android: detekt caught a callback that never reached the cards

Not a style finding. `onToggleItem` was added to BoardScreen's signature and read
inside NoteBoard — which is a separate top-level composable, not a nested one, so
the two were never connected. detekt reported it as an unused parameter; the
compiler would have called it an unresolved reference. Neither had run: Kotlin is
compiled at the "Unit tests" step, which is gated behind detekt, so nothing in this
lane had type-checked the Android changes yet.

Threaded properly now, which is what makes ticking a box from the board actually
work rather than merely appear to.

Two more from reading it again with that in mind:

  * `when { item != null -> … onToggleItem(index, …) }` would not have compiled.
    Kotlin does not infer that a non-null item implies a non-null index, so the
    index stayed `Int?` against an `Int` parameter. Both are in the condition now.
  * continueChecklist had six returns against detekt's limit of two. Collapsed to
    one `when`, with the two intermediate values guarded on `typedNewline` —
    `caret - 1` is only a real index once it is known to be the newline just typed.

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

@@ -141,7 +141,12 @@ fun BoardScreen(
                     when {
                         state.loading -> LoadingBoard()
                         state.notes.isEmpty() -> EmptyBoard(state)
-                        else -> NoteBoard(notes = state.notes, onOpenNote = onOpenNote)
+                        else ->
+                            NoteBoard(
+                                notes = state.notes,
+                                onOpenNote = onOpenNote,
+                                onToggleItem = onToggleItem,
+                            )
                     }
                     // `PullToRefreshBox` would be less code, but it takes no
                     // `enabled`, so the modifier and the indicator are wired by
@@ -324,6 +329,7 @@ private fun DrawerRow(
 private fun NoteBoard(
     notes: List<Note>,
     onOpenNote: (Note) -> Unit,
+    onToggleItem: (Note, Int, Boolean) -> Unit,
 ) {
     LazyVerticalStaggeredGrid(
         columns = StaggeredGridCells.Fixed(BOARD_COLUMNS),

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

@@ -109,7 +109,11 @@ private fun NoteBody(
             val index = itemAtLine[n]
             val item = index?.let { note.items.getOrNull(it) }
             when {
-                item != null -> ChecklistRow(item) { onToggleItem(index, !item.checked) }
+                // Both in the condition, not just `item`: Kotlin will not infer that a
+                // non-null item implies a non-null index, and `onToggleItem` needs the
+                // index smart-cast to act on it.
+                index != null && item != null ->
+                    ChecklistRow(item) { onToggleItem(index, !item.checked) }
                 // Kept as a gap rather than dropped: it is the paragraph break
                 // somebody typed, and the card reads as a wall without it.
                 line.isBlank() -> Spacer(Modifier.height(4.dp))

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

@@ -396,21 +396,31 @@ private fun continueChecklist(
     new: TextFieldValue,
 ): TextFieldValue {
     val caret = new.selection.start
-    if (new.selection.length != 0) return new
-    if (new.text.length != old.text.length + 1) return new
-    if (caret == 0 || new.text[caret - 1] != '\n') return new
+    val typedNewline =
+        new.selection.length == 0 &&
+            new.text.length == old.text.length + 1 &&
+            caret > 0 &&
+            new.text[caret - 1] == '\n'
+    // Both guarded on `typedNewline`, because caret - 1 is only a real index once it
+    // is known to be the newline that was just typed.
+    val lineStart = if (typedNewline) new.text.take(caret - 1).lastIndexOf('\n') + 1 else 0
+    val marker =
+        if (typedNewline) checklistContinuation(new.text.substring(lineStart, caret - 1)) else null
 
-    val before = new.text.take(caret - 1)
-    val lineStart = before.lastIndexOf('\n') + 1
-    val marker = checklistContinuation(before.substring(lineStart)) ?: return new
-
-    if (marker.isEmpty()) {
+    return when {
+        marker == null -> new
         // An empty item: take the marker line away rather than adding another.
-        val text = new.text.take(lineStart) + new.text.substring(caret)
-        return TextFieldValue(text, TextRange(lineStart))
+        marker.isEmpty() ->
+            TextFieldValue(
+                new.text.take(lineStart) + new.text.substring(caret),
+                TextRange(lineStart),
+            )
+        else ->
+            TextFieldValue(
+                new.text.take(caret) + marker + new.text.substring(caret),
+                TextRange(caret + marker.length),
+            )
     }
-    val text = new.text.take(caret) + marker + new.text.substring(caret)
-    return TextFieldValue(text, TextRange(caret + marker.length))
 }
 
 private const val CHECKLIST_MARKER = "- [ ] "