refactor: inject CLI I/O and diagnostics

src/apps/cli/cliOutput.ts

@@ -0,0 +1,30 @@
+import type { StandardIo } from "@vrtmrz/livesync-commonlib/context";
+
+/** Report a CLI-owned diagnostic without selecting its final presentation channel. */
+export type CliDiagnosticReporter = (message: string, detail?: unknown) => void;
+
+function formatValue(value: unknown): string {
+    if (typeof value === "string") return value;
+    if (value instanceof Error) return value.stack ?? value.message;
+    try {
+        const encoded = JSON.stringify(value);
+        if (encoded !== undefined) return encoded;
+    } catch {
+        // Fall through to the host-independent string conversion.
+    }
+    return String(value);
+}
+
+function formatLine(values: readonly unknown[]): string {
+    return `${values.map(formatValue).join(" ")}\n`;
+}
+
+/** Render one user-facing line on standard output. */
+export function writeStdoutLine(standardIo: StandardIo, ...values: readonly unknown[]): void {
+    standardIo.writeStdout(formatLine(values));
+}
+
+/** Render one user-facing or diagnostic line on standard error. */
+export function writeStderrLine(standardIo: StandardIo, ...values: readonly unknown[]): void {
+    standardIo.writeStderr(formatLine(values));
+}