android/app/src/main/java/com/fabledsword/inkwell/ui/BlockBody.kt

@@ -20,7 +20,10 @@ import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.LaunchedEffect
+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.focus.FocusRequester
@@ -28,6 +31,7 @@ import androidx.compose.ui.focus.focusRequester
 import androidx.compose.ui.focus.onFocusChanged
 import androidx.compose.ui.graphics.SolidColor
 import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.TextLayoutResult
 import androidx.compose.ui.text.TextStyle
 import androidx.compose.ui.text.input.ImeAction
 import androidx.compose.ui.text.input.TextFieldValue
@@ -241,6 +245,15 @@ private fun BlockField(
     keyboardActions: KeyboardActions = KeyboardActions.Default,
 ) {
     val style = textStyle.copy(color = MaterialTheme.colorScheme.onSurface)
+    // Kept for the arrow keys, which ask which line the caret is on. Read only when
+    // one is pressed, never while composing.
+    var layout by remember { mutableStateOf<TextLayoutResult?>(null) }
+    val line = { offset: Int -> layout?.getLineForOffset(offset) ?: 0 }
+    val arrows =
+        Modifier.arrowKeysMoveCaret(
+            atTop = { line(value.selection.end) == 0 },
+            atBottom = { line(value.selection.end) == (layout?.lineCount ?: 1) - 1 },
+        )
     Box(modifier = modifier) {
         if (hint != null && value.text.isEmpty()) {
             Text(
@@ -252,12 +265,13 @@ private fun BlockField(
         BasicTextField(
             value = value,
             onValueChange = onValueChange,
-            modifier = Modifier.fillMaxWidth(),
+            modifier = Modifier.fillMaxWidth().then(arrows),
             enabled = enabled,
             singleLine = singleLine,
             textStyle = style,
             keyboardOptions = keyboardOptions,
             keyboardActions = keyboardActions,
+            onTextLayout = { layout = it },
             cursorBrush = SolidColor(MaterialTheme.colorScheme.primary),
         )
     }

android/app/src/main/java/com/fabledsword/inkwell/ui/PlainField.kt

@@ -13,6 +13,8 @@ import androidx.compose.material3.TextFieldColors
 import androidx.compose.material3.TextFieldDefaults
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.focus.FocusRequester
+import androidx.compose.ui.focus.focusProperties
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.TextStyle
@@ -54,7 +56,7 @@ fun PlainTextField(
     TextField(
         value = value,
         onValueChange = onValueChange,
-        modifier = modifier.fillMaxWidth(),
+        modifier = modifier.fillMaxWidth().arrowKeysMoveCaret(atTop = { singleLine }, atBottom = { singleLine }),
         enabled = enabled,
         placeholder = hint?.let { { Text(stringResource(it)) } },
         singleLine = singleLine,
@@ -86,3 +88,29 @@ private fun plainFieldColors(): TextFieldColors =
         unfocusedIndicatorColor = Color.Transparent,
         disabledIndicatorColor = Color.Transparent,
     )
+
+/**
+ * Arrow keys on a hardware keyboard move the caret, not the focus.
+ *
+ * Compose's text field gives the arrow keys of any device that reports D-pad keys
+ * to focus search before the field sees them, and a physical keyboard with arrow
+ * keys reports exactly that — so without this, ← and → jump to whatever sits beside
+ * the field instead of moving through the text. Cancelling the search in a
+ * direction hands the key back: the search reports that nothing moved, and the
+ * field takes the key as editing.
+ *
+ * ← and → never leave the field. ↑ and ↓ move between its lines, and from the first
+ * or last line — [atTop], [atBottom] — on to the field above or below, the way a
+ * caret leaves one paragraph for the next. Both are asked at the moment of the key
+ * press, so they can read where the caret is now.
+ */
+fun Modifier.arrowKeysMoveCaret(
+    atTop: () -> Boolean,
+    atBottom: () -> Boolean,
+): Modifier =
+    focusProperties {
+        left = FocusRequester.Cancel
+        right = FocusRequester.Cancel
+        if (!atTop()) up = FocusRequester.Cancel
+        if (!atBottom()) down = FocusRequester.Cancel
+    }