Yes, there is technically UB here, but it's a different and lower-risk pattern than the one in determine_module_exports_kind.
Lines 47 and 49 create &mut references to fields of importer (which is &NormalModule — immutable):

let stmt_infos = unsafe { &mut *(addr_of!(importer.stmt_infos).cast_mut()) };
let depended_runtime_helper_map =
  unsafe { &mut *(addr_of!(importer.depended_runtime_helper).cast_mut()) };

This violates Rust's aliasing rules: &importer (immutable, covers the whole struct) coexists with &mut importer.stmt_infos (mutable).

Send: Safe in practice. Moving the entire EcmaAst (self-cell of allocator + program together) to another thread is fine since no dangling references remain.
Sync: Technically unsound, but safe given current usage patterns. The concern is:

1. Program<'cell> contains Cell types (e.g., Cell<Option<ScopeId>> on AST nodes). Cell is !Sync because &Cell<T> allows mutation via .set(). If two threads hold &EcmaAst and both call .set() on the same Cell, that's a data race.
2. Allocator (wraps bumpalo::Bump) is !Sync because &Bump allows allocation, which mutates internal state without synchronization. EcmaAst::allocator() exposes &Allocator.

In practice this is fine because:

• &EcmaAst is only used for reading the AST in parallel (par_iter in scan/link stages)
• Mutations go through &mut EcmaAst via with_mut(), which requires exclusive access
• Nobody allocates through &Allocator from shared references

So it's a "safe by convention" pattern — correct given current usage, but fragile. A future change that mutates Cell fields or allocates through a shared &EcmaAst would silently introduce a data race.