fix(python): report an unsatisfiable version floor instead of recursing

camoufox_path() ended in `return camoufox_path()` after a fetch. When the
newest published build is still below CONSTRAINTS.MIN_VERSION, install() is a
no-op ("already installed") and that tail recursed ~1000 times -- each
iteration firing another GitHub API call, which exhausts the unauthenticated
rate limit (60/hr) long before the RecursionError lands.

That is precisely the state a library published ahead of its browser release
puts every user in, and it is reachable now that the floor is raised. It also
hits permanently for anyone using a repos.yml source that does not carry the
required build.

Re-check after the fetch instead, and raise UnsupportedVersion naming the
required minimum.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

pythonlib/tests/test_version_floor_upgrade.py

@@ -95,3 +95,27 @@ def test_root_probe_tolerates_the_versioned_layout(tmp_path, monkeypatch):
     monkeypatch.setattr(pkgman, "INSTALL_DIR", root)
 
     assert pkgman._root_install_supported() is False
+
+
+def test_unsatisfiable_floor_reports_instead_of_recursing(tmp_path, monkeypatch):
+    """A floor no published build satisfies must report, not spin.
+
+    install() is a no-op when the newest release is already installed, so the
+    old `return camoufox_path()` tail recursed ~1000 times -- each iteration
+    firing another GitHub API call, which exhausts the unauthenticated rate
+    limit long before the RecursionError lands. That is the state a library
+    published ahead of its browser release puts every user in.
+    """
+    _install(tmp_path, monkeypatch, "versioned", build="beta.29", floor="beta.30")
+    attempts = []
+
+    class StubFetcher:
+        def install(self):
+            attempts.append(True)  # newest published build is still below the floor
+
+    monkeypatch.setattr(pkgman, "CamoufoxFetcher", StubFetcher)
+
+    with pytest.raises(UnsupportedVersion):
+        pkgman.camoufox_path()
+
+    assert attempts == [True], "should fetch once, not spin"