Suppress Node DEP0040 punycode warning in CLI startup

src/cli/index.ts

@@ -4,6 +4,7 @@
 // Silent no-op if the file doesn't exist.
 try { process.loadEnvFile(); } catch { /* .env not found — that's fine */ }
 
+import './suppressNodeWarnings.js';
 import { Command } from 'commander';
 import { registerStartCommand } from './start.js';
 import { registerSendCommand } from './send.js';

src/cli/suppressNodeWarnings.test.ts

@@ -0,0 +1,16 @@
+import { describe, expect, it } from 'vitest';
+import { shouldSuppressNodeWarning } from './suppressNodeWarnings.js';
+
+describe('shouldSuppressNodeWarning', () => {
+  it('suppresses DEP0040 warning code', () => {
+    expect(shouldSuppressNodeWarning('DEP0040', 'any message')).toBe(true);
+  });
+
+  it('suppresses punycode deprecation by message text', () => {
+    expect(shouldSuppressNodeWarning(undefined, 'The `punycode` module is deprecated.')).toBe(true);
+  });
+
+  it('does not suppress unrelated warnings', () => {
+    expect(shouldSuppressNodeWarning('DEP0001', 'different deprecation')).toBe(false);
+  });
+});

src/cli/suppressNodeWarnings.ts

@@ -0,0 +1,47 @@
+/**
+ * Suppress known noisy runtime deprecations from transitive dependencies while
+ * keeping all other warnings visible.
+ */
+export function shouldSuppressNodeWarning(code: string | undefined, message: string): boolean {
+  if (code === 'DEP0040') {
+    return true;
+  }
+  return /`punycode` module is deprecated/i.test(message);
+}
+
+export function installNodeWarningFilter(): void {
+  const stateKey = Symbol.for('flynn.nodeWarningFilterInstalled');
+  const globalState = globalThis as Record<PropertyKey, unknown>;
+  if (globalState[stateKey]) {
+    return;
+  }
+  globalState[stateKey] = true;
+
+  const originalEmitWarning = process.emitWarning.bind(process);
+
+  process.emitWarning = ((warning: unknown, ...args: unknown[]) => {
+    const message = warning instanceof Error
+      ? warning.message
+      : typeof warning === 'string'
+        ? warning
+        : String(warning);
+
+    let code: string | undefined;
+    if (warning instanceof Error && typeof (warning as { code?: unknown }).code === 'string') {
+      code = (warning as { code?: string }).code;
+    }
+    if (typeof args[0] === 'string') {
+      code = args[0];
+    } else if (args[0] && typeof args[0] === 'object' && typeof (args[0] as { code?: unknown }).code === 'string') {
+      code = (args[0] as { code?: string }).code;
+    }
+
+    if (shouldSuppressNodeWarning(code, message)) {
+      return;
+    }
+
+    (originalEmitWarning as (...params: unknown[]) => void)(warning, ...args);
+  }) as typeof process.emitWarning;
+}
+
+installNodeWarningFilter();