fixed some spacing issues

src/renderer.typ

@@ -86,6 +86,21 @@
     )
   }
 
+  // Compute minimum width for self sequences
+  for cell in cells.filter(c => c.i1 == c.i2) {
+    let m = measure(cell.cell)
+    let i = cell.i1
+    if cell.elmt.flip {
+      i -= 1
+    }
+    if 0 <= i and i < widths.len() {
+      widths.at(i) = calc.max(
+        widths.at(i),
+        m.width / 1pt + COMMENT-PAD
+      )
+    }
+  }
+
   // Compute remaining widths for longer sequences (spanning multiple columns)
   let multicol-cells = cells.filter(c => c.i2 - c.i1 > 1)
   multicol-cells = multicol-cells.sorted(key: c => {
@@ -136,7 +151,7 @@
     }
   }
 
-  let y = -Y-SPACE
+  let y = 0
   let groups = ()
   let lifelines = participants.map(_ => (
     level: 0,
@@ -153,6 +168,7 @@
 
     // Groups (start) -> reserve space for labels + store position
     } else if elmt.type == "grp" {
+      y -= Y-SPACE
       let m = measure(
         box(
           elmt.name,
@@ -165,17 +181,16 @@
         g
       })
       groups.push((y, elmt, 0, 0))
-      y -= m.height / 1pt + Y-SPACE
+      y -= m.height / 1pt
     
     // Groups (end) -> actual drawing
     } else if elmt.type == "grp-end" {
+      y -= Y-SPACE
       let (start-y, group, start-lvl, end-lvl) = groups.pop()
       let x0 = x-pos.at(group.min-i) - start-lvl * 10 - 20
       let x1 = x-pos.at(group.max-i) + end-lvl * 10 + 20
       shapes += draw-group(x0, x1, start-y, y, group)
 
-      y -= Y-SPACE
-
     // Separator
     } else if elmt.type == "sep" {
       let shps
@@ -211,6 +226,8 @@
     }
   }
 
+  y -= Y-SPACE
+
   // Draw vertical lines + lifelines + end participants
   shapes += draw.on-layer(-1, {
     if DEBUG-INVISIBLE {