Bolster LinearMemory's safety documentation

crates/wasmtime/src/runtime/memory.rs

@@ -738,6 +738,14 @@ impl Memory {
 /// guard page.  Additionally the safety concerns explained in ['Memory'], for
 /// accessing the memory apply here as well.
 ///
+/// The value returned by [`LinearMemory::byte_size`] must be at least the
+/// `minimum` size the memory was created with, must be at least `new_size`
+/// after a successful [`LinearMemory::grow_to`], and must never decrease.
+/// At least that many bytes starting at [`LinearMemory::as_ptr`] must be
+/// valid to read and write. Compiled WebAssembly code relies on these
+/// properties when performing bounds checks, so violating them can lead to
+/// out-of-bounds memory accesses.
+///
 /// Note that this is a relatively advanced feature and it is recommended to be
 /// familiar with wasmtime runtime code to use it.
 pub unsafe trait LinearMemory: Send + Sync + 'static {