The global postMessage listener was broadcasting incoming messages to all
loaded plugins without validating the origin or routing to the correct
sender. This allowed any plugin (or any iframe from any origin) to inject
messages into other plugins.
- Added origin validation — messages from origins other than
window.location.origin are rejected.
- Added sender-based routing — a message is only delivered to the plugin
whose iframe contentWindow matches event.source.
- Exposed iframeWindow getters in PluginManager, PluginModalElement, and
createPlugin so the runtime can compare event.source against the correct
iframe reference.
- Updated documentation examples to include origin validation and
recommend window.location.origin over '*' for postMessage targetOrigin.
AI-assisted-by: qwen3.7-plus
