CVE-2026-33940: Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial

A crafted object placed in the template context can bypass all conditional guards in resolvePartial() and cause invokePartial() to return undefined. The Handlebars runtime then treats the unresolved partial as a source that needs to be compiled, passing the crafted object to env.compile(). Because the object is a valid Handlebars AST containing injected code, the generated JavaScript executes arbitrary commands on the server. The attack requires the adversary to control a value that can be returned by a dynamic partial lookup.