Main frame (precursor origin)

Embedding a sandboxed iframe. With kIsolateSandboxedIframes (default-on) the iframe runs in a dedicated process whose ProcessLock.is_sandboxed()==true. Its committed origin is opaque, but its GetLastCommittedURL() is the precursor URL (this server's origin).

The injected renderer code (simulating a compromised renderer in the sandboxed-iframe process) sends:

1. PasswordGenerationDriver::PresaveGeneratedPassword — NOT CPSP-gated; reaches the browser handler with form.url = precursor origin URL.
2. PasswordManagerDriver::PasswordFormSubmitted — IS CPSP-gated via HasValidURL(); the browser kills the sandboxed renderer with "Terminating renderer for bad PasswordManager IPC message, reason 3".