fix: validate content type earlier in diff parsing

- Move type check to where content is first extracted from XML
- Remove redundant check since content is now guaranteed to be string
- Add test for early content validation

Author: daniel-lxs

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

@@ -91,6 +91,56 @@ describe("multiApplyDiffTool", () => {
 		;(pathUtils.getReadablePath as any).mockImplementation((cwd: string, path: string) => path)
 	})
 
+	describe("Early content validation", () => {
+		it("should filter out non-string content at parse time", async () => {
+			mockBlock = {
+				params: {
+					args: `<file>
+						<path>test.ts</path>
+						<diff>
+							<content>valid string content</content>
+						</diff>
+					</file>`,
+				},
+				partial: false,
+			}
+
+			// Mock parseXml to return mixed content types
+			const parseXml = await import("../../../utils/xml")
+			;(parseXml.parseXml as any).mockReturnValue({
+				file: {
+					path: "test.ts",
+					diff: [
+						{ content: "<<<<<<< SEARCH\ntest\n=======\nreplaced\n>>>>>>> REPLACE" },
+						{ content: null },
+						{ content: undefined },
+						{ content: 42 },
+						{ content: "" }, // Empty string should also be filtered
+						{ content: "<<<<<<< SEARCH\nmore\n=======\nchanges\n>>>>>>> REPLACE" },
+					],
+				},
+			})
+
+			await applyDiffTool(
+				mockCline,
+				mockBlock,
+				mockAskApproval,
+				mockHandleError,
+				mockPushToolResult,
+				mockRemoveClosingTag,
+			)
+
+			// Should complete without error and only process valid string content
+			expect(mockPushToolResult).toHaveBeenCalled()
+			expect(mockHandleError).not.toHaveBeenCalled()
+
+			// Verify that only valid diffs were processed
+			const resultCall = mockPushToolResult.mock.calls[0][0]
+			// Should not include the single block notice since we have 2 valid blocks
+			expect(resultCall).not.toContain("Making multiple related changes")
+		})
+	})
+
 	describe("SEARCH block counting with non-string content", () => {
 		it("should handle diffItem.content being undefined", async () => {
 			mockBlock = {

src/core/tools/multiApplyDiffTool.ts

@@ -132,13 +132,17 @@ export async function applyDiffTool(
 					let diffContent: string
 					let startLine: number | undefined
 
-					diffContent = diff.content
+					// Ensure content is a string before storing it
+					diffContent = typeof diff.content === "string" ? diff.content : ""
 					startLine = diff.start_line ? parseInt(diff.start_line) : undefined
 
-					operationsMap[filePath].diff.push({
-						content: diffContent,
-						startLine,
-					})
+					// Only add to operations if we have valid content
+					if (diffContent) {
+						operationsMap[filePath].diff.push({
+							content: diffContent,
+							startLine,
+						})
+					}
 				}
 			}
 		} catch (error) {
@@ -656,11 +660,9 @@ ${errorDetails ? `\nTechnical details:\n${errorDetails}\n` : ""}
 		let totalSearchBlocks = 0
 		for (const operation of operations) {
 			for (const diffItem of operation.diff) {
-				// Ensure content is a string before calling match
-				if (typeof diffItem.content === "string") {
-					const searchBlocks = (diffItem.content.match(/<<<<<<< SEARCH/g) || []).length
-					totalSearchBlocks += searchBlocks
-				}
+				// Content is guaranteed to be a string due to early validation
+				const searchBlocks = (diffItem.content.match(/<<<<<<< SEARCH/g) || []).length
+				totalSearchBlocks += searchBlocks
 			}
 		}