fix(write-to-file): address partial filesystem error review

src/core/task/Task.ts

@@ -1831,6 +1831,39 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 		return formatResponse.toolError(formatResponse.missingToolParameterError(paramName))
 	}
 
+	/**
+	 * Finalize a partial "tool" ask message without blocking for user input.
+	 * Call this in error paths where a partial tool message was opened during streaming
+	 * but execution failed before the normal approval flow could close it, so the webview
+	 * spinner does not get stuck in a loading state.
+	 *
+	 * The matching partial message may no longer be the final entry if another asynchronous
+	 * message was inserted between the partial ask and the error handler, so search backward
+	 * instead of relying on clineMessages.at(-1).
+	 */
+	async finalizePartialToolAsk(text?: string): Promise<void> {
+		const partialToolAsk = this.clineMessages
+			.slice()
+			.reverse()
+			.find(
+				(message) =>
+					message.partial === true &&
+					message.type === "ask" &&
+					message.ask === "tool" &&
+					(text === undefined || message.text === text),
+			)
+
+		if (!partialToolAsk) {
+			return
+		}
+
+		partialToolAsk.partial = false
+		await this.saveClineMessages()
+		await this.updateClineMessage(partialToolAsk).catch((error) => {
+			console.error("[Task#finalizePartialToolAsk] updateClineMessage failed:", error)
+		})
+	}
+
 	// Lifecycle
 	// Start / Resume / Abort / Dispose
 

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

@@ -2857,6 +2857,78 @@ describe("Cline", () => {
 			saveSpy.mockRestore()
 		})
 
+		it("finalizePartialToolAsk persists and updates a non-last partial tool ask", async () => {
+			const updateSpy = vi
+				.spyOn(getTaskTestAccess(Task.prototype), "updateClineMessage")
+				.mockResolvedValue(undefined)
+			const saveSpy = vi.spyOn(getTaskTestAccess(Task.prototype), "saveClineMessages").mockResolvedValue(true)
+
+			const task = new Task({
+				provider: mockProvider,
+				apiConfiguration: mockApiConfig,
+				task: "test task",
+				startTask: false,
+			})
+
+			const partialToolAsk = {
+				ts: Date.now() - 2,
+				type: "ask" as const,
+				ask: "tool" as const,
+				text: "partial tool message",
+				partial: true,
+			}
+
+			task.clineMessages.push(partialToolAsk)
+			task.clineMessages.push({
+				ts: Date.now() - 1,
+				type: "say",
+				say: "error",
+				text: "intervening async message",
+			})
+
+			await task.finalizePartialToolAsk("partial tool message")
+			await flushMicrotasks()
+
+			expect(partialToolAsk.partial).toBe(false)
+			expect(saveSpy).toHaveBeenCalled()
+			expect(updateSpy).toHaveBeenCalledWith(partialToolAsk)
+
+			updateSpy.mockRestore()
+			saveSpy.mockRestore()
+		})
+
+		it("finalizePartialToolAsk ignores non-matching partial tool asks when text is provided", async () => {
+			const updateSpy = vi
+				.spyOn(getTaskTestAccess(Task.prototype), "updateClineMessage")
+				.mockResolvedValue(undefined)
+			const saveSpy = vi.spyOn(getTaskTestAccess(Task.prototype), "saveClineMessages").mockResolvedValue(true)
+
+			const task = new Task({
+				provider: mockProvider,
+				apiConfiguration: mockApiConfig,
+				task: "test task",
+				startTask: false,
+			})
+
+			task.clineMessages.push({
+				ts: Date.now() - 1,
+				type: "ask",
+				ask: "tool",
+				text: "other partial tool message",
+				partial: true,
+			})
+
+			await task.finalizePartialToolAsk("target partial tool message")
+			await flushMicrotasks()
+
+			expect(task.clineMessages[0].partial).toBe(true)
+			expect(saveSpy).not.toHaveBeenCalled()
+			expect(updateSpy).not.toHaveBeenCalled()
+
+			updateSpy.mockRestore()
+			saveSpy.mockRestore()
+		})
+
 		it("logs (instead of crashing) when updateClineMessage rejects from the ask() ignore-partial path", async () => {
 			// Pins the .catch arm on the fire-and-forget updateClineMessage call
 			// in ask() when a new partial ask arrives while the previous partial

src/core/task/__tests__/Task.throttle.test.ts

@@ -64,10 +64,12 @@ describe("Task token usage throttling", () => {
 	let mockProvider: any
 	let mockApiConfiguration: ProviderSettings
 	let task: Task
+	let consoleLogSpy: ReturnType<typeof vi.spyOn>
 
 	beforeEach(() => {
 		// Reset all mocks
 		vi.clearAllMocks()
+		consoleLogSpy = vi.spyOn(console, "log").mockImplementation(() => {})
 		vi.useFakeTimers()
 
 		// Mock provider
@@ -101,6 +103,7 @@ describe("Task token usage throttling", () => {
 		if (task && !task.abort) {
 			task.dispose()
 		}
+		consoleLogSpy.mockRestore()
 	})
 
 	test("should emit TaskTokenUsageUpdated immediately on first change", async () => {

src/core/tools/WriteToFileTool.ts

@@ -26,10 +26,60 @@ interface WriteToFileParams {
 export class WriteToFileTool extends BaseTool<"write_to_file"> {
 	readonly name = "write_to_file" as const
 
+	/**
+	 * Tracks filesystem failures from diff-view streaming by task id. Tool instances are
+	 * singletons, so this state must be keyed per task to avoid one task's failing partial
+	 * stream suppressing another task's streaming deltas.
+	 */
+	private partialStreamFailuresByTaskId = new Set<string>()
+
+	/**
+	 * Tracks partial path stabilization by task id. The tool is a singleton, so using the
+	 * BaseTool singleton path state lets concurrent tasks incorrectly stabilize each other.
+	 */
+	private lastSeenPartialPathByTaskId = new Map<string, string | undefined>()
+
+	private getPartialStreamFailureKey(task: Task): string {
+		return `${task.taskId}.${task.instanceId}`
+	}
+
+	private hasPathStabilizedForTask(task: Task, partialPath: string | undefined): boolean {
+		const key = this.getPartialStreamFailureKey(task)
+		const lastSeenPath = this.lastSeenPartialPathByTaskId.get(key)
+		const pathHasStabilized = lastSeenPath !== undefined && lastSeenPath === partialPath
+		this.lastSeenPartialPathByTaskId.set(key, partialPath)
+		return pathHasStabilized && !!partialPath
+	}
+
+	private resetTaskPartialState(task: Task): void {
+		const key = this.getPartialStreamFailureKey(task)
+		this.lastSeenPartialPathByTaskId.delete(key)
+		this.partialStreamFailuresByTaskId.delete(key)
+	}
+
+	private async resetDiffViewAfterWrite(task: Task): Promise<void> {
+		await task.diffViewProvider.reset().catch((resetError) => {
+			console.error("Error resetting write_to_file diff view:", resetError)
+		})
+	}
+
+	private async finalizePartialToolAskAfterFailure(task: Task, text?: string): Promise<void> {
+		await task.finalizePartialToolAsk(text).catch((finalizeError) => {
+			console.error("Error finalizing write_to_file partial tool ask:", finalizeError)
+		})
+	}
+
+	override resetPartialState(): void {
+		super.resetPartialState()
+		this.partialStreamFailuresByTaskId.clear()
+		this.lastSeenPartialPathByTaskId.clear()
+	}
+
 	async execute(params: WriteToFileParams, task: Task, callbacks: ToolCallbacks): Promise<void> {
 		const { pushToolResult, handleError, askApproval } = callbacks
 		const relPath = params.path
 		let newContent = params.content
+		const partialStreamFailureKey = this.getPartialStreamFailureKey(task)
 
 		if (!relPath) {
 			task.consecutiveMistakeCount++
@@ -67,12 +117,6 @@ export class WriteToFileTool extends BaseTool<"write_to_file"> {
 			task.diffViewProvider.editType = fileExists ? "modify" : "create"
 		}
 
-		// Create parent directories early for new files to prevent ENOENT errors
-		// in subsequent operations (e.g., diffViewProvider.open, fs.readFile)
-		if (!fileExists) {
-			await createDirectoriesForFile(absolutePath)
-		}
-
 		if (newContent.startsWith("```")) {
 			newContent = newContent.split("\n").slice(1).join("\n")
 		}
@@ -97,6 +141,13 @@ export class WriteToFileTool extends BaseTool<"write_to_file"> {
 		}
 
 		try {
+			// Create parent directories for new files inside the try block so filesystem
+			// errors (EROFS, EACCES, etc.) route through handleError with proper cleanup
+			// and consecutive-mistake counting, rather than escaping unhandled.
+			if (!fileExists) {
+				await createDirectoriesForFile(absolutePath)
+			}
+
 			task.consecutiveMistakeCount = 0
 
 			const provider = task.providerRef.deref()
@@ -179,26 +230,40 @@ export class WriteToFileTool extends BaseTool<"write_to_file"> {
 
 			pushToolResult(message)
 
-			await task.diffViewProvider.reset()
-			this.resetPartialState()
+			await this.resetDiffViewAfterWrite(task)
 
 			task.processQueuedMessages()
 
 			return
 		} catch (error) {
+			// Finalize any open partial tool message so the UI spinner doesn't get stuck.
+			// The partial ask fired during streaming (handlePartial) or early in execute sets
+			// partial: true on the webview message; without this, the spinner persists even
+			// after the error bubble appears.
+			await this.finalizePartialToolAskAfterFailure(task)
 			await handleError("writing file", error as Error)
-			await task.diffViewProvider.reset()
-			this.resetPartialState()
+			await this.resetDiffViewAfterWrite(task)
 			return
+		} finally {
+			this.resetTaskPartialState(task)
 		}
 	}
 
 	override async handlePartial(task: Task, block: ToolUse<"write_to_file">): Promise<void> {
 		const relPath: string | undefined = block.params.path
 		const newContent: string | undefined = block.params.content
 
+		const partialStreamFailureKey = this.getPartialStreamFailureKey(task)
+
+		// A prior streaming delta for this task already hit a fatal filesystem error.
+		// Skip further streaming work so we don't create a new partial tool message on every
+		// subsequent delta. execute() will report the error once when the block completes.
+		if (this.partialStreamFailuresByTaskId.has(partialStreamFailureKey)) {
+			return
+		}
+
 		// Wait for path to stabilize before showing UI (prevents truncated paths)
-		if (!this.hasPathStabilized(relPath) || newContent === undefined) {
+		if (!this.hasPathStabilizedForTask(task, relPath) || newContent === undefined) {
 			return
 		}
 
@@ -224,12 +289,6 @@ export class WriteToFileTool extends BaseTool<"write_to_file"> {
 			task.diffViewProvider.editType = fileExists ? "modify" : "create"
 		}
 
-		// Create parent directories early for new files to prevent ENOENT errors
-		// in subsequent operations (e.g., diffViewProvider.open)
-		if (!fileExists) {
-			await createDirectoriesForFile(absolutePath)
-		}
-
 		const isWriteProtected = task.rooProtectedController?.isWriteProtected(relPath!) || false
 		const isOutsideWorkspace = isPathOutsideWorkspace(absolutePath)
 
@@ -245,14 +304,31 @@ export class WriteToFileTool extends BaseTool<"write_to_file"> {
 		await task.ask("tool", partialMessage, block.partial).catch(() => {})
 
 		if (newContent) {
-			if (!task.diffViewProvider.isEditing) {
-				await task.diffViewProvider.open(relPath!)
-			}
+			try {
+				if (!task.diffViewProvider.isEditing) {
+					await task.diffViewProvider.open(relPath!)
+				}
 
-			await task.diffViewProvider.update(
-				everyLineHasLineNumbers(newContent) ? stripLineNumbers(newContent) : newContent,
-				false,
-			)
+				await task.diffViewProvider.update(
+					everyLineHasLineNumbers(newContent) ? stripLineNumbers(newContent) : newContent,
+					false,
+				)
+			} catch (error) {
+				// Opening or updating the diff view can throw on filesystem errors
+				// (EACCES/EROFS on read-only paths). Finalize the partial tool message
+				// so the UI spinner doesn't get stuck and reset the diff view. Do NOT
+				// rethrow: the same filesystem operation is retried in execute() once the
+				// block completes, and that authoritative non-partial path reports the
+				// error to the user. Surfacing it here too would show the same error twice.
+				// Swallowing it here is safe because the agent loop advances naturally when
+				// the non-partial block arrives (it does not depend on this throw).
+				console.error(`Error streaming write_to_file diff view:`, error)
+				// Mark the stream as failed so later deltas don't re-attempt and spawn a new
+				// partial tool message each time.
+				this.partialStreamFailuresByTaskId.add(partialStreamFailureKey)
+				await this.finalizePartialToolAskAfterFailure(task, partialMessage)
+				await this.resetDiffViewAfterWrite(task)
+			}
 		}
 	}
 }