Be stricter about python specs for freethreading

src/runez/logsetup.py

@@ -967,8 +967,9 @@ def enable_faulthandler(cls, signum=UNSET):
 
             cls.faulthandler_signum = signum
             dump_file = cls.file_handler.stream
-            faulthandler.enable(file=dump_file, all_threads=True)
-            faulthandler.register(signum, file=dump_file, all_threads=True, chain=False)
+            if dump_file is not None:
+                faulthandler.enable(file=dump_file, all_threads=True)
+                faulthandler.register(signum, file=dump_file, all_threads=True, chain=False)
 
     @classmethod
     def override_spec(cls, **settings):

src/runez/pyenv.py

@@ -828,7 +828,7 @@ def mm(self):
     def mm_spec(self):
         """Major/minor spec, e.g: cpython:3.11"""
         if self.mm:
-            return PythonSpec(self.family, self.mm)
+            return PythonSpec(self.family, self.mm, freethreading=self.inspection.freethreading)
 
     @cached_property
     def machine(self):

tests/test_pyenv.py

@@ -354,6 +354,44 @@ def test_spec():
     assert freeth.freethreading
 
 
+def test_freethreading_satisfies(temp_folder):
+    # A freethreaded installation must not satisfy a non-freethreaded spec (and vice versa)
+    arch = runez.SYS_INFO.platform_id.arch
+    mk_python("3.14.0", content={"version": "3.14.0", "machine": arch, "freethreading": True})
+    from runez.pyenv import PythonInstallation
+
+    path = runez.to_path(".pyenv/versions/3.14.0/bin/python3.14")
+    install = PythonInstallation(path)
+    assert install.inspection.freethreading
+    assert install.mm_spec.freethreading
+    assert not install.satisfies(PythonSpec.from_text("3.14"))
+    assert install.satisfies(PythonSpec.from_text("3.14t"))
+
+    # Confirm a depot won't hand a freethreaded binary to a non-freethreaded spec
+    depot = PythonDepot(".pyenv/versions/**")
+    depot.invoker = None  # Don't let the running interpreter satisfy specs from outside the depot
+    assert depot.find_python("3.14").problem  # no non-freethreaded 3.14 available
+    found = depot.find_python("3.14t")
+    assert not found.problem
+    assert found.inspection.freethreading
+
+    # Confirm the invoker fallback also respects the freethreading boundary
+    mk_python("3.14.1", content={"version": "3.14.1", "machine": arch, "freethreading": False})
+    nft_path = runez.to_path(".pyenv/versions/3.14.1/bin/python3.14")
+    nft_install = PythonInstallation(nft_path)
+    assert not nft_install.inspection.freethreading
+
+    ft_depot = PythonDepot()  # no locations, only invoker
+    ft_depot.invoker = install  # freethreaded invoker
+    assert not ft_depot.find_python("3.14t").problem  # invoker satisfies 3.14t
+    assert ft_depot.find_python("3.14").problem  # invoker does NOT satisfy non-freethreaded 3.14
+
+    nft_depot = PythonDepot()
+    nft_depot.invoker = nft_install  # non-freethreaded invoker
+    assert not nft_depot.find_python("3.14").problem  # invoker satisfies 3.14
+    assert nft_depot.find_python("3.14t").problem  # invoker does NOT satisfy 3.14t
+
+
 def test_spec_equivalent():
     def check_equivalent_specs(*text):
         specs = [PythonSpec.from_text(x) for x in text]