feat(task): track task nesting depth with cycle-safe backfill

packages/types/src/history.ts

@@ -24,6 +24,7 @@ export const historyItemSchema = z.object({
 	delegatedToId: z.string().optional(), // Last child this parent delegated to
 	childIds: z.array(z.string()).optional(), // All children spawned by this task
 	awaitingChildId: z.string().optional(), // Child currently awaited (set when delegated)
+	depth: z.number().int().min(0).optional(), // Nesting level; root = 0, child = parent.depth + 1
 	completedByChildId: z.string().optional(), // Child that completed and resumed this parent
 	completionResultSummary: z.string().optional(), // Summary from completed child
 })

packages/types/src/task.ts

@@ -94,6 +94,8 @@ export interface CreateTaskOptions {
 	/** Whether to start the task loop immediately (default: true).
 	 *  When false, the caller must invoke `task.start()` manually. */
 	startTask?: boolean
+	/** Nesting level for newly created tasks; root = 0, child = parent.depth + 1. */
+	depth?: number
 }
 
 export enum TaskStatus {
@@ -116,6 +118,8 @@ export interface TaskLike {
 	readonly rootTaskId?: string
 	readonly parentTaskId?: string
 	readonly childTaskId?: string
+	/** Nesting level; root = 0, child = parent.depth + 1. */
+	readonly depth: number
 	readonly metadata: TaskMetadata
 	readonly taskStatus: TaskStatus
 	readonly taskAsk: ClineMessage | undefined

src/__tests__/single-open-invariant.spec.ts

@@ -169,6 +169,7 @@ describe("Single-open-task invariant", () => {
 			getCurrentTask: vi.fn(() => undefined), // ensure not rehydrating
 			taskHistoryStore: { get: vi.fn(() => undefined) },
 			markDelegatedChildInterrupted: vi.fn().mockResolvedValue(undefined),
+			backfillTaskDepth: vi.fn().mockResolvedValue(undefined),
 			get evictCurrentTask() {
 				return privateClineProvider.evictCurrentTask.bind(this)
 			},
@@ -268,6 +269,7 @@ describe("Single-open-task invariant", () => {
 			taskScheduler: { schedule: schedulespy },
 			taskEventListeners: new WeakMap(),
 			performPreparationTasks: vi.fn().mockResolvedValue(undefined),
+			backfillTaskDepth: vi.fn().mockResolvedValue(undefined),
 			context: { extension: { packageJSON: {} }, globalStorageUri: { fsPath: "/tmp" } },
 			contextProxy: {
 				extensionUri: {},
@@ -340,6 +342,7 @@ describe("Single-open-task invariant", () => {
 			taskScheduler: { schedule: schedulespy },
 			taskEventListeners: new WeakMap(),
 			performPreparationTasks: vi.fn().mockResolvedValue(undefined),
+			backfillTaskDepth: vi.fn().mockResolvedValue(undefined),
 			context: { extension: { packageJSON: {} }, globalStorageUri: { fsPath: "/tmp" } },
 			contextProxy: {
 				extensionUri: {},

src/core/task-persistence/taskMetadata.ts

@@ -25,6 +25,8 @@ export type TaskMetadataOptions = {
 	apiConfigName?: string
 	/** Initial status for the task (e.g., "active" for child tasks) */
 	initialStatus?: "active" | "delegated" | "completed" | "interrupted"
+	/** Nesting level; root = 0, child = parent.depth + 1. Persisted when known. */
+	depth?: number
 }
 
 export async function taskMetadata({
@@ -38,6 +40,7 @@ export async function taskMetadata({
 	mode,
 	apiConfigName,
 	initialStatus,
+	depth,
 }: TaskMetadataOptions) {
 	const taskDir = await getTaskDirectoryPath(globalStoragePath, id)
 
@@ -112,6 +115,7 @@ export async function taskMetadata({
 		mode,
 		...(typeof apiConfigName === "string" && apiConfigName.length > 0 ? { apiConfigName } : {}),
 		...(initialStatus && { status: initialStatus }),
+		...(typeof depth === "number" && Number.isInteger(depth) && depth >= 0 ? { depth } : {}),
 	}
 
 	return { historyItem, tokenUsage }

src/core/task/Task.ts

@@ -170,6 +170,14 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 	readonly rootTaskId?: string
 	readonly parentTaskId?: string
 	childTaskId?: string
+	/** Nesting level; root = 0, child = parent.depth + 1. */
+	readonly depth: number
+	/**
+	 * True when `depth` was derived authoritatively (persisted value, live parent,
+	 * or a genuine root) and is safe to persist on save. False for legacy children
+	 * resumed without their live parent — the provider backfills those before first save.
+	 */
+	readonly depthAuthoritative: boolean
 	pendingNewTaskToolCallId?: string
 
 	readonly instanceId: string
@@ -505,6 +513,28 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 		this.parentTaskId = historyItem ? historyItem.parentTaskId : parentTask?.taskId
 		this.childTaskId = undefined
 
+		// Nesting depth (root = 0). A persisted value is authoritative; otherwise derive it
+		// from the live parent task (parent.depth + 1) or default to root (0).
+		const persistedDepth = historyItem?.depth
+		if (typeof persistedDepth === "number" && Number.isInteger(persistedDepth) && persistedDepth >= 0) {
+			this.depth = persistedDepth
+			this.depthAuthoritative = true
+		} else if (parentTask) {
+			// Live parent available: its depth is authoritative, so the child's is too.
+			this.depth = parentTask.depth + 1
+			this.depthAuthoritative = true
+		} else if (!this.parentTaskId) {
+			// No persisted depth and no parent reference at all: this task is a root.
+			this.depth = 0
+			this.depthAuthoritative = true
+		} else {
+			// Legacy child resumed without its live parent (e.g. reopened from history):
+			// the depth cannot be derived here, so mark it non-authoritative and let
+			// ClineProvider.createTaskWithHistoryItem() backfill it before first save.
+			this.depth = 0
+			this.depthAuthoritative = false
+		}
+
 		this.metadata = {
 			task: historyItem ? historyItem.task : task,
 			images: historyItem ? [] : images,
@@ -1121,6 +1151,9 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 				mode: this._taskMode || defaultModeSlug, // Use the task's own mode, not the current provider mode.
 				apiConfigName: this._taskApiConfigName, // Use the task's own provider profile, not the current provider profile.
 				initialStatus: this.initialStatus,
+				// Only persist depth when it was derived authoritatively; a legacy child resumed
+				// without its live parent carries a placeholder 0 that must not be written back.
+				depth: this.depthAuthoritative ? this.depth : undefined,
 			})
 
 			// Emit token/tool usage updates using debounced function

src/core/task/__tests__/Task.spec.ts

@@ -547,6 +547,98 @@ describe("Cline", () => {
 				new Task({ provider: mockProvider, apiConfiguration: mockApiConfig })
 			}).toThrow("Either historyItem or task/images must be provided")
 		})
+
+		describe("nesting depth", () => {
+			it("assigns depth 0 and authoritative to a new root task", () => {
+				const task = new Task({
+					provider: mockProvider,
+					apiConfiguration: mockApiConfig,
+					task: "root task",
+					startTask: false,
+				})
+
+				expect(task.depth).toBe(0)
+				expect(task.depthAuthoritative).toBe(true)
+			})
+
+			it("derives child depth from the live parent (parent.depth + 1)", () => {
+				const parent = new Task({
+					provider: mockProvider,
+					apiConfiguration: mockApiConfig,
+					task: "parent task",
+					startTask: false,
+				})
+
+				const child = new Task({
+					provider: mockProvider,
+					apiConfiguration: mockApiConfig,
+					task: "child task",
+					parentTask: parent,
+					startTask: false,
+				})
+
+				expect(parent.depth).toBe(0)
+				expect(child.depth).toBe(1)
+				expect(child.depthAuthoritative).toBe(true)
+				expect(child.parentTaskId).toBe(parent.taskId)
+			})
+
+			it("prefers a persisted depth over the live parent", () => {
+				const parent = new Task({
+					provider: mockProvider,
+					apiConfiguration: mockApiConfig,
+					task: "parent task",
+					startTask: false,
+				})
+
+				const child = new Task({
+					provider: mockProvider,
+					apiConfiguration: mockApiConfig,
+					task: "child task",
+					parentTask: parent,
+					historyItem: {
+						id: "persisted-child",
+						ts: Date.now(),
+						task: "child task",
+						number: 1,
+						tokensIn: 0,
+						tokensOut: 0,
+						cacheWrites: 0,
+						cacheReads: 0,
+						totalCost: 0,
+						parentTaskId: parent.taskId,
+						depth: 7,
+					},
+					startTask: false,
+				})
+
+				expect(child.depth).toBe(7)
+				expect(child.depthAuthoritative).toBe(true)
+			})
+
+			it("marks a legacy child resumed without its live parent as non-authoritative", () => {
+				const task = new Task({
+					provider: mockProvider,
+					apiConfiguration: mockApiConfig,
+					historyItem: {
+						id: "legacy-child",
+						ts: Date.now(),
+						task: "legacy child",
+						number: 1,
+						tokensIn: 0,
+						tokensOut: 0,
+						cacheWrites: 0,
+						cacheReads: 0,
+						totalCost: 0,
+						parentTaskId: "missing-parent",
+					},
+					startTask: false,
+				})
+
+				expect(task.depth).toBe(0)
+				expect(task.depthAuthoritative).toBe(false)
+			})
+		})
 	})
 
 	describe("task-local configuration isolation", () => {

src/core/task/__tests__/taskDepth.spec.ts

@@ -0,0 +1,85 @@
+// npx vitest core/task/__tests__/taskDepth.spec.ts
+
+import { computeTaskDepth, MAX_DEPTH_WALK } from "../taskDepth"
+
+describe("computeTaskDepth", () => {
+	it("returns a valid persisted depth as-is", () => {
+		expect(computeTaskDepth("a", 3, () => undefined)).toBe(3)
+	})
+
+	it("rejects non-integer / negative persisted depths and falls through to the walk", () => {
+		// ownDepth invalid -> walk; no parent -> root at depth 0
+		expect(computeTaskDepth("a", -1, (id) => ({ parentTaskId: undefined }))).toBe(0)
+		expect(computeTaskDepth("a", 1.5, (id) => ({ parentTaskId: undefined }))).toBe(0)
+	})
+
+	it("derives depth from a live root with no persisted value", () => {
+		// c -> b -> a(root). No depths persisted anywhere.
+		const lookup = (id: string) => {
+			switch (id) {
+				case "c":
+					return { parentTaskId: "b" }
+				case "b":
+					return { parentTaskId: "a" }
+				case "a":
+					return { parentTaskId: undefined }
+			}
+			return undefined
+		}
+		expect(computeTaskDepth("c", undefined, lookup)).toBe(2)
+	})
+
+	it("derives depth from the nearest ancestor with a persisted value", () => {
+		// c -> b(depth 5) -> a. Only b has a persisted depth.
+		const lookup = (id: string) => {
+			switch (id) {
+				case "c":
+					return { parentTaskId: "b" }
+				case "b":
+					return { parentTaskId: "a", depth: 5 }
+				case "a":
+					return { parentTaskId: undefined, depth: 4 }
+			}
+			return undefined
+		}
+		expect(computeTaskDepth("c", undefined, lookup)).toBe(6)
+	})
+
+	it("returns undefined for a cycle in the parent chain", () => {
+		const lookup = (id: string) => {
+			switch (id) {
+				case "a":
+					return { parentTaskId: "b" }
+				case "b":
+					return { parentTaskId: "c" }
+				case "c":
+					return { parentTaskId: "a" } // cycle
+			}
+			return undefined
+		}
+		expect(computeTaskDepth("a", undefined, lookup)).toBeUndefined()
+	})
+
+	it("returns undefined when the chain dangles (parent not loadable)", () => {
+		const lookup = (id: string) => {
+			if (id === "c") return { parentTaskId: "missing" }
+			return undefined // "missing" cannot be loaded
+		}
+		expect(computeTaskDepth("c", undefined, lookup)).toBeUndefined()
+	})
+
+	it("returns undefined for a chain longer than MAX_DEPTH_WALK hops", () => {
+		// Build a linear chain of length > MAX_DEPTH_WALK with no persisted depths.
+		const nodes: Record<string, { parentTaskId?: string }> = {}
+		for (let i = 0; i < MAX_DEPTH_WALK + 5; i++) {
+			nodes[`t${i}`] = { parentTaskId: i === 0 ? undefined : `t${i - 1}` }
+		}
+		const lookup = (id: string) => nodes[id]
+		expect(computeTaskDepth(`t${MAX_DEPTH_WALK + 4}`, undefined, lookup)).toBeUndefined()
+	})
+
+	it("handles a self-referencing parent", () => {
+		const lookup = (id: string) => ({ parentTaskId: id })
+		expect(computeTaskDepth("a", undefined, lookup)).toBeUndefined()
+	})
+})

src/core/task/taskDepth.ts

@@ -0,0 +1,69 @@
+/**
+ * Pure helpers for task nesting depth.
+ *
+ * Depth is the number of delegation hops from the root task (root = 0).
+ * It is derived from the `parentTaskId` chain so that legacy tasks without a
+ * persisted `depth` field can be backfilled on load, and so that a corrupted
+ * or circular parent chain cannot produce an invalid depth.
+ */
+
+/** Maximum ancestor hops to follow before giving up (guards against cycles). */
+export const MAX_DEPTH_WALK = 32
+
+export type DepthLookup = (taskId: string) => { parentTaskId?: string; depth?: number } | undefined
+
+function isValidDepth(value: unknown): value is number {
+	return typeof value === "number" && Number.isInteger(value) && value >= 0
+}
+
+/**
+ * Compute the nesting depth for a task.
+ *
+ * - A persisted `depth` on the task itself is authoritative.
+ * - Otherwise, walk up the `parentTaskId` chain:
+ *   - if an ancestor has a valid persisted depth, the task sits that many hops below it;
+ *   - if we reach a root (no parent) without a persisted depth, the task's depth equals
+ *     the number of hops taken to get there (a root is at depth 0);
+ *   - on a cycle, a dangling reference, or an overly long chain, return `undefined`
+ *     so callers fall back to treating the task as a root without persisting a bogus value.
+ */
+export function computeTaskDepth(
+	taskId: string,
+	ownDepth: number | undefined,
+	lookup: DepthLookup,
+): number | undefined {
+	if (isValidDepth(ownDepth)) {
+		return ownDepth
+	}
+
+	const seen = new Set<string>([taskId])
+	let currentId: string | undefined = taskId
+	let hopsFromTask = 0
+
+	while (hopsFromTask < MAX_DEPTH_WALK) {
+		const node: { parentTaskId?: string; depth?: number } | undefined = currentId ? lookup(currentId) : undefined
+		if (!node) {
+			// Parent chain references a task we cannot load — stop.
+			return undefined
+		}
+		if (isValidDepth(node.depth)) {
+			// Nearest ancestor with an authoritative depth: the original task sits
+			// `hopsFromTask` levels below it.
+			return node.depth + hopsFromTask
+		}
+		const parentId: string | undefined = node.parentTaskId
+		if (parentId === undefined) {
+			// Reached a root without a persisted depth (root = 0).
+			return hopsFromTask
+		}
+		if (seen.has(parentId)) {
+			// Cycle detected — refuse to persist a derived depth.
+			return undefined
+		}
+		seen.add(parentId)
+		currentId = parentId
+		hopsFromTask += 1
+	}
+
+	return undefined
+}