perf(editor): extend textkit profiling probes

Sources/SaplingEditor/EditorPerformanceProfiling.swift

@@ -391,6 +391,31 @@ public enum EditorBenchmarkProfiler {
             notes: "\(attributedStringResult.value.styledLineCount) styled lines"
         ))
 
+        let coldViewportStack = makeTextKitStack(attributedString: textStorage)
+        let coldViewportResult = measure {
+            coldViewportStack.layoutManager.glyphRange(
+                forBoundingRect: NSRect(x: 0, y: 50_000, width: 760, height: 900),
+                in: coldViewportStack.textContainer
+            )
+        }
+        measurements.append(EditorBenchmarkMeasurement(
+            name: "cold_viewport_glyph_range_middle",
+            category: .layout,
+            durationMilliseconds: coldViewportResult.durationMilliseconds,
+            notes: "Visible glyph range before explicit full-document layout"
+        ))
+
+        let coldLineFragmentStack = makeTextKitStack(attributedString: textStorage)
+        let coldLineFragmentResult = measure {
+            lineFragmentRect(atCharacterLocation: coldLineFragmentStack.textStorage.length / 2, in: coldLineFragmentStack)
+        }
+        measurements.append(EditorBenchmarkMeasurement(
+            name: "cold_line_fragment_calculation_midpoint",
+            category: .layout,
+            durationMilliseconds: coldLineFragmentResult.durationMilliseconds,
+            notes: "lineFragmentRect near midpoint before explicit full-document layout"
+        ))
+
         let layoutInvalidationResult = measure {
             var actualRange = NSRange(location: 0, length: 0)
             layoutManager.invalidateLayout(
@@ -425,6 +450,30 @@ public enum EditorBenchmarkProfiler {
             notes: "NSLayoutManager.ensureLayout for text container"
         ))
 
+        let cachedLineFragmentResult = measure {
+            lineFragmentRect(atCharacterLocation: textStorage.length / 2, in: (
+                textStorage: textStorage,
+                layoutManager: layoutManager,
+                textContainer: textContainer
+            ))
+        }
+        measurements.append(EditorBenchmarkMeasurement(
+            name: "cached_line_fragment_calculation_midpoint",
+            category: .layout,
+            durationMilliseconds: cachedLineFragmentResult.durationMilliseconds,
+            notes: "lineFragmentRect near midpoint after full layout"
+        ))
+
+        let textContainerUsedRectResult = measure {
+            layoutManager.usedRect(for: textContainer)
+        }
+        measurements.append(EditorBenchmarkMeasurement(
+            name: "text_container_used_rect_after_full_layout",
+            category: .layout,
+            durationMilliseconds: textContainerUsedRectResult.durationMilliseconds,
+            notes: "NSTextContainer usedRect after full layout"
+        ))
+
         let firstViewportResult = measure {
             layoutManager.glyphRange(
                 forBoundingRect: NSRect(x: 0, y: 0, width: 760, height: 900),
@@ -544,5 +593,37 @@ public enum EditorBenchmarkProfiler {
         _ = changedSource
         return measurements
     }
+
+    private static func makeTextKitStack(attributedString: NSAttributedString) -> (
+        textStorage: NSTextStorage,
+        layoutManager: NSLayoutManager,
+        textContainer: NSTextContainer
+    ) {
+        let textStorage = NSTextStorage(attributedString: attributedString)
+        let layoutManager = NSLayoutManager()
+        let textContainer = NSTextContainer(size: NSSize(width: 760, height: CGFloat.greatestFiniteMagnitude))
+        textContainer.widthTracksTextView = false
+        textContainer.heightTracksTextView = false
+        layoutManager.addTextContainer(textContainer)
+        textStorage.addLayoutManager(layoutManager)
+        return (textStorage, layoutManager, textContainer)
+    }
+
+    @discardableResult
+    private static func lineFragmentRect(
+        atCharacterLocation characterLocation: Int,
+        in stack: (
+            textStorage: NSTextStorage,
+            layoutManager: NSLayoutManager,
+            textContainer: NSTextContainer
+        )
+    ) -> NSRect {
+        guard stack.textStorage.length > 0 else { return .zero }
+
+        let characterLocation = max(0, min(characterLocation, stack.textStorage.length - 1))
+        let glyphIndex = stack.layoutManager.glyphIndexForCharacter(at: characterLocation)
+        var effectiveRange = NSRange(location: 0, length: 0)
+        return stack.layoutManager.lineFragmentRect(forGlyphAt: glyphIndex, effectiveRange: &effectiveRange)
+    }
     #endif
 }