feat(layout): implement right-growth 2xK grid layout engine in lib_py.layout and refactor lib.sh (B-20)

.agents/skills/lib.sh

@@ -428,36 +428,10 @@ except Exception:
 
       split_dir=""
       if [ -n "$sample_pane" ]; then
-        split_dir=$(_real_herdr pane layout --pane "$sample_pane" 2>/dev/null | MAM_MIN_COLS="${MAM_MIN_PANE_COLS:-60}" MAM_MIN_ROWS="${MAM_MIN_PANE_ROWS:-20}" python3 -c "
-import sys, json, os
-min_cols = int(os.environ.get('MAM_MIN_COLS', 60))
-min_rows = int(os.environ.get('MAM_MIN_ROWS', 20))
-try:
-    d = json.loads(sys.stdin.read()).get('result', {})
-    focused_id = d.get('focused_pane_id', '')
-    panes = d.get('panes', [])
-    anchor = None
-    for p in panes:
-        if p.get('pane_id') == focused_id:
-            anchor = p.get('rect', {})
-            break
-    if not anchor and panes:
-        anchor = panes[0].get('rect', {})
-    if anchor:
-        w = anchor.get('width', 0)
-        h = anchor.get('height', 0)
-        if w <= 0 or h <= 0:
-            # Headless or detached session with unmeasured/zero dimensions
-            print('right')
-        elif w // 2 >= min_cols:
-            print('right')
-        elif h // 2 >= min_rows:
-            print('down')
-        else:
-            print('overflow')
-except Exception:
-    pass
-" 2>/dev/null || echo "")
+        layout_raw=$(_real_herdr pane layout --pane "$sample_pane" 2>/dev/null || echo "")
+        read -r split_dir split_target < <(printf '%s' "$layout_raw" | python3 -m lib_py.layout --min-cols "${MAM_MIN_PANE_COLS:-60}" --min-rows "${MAM_MIN_PANE_ROWS:-20}" --sample-pane "$sample_pane" 2>/dev/null || echo "right $sample_pane")
+        split_dir="${split_dir:-right}"
+        sample_pane="${split_target:-$sample_pane}"
       fi
 
       if [ "$split_dir" = "right" ] || [ "$split_dir" = "down" ]; then