diff --git a/backend/app/api/routes/nodes.py b/backend/app/api/routes/nodes.py
index 28ea124..0ef1bc2 100644
--- a/backend/app/api/routes/nodes.py
+++ b/backend/app/api/routes/nodes.py
@@ -37,10 +37,13 @@ async def _find_free_position(db: AsyncSession, design_id: str | None) -> tuple[
     if not positions:
         return 0.0, 0.0
 
+    # Snap each existing node to its true grid cell (negatives kept as-is). The
+    # search below only visits col >= 0 / row >= 0, so nodes parked in negative
+    # space never falsely block — or falsely free — a positive slot.
     occupied: set[tuple[int, int]] = set()
     for (px, py) in positions:
-        col = max(0, round(px / _SLOT_W))
-        row = max(0, round(py / _SLOT_H))
+        col = round(px / _SLOT_W)
+        row = round(py / _SLOT_H)
         occupied.add((col, row))
 
     for row in range(10_000):
diff --git a/backend/tests/test_edges.py b/backend/tests/test_edges.py
index 09b51d1..4110291 100644
--- a/backend/tests/test_edges.py
+++ b/backend/tests/test_edges.py
@@ -220,3 +220,113 @@ async def test_source_and_target_handle_persist_through_update(client: AsyncClie
     assert data["source_handle"] == "cluster-right"
     assert data["target_handle"] == "cluster-left"
     assert data["label"] == "corosync"
+
+
+# ---------------------------------------------------------------------------
+# Auto edge handles (issue #265): omitting source_handle/target_handle lets
+# the backend infer up/downstream sides from the nodes' absolute canvas Y.
+# ---------------------------------------------------------------------------
+
+
+@pytest.fixture
+async def stacked_nodes(client: AsyncClient, headers: dict):
+    """Two root nodes at known, distinct Y positions (top at y=0, bottom at y=300)."""
+    top = (
+        await client.post(
+            "/api/v1/nodes",
+            json={"type": "router", "label": "Top", "status": "online", "pos_x": 0, "pos_y": 0},
+            headers=headers,
+        )
+    ).json()
+    bottom = (
+        await client.post(
+            "/api/v1/nodes",
+            json={"type": "switch", "label": "Bottom", "status": "online", "pos_x": 0, "pos_y": 300},
+            headers=headers,
+        )
+    ).json()
+    return top["id"], bottom["id"]
+
+
+async def test_create_edge_auto_handles_source_above_target(client: AsyncClient, headers: dict, stacked_nodes):
+    """Source above target -> downstream flow: exit bottom, enter top-t."""
+    top, bottom = stacked_nodes
+    res = await client.post(
+        "/api/v1/edges", json={"source": top, "target": bottom, "type": "ethernet"}, headers=headers
+    )
+    assert res.status_code == 201
+    data = res.json()
+    assert data["source_handle"] == "bottom"
+    assert data["target_handle"] == "top-t"
+
+
+async def test_create_edge_auto_handles_source_below_target(client: AsyncClient, headers: dict, stacked_nodes):
+    """Source below target -> upstream flow: exit top, enter bottom-t."""
+    top, bottom = stacked_nodes
+    res = await client.post(
+        "/api/v1/edges", json={"source": bottom, "target": top, "type": "ethernet"}, headers=headers
+    )
+    assert res.status_code == 201
+    data = res.json()
+    assert data["source_handle"] == "top"
+    assert data["target_handle"] == "bottom-t"
+
+
+async def test_create_edge_auto_handles_equal_y_defaults_downstream(client: AsyncClient, headers: dict, two_nodes):
+    """Same Y (auto-placed side by side) falls back to the default bottom/top-t."""
+    src, tgt = two_nodes
+    res = await client.post(
+        "/api/v1/edges", json={"source": src, "target": tgt, "type": "ethernet"}, headers=headers
+    )
+    assert res.status_code == 201
+    data = res.json()
+    assert data["source_handle"] == "bottom"
+    assert data["target_handle"] == "top-t"
+
+
+async def test_create_edge_partial_handle_auto_fills_the_other(client: AsyncClient, headers: dict, stacked_nodes):
+    """An explicit source_handle is kept; the omitted target_handle is inferred."""
+    top, bottom = stacked_nodes
+    res = await client.post(
+        "/api/v1/edges",
+        json={"source": top, "target": bottom, "type": "ethernet", "source_handle": "cluster-right"},
+        headers=headers,
+    )
+    assert res.status_code == 201
+    data = res.json()
+    assert data["source_handle"] == "cluster-right"
+    assert data["target_handle"] == "top-t"
+
+
+async def test_create_edge_child_node_abs_y_resolved_through_parent(client: AsyncClient, headers: dict):
+    """A child's absolute Y = parent Y + its own pos_y, so a VM low inside a high
+    container still resolves as downstream of a node above the container."""
+    parent = (
+        await client.post(
+            "/api/v1/nodes",
+            json={"type": "proxmox", "label": "PVE", "status": "online", "container_mode": True, "pos_x": 0, "pos_y": 0},
+            headers=headers,
+        )
+    ).json()
+    child = (
+        await client.post(
+            "/api/v1/nodes",
+            json={"type": "vm", "label": "VM", "status": "online", "parent_id": parent["id"], "pos_x": 0, "pos_y": 50},
+            headers=headers,
+        )
+    ).json()
+    below = (
+        await client.post(
+            "/api/v1/nodes",
+            json={"type": "server", "label": "Below", "status": "online", "pos_x": 0, "pos_y": 500},
+            headers=headers,
+        )
+    ).json()
+    # child abs Y = 0 + 50 = 50, below at 500 -> child is upstream.
+    res = await client.post(
+        "/api/v1/edges", json={"source": child["id"], "target": below["id"], "type": "virtual"}, headers=headers
+    )
+    assert res.status_code == 201
+    data = res.json()
+    assert data["source_handle"] == "bottom"
+    assert data["target_handle"] == "top-t"
diff --git a/backend/tests/test_nodes.py b/backend/tests/test_nodes.py
index 0d5ad59..a11b7e4 100644
--- a/backend/tests/test_nodes.py
+++ b/backend/tests/test_nodes.py
@@ -286,3 +286,80 @@ async def test_properties_icon_can_be_null(client: AsyncClient, headers: dict):
     )
     assert create.status_code == 201
     assert create.json()["properties"] == props
+
+
+# ---------------------------------------------------------------------------
+# Auto-positioning (issue #265): omitting pos_x/pos_y snaps the node to the
+# first free 200x100 grid slot instead of stacking everything at (0, 0).
+# ---------------------------------------------------------------------------
+
+
+async def test_create_node_auto_positions_first_at_origin(client: AsyncClient, headers: dict):
+    """First root node with no coordinates lands at (0, 0)."""
+    res = await client.post(
+        "/api/v1/nodes", json={"type": "server", "label": "A", "status": "unknown"}, headers=headers
+    )
+    assert res.status_code == 201
+    data = res.json()
+    assert (data["pos_x"], data["pos_y"]) == (0.0, 0.0)
+
+
+async def test_create_node_auto_position_avoids_collision(client: AsyncClient, headers: dict):
+    """A second auto-placed root node takes the next free grid cell, not (0, 0)."""
+    first = await client.post(
+        "/api/v1/nodes", json={"type": "server", "label": "A", "status": "unknown"}, headers=headers
+    )
+    assert (first.json()["pos_x"], first.json()["pos_y"]) == (0.0, 0.0)
+
+    second = await client.post(
+        "/api/v1/nodes", json={"type": "server", "label": "B", "status": "unknown"}, headers=headers
+    )
+    assert second.status_code == 201
+    # Next free cell in row 0 is column 1 -> x = 1 * 200.
+    assert (second.json()["pos_x"], second.json()["pos_y"]) == (200.0, 0.0)
+
+
+async def test_create_node_child_defaults_to_parent_origin(client: AsyncClient, headers: dict):
+    """A child node (parent_id set) with no coordinates defaults to (0, 0) relative to its parent."""
+    parent = (
+        await client.post(
+            "/api/v1/nodes",
+            json={"type": "proxmox", "label": "PVE", "status": "online", "container_mode": True},
+            headers=headers,
+        )
+    ).json()
+    res = await client.post(
+        "/api/v1/nodes",
+        json={"type": "vm", "label": "VM1", "status": "online", "parent_id": parent["id"]},
+        headers=headers,
+    )
+    assert res.status_code == 201
+    data = res.json()
+    assert (data["pos_x"], data["pos_y"]) == (0.0, 0.0)
+
+
+async def test_create_node_explicit_position_preserved(client: AsyncClient, headers: dict):
+    """Explicit coordinates are honored, never auto-placed."""
+    res = await client.post(
+        "/api/v1/nodes",
+        json={"type": "server", "label": "A", "status": "unknown", "pos_x": 512.0, "pos_y": 384.0},
+        headers=headers,
+    )
+    assert res.status_code == 201
+    data = res.json()
+    assert (data["pos_x"], data["pos_y"]) == (512.0, 384.0)
+
+
+async def test_create_node_explicit_zero_position_preserved(client: AsyncClient, headers: dict):
+    """pos=0 is an explicit value, not 'omitted' — auto-position must not treat 0 as None."""
+    await client.post(
+        "/api/v1/nodes", json={"type": "server", "label": "A", "status": "unknown"}, headers=headers
+    )
+    # Second node explicitly pinned to (0, 0) even though the cell is taken.
+    res = await client.post(
+        "/api/v1/nodes",
+        json={"type": "server", "label": "B", "status": "unknown", "pos_x": 0, "pos_y": 0},
+        headers=headers,
+    )
+    assert res.status_code == 201
+    assert (res.json()["pos_x"], res.json()["pos_y"]) == (0.0, 0.0)