error cline if someone piped in empty text (#9038)

Co-authored-by: Max Paulus 🥪 <max@cline.bot>

cli/src/index.ts

@@ -775,6 +775,12 @@ program
 		// Always check for piped stdin content
 		const stdinInput = await readStdinIfPiped()
 
+		// Error if stdin was piped but empty (e.g., `echo "" | cline`)
+		if (stdinInput === "") {
+			printWarning("Empty input received from stdin. Please provide content to process.")
+			exit(1)
+		}
+
 		// If no prompt argument, check if input is piped via stdin
 		let effectivePrompt = prompt
 		if (stdinInput) {

cli/src/utils/piped.ts

@@ -40,7 +40,10 @@ export async function readStdinIfPiped(): Promise<string | null> {
 
 		process.stdin.on("end", () => {
 			clearTimeout(timeout)
-			resolve(data.trim() || null)
+			// Return empty string (not null) when stdin was piped but empty
+			// This allows callers to distinguish between "no piped input" (null)
+			// and "empty piped input" ("") for proper error handling
+			resolve(data.trim())
 		})
 
 		process.stdin.on("error", () => {