`overload`s not recognised when `self` is typed as a `Protocol`

Bug Report

When subclassing a base class with overloads, and self is typed as a Protocol, only the first overload is recognised.

To Reproduce

from datetime import timedelta
from typing import Generic, Protocol, TypeVar, overload, reveal_type


T = TypeVar("T")
T_CT = TypeVar("T_CT", contravariant=True)

class Mixin(Generic[T]):
    @overload
    def d(self: Mixin[timedelta], other: float) -> Mixin[timedelta]: ...
    @overload
    def d(self: Mixin[timedelta], other: timedelta) -> Mixin[float]: ...

reveal_type(Mixin[timedelta]().d(5.0))  # Mixin[timedelta], fine
reveal_type(Mixin[timedelta]().d(timedelta(days=1)))  # Mixin[float], fine

class SupportsD(Protocol[T_CT, T]):
    def d(self, other: T_CT, /) -> Mixin[T]: ...

class S(Mixin[T]):
    def div(self: SupportsD[T_CT, T], other: T_CT) -> S[T]: ...

reveal_type(S[timedelta]().div(5.0))  # S[timedelta], fine
reveal_type(S[timedelta]().div(timedelta(days=1)))  # mypy arg-type

Expected Behavior

S[timedelta]().div(timedelta(days=1)) is revealed as S[float]

Actual Behavior

ttest.pyi:24: error: Argument 1 to "div" of "S" has incompatible type "timedelta"; expected "float"  [arg-type]

Your Environment

Mypy version used

1.18.2

Mypy command-line flags

none

Mypy configuration options from mypy.ini (and other config files):

[tool.mypy]
# Import discovery
namespace_packages = false
explicit_package_bases = false
ignore_missing_imports = true
follow_imports = "normal"
follow_imports_for_stubs = false
no_site_packages = false
no_silence_site_packages = false
# Disallow dynamic typing
disallow_any_unimported = false  # TODO
disallow_any_expr = false        # TODO
disallow_any_decorated = false   # TODO
disallow_any_explicit = false    # TODO
disallow_any_generics = false    # TODO
disallow_subclassing_any = false # TODO
# Untyped definitions and calls
disallow_untyped_calls = false     # TODO
disallow_untyped_defs = false      # TODO
disallow_incomplete_defs = false   # TODO
check_untyped_defs = true
disallow_untyped_decorators = true
# None and Optional handling
no_implicit_optional = true
strict_optional = true
# Configuring warnings
warn_redundant_casts = true
warn_unused_ignores = true
warn_no_return = true
warn_return_any = false     # TODO
warn_unreachable = false    # GH#27396
# Suppressing errors
ignore_errors = false
enable_error_code = "ignore-without-code" # same as in pandas
# Miscellaneous strictness flags
allow_untyped_globals = false
allow_redefinition = false
local_partial_types = false
implicit_reexport = false     # pyright behaves the same
strict_equality = true
# Configuring error messages
show_error_context = false
show_column_numbers = false
show_error_codes = true

Python version used:

3.12.10

Start by running the supplied reproduction with Python 3.12.10 and mypy 1.18.2, focusing on overload resolution for Mixin.d when self is viewed through SupportsD. Trace the handling of the two overloads and Protocol typing; done means the timedelta call is accepted and revealed as S[float], while the existing float case remains S[timedelta].