feat(chat): support hierarchical nested subtasks in Todos via parent property (#1018) (#1028)

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/java/com/m57/hermescontrol/data/ws/EventParser.kt

@@ -1,6 +1,7 @@
 package com.m57.hermescontrol.data.ws
 
 import android.util.Log
+import com.m57.hermescontrol.ui.chat.extractTodosFromMap
 
 /**
  * Converts raw [JsonRpcResponse] objects into typed [WsEvent] instances.
@@ -189,6 +190,15 @@ object EventParser {
                 WsEvent.SessionUsage(payload, sessionId)
             }
 
+            "todo.updated" -> {
+                val revision =
+                    (payload?.get("revision") as? Number)?.toInt()
+                        ?: (params["revision"] as? Number)?.toInt()
+                val rawTodos = payload ?: params
+                val todos = extractTodosFromMap(rawTodos) ?: emptyList()
+                WsEvent.TodoUpdated(todos, revision, sessionId)
+            }
+
             "reaction" -> {
                 val kind = payload?.get("kind") as? String ?: ""
                 WsEvent.ReactionEvent(kind)

app/src/main/java/com/m57/hermescontrol/data/ws/WsEvent.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.ws
 
+import com.m57.hermescontrol.ui.chat.TodoItem
+
 /** Parsed WebSocket events emitted by [HermesWsClient]. */
 sealed class WsEvent {
     // ── Gateway lifecycle ────────────────────────────────────────────────
@@ -183,6 +185,17 @@ sealed class WsEvent {
         val sessionId: String? = null,
     ) : WsEvent()
 
+    /**
+     * Revisioned todo snapshot event emitted by backend todo tool updates (issue #1018).
+     * Event: `todo.updated`
+     * Payload: `{ "todos": [...], "revision": Int }`
+     */
+    data class TodoUpdated(
+        val todos: List<TodoItem> = emptyList(),
+        val revision: Int? = null,
+        val sessionId: String? = null,
+    ) : WsEvent()
+
     // ── RPC responses ────────────────────────────────────────────────────
 
     data class RpcResult(

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatMessage.kt

@@ -85,11 +85,13 @@ data class TodoItem(
     val id: String,
     val content: String,
     val status: String = "pending", // "pending" | "in_progress" | "completed" | "cancelled"
+    val parent: String? = null,
 ) {
     val isCompleted: Boolean get() = status == "completed" || status == "done"
     val isInProgress: Boolean get() = status == "in_progress" || status == "running"
     val isCancelled: Boolean get() = status == "cancelled" || status == "failed"
     val isPending: Boolean get() = status == "pending" || status == "queued"
+    val isSubtask: Boolean get() = !parent.isNullOrBlank()
 }
 
 /**

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatWsEventReducer.kt

@@ -134,6 +134,8 @@ object ChatWsEventReducer {
 
             is WsEvent.SessionUsage -> onSessionUsage(state, streamingState, event)
 
+            is WsEvent.TodoUpdated -> onTodoUpdated(state, streamingState, event)
+
             is WsEvent.RpcError -> onRpcError(state, streamingState, event)
 
             is WsEvent.GatewayError -> onGatewayError(state, streamingState, event)
@@ -870,6 +872,20 @@ object ChatWsEventReducer {
         )
     }
 
+    private fun onTodoUpdated(
+        state: ChatUiState,
+        streamingState: StreamingState,
+        event: WsEvent.TodoUpdated,
+    ): ReducerResult {
+        if (event.sessionId != null && state.currentSessionId != null && event.sessionId != state.currentSessionId) {
+            return ReducerResult(state = state, streamingState = streamingState)
+        }
+        return ReducerResult(
+            state = state.copy(todos = event.todos),
+            streamingState = streamingState,
+        )
+    }
+
     private fun onSessionUsage(
         state: ChatUiState,
         streamingState: StreamingState,
@@ -957,7 +973,8 @@ fun extractTodosFromMap(data: Map<String, Any?>?): List<TodoItem>? {
         val id = (map["id"] as? String) ?: continue
         val content = (map["content"] as? String) ?: (map["text"] as? String) ?: ""
         val status = (map["status"] as? String) ?: "pending"
-        items.add(TodoItem(id = id, content = content, status = status))
+        val parent = (map["parent"] as? String)?.takeIf { it.isNotBlank() }
+        items.add(TodoItem(id = id, content = content, status = status, parent = parent))
     }
     return items.takeIf { it.isNotEmpty() }
 }
@@ -982,7 +999,8 @@ fun extractTodosFromJson(content: String): List<TodoItem>? {
                     (itemObj["content"] as? JsonPrimitive)?.content
                         ?: (itemObj["text"] as? JsonPrimitive)?.content ?: ""
                 val status = (itemObj["status"] as? JsonPrimitive)?.content ?: "pending"
-                TodoItem(id = id, content = contentStr, status = status)
+                val parent = (itemObj["parent"] as? JsonPrimitive)?.content?.takeIf { it.isNotBlank() }
+                TodoItem(id = id, content = contentStr, status = status, parent = parent)
             }.takeIf { it.isNotEmpty() }
     } catch (_: Exception) {
         null

app/src/main/java/com/m57/hermescontrol/ui/chat/components/SubagentInspectionSheet.kt

@@ -1,6 +1,7 @@
 package com.m57.hermescontrol.ui.chat.components
 
 import androidx.compose.foundation.background
+import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
@@ -11,6 +12,7 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
 import androidx.compose.foundation.lazy.itemsIndexed
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material.icons.Icons
@@ -19,6 +21,8 @@ import androidx.compose.material.icons.filled.Autorenew
 import androidx.compose.material.icons.filled.Cancel
 import androidx.compose.material.icons.filled.CheckCircle
 import androidx.compose.material.icons.filled.Close
+import androidx.compose.material.icons.filled.ExpandLess
+import androidx.compose.material.icons.filled.ExpandMore
 import androidx.compose.material.icons.filled.Groups
 import androidx.compose.material.icons.filled.RadioButtonUnchecked
 import androidx.compose.material3.ExperimentalMaterial3Api
@@ -30,6 +34,10 @@ import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.material3.rememberModalBottomSheetState
 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
@@ -57,6 +65,9 @@ fun SubagentInspectionSheet(
     modifier: Modifier = Modifier,
 ) {
     val sheetState = rememberModalBottomSheetState(skipPartiallyExpanded = true)
+    val todoTree = remember(todos) { buildTodoTree(todos) }
+    var collapsedParentIds by remember { mutableStateOf(setOf<String>()) }
+    val displayRows = remember(todoTree, collapsedParentIds) { flattenTodoTree(todoTree, collapsedParentIds) }
 
     ModalBottomSheet(
         onDismissRequest = onDismiss,
@@ -111,9 +122,9 @@ fun SubagentInspectionSheet(
             } else {
                 LazyColumn(
                     modifier = Modifier.fillMaxWidth(),
-                    verticalArrangement = Arrangement.spacedBy(12.dp),
+                    verticalArrangement = Arrangement.spacedBy(8.dp),
                 ) {
-                    if (todos.isNotEmpty()) {
+                    if (displayRows.isNotEmpty()) {
                         item(key = "todos_header") {
                             Row(
                                 verticalAlignment = Alignment.CenterVertically,
@@ -134,11 +145,26 @@ fun SubagentInspectionSheet(
                                 )
                             }
                         }
-                        itemsIndexed(
+                        items(
-                            items = todos,
+                            items = displayRows,
-                            key = { index, todo -> "todo-${todo.id}_$index" },
+                            key = { row -> "todo-${row.todo.id}_${row.depth}" },
-                        ) { _, todo ->
+                        ) { row ->
-                            TodoInspectionCard(todo = todo)
+                            TodoInspectionCard(
+                                row = row,
+                                onToggleExpand =
+                                    if (row.hasChildren) {
+                                        {
+                                            collapsedParentIds =
+                                                if (row.todo.id in collapsedParentIds) {
+                                                    collapsedParentIds - row.todo.id
+                                                } else {
+                                                    collapsedParentIds + row.todo.id
+                                                }
+                                        }
+                                    } else {
+                                        null
+                                    },
+                            )
                         }
                     }
 
@@ -180,12 +206,128 @@ fun SubagentInspectionSheet(
     }
 }
 
+/**
+ * Node in the hierarchical todo tree.
+ */
+data class TodoNode(
+    val item: TodoItem,
+    val children: List<TodoNode> = emptyList(),
+    val depth: Int = 0,
+)
+
+/**
+ * Flattened row representation ready for lazy column rendering with indentation and collapse state.
+ */
+data class TodoDisplayRow(
+    val todo: TodoItem,
+    val depth: Int,
+    val hasChildren: Boolean,
+    val isExpanded: Boolean,
+    val completedSubtasksCount: Int,
+    val totalSubtasksCount: Int,
+)
+
+/**
+ * Constructs a hierarchical tree from a flat list of [TodoItem]s using the [TodoItem.parent] property.
+ */
+fun buildTodoTree(todos: List<TodoItem>): List<TodoNode> {
+    val itemsById = todos.associateBy { it.id }
+    val childrenByParent = mutableMapOf<String, MutableList<TodoItem>>()
+    val rootItems = mutableListOf<TodoItem>()
+
+    for (item in todos) {
+        val p = item.parent
+        if (p != null && itemsById.containsKey(p) && p != item.id) {
+            childrenByParent.getOrPut(p) { mutableListOf() }.add(item)
+        } else {
+            rootItems.add(item)
+        }
+    }
+
+    fun buildNode(
+        item: TodoItem,
+        depth: Int,
+    ): TodoNode {
+        val children = childrenByParent[item.id]?.map { buildNode(it, depth + 1) } ?: emptyList()
+        return TodoNode(item = item, children = children, depth = depth)
+    }
+
+    return rootItems.map { buildNode(it, 0) }
+}
+
+fun getAllDescendantTodos(node: TodoNode): List<TodoItem> {
+    val descendants = mutableListOf<TodoItem>()
+    for (child in node.children) {
+        descendants.add(child.item)
+        descendants.addAll(getAllDescendantTodos(child))
+    }
+    return descendants
+}
+
+fun flattenTodoTree(
+    nodes: List<TodoNode>,
+    collapsedParentIds: Set<String>,
+): List<TodoDisplayRow> {
+    val result = mutableListOf<TodoDisplayRow>()
+
+    fun traverse(node: TodoNode) {
+        val isExpanded = node.item.id !in collapsedParentIds
+        val descendants = getAllDescendantTodos(node)
+        val completedCount = descendants.count { it.isCompleted }
+        val totalCount = descendants.size
+
+        result.add(
+            TodoDisplayRow(
+                todo = node.item,
+                depth = node.depth,
+                hasChildren = node.children.isNotEmpty(),
+                isExpanded = isExpanded,
+                completedSubtasksCount = completedCount,
+                totalSubtasksCount = totalCount,
+            ),
+        )
+        if (node.children.isNotEmpty() && isExpanded) {
+            for (child in node.children) {
+                traverse(child)
+            }
+        }
+    }
+
+    for (root in nodes) {
+        traverse(root)
+    }
+    return result
+}
+
 @Composable
-private fun TodoInspectionCard(todo: TodoItem) {
+private fun TodoInspectionCard(
+    row: TodoDisplayRow,
+    onToggleExpand: (() -> Unit)? = null,
+    modifier: Modifier = Modifier,
+) {
+    val todo = row.todo
+    val depth = row.depth
+    val startPadding = (depth * 20).coerceAtMost(60).dp
+
     Surface(
-        modifier = Modifier.fillMaxWidth(),
+        modifier =
+            modifier
+                .fillMaxWidth()
+                .padding(start = startPadding)
+                .then(
+                    if (onToggleExpand != null) {
+                        Modifier.clickable(onClick = onToggleExpand)
+                    } else {
+                        Modifier
+                    },
+                ),
         shape = RoundedCornerShape(12.dp),
-        color = MaterialTheme.colorScheme.surfaceContainerHigh,
+        color =
+            if (depth > 0) {
+                MaterialTheme.colorScheme.surfaceContainer
+            } else {
+                MaterialTheme.colorScheme.surfaceContainerHigh
+            },
     ) {
         Row(
             modifier = Modifier.padding(12.dp),
@@ -211,19 +353,35 @@ private fun TodoInspectionCard(todo: TodoItem) {
                             MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.5f)
                     }
                 }
+
+            if (depth > 0) {
+                Text(
+                    text = "↳",
+                    style = MaterialTheme.typography.bodySmall,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.6f),
+                    modifier = Modifier.padding(end = 6.dp),
+                )
+            }
+
             Icon(
                 imageVector = statusIcon,
                 contentDescription = null,
                 tint = statusTint,
-                modifier = Modifier.size(18.dp),
+                modifier = Modifier.size(if (depth > 0) 16.dp else 18.dp),
             )
             Spacer(modifier = Modifier.width(10.dp))
             Text(
                 text = todo.content,
                 style =
-                    MaterialTheme.typography.bodyMedium.copy(
+                    if (depth > 0) {
-                        textDecoration = if (todo.isCompleted) TextDecoration.LineThrough else TextDecoration.None,
+                        MaterialTheme.typography.bodySmall.copy(
-                    ),
+                            textDecoration = if (todo.isCompleted) TextDecoration.LineThrough else TextDecoration.None,
+                        )
+                    } else {
+                        MaterialTheme.typography.bodyMedium.copy(
+                            textDecoration = if (todo.isCompleted) TextDecoration.LineThrough else TextDecoration.None,
+                        )
+                    },
                 fontWeight = if (todo.isInProgress) FontWeight.Bold else FontWeight.Normal,
                 color =
                     if (todo.isCompleted) {
@@ -233,6 +391,28 @@ private fun TodoInspectionCard(todo: TodoItem) {
                     },
                 modifier = Modifier.weight(1f),
             )
+
+            if (row.hasChildren) {
+                Spacer(modifier = Modifier.width(8.dp))
+                Surface(
+                    shape = RoundedCornerShape(8.dp),
+                    color = MaterialTheme.colorScheme.surfaceContainerHighest,
+                ) {
+                    Text(
+                        text = "${row.completedSubtasksCount}/${row.totalSubtasksCount}",
+                        style = MaterialTheme.typography.labelSmall,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant,
+                        modifier = Modifier.padding(horizontal = 6.dp, vertical = 2.dp),
+                    )
+                }
+                Spacer(modifier = Modifier.width(4.dp))
+                Icon(
+                    imageVector = if (row.isExpanded) Icons.Filled.ExpandLess else Icons.Filled.ExpandMore,
+                    contentDescription = if (row.isExpanded) "Collapse" else "Expand",
+                    tint = MaterialTheme.colorScheme.onSurfaceVariant,
+                    modifier = Modifier.size(20.dp),
+                )
+            }
         }
     }
 }

app/src/main/java/com/m57/hermescontrol/ui/chat/tool/ToolViewBuilder.kt

@@ -1769,6 +1769,7 @@ object ToolViewBuilder {
                 val id = firstString(item, listOf("id"))
                 val content = firstString(item, listOf("content"))
                 val status = firstString(item, listOf("status")).ifEmpty { "pending" }
+                val parent = firstString(item, listOf("parent"))
                 val marker =
                     when (status) {
                         "completed" -> "[x]"
@@ -1776,7 +1777,8 @@ object ToolViewBuilder {
                         "cancelled" -> "[~]"
                         else -> "[ ]"
                     }
-                "$marker $id. $content"
+                val indent = if (parent.isNotEmpty()) "  ↳ " else ""
+                "$indent$marker $id. $content"
             }.joinToString("\n")
             .takeIf { it.isNotEmpty() }
     }

app/src/test/java/com/m57/hermescontrol/data/ws/EventParserTest.kt

@@ -6,6 +6,7 @@ import io.mockk.unmockkAll
 import kotlinx.serialization.json.JsonObject
 import org.junit.After
 import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
 import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Test
@@ -700,4 +701,49 @@ class EventParserTest {
         assertEquals("terminal", toolEvent.name)
         assertEquals("sess-replay-2", toolEvent.sessionId)
     }
+
+    @Test
+    fun testParseTodoUpdated_returnsTodoUpdatedEvent() {
+        val response =
+            createJsonRpcResponse(
+                jsonrpc = "2.0",
+                id = null,
+                result = null,
+                error = null,
+                method = "event",
+                params =
+                    mapOf(
+                        "type" to "todo.updated",
+                        "session_id" to "sess-abc",
+                        "payload" to
+                            mapOf(
+                                "revision" to 5,
+                                "todos" to
+                                    listOf(
+                                        mapOf("id" to "1", "content" to "Parent task", "status" to "in_progress"),
+                                        mapOf(
+                                            "id" to "2",
+                                            "content" to "Sub task",
+                                            "status" to "pending",
+                                            "parent" to "1",
+                                        ),
+                                    ),
+                            ),
+                    ),
+            )
+        val event = EventParser.parse(response)
+        assertTrue(event is WsEvent.TodoUpdated)
+        val todoUpdated = event as WsEvent.TodoUpdated
+        assertEquals("sess-abc", todoUpdated.sessionId)
+        assertEquals(5, todoUpdated.revision)
+        assertEquals(2, todoUpdated.todos.size)
+        assertEquals("1", todoUpdated.todos[0].id)
+        assertEquals("Parent task", todoUpdated.todos[0].content)
+        assertEquals(null, todoUpdated.todos[0].parent)
+        assertFalse(todoUpdated.todos[0].isSubtask)
+        assertEquals("2", todoUpdated.todos[1].id)
+        assertEquals("Sub task", todoUpdated.todos[1].content)
+        assertEquals("1", todoUpdated.todos[1].parent)
+        assertTrue(todoUpdated.todos[1].isSubtask)
+    }
 }

app/src/test/java/com/m57/hermescontrol/ui/chat/ChatWsEventReducerTest.kt

@@ -979,4 +979,88 @@ class ChatWsEventReducerTest {
         assertEquals(1, result.state.compressionCount)
         assertEquals(null, result.state.usedContextTokens)
     }
+
+    @Test
+    fun testTodoUpdated_updatesStateTodos() {
+        val state = ChatUiState(currentSessionId = "session-1")
+        val todos =
+            listOf(
+                TodoItem(id = "1", content = "Main task", status = "in_progress"),
+                TodoItem(id = "2", content = "Subtask 1", status = "completed", parent = "1"),
+                TodoItem(id = "3", content = "Subtask 2", status = "pending", parent = "1"),
+            )
+        val event = WsEvent.TodoUpdated(todos = todos, revision = 1, sessionId = "session-1")
+
+        val result =
+            ChatWsEventReducer.reduce(
+                state = state,
+                streamingState = StreamingState(),
+                event = event,
+                currentSessionId = "session-1",
+            )
+
+        assertEquals(3, result.state.todos.size)
+        assertEquals("Main task", result.state.todos[0].content)
+        assertEquals(null, result.state.todos[0].parent)
+        assertEquals("1", result.state.todos[1].parent)
+        assertTrue(result.state.todos[1].isCompleted)
+        assertTrue(result.state.todos[1].isSubtask)
+    }
+
+    @Test
+    fun testTodoUpdated_differentSession_isIgnored() {
+        val state =
+            ChatUiState(
+                currentSessionId = "session-1",
+                todos = listOf(TodoItem(id = "orig", content = "Original", status = "pending")),
+            )
+        val event =
+            WsEvent.TodoUpdated(
+                todos = listOf(TodoItem(id = "new", content = "New", status = "in_progress")),
+                revision = 1,
+                sessionId = "session-other",
+            )
+
+        val result =
+            ChatWsEventReducer.reduce(
+                state = state,
+                streamingState = StreamingState(),
+                event = event,
+                currentSessionId = "session-1",
+            )
+
+        assertEquals(1, result.state.todos.size)
+        assertEquals("Original", result.state.todos[0].content)
+    }
+
+    @Test
+    fun testExtractTodosFromMap_preservesParentHierarchy() {
+        val payload =
+            mapOf(
+                "todos" to
+                    listOf(
+                        mapOf("id" to "t1", "content" to "Root", "status" to "in_progress"),
+                        mapOf("id" to "t2", "content" to "Child", "status" to "pending", "parent" to "t1"),
+                    ),
+            )
+        val extracted = extractTodosFromMap(payload)
+        assertEquals(2, extracted?.size)
+        assertEquals("t1", extracted?.get(0)?.id)
+        assertEquals(null, extracted?.get(0)?.parent)
+        assertEquals("t2", extracted?.get(1)?.id)
+        assertEquals("t1", extracted?.get(1)?.parent)
+    }
+
+    @Test
+    fun testExtractTodosFromJson_preservesParentHierarchy() {
+        val json =
+            """{"todos":[{"id":"a","content":"Task A","status":"done"},""" +
+                """{"id":"b","content":"Task B","status":"pending","parent":"a"}]}"""
+        val extracted = extractTodosFromJson(json)
+        assertEquals(2, extracted?.size)
+        assertEquals("a", extracted?.get(0)?.id)
+        assertEquals(null, extracted?.get(0)?.parent)
+        assertEquals("b", extracted?.get(1)?.id)
+        assertEquals("a", extracted?.get(1)?.parent)
+    }
 }

app/src/test/java/com/m57/hermescontrol/ui/chat/TaskProgressChipTest.kt

@@ -1,6 +1,9 @@
 package com.m57.hermescontrol.ui.chat
 
+import com.m57.hermescontrol.ui.chat.components.buildTodoTree
 import com.m57.hermescontrol.ui.chat.components.computeChipDisplay
+import com.m57.hermescontrol.ui.chat.components.flattenTodoTree
+import com.m57.hermescontrol.ui.chat.components.getAllDescendantTodos
 import com.m57.hermescontrol.ui.chat.components.shouldShowProgressChip
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertFalse
@@ -142,4 +145,72 @@ class TaskProgressChipTest {
             )
         assertTrue(hydrateTodosFromMessages(messages).isEmpty())
     }
+
+    @Test
+    fun `buildTodoTree constructs correct multi-level hierarchy`() {
+        val todos =
+            listOf(
+                TodoItem(id = "1", content = "Root 1", status = "in_progress"),
+                TodoItem(id = "1.1", content = "Child 1.1", status = "completed", parent = "1"),
+                TodoItem(id = "1.2", content = "Child 1.2", status = "pending", parent = "1"),
+                TodoItem(id = "1.2.1", content = "Grandchild 1.2.1", status = "pending", parent = "1.2"),
+                TodoItem(id = "2", content = "Root 2", status = "pending"),
+            )
+
+        val tree = buildTodoTree(todos)
+        assertEquals(2, tree.size)
+        assertEquals("1", tree[0].item.id)
+        assertEquals(0, tree[0].depth)
+        assertEquals(2, tree[0].children.size)
+        assertEquals("1.1", tree[0].children[0].item.id)
+        assertEquals(1, tree[0].children[0].depth)
+        assertEquals("1.2", tree[0].children[1].item.id)
+        assertEquals(1, tree[0].children[1].depth)
+        assertEquals(1, tree[0].children[1].children.size)
+        assertEquals(
+            "1.2.1",
+            tree[0]
+                .children[1]
+                .children[0]
+                .item.id,
+        )
+        assertEquals(2, tree[0].children[1].children[0].depth)
+        assertEquals("2", tree[1].item.id)
+        assertEquals(0, tree[1].depth)
+    }
+
+    @Test
+    fun `flattenTodoTree collapses and expands subtasks correctly`() {
+        val todos =
+            listOf(
+                TodoItem(id = "1", content = "Root 1", status = "in_progress"),
+                TodoItem(id = "1.1", content = "Child 1.1", status = "completed", parent = "1"),
+                TodoItem(id = "1.2", content = "Child 1.2", status = "pending", parent = "1"),
+                TodoItem(id = "2", content = "Root 2", status = "pending"),
+            )
+        val tree = buildTodoTree(todos)
+
+        // Expanded state
+        val expandedRows = flattenTodoTree(tree, collapsedParentIds = emptySet())
+        assertEquals(4, expandedRows.size)
+        assertEquals("1", expandedRows[0].todo.id)
+        assertTrue(expandedRows[0].hasChildren)
+        assertTrue(expandedRows[0].isExpanded)
+        assertEquals(1, expandedRows[0].completedSubtasksCount)
+        assertEquals(2, expandedRows[0].totalSubtasksCount)
+        assertEquals("1.1", expandedRows[1].todo.id)
+        assertEquals(1, expandedRows[1].depth)
+        assertEquals("1.2", expandedRows[2].todo.id)
+        assertEquals(1, expandedRows[2].depth)
+        assertEquals("2", expandedRows[3].todo.id)
+        assertEquals(0, expandedRows[3].depth)
+
+        // Collapsed state
+        val collapsedRows = flattenTodoTree(tree, collapsedParentIds = setOf("1"))
+        assertEquals(2, collapsedRows.size)
+        assertEquals("1", collapsedRows[0].todo.id)
+        assertTrue(collapsedRows[0].hasChildren)
+        assertFalse(collapsedRows[0].isExpanded)
+        assertEquals("2", collapsedRows[1].todo.id)
+    }
 }