replace paragraph-spacing positioning hack with compositor block arithmetic

src/CompositorView.swift

@@ -1299,62 +1299,54 @@ struct CompositorRepresentable: NSViewRepresentable {
                 }
             }
 
-            // Collapse source lines and create gaps via paragraph spacing
             isUpdatingTables = true
             let tinyFont = NSFont.systemFont(ofSize: 0.1)
+            let collapsedPara = NSMutableParagraphStyle()
+            collapsedPara.minimumLineHeight = 0.1
+            collapsedPara.maximumLineHeight = 0.1
+            collapsedPara.lineSpacing = 0
+            collapsedPara.paragraphSpacing = 0
+            collapsedPara.paragraphSpacingBefore = 0
+
             ts.beginEditing()
             for (range, height) in blockSpacings {
-                // Make source text invisible: tiny font, zero foreground alpha
                 ts.addAttribute(.font, value: tinyFont, range: range)
                 ts.addAttribute(.foregroundColor, value: NSColor.clear, range: range)
+                ts.addAttribute(.paragraphStyle, value: collapsedPara.copy() as! NSParagraphStyle, range: range)
 
-                // Collapse line heights and add spacing for the block view
-                let para = NSMutableParagraphStyle()
-                para.minimumLineHeight = 0.1
-                para.maximumLineHeight = 0.1
-                para.lineSpacing = 0
-                para.paragraphSpacing = 0
-                para.paragraphSpacingBefore = 0
-                ts.addAttribute(.paragraphStyle, value: para, range: range)
-
-                // On the last line, add paragraph spacing equal to block height
                 let lastLineRange = text.lineRange(for: NSRange(location: max(0, NSMaxRange(range) - 1), length: 0))
-                let lastPara = NSMutableParagraphStyle()
+                let spacerPara = collapsedPara.mutableCopy() as! NSMutableParagraphStyle
-                lastPara.minimumLineHeight = 0.1
+                spacerPara.paragraphSpacing = height
-                lastPara.maximumLineHeight = 0.1
+                ts.addAttribute(.paragraphStyle, value: spacerPara, range: lastLineRange)
-                lastPara.lineSpacing = 0
-                lastPara.paragraphSpacing = height
-                lastPara.paragraphSpacingBefore = 0
-                ts.addAttribute(.paragraphStyle, value: lastPara, range: lastLineRange)
             }
             ts.endEditing()
             isUpdatingTables = false
 
             lm.ensureLayout(for: tc)
 
-            // Position blocks at the origin of their collapsed source text
+            // Position blocks using first-glyph origin of collapsed source text
             var tableIdx = 0
             var hrIdx = 0
+            let x = origin.x + 4
             for block in lm.blockRanges {
                 let glyphRange = lm.glyphRange(forCharacterRange: block.range, actualCharacterRange: nil)
-                let rect = lm.boundingRect(forGlyphRange: glyphRange, in: tc)
+                guard glyphRange.length > 0 else { continue }
-                let x = origin.x + 4
+                let lineRect = lm.lineFragmentRect(forGlyphAt: glyphRange.location, effectiveRange: nil)
+                let blockY = lineRect.origin.y + origin.y
 
                 switch block.kind {
                 case .tableBlock:
                     guard tableIdx < tableBlocks.count else { continue }
                     let tb = tableBlocks[tableIdx]
                     tableIdx += 1
-                    let tableW = tb.view.frame.width
+                    tb.view.frame = NSRect(x: x, y: blockY, width: tb.view.frame.width, height: tb.blockHeight)
-                    tb.view.frame = NSRect(x: x, y: rect.origin.y + origin.y, width: tableW, height: tb.blockHeight)
                     tv.addSubview(tb.view)
 
                 case .horizontalRule:
                     guard hrIdx < hrBlocks.count else { continue }
                     let hb = hrBlocks[hrIdx]
                     hrIdx += 1
-                    let w = tc.containerSize.width - 8
+                    hb.view.frame = NSRect(x: x, y: blockY, width: tc.containerSize.width - 8, height: hb.blockHeight)
-                    hb.view.frame = NSRect(x: x, y: rect.origin.y + origin.y, width: w, height: hb.blockHeight)
                     tv.addSubview(hb.view)
 
                 default:
@@ -1373,32 +1365,6 @@ struct CompositorRepresentable: NSViewRepresentable {
             ts.beginEditing()
             ts.replaceCharacters(in: sourceRange, with: newMarkdown)
             applySyntaxHighlighting(to: ts, format: parent.fileFormat)
-
-            // Collapse new source text and set paragraph spacing for updated table height
-            let newRange = NSRange(location: sourceRange.location, length: (newMarkdown as NSString).length)
-            let blockHeight: CGFloat = 28 + CGFloat(table.rows.count) * 26 + 2
-            let tinyFont = NSFont.systemFont(ofSize: 0.1)
-            ts.addAttribute(.font, value: tinyFont, range: newRange)
-            ts.addAttribute(.foregroundColor, value: NSColor.clear, range: newRange)
-
-            let collapsePara = NSMutableParagraphStyle()
-            collapsePara.minimumLineHeight = 0.1
-            collapsePara.maximumLineHeight = 0.1
-            collapsePara.lineSpacing = 0
-            collapsePara.paragraphSpacing = 0
-            collapsePara.paragraphSpacingBefore = 0
-            ts.addAttribute(.paragraphStyle, value: collapsePara, range: newRange)
-
-            let text = ts.string as NSString
-            let lastLineRange = text.lineRange(for: NSRange(location: max(0, NSMaxRange(newRange) - 1), length: 0))
-            let lastPara = NSMutableParagraphStyle()
-            lastPara.minimumLineHeight = 0.1
-            lastPara.maximumLineHeight = 0.1
-            lastPara.lineSpacing = 0
-            lastPara.paragraphSpacing = blockHeight
-            lastPara.paragraphSpacingBefore = 0
-            ts.addAttribute(.paragraphStyle, value: lastPara, range: lastLineRange)
-
             ts.endEditing()
             (tv as? LineNumberTextView)?.applyEvalSpacing()
             tv.selectedRanges = sel