fix: restrict insert_content to append-only

The insert_content tool was intended for appending content only, but the code
allowed arbitrary line numbers which could corrupt files. This change enforces
that line_number must be 0 (append-only mode) to prevent file corruption.

Signed-off-by: Eric Wheeler <[email protected]>

Author: Eric Wheeler

src/core/tools/insertContentTool.ts

@@ -78,6 +78,13 @@ export async function insertContentTool(
 			return
 		}
 
+		if (lineNumber !== 0) {
+			cline.consecutiveMistakeCount++
+			cline.recordToolError("insert_content")
+			pushToolResult(formatResponse.toolError("Invalid line number: only append is supported so line must be 0"))
+			return
+		}
+
 		cline.consecutiveMistakeCount = 0
 
 		// Read the file