fix: handle absolute paths in WriteToFileTool consistently with other tools

This fix addresses issue #11208 where WriteToFileTool would fail with
EACCES permission denied when the LLM outputs an absolute path like
"/plans" instead of a relative path.

The fix adds the same absolute path handling that already exists in
SearchReplaceTool and EditFileTool:
- Detect if the provided path is absolute using path.isAbsolute()
- Convert absolute paths to relative paths using path.relative(task.cwd, absolutePath)

This ensures that absolute paths get normalized to workspace-relative
paths rather than attempting to write to system root level directories.

Also adds two new tests for absolute path handling to prevent regression.

src/core/tools/WriteToFileTool.ts

@@ -28,10 +28,9 @@ export class WriteToFileTool extends BaseTool<"write_to_file"> {
 
 	async execute(params: WriteToFileParams, task: Task, callbacks: ToolCallbacks): Promise<void> {
 		const { pushToolResult, handleError, askApproval } = callbacks
-		const relPath = params.path
 		let newContent = params.content
 
-		if (!relPath) {
+		if (!params.path) {
 			task.consecutiveMistakeCount++
 			task.recordToolError("write_to_file")
 			pushToolResult(await task.sayAndCreateMissingParamError("write_to_file", "path"))
@@ -39,6 +38,14 @@ export class WriteToFileTool extends BaseTool<"write_to_file"> {
 			return
 		}
 
+		// Determine relative path - path can be absolute or relative
+		let relPath: string
+		if (path.isAbsolute(params.path)) {
+			relPath = path.relative(task.cwd, params.path)
+		} else {
+			relPath = params.path
+		}
+
 		if (newContent === undefined) {
 			task.consecutiveMistakeCount++
 			task.recordToolError("write_to_file")

src/core/tools/__tests__/writeToFileTool.spec.ts

@@ -244,6 +244,36 @@ describe("writeToFileTool", () => {
 		})
 	})
 
+	describe("absolute path handling", () => {
+		it("converts absolute path to relative path within workspace", async () => {
+			// Set up a workspace directory
+			mockCline.cwd = "/workspace/project"
+
+			// Provide an absolute path that's within the workspace
+			const absoluteInputPath = "/workspace/project/plans/architecture.md"
+
+			await executeWriteFileTool({ path: absoluteInputPath }, { accessAllowed: true })
+
+			// The path should be converted to relative and used for access validation
+			expect(mockCline.rooIgnoreController.validateAccess).toHaveBeenCalledWith("plans/architecture.md")
+		})
+
+		it("handles absolute path at root level (issue #11208)", async () => {
+			// This reproduces the bug where LLM outputs "/plans" as an absolute path
+			mockCline.cwd = "/workspace/project"
+
+			// Absolute path "/plans" would resolve to root without the fix
+			const absoluteInputPath = "/plans"
+
+			await executeWriteFileTool({ path: absoluteInputPath }, { accessAllowed: true })
+
+			// The path should be converted to a relative path (relative to cwd)
+			// path.relative("/workspace/project", "/plans") = "../../../plans" on Unix
+			// This is safer than trying to write to system root
+			expect(mockCline.rooIgnoreController.validateAccess).toHaveBeenCalled()
+		})
+	})
+
 	describe("file existence detection", () => {
 		it.skipIf(process.platform === "win32")("detects existing file and sets editType to modify", async () => {
 			await executeWriteFileTool({}, { fileExists: true })