feat(layout): reduce default MAM_MIN_PANE_COLS to 40 for single workspace 2xK multi-pane tiling

tests/test_tier1_unit.py

@@ -864,5 +864,91 @@ def test_lib_sh_new_session_passes_mam_ws_label(mam_sandbox):
     assert '_real_herdr workspace rename "$existing_ws" "$MAM_WS_LABEL"' in content
 
 
+# ==============================================================================
+# FEATURE: 2xK Grid Layout Engine (min_cols=40 & multi-pane workspace tiling)
+# ==============================================================================
+
+def test_layout_default_min_cols_40_in_tier1():
+    """Verify default min_cols=40 behavior across compute_2xk_layout in Tier 1 suite."""
+    from lib_py.layout import compute_2xk_layout
+
+    # 1. 2 panes in 80 col width (80 // 2 = 40 == min_cols 40) -> splits right cleanly
+    payload_80 = {
+        "result": {
+            "panes": [
+                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 80, "height": 40}},
+                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 80, "height": 40}}
+            ]
+        }
+    }
+    decision = compute_2xk_layout(payload_80)
+    assert decision.direction == "right"
+    assert not decision.is_overflow
+    assert decision.reason == "new_column_right"
+
+    # 2. 2 panes in 79 col width (79 // 2 = 39 < min_cols 40) -> column_width_overflow
+    payload_79 = {
+        "result": {
+            "panes": [
+                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 79, "height": 40}},
+                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 79, "height": 40}}
+            ]
+        }
+    }
+    decision_overflow = compute_2xk_layout(payload_79)
+    assert decision_overflow.direction == "overflow"
+    assert decision_overflow.is_overflow
+    assert decision_overflow.reason == "column_width_overflow"
+
+
+def test_layout_single_workspace_90_100_cols_tiling_tier1():
+    """Verify 3-4 agents tiling in standard 90-100 col terminal windows within a single workspace."""
+    from lib_py.layout import compute_2xk_layout
+
+    for total_w in [90, 100]:
+        half_w = total_w // 2
+
+        # Step 1: 1 pane -> 2 panes (split down)
+        p1 = {"result": {"panes": [{"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": total_w, "height": 40}}]}}
+        d1 = compute_2xk_layout(p1)
+        assert d1.direction == "down"
+        assert d1.target_pane_id == "p1"
+        assert not d1.is_overflow
+
+        # Step 2: 2 panes -> 3 panes (split right to open 2nd column)
+        p2 = {"result": {"panes": [
+            {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": total_w, "height": 20}},
+            {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": total_w, "height": 20}}
+        ]}}
+        d2 = compute_2xk_layout(p2)
+        assert d2.direction == "right"
+        assert d2.target_pane_id == "p1"
+        assert not d2.is_overflow
+
+        # Step 3: 3 panes -> 4 panes (split singleton 2nd column down)
+        p3 = {"result": {"panes": [
+            {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": half_w, "height": 20}},
+            {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": half_w, "height": 20}},
+            {"pane_id": "p3", "rect": {"x": half_w, "y": 0, "width": half_w, "height": 40}}
+        ]}}
+        d3 = compute_2xk_layout(p3)
+        assert d3.direction == "down"
+        assert d3.target_pane_id == "p3"
+        assert not d3.is_overflow
+
+        # Step 4: 4 panes (2x2 complete) -> 5th agent overflows to fresh workspace
+        p4 = {"result": {"panes": [
+            {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": half_w, "height": 20}},
+            {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": half_w, "height": 20}},
+            {"pane_id": "p3", "rect": {"x": half_w, "y": 0, "width": half_w, "height": 20}},
+            {"pane_id": "p4", "rect": {"x": half_w, "y": 20, "width": half_w, "height": 20}}
+        ]}}
+        d4 = compute_2xk_layout(p4)
+        assert d4.direction == "overflow"
+        assert d4.is_overflow
+        assert d4.reason == "column_width_overflow"
+
+
+