feat(compose): add font size control to the formatting toolbar

Add a preset-size dropdown (10/12/14/18/24pt, plus Default to clear) to the
compose FormattingToolbar via a new FontSizePicker composable, applying
RichStyle.FontSize over the selection through the existing generalized
applyStyle/clearStyle toggle path (no font-size-specific branching needed).
The anchor button shows the selection's current size, or "Default" when
unset/mixed. The rich-text foundation already provided RichStyle.FontSize,
its pt/px-tolerant HTML round-trip, and pt->sp mapping for in-editor
rendering; this ticket wires up the missing UI control.

Closes #73

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/androidTest/kotlin/org/libremail/ui/compose/format/FontSizePickerTest.kt

@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+package org.libremail.ui.compose.format
+
+import androidx.activity.ComponentActivity
+import androidx.compose.ui.test.assertIsDisplayed
+import androidx.compose.ui.test.junit4.createAndroidComposeRule
+import androidx.compose.ui.test.onNodeWithText
+import androidx.compose.ui.test.performClick
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import org.junit.Assert.assertEquals
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.libremail.R
+import org.libremail.ui.theme.LibreMailTheme
+
+/**
+ * UI tests for the compose formatting toolbar's font-size dropdown (#73). [FontSizePicker] is
+ * presentational, so it is driven directly - independent of the surrounding
+ * [org.libremail.ui.compose.RichTextBodyField] editor - mirroring how `ContactAutocompleteRowTest`
+ * exercises its row composable in isolation.
+ */
+@RunWith(AndroidJUnit4::class)
+class FontSizePickerTest {
+
+    @get:Rule
+    val composeTestRule = createAndroidComposeRule<ComponentActivity>()
+
+    private fun string(resId: Int) = composeTestRule.activity.getString(resId)
+
+    private fun string(resId: Int, vararg args: Any) = composeTestRule.activity.getString(resId, *args)
+
+    private fun setContent(selectedPt: Int?, onSelect: (Int?) -> Unit = {}) {
+        composeTestRule.setContent {
+            LibreMailTheme(darkTheme = false, dynamicColor = false) {
+                FontSizePicker(selectedPt = selectedPt, onSelect = onSelect)
+            }
+        }
+    }
+
+    @Test
+    fun noSizeSelected_buttonShowsDefaultLabel() {
+        setContent(selectedPt = null)
+        composeTestRule.onNodeWithText(string(R.string.format_size_default)).assertIsDisplayed()
+    }
+
+    @Test
+    fun aSizeSelected_buttonShowsItsPointValue() {
+        setContent(selectedPt = 18)
+        composeTestRule.onNodeWithText(string(R.string.format_size_pt, 18)).assertIsDisplayed()
+    }
+
+    @Test
+    fun tappingTheButton_opensAMenuListingDefaultAndEveryPreset() {
+        setContent(selectedPt = null)
+        // Before the menu opens, "Default" only labels the anchor button itself - a unique match.
+        composeTestRule.onNodeWithText(string(R.string.format_size_default)).performClick()
+        FONT_SIZE_PRESETS_PT.forEach { pt ->
+            composeTestRule.onNodeWithText(string(R.string.format_size_pt, pt)).assertIsDisplayed()
+        }
+    }
+
+    @Test
+    fun pickingAPresetFromTheMenu_reportsItsPointSize() {
+        var picked: Int? = -1
+        setContent(selectedPt = null) { picked = it }
+        composeTestRule.onNodeWithText(string(R.string.format_size_default)).performClick()
+        composeTestRule.onNodeWithText(string(R.string.format_size_pt, 14)).performClick()
+        assertEquals(14, picked)
+    }
+
+    @Test
+    fun pickingDefaultFromTheMenu_clearsBySelectingNull() {
+        var picked: Int? = 12
+        setContent(selectedPt = 12) { picked = it }
+        // The button reads "12 pt" here, so the menu's own "Default" entry is the only such match.
+        composeTestRule.onNodeWithText(string(R.string.format_size_pt, 12)).performClick()
+        composeTestRule.onNodeWithText(string(R.string.format_size_default)).performClick()
+        assertEquals(null, picked)
+    }
+}

app/src/main/kotlin/org/libremail/ui/compose/RichTextEditor.kt

@@ -58,6 +58,7 @@ import org.libremail.richtext.RichTextEditing
 import org.libremail.richtext.RichTextHtml
 import org.libremail.ui.compose.format.ColorSwatch
 import org.libremail.ui.compose.format.ColorSwatchRow
+import org.libremail.ui.compose.format.FontSizePicker
 
 /** String-annotation tag the editor uses to carry a span's link target inside the [AnnotatedString]. */
 private const val URL_TAG = "libremail:url"
@@ -74,7 +75,7 @@ internal const val IMAGE_TAG = "libremail:image"
 
 /**
  * A rich-text body editor: a formatting toolbar (bold / italic / underline / strikethrough, font
- * color and highlight, bulleted + numbered lists, block quote, and link) above a rounded
+ * size, font color and highlight, bulleted + numbered lists, block quote, and link) above a rounded
  * [OutlinedTextField]. It converts its [AnnotatedString] to the app's [RichTextContent] model and
  * reports both the plaintext form and its HTML — or null HTML when nothing is formatted, so an
  * unformatted message stays plaintext-only and feels exactly like the old editor.
@@ -83,7 +84,8 @@ internal const val IMAGE_TAG = "libremail:image"
  * work as usual; each toolbar button exposes its accessible action label via `onClickLabel` on its
  * [Modifier.clickable] (not a `contentDescription`), and still carries toggle state for accessibility.
  * The font-color and highlight buttons open a [ColorPickerDialog] built on the shared
- * [ColorSwatchRow], whose individual swatches carry their own `contentDescription` instead.
+ * [ColorSwatchRow], whose individual swatches carry their own `contentDescription` instead; the font
+ * size button opens the self-contained [FontSizePicker] dropdown.
  *
  * [resolveFont] maps a CSS font-family stack to a Compose [FontFamily] for display; the default
  * resolves nothing, leaving the system font (the model still round-trips the CSS value untouched).
@@ -134,6 +136,15 @@ fun RichTextBodyField(
             onLink = { showLinkDialog = true },
             onFontColor = { showFontColorPicker = true },
             onHighlight = { showHighlightPicker = true },
+            onFontSize = { pt ->
+                emit(
+                    if (pt != null) {
+                        applyStyle(value, RichStyle.FontSize(pt), linkColor, resolveFont)
+                    } else {
+                        clearStyle(value, RichStyle.FontSize::class.java, linkColor, resolveFont)
+                    },
+                )
+            },
         )
         OutlinedTextField(
             value = value,
@@ -217,6 +228,7 @@ private fun FormattingToolbar(
     onLink: () -> Unit,
     onFontColor: () -> Unit,
     onHighlight: () -> Unit,
+    onFontSize: (Int?) -> Unit,
 ) {
     val content = value.annotatedString.toRichContent()
     val start = value.selection.min
@@ -257,6 +269,8 @@ private fun FormattingToolbar(
             strikethrough = true,
             onClick = { onToggleStyle(RichStyle.Strikethrough) },
         )
+        val fontSizePt = RichTextEditing.styleAt(content, start, end, RichStyle.FontSize::class.java)?.pt
+        FontSizePicker(selectedPt = fontSizePt, onSelect = onFontSize)
         val fontColorArgb = RichTextEditing.styleAt(content, start, end, RichStyle.FontColor::class.java)?.argb
         FormatButton(
             label = "A",

app/src/main/kotlin/org/libremail/ui/compose/format/FontSizePicker.kt

@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+package org.libremail.ui.compose.format
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.ArrowDropDown
+import androidx.compose.material3.DropdownMenu
+import androidx.compose.material3.DropdownMenuItem
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.semantics.Role
+import androidx.compose.ui.unit.dp
+import org.libremail.R
+
+/** The fixed preset sizes [FontSizePicker] offers, in points. */
+internal val FONT_SIZE_PRESETS_PT = listOf(10, 12, 14, 18, 24)
+
+/**
+ * A toolbar dropdown for [org.libremail.richtext.RichStyle.FontSize]: the anchor button shows the
+ * selection's current size, or "Default" when [selectedPt] is null (no size applied, or a mixed
+ * selection), and opens a menu of [FONT_SIZE_PRESETS_PT] plus a leading "Default" entry that clears
+ * the style outright. Mirrors [ColorSwatchRow]'s "no color" convention: [onSelect] receives null for
+ * "Default" and a preset point size otherwise, so the caller routes the choice straight through the
+ * generalized `applyStyle`/`clearStyle` toggle path with no font-size-specific branching of its own.
+ */
+@Composable
+fun FontSizePicker(selectedPt: Int?, onSelect: (Int?) -> Unit, modifier: Modifier = Modifier) {
+    var expanded by remember { mutableStateOf(false) }
+    val colors = MaterialTheme.colorScheme
+    val description = stringResource(R.string.format_size)
+    val label = if (selectedPt != null) {
+        stringResource(R.string.format_size_pt, selectedPt)
+    } else {
+        stringResource(R.string.format_size_default)
+    }
+    val contentColor = if (selectedPt != null) colors.onSecondaryContainer else colors.onSurfaceVariant
+    Box(modifier = modifier) {
+        Row(
+            modifier = Modifier
+                .clip(MaterialTheme.shapes.small)
+                .background(if (selectedPt != null) colors.secondaryContainer else Color.Transparent)
+                .clickable(onClick = { expanded = true }, role = Role.Button, onClickLabel = description)
+                .padding(horizontal = 12.dp, vertical = 8.dp),
+            horizontalArrangement = Arrangement.spacedBy(2.dp),
+            verticalAlignment = Alignment.CenterVertically,
+        ) {
+            Text(text = label, color = contentColor)
+            Icon(
+                Icons.Filled.ArrowDropDown,
+                contentDescription = null,
+                modifier = Modifier.size(18.dp),
+                tint = contentColor,
+            )
+        }
+        DropdownMenu(expanded = expanded, onDismissRequest = { expanded = false }) {
+            DropdownMenuItem(
+                text = { Text(stringResource(R.string.format_size_default)) },
+                onClick = {
+                    expanded = false
+                    onSelect(null)
+                },
+            )
+            FONT_SIZE_PRESETS_PT.forEach { pt ->
+                DropdownMenuItem(
+                    text = { Text(stringResource(R.string.format_size_pt, pt)) },
+                    onClick = {
+                        expanded = false
+                        onSelect(pt)
+                    },
+                )
+            }
+        }
+    }
+}

app/src/main/res/values/strings.xml

@@ -121,6 +121,9 @@
     <string name="format_highlight_green">Green</string>
     <string name="format_highlight_cyan">Cyan</string>
     <string name="format_highlight_pink">Pink</string>
+    <string name="format_size">Font size</string>
+    <string name="format_size_default">Default</string>
+    <string name="format_size_pt">%1$d pt</string>
 
     <!-- Drafts -->
     <string name="drafts_title">Drafts</string>

app/src/test/kotlin/org/libremail/ui/compose/RichTextEditorTest.kt

@@ -207,6 +207,14 @@ class RichTextEditorTest {
         assertEquals(colored.annotatedString.toRichContent().spans, result.annotatedString.toRichContent().spans)
     }
 
+    @Test
+    fun `clearStyle removes a font size span regardless of its value`() {
+        val value = field("hello", TextRange(0, 5))
+        val sized = applyStyle(value, RichStyle.FontSize(18), linkColor)
+        val cleared = clearStyle(sized, RichStyle.FontSize::class.java, linkColor)
+        assertTrue(cleared.annotatedString.toRichContent().spans.isEmpty())
+    }
+
     // --- applyBlock ---
 
     @Test