Loosen buffer line spacing for all fonts

Add extra vertical space to every buffer line (LINE_SPACING_EXTRA, 30% of font size) on top of the font natural line height. The same style measures and draws rows so whole-line snapping stays in step.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JW57ZwRSygeowNBguQEUUB

src/main/kotlin/ui/ChannelScreen.kt

@@ -1,3 +1,5 @@
+@file:OptIn(androidx.compose.ui.text.ExperimentalTextApi::class)
+
 package ui
 
 import androidx.compose.animation.core.animateFloatAsState
@@ -847,14 +849,30 @@ fun MessageScrollback(
         // then converts that now-stale pixel value using the NEW density, so the
         // two silently disagreed until the window (and this remember scope) was
         // recreated by closing and reopening it.
-        val lineHeightPx = remember(displaySettings.fontSize, displaySettings.fontId, density) {
-            textMeasurer.measure(
-                text = "Mg",
-                style = androidx.compose.ui.text.TextStyle(
-                    fontFamily = AppFonts.familyFor(displaySettings.fontId),
-                    fontSize = displaySettings.fontSize.sp
+        // The buffer text style gets extra vertical air on top of the font's own natural
+        // line height (every bundled font has different metrics, so a fixed multiplier
+        // would loosen some fonts and tighten others). The same style is used to measure
+        // the line height below AND to draw every row, so the whole-line snapping stays
+        // exactly in step with what is on screen. LineHeightStyle with Trim.None and a
+        // centered alignment makes each line exactly lineHeight tall, with the extra
+        // space split above and below the text.
+        val bufferTextStyle = remember(displaySettings.fontSize, displaySettings.fontId, density) {
+            val base = androidx.compose.ui.text.TextStyle(
+                fontFamily = AppFonts.familyFor(displaySettings.fontId),
+                fontSize = displaySettings.fontSize.sp
+            )
+            val naturalPx = textMeasurer.measure(text = "Mg", style = base).size.height
+            val spacedLine = with(density) { naturalPx.toSp() } + (displaySettings.fontSize * LINE_SPACING_EXTRA).sp
+            base.copy(
+                lineHeight = spacedLine,
+                lineHeightStyle = androidx.compose.ui.text.style.LineHeightStyle(
+                    alignment = androidx.compose.ui.text.style.LineHeightStyle.Alignment.Center,
+                    trim = androidx.compose.ui.text.style.LineHeightStyle.Trim.None
                 )
-            ).size.height
+            )
+        }
+        val lineHeightPx = remember(bufferTextStyle, density) {
+            textMeasurer.measure(text = "Mg", style = bufferTextStyle).size.height
         }
         val lineHeightDp = with(density) { lineHeightPx.toDp() }
         // Ruled out (see task: newest-message-missing investigation) as the
@@ -885,10 +903,7 @@ fun MessageScrollback(
         // offset correction through stickToBottom's own effect instead of a
         // second independent one.
 
-    val textStyle = androidx.compose.ui.text.TextStyle(
-        fontFamily = AppFonts.familyFor(displaySettings.fontId),
-        fontSize = displaySettings.fontSize.sp
-    )
+    val textStyle = bufferTextStyle
     val selection = selectionState.selection
 
     Column(modifier = Modifier.fillMaxSize()) {
@@ -1114,6 +1129,11 @@ fun MessageScrollback(
     }
 }
 
+// Extra vertical space added to every buffer line, as a fraction of the font size, on top of
+// the font's natural line height. 0.30 is a modest loosening; raise it for more air between
+// lines (0.45 is roomy), lower it for less. Applies to every font in the font list.
+private const val LINE_SPACING_EXTRA = 0.30f
+
 // Reports this element's height as a whole number of text lines ([linePx] each): rounded up
 // for image slots (the picture is never cut), to the nearest line for text rows (a wrapped
 // message can measure a pixel or two off an exact multiple). Content is drawn from the top.