h in hyperedges:
         if h.get("id") and h["id"] not in seen_ids:
             existing.append(h)
diff --git a/tests/test_hypergraph.py b/tests/test_hypergraph.py
index 20e79e67..10a57e9a 100644
--- a/tests/test_hypergraph.py
+++ b/tests/test_hypergraph.py
@@ -137,6 +137,20 @@ def test_attach_hyperedges_skips_entry_without_id():
     assert G.graph.get("hyperedges", []) == []
 
 
+def test_attach_hyperedges_tolerates_id_less_persisted():
+    # Regression for #2775: the semantic extractor emits hyperedges with no `id`
+    # and build.py persists them verbatim, so a prior graph.json can carry id-less
+    # hyperedges. On the next (incremental) run, attach_hyperedges read that
+    # persisted set with a hard `h["id"]` and died with `KeyError: 'id'`, writing
+    # nothing. Reading the persisted set must tolerate missing ids.
+    G = nx.DiGraph()
+    G.graph["hyperedges"] = [{"nodes": ["a", "b"], "type": "project", "attributes": {}}]
+    attach_hyperedges(G, [{"id": "flow_a", "label": "Flow A", "nodes": ["A", "B"]}])
+    # No crash; the id-less persisted entry is retained and the new id-bearing
+    # incoming hyperedge is appended.
+    assert len(G.graph["hyperedges"]) == 2
+
+
 # ---------------------------------------------------------------------------
 # 3. to_json includes hyperedges key
 # ---------------------------------------------------------------------------