Update safety comments for case.

src/lib.rs

@@ -83,8 +83,10 @@ impl TypeErasedVec {
     /// Casts the present elements to the new type without calling their destructor.
     ///
     /// # Safety
-    /// The caller must ensure that the existing elements can be safely transmuted
-    /// into the new type `T` and that dropping them as `T` is sound.
+    /// `T` must have exactly the same [`Layout`] as the erased element type.
+    /// Matching size alone is insufficient because the allocation must also have
+    /// the alignment required by `T`. The caller must additionally ensure that
+    /// every existing element is valid as `T` and can be soundly dropped as `T`.
     pub unsafe fn cast_type<T>(&mut self) -> ContentGuard<'_, T> {
         debug_assert_eq!(self.layout, Layout::new::<T>());
 
@@ -171,8 +173,10 @@ impl TypeErasedVec {
     /// Convert the capacity of the erased `Vec` into a `Vec<T>`.
     ///
     /// # Safety
-    /// The caller must ensure that the existing elements can be safely transmuted
-    /// into the new type `T` and that dropping them as `T` is sound.
+    /// `T` must have exactly the same [`Layout`] as the erased element type.
+    /// Matching size alone is insufficient because the allocation must also have
+    /// the alignment required by `T`. The caller must additionally ensure that
+    /// every existing element is valid as `T` and can be soundly dropped as `T`.
     #[must_use]
     pub unsafe fn cast_into_vec<T>(mut self) -> Vec<T> {
         unsafe { self.cast_type::<T>() }.take()

src/send.rs

@@ -58,8 +58,11 @@ macro_rules! define_thread_safe_erased_vec {
             /// Access the erased vector as `T` without clearing its elements.
             ///
             /// # Safety
-            /// The caller must ensure that the existing elements can be safely
-            /// transmuted into `T` and that dropping them as `T` is sound.
+            /// `T` must have exactly the same [`Layout`] as the erased element
+            /// type. Matching size alone is insufficient because the allocation
+            /// must also have the alignment required by `T`. The caller must
+            /// additionally ensure that every existing element is valid as `T`
+            /// and can be soundly dropped as `T`.
             pub unsafe fn cast_type<T>(&mut self) -> ContentGuard<'_, T>
             where
                 T: $first_bound $(+ $remaining_bound)*,
@@ -128,8 +131,11 @@ macro_rules! define_thread_safe_erased_vec {
             /// Convert the erased vector into a `Vec<T>` without clearing it.
             ///
             /// # Safety
-            /// The caller must ensure that the existing elements can be safely
-            /// transmuted into `T` and that dropping them as `T` is sound.
+            /// `T` must have exactly the same [`Layout`] as the erased element
+            /// type. Matching size alone is insufficient because the allocation
+            /// must also have the alignment required by `T`. The caller must
+            /// additionally ensure that every existing element is valid as `T`
+            /// and can be soundly dropped as `T`.
             #[must_use]
             pub unsafe fn cast_into_vec<T>(self) -> Vec<T>
             where