Assertion failure crash with `__module__` annotation: assert fullname

[correctmost]

Crash Report

The snippet below crashes mypy 1.18.2 and the latest code from master (96fac3a).

Traceback

Traceback (most recent call last):
  File ".venv-mypy/bin/mypy", line 7, in <module>
    sys.exit(console_entry())
  File "mypy/mypy/__main__.py", line 15, in console_entry
    main()
  File "mypy/mypy/main.py", line 127, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "mypy/mypy/main.py", line 211, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "mypy/mypy/build.py", line 215, in build
    result = _build(
  File "mypy/mypy/build.py", line 294, in _build
    graph = dispatch(sources, manager, stdout)
  File "mypy/mypy/build.py", line 2945, in dispatch
    process_graph(graph, manager)
  File "mypy/mypy/build.py", line 3336, in process_graph
    done, still_working = manager.wait_for_done(graph)
  File "mypy/mypy/build.py", line 918, in wait_for_done
    process_stale_scc(graph, next_scc, self)
  File "mypy/mypy/build.py", line 3468, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "mypy/mypy/semanal_main.py", line 95, in semantic_analysis_for_scc
    process_top_levels(graph, scc, patches)
  File "mypy/mypy/semanal_main.py", line 233, in process_top_levels
    deferred, incomplete, progress = semantic_analyze_target(
  File "mypy/mypy/semanal_main.py", line 410, in semantic_analyze_target
    analyzer.refresh_partial(
  File "mypy/mypy/semanal.py", line 701, in refresh_partial
    self.refresh_top_level(node)
  File "mypy/mypy/semanal.py", line 719, in refresh_top_level
    self.accept(d)
  File "mypy/mypy/semanal.py", line 7563, in accept
    node.accept(self)
  File "mypy/mypy/nodes.py", line 1478, in accept
    return visitor.visit_class_def(self)
  File "mypy/mypy/semanal.py", line 1827, in visit_class_def
    self.analyze_class(defn)
  File "mypy/mypy/semanal.py", line 2044, in analyze_class
    self.analyze_class_body_common(defn)
  File "mypy/mypy/semanal.py", line 2090, in analyze_class_body_common
    defn.defs.accept(self)
  File "mypy/mypy/nodes.py", line 1573, in accept
    return visitor.visit_block(self)
  File "mypy/mypy/semanal.py", line 5375, in visit_block
    self.accept(s)
  File "mypy/mypy/semanal.py", line 7563, in accept
    node.accept(self)
    ~~~~~~~~~~~^^^^^^
  File "mypy/mypy/nodes.py", line 1660, in accept
    return visitor.visit_assignment_stmt(self)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/semanal.py", line 3324, in visit_assignment_stmt
    self.process_type_annotation(s)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^
  File "mypy/mypy/semanal.py", line 3860, in process_type_annotation
    analyzed = self.anal_type(s.type, allow_tuple_literal=allow_tuple_literal)
  File "mypy/mypy/semanal.py", line 7720, in anal_type
    typ = typ.accept(a)
  File "mypy/mypy/types.py", line 1096, in accept
    return visitor.visit_unbound_type(self)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/typeanal.py", line 285, in visit_unbound_type
    typ = self.visit_unbound_type_nonoptional(t, defining_literal)
  File "mypy/mypy/typeanal.py", line 348, in visit_unbound_type_nonoptional
    tvar_def = self.tvar_scope.get_binding(sym)
  File "mypy/mypy/tvar_scope.py", line 204, in get_binding
    assert fullname
           ^^^^^^^^
AssertionError: 

To Reproduce

class C:
    a: __module__

Your Environment

• Mypy version used: 96fac3a (and 1.18.2)
• Mypy command-line flags: N/A
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.13.7
• Operating system and version: Arch Linux