d2sequence: fix note overlap

ci/release/changelogs/next.md

@@ -20,3 +20,4 @@
 - Imports: fixes using substitutions in `icon` values [#2207](https://github.com/terrastruct/d2/pull/2207)
 - Markdown: fixes ampersands in URLs in markdown [#2219](https://github.com/terrastruct/d2/pull/2219)
 - Globs: fixes edge case where globs with imported boards would create empty boards [#2247](https://github.com/terrastruct/d2/pull/2247)
+- Sequence diagrams: fixes alignment of notes when self messages are above it [#2264](https://github.com/terrastruct/d2/pull/2264)

d2layouts/d2sequence/sequence_diagram.go

@@ -466,7 +466,12 @@ func (sd *sequenceDiagram) placeNotes() {
 
 		for _, msg := range sd.messages {
 			if sd.verticalIndices[msg.AbsID()] < verticalIndex {
-				y += sd.yStep + float64(msg.LabelDimensions.Height)
+				if msg.Src == msg.Dst {
+					// For self-messages, account for the full vertical space they occupy
+					y += sd.yStep + math.Max(float64(msg.LabelDimensions.Height), MIN_MESSAGE_DISTANCE)*1.5
+				} else {
+					y += sd.yStep + float64(msg.LabelDimensions.Height)
+				}
 			}
 		}
 		for _, otherNote := range sd.notes {