List constant expression treated differently to list literal

Bug Report

When assigning a list literal to a variable with a known type, mypy uses that type in inferring the type of the list literal. This gives the appearance that invariance is relaxed e.g.

x: list[int | None] = [0, 1, 2, 10]  # ok

is accepted even though normally a list[int] cannot be assigned to a list[int | None].

However, when the list literal is written as a more complex expression, that stops working:

x: list[int | None] = [0, 1, 2] + [10]  # error

That's obviously a bit contrived. My actual use case is more similar to this:

x: list[int | None] = [i for i in range(3)] + [10]  # error

Maybe this isn't fixable - it's only sound because list.__add__ returns a new list which has no other references, but I don't think there is a way to represent that in typeshed.

To Reproduce

x: list[int | None] = [0, 1, 2] + [10]

Expected Behavior

No error

Actual Behavior

concat2.py:1: error: Incompatible types in assignment (expression has type "list[int]", variable has type "list[int | None]")  [assignment]
concat2.py:1: note: "list" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
concat2.py:1: note: Consider using "Sequence" instead, which is covariant

Your Environment

• Mypy version used: 2.2.0
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.12.3

No implementation file or test is named in the issue. Start by reproducing the reported assignment with mypy, then trace how list literals, list concatenation, and comprehensions are inferred and checked against the annotated variable. Done means the reported concatenation cases pass without weakening ordinary list invariance checks.