diff --git a/src/iai_mcp/qdrant_store.py b/src/iai_mcp/qdrant_store.py
index 4900a4d..99e674c 100644
--- a/src/iai_mcp/qdrant_store.py
+++ b/src/iai_mcp/qdrant_store.py
@@ -934,13 +934,15 @@ class QdrantStore:
         if not coalesced:
             return {}
 
-        # Fetch existing edges from metadata collection
+        # Fetch existing edges from metadata collection.
+        # existing_map: edge_key -> (point_id, weight) so we can update
+        # in-place by reusing the existing point ID (avoids duplicates).
         all_edges = self._scroll_all(METADATA_TABLE, table_filter=EDGES_TABLE)
-        existing_map: dict[tuple[str, str, str], float] = {}
+        existing_map: dict[tuple[str, str, str], tuple[str, float]] = {}
         for point in all_edges:
             p = point.payload
             edge_key = (p.get("src", ""), p.get("dst", ""), p.get("edge_type", ""))
-            existing_map[edge_key] = float(p.get("weight", 0.0))
+            existing_map[edge_key] = (str(point.id), float(p.get("weight", 0.0)))
 
         now = datetime.now(timezone.utc).isoformat()
         points_to_upsert: list[PointStruct] = []
@@ -949,13 +951,15 @@ class QdrantStore:
         for (src_str, dst_str), accum_delta in coalesced.items():
             edge_key = (src_str, dst_str, edge_type)
             if edge_key in existing_map:
-                nw = existing_map[edge_key] + accum_delta
+                nw = existing_map[edge_key][1] + accum_delta
+                point_id = existing_map[edge_key][0]  # reuse existing point ID
             else:
                 nw = accum_delta
+                point_id = str(uuid4())  # new edge → new ID
 
-            # Create payload-only point (use UUID string for Qdrant compatibility)
+            # Create payload-only point (reuses existing ID to update in-place)
             points_to_upsert.append(PointStruct(
-                id=str(uuid4()),
+                id=point_id,
                 vector={},
                 payload={
                     "table": EDGES_TABLE,
@@ -992,17 +996,33 @@ class QdrantStore:
         return self.boost_edges([pair], delta=delta, edge_type=edge_type)
 
     def add_contradicts_edge(self, original: UUID, new_id: UUID) -> None:
-        """Add a contradicts edge in the metadata collection (table=edges)."""
+        """Add or update a contradicts edge in the metadata collection (table=edges).
+
+        Reuses existing point ID if the edge already exists to avoid duplicates.
+        """
+        src_str = str(original)
+        dst_str = str(new_id)
+        edge_key = (src_str, dst_str, "contradicts")
+
+        # Check if edge already exists
+        all_edges = self._scroll_all(METADATA_TABLE, table_filter=EDGES_TABLE)
+        point_id = str(uuid4())  # default: new edge
+        for point in all_edges:
+            p = point.payload
+            if (p.get("src"), p.get("dst"), p.get("edge_type")) == edge_key:
+                point_id = str(point.id)
+                break
+
         self._client.upsert(
             collection_name=METADATA_TABLE,
             points=[PointStruct(
-                id=str(uuid4()),
+                id=point_id,
                 vector={},
                 payload={
                     "table": EDGES_TABLE,
                     "group_id": self._group_id,
-                    "src": str(original),
-                    "dst": str(new_id),
+                    "src": src_str,
+                    "dst": dst_str,
                     "edge_type": "contradicts",
                     "weight": 1.0,
                     "updated_at": datetime.now(timezone.utc).isoformat(),
diff --git a/src/iai_mcp/sigma.py b/src/iai_mcp/sigma.py
index df4f9ec..15ff064 100644
--- a/src/iai_mcp/sigma.py
+++ b/src/iai_mcp/sigma.py
@@ -151,11 +151,17 @@ def fast_sigma(
 def compute_sigma(graph: "nx.Graph", *, seed: int = 42) -> Optional[float]:
     """D-SIGMA-01: sigma at N>=SIGMA_N_FLOOR; otherwise None.
 
-    Returns None for graphs with fewer than SIGMA_N_FLOOR nodes -- below
-    that threshold, the random-graph baselines are too noisy to interpret
-    (Humphries-Gurney 2008).
+    Returns None for graphs whose largest connected component has fewer
+    than SIGMA_N_FLOOR nodes -- below that threshold, the random-graph
+    baselines are too noisy to interpret (Humphries-Gurney 2008).
+
+    This checks the largest CC rather than total node count because a
+    graph with many isolated nodes (e.g. 311 nodes, 310 components) would
+    otherwise pass the floor check while the actual connected subgraph is
+    too small for meaningful sigma computation.
     """
-    if graph.number_of_nodes() < SIGMA_N_FLOOR:
+    g_cc = _largest_cc(graph)
+    if g_cc.number_of_nodes() < SIGMA_N_FLOOR:
         return None
     sigma_val, *_ = fast_sigma(graph, seed=seed)
     if isinstance(sigma_val, float) and math.isnan(sigma_val):