android: open an existing note ready to keep writing

Opening a note put no cursor anywhere, so carrying on cost a tap into the
body and usually a second one to drag the caret past the existing text.
The compose sheet has always focused its field on open; the editor never
did, and continuing a note is the more common act of the two.

Focus the body on open, caret at the end. Not for a trashed note — that
renders read-only and a keyboard over a record you cannot edit is noise.
Keyed on note.id so the reused editor re-requests when pointed at a
different note.

The caret position is why the body state moves from String to
TextFieldValue: a String field always starts its selection at offset zero,
so focusing one lands the cursor before the first character — the wrong
end of a note you meant to continue. PlainTextField gains a TextFieldValue
overload for it, and the two overloads share one colours definition rather
than growing a second copy of the "no box" treatment this file exists to
keep in one place.

I recorded this backwards in Scribe 2947 — as the keyboard opening
unwanted, when the report was the opposite. The source having no
FocusRequester was the tell, and I read it as a mystery instead of as
evidence I had the direction wrong.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

android/app/src/main/java/com/fabledsword/thoughtsync/ui/NoteEditorScreen.kt

@@ -23,12 +23,17 @@ import androidx.compose.material3.TextButton
 import androidx.compose.material3.TopAppBar
 import androidx.compose.material3.TopAppBarDefaults
 import androidx.compose.runtime.Composable
+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.Modifier
+import androidx.compose.ui.focus.FocusRequester
+import androidx.compose.ui.focus.focusRequester
 import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.TextRange
+import androidx.compose.ui.text.input.TextFieldValue
 import androidx.compose.ui.unit.dp
 import com.fabledsword.thoughtsync.R
 import com.fabledsword.thoughtsync.core.Label
@@ -60,7 +65,15 @@ fun NoteEditorScreen(
 
     // Keyed by note id: the editor is reused across notes, and without the key the
     // second note opened would show the first one's text.
-    var body by remember(note.id) { mutableStateOf(note.body) }
+    //
+    // TextFieldValue rather than String so the CARET can start at the end of the
+    // text. A String field always begins its selection at offset zero, which would
+    // drop the cursor before the first character — the wrong place for "carry on
+    // writing this note", which is what opening an existing one usually means.
+    var body by
+        remember(note.id) {
+            mutableStateOf(TextFieldValue(note.body, TextRange(note.body.length)))
+        }
     var picker by remember(note.id) { mutableStateOf(Picker.NONE) }
     var confirmingDelete by remember(note.id) { mutableStateOf(false) }
 
@@ -74,8 +87,8 @@ fun NoteEditorScreen(
     // would bump `updated_at`, mark the note dirty for sync, and snapshot a
     // revision identical to the one before it.
     val flush = {
-        if (!readOnly && body != note.body) {
-            onAction(EditorAction.SaveText(body))
+        if (!readOnly && body.text != note.body) {
+            onAction(EditorAction.SaveText(body.text))
         }
     }
     val leave = {
@@ -83,6 +96,18 @@ fun NoteEditorScreen(
         onAction(EditorAction.Close)
     }
 
+    // Opening an existing note means continuing it. Without this the note arrives
+    // unfocused, and carrying on costs a tap into the body and often a second to
+    // drag the caret to the end — the friction the operator reported.
+    //
+    // Not for a trashed note: it renders read-only, and a keyboard over a record
+    // you cannot edit is noise. `note.id` as the key so the request fires again
+    // when the reused editor is pointed at a different note.
+    val bodyFocus = remember { FocusRequester() }
+    LaunchedEffect(note.id) {
+        if (!readOnly) bodyFocus.requestFocus()
+    }
+
     BackHandler(onBack = leave)
 
     // Leaving the APP is not closing the editor, so the text has to be saved
@@ -151,6 +176,7 @@ fun NoteEditorScreen(
                 hint = R.string.editor_body_hint,
                 enabled = !readOnly,
                 minLines = MIN_BODY_LINES,
+                modifier = Modifier.focusRequester(bodyFocus),
             )
 
             // Below the body, not instead of it, and only once the note has items —
@@ -259,15 +285,17 @@ private fun EditorOverlays(
  */
 @Composable
 private fun EditorField(
-    value: String,
-    onValueChange: (String) -> Unit,
+    value: TextFieldValue,
+    onValueChange: (TextFieldValue) -> Unit,
     @StringRes hint: Int,
     enabled: Boolean,
     minLines: Int = 1,
+    modifier: Modifier = Modifier,
 ) {
     PlainTextField(
         value = value,
         onValueChange = onValueChange,
+        modifier = modifier,
         hint = hint,
         enabled = enabled,
         minLines = minLines,

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

@@ -9,12 +9,14 @@ import androidx.compose.material3.LocalTextStyle
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextField
+import androidx.compose.material3.TextFieldColors
 import androidx.compose.material3.TextFieldDefaults
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.TextStyle
+import androidx.compose.ui.text.input.TextFieldValue
 import androidx.compose.ui.text.input.VisualTransformation
 
 /**
@@ -58,18 +60,65 @@ fun PlainTextField(
         keyboardOptions = keyboardOptions,
         keyboardActions = keyboardActions,
         visualTransformation = visualTransformation,
-        colors =
-            TextFieldDefaults.colors(
-                // Full-strength, not Material's 38%-alpha disabled treatment: a
-                // trashed note is rendered read-only through this field and its
-                // text is meant to be READ, not visually retired.
-                disabledTextColor = MaterialTheme.colorScheme.onSurface,
-                focusedContainerColor = Color.Transparent,
-                unfocusedContainerColor = Color.Transparent,
-                disabledContainerColor = Color.Transparent,
-                focusedIndicatorColor = Color.Transparent,
-                unfocusedIndicatorColor = Color.Transparent,
-                disabledIndicatorColor = Color.Transparent,
-            ),
+        colors = plainFieldColors(),
     )
 }
+
+/**
+ * The same field over a [TextFieldValue], for the one caller that needs to control
+ * the SELECTION as well as the text — the editor, which opens an existing note with
+ * the cursor at the end so continuing to write costs no extra taps.
+ *
+ * A `String` field cannot express that: Compose starts its internal selection at
+ * offset zero, so focusing one drops the cursor before the first character.
+ */
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun PlainTextField(
+    value: TextFieldValue,
+    onValueChange: (TextFieldValue) -> Unit,
+    modifier: Modifier = Modifier,
+    @StringRes hint: Int? = null,
+    enabled: Boolean = true,
+    singleLine: Boolean = false,
+    minLines: Int = 1,
+    textStyle: TextStyle = LocalTextStyle.current,
+    keyboardOptions: KeyboardOptions = KeyboardOptions.Default,
+    keyboardActions: KeyboardActions = KeyboardActions.Default,
+    visualTransformation: VisualTransformation = VisualTransformation.None,
+) {
+    TextField(
+        value = value,
+        onValueChange = onValueChange,
+        modifier = modifier.fillMaxWidth(),
+        enabled = enabled,
+        placeholder = hint?.let { { Text(stringResource(it)) } },
+        singleLine = singleLine,
+        minLines = minLines,
+        textStyle = textStyle,
+        keyboardOptions = keyboardOptions,
+        keyboardActions = keyboardActions,
+        visualTransformation = visualTransformation,
+        colors = plainFieldColors(),
+    )
+}
+
+/**
+ * One definition of "no box", shared by both overloads. Two copies of this is
+ * exactly the drift this file exists to prevent.
+ */
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+private fun plainFieldColors(): TextFieldColors =
+    TextFieldDefaults.colors(
+        // Full-strength, not Material's 38%-alpha disabled treatment: a trashed
+        // note is rendered read-only through this field and its text is meant to
+        // be READ, not visually retired.
+        disabledTextColor = MaterialTheme.colorScheme.onSurface,
+        focusedContainerColor = Color.Transparent,
+        unfocusedContainerColor = Color.Transparent,
+        disabledContainerColor = Color.Transparent,
+        focusedIndicatorColor = Color.Transparent,
+        unfocusedIndicatorColor = Color.Transparent,
+        disabledIndicatorColor = Color.Transparent,
+    )