[expr.call] says that a parameter's end of lifetime is implementation-defined. But there's an exception for temporary objects in [class.temporary]. Is it worth adding a note about it here? Perhaps there are more exceptions that I'm not aware of, given the way the standard strictly specifies behavior before relaxing elsewhere.

It is implementation-defined whether the lifetime of a parameter ends when the function in which it is defined returns or at the end of the enclosing full-expression.
-- https://timsong-cpp.github.io/cppwp/n4861/expr.call#7.sentence-9

Temporary objects are destroyed as the last step in evaluating the full-expression ([intro.execution]) that (lexically) contains the point where they were created.
-- https://timsong-cpp.github.io/cppwp/n4861/class.temporary#4.sentence-3

And for completeness:

The materialization of a temporary object is generally delayed as long as possible in order to avoid creating unnecessary temporary objects.
[ Note: Temporary objects are materialized:
(2.1)
when binding a reference to a prvalue ([dcl.init.ref], [expr.type.conv], [expr.dynamic.cast], [expr.static.cast], [expr.const.cast], [expr.cast]),
-- https://timsong-cpp.github.io/cppwp/n4861/class.temporary#2.1

5
A reference to type “cv1 T1” is initialized by an expression of type “cv2 T2” as follows:
(5.4)
Otherwise:
(5.4.2)
Otherwise, the initializer expression is implicitly converted to a prvalue of type “cv1 T1”. The temporary materialization conversion is applied and the reference is bound to the result.
-- https://timsong-cpp.github.io/cppwp/n4861/dcl.init.ref#5.4.2

5
There are three contexts in which temporaries are destroyed at a different point than the end of the full-expression.
-- https://timsong-cpp.github.io/cppwp/n4861/class.temporary#5.sentence-1

6
The third context is when a reference is bound to a temporary object.35
The temporary object to which the reference is bound or the temporary object that is the complete object of a subobject to which the reference is bound persists for the lifetime of the reference if the glvalue to which the reference is bound was obtained through one of the following:
(6.1)
a temporary materialization conversion ([conv.rval]),
-- https://timsong-cpp.github.io/cppwp/n4861/class.temporary#6.1
The exceptions to this lifetime rule are:
(6.9)
A temporary object bound to a reference parameter in a function call ([expr.call]) persists until the completion of the full-expression containing the call.
-- https://timsong-cpp.github.io/cppwp/n4861/class.temporary#6.9