Chrome for Testing macOS: Keychain Unlock Prompt with omp Browser Verification
When using Chrome for Testing with omp's browser verification on macOS, a persistent 'wants to use your confidential information' keychain unlock prompt appears even with headed: false (headless mode), blocking browser automation. The prompt appears specifically when creating a fresh --user-data-dir; existing profiles do not trigger it. The dialog requests the login keychain password, but no valid password input works because the real issue is an ACL code-signature mismatch.
Chrome for Testing stores cookie-encryption keys in the macOS keychain under Chromium Safe Storage, protected by an ACL bound to the original binary's code signature. When Playwright's bundled Chrome for Testing launches with a new --user-data-dir, it tries to access the keychain item from a previous build, but the new binary's code signature doesn't match the ACL, triggering an OS authorization prompt that blocks headless execution. Workaround: add the flags --use-mock-keychain and --password-store=basic when launching Chrome for Testing; these bypass the OS keychain and use an in-memory mock credential store instead, eliminating all prompts for headless testing and browser relay scenarios.