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e5ac9a2734
The Rego VM was designed around Rego's semantics, but Azure Policy needs a few things Rego doesn't: host-supplied context alongside input/data, undefined-to-null coercion for missing fields, skip-undefined collection behavior for wildcard aliases, and non-vacuous iteration over non-array values. This commit adds five new instructions to bridge those gaps: LoadContext / LoadMetadata — give programs access to host-supplied evaluation context and cached program metadata at runtime. ArrayPushDefined — like ArrayPush but silently drops undefined values, so wildcard alias collection (field[*].property) excludes absent nested properties instead of leaking undefined entries into the array. ReturnUndefinedIfNotTrue — early return with Undefined when a guard condition isn't satisfied, without tripping a VM assertion failure. This models "condition doesn't match" cleanly. CoalesceUndefinedToNull — turns Undefined into Null in-place so that downstream builtins see null rather than short-circuiting on undefined. The loop engine also gains an Azure Policy mode: when the source language is "azure_policy", an Every loop over a non-array value (scalars, null, objects) iterates once over a virtual Null element instead of being vacuously true. This matches how field[*] behaves on non-array fields in Azure Policy — the condition body runs once against Null, which typically evaluates to false. On the plumbing side: the VM gets a context field with set_context(), metadata is cached as a Value on program load, and map_limit_error is inlined into memory_check since it had only one call site. Four new YAML test suites (~880 lines) cover the new instructions and context/metadata loading, along with instruction parser, display, and assembly listing support for everything added here.