Add gumbel/learn_centers/learn_width/learn_temperature to out-dir naming

Extends default_out_dir_name's non-default-field convention to the
router's new gumbel combine-weight flag and its learnable-knob toggles,
so gumbel sweep configs (learn_centers on/off, learn_width,
learn_temperature) resolve to distinguishable checkpoint directory
names instead of colliding on the same r-<type><n> token.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_config.py

@@ -207,6 +207,64 @@ def test_default_out_dir_name_router_disabled_omitted_even_if_subfields_nondefau
     assert gconfig.default_out_dir_name(cfg, now=_NOW) == "20260729_1430"
 
 
+def test_default_out_dir_name_router_gumbel_shown_when_enabled():
+    cfg = _default_cfg(
+        router={"enabled": True, "type": "energy", "n_experts": 8, "gumbel": True}
+    )
+    assert gconfig.default_out_dir_name(cfg, now=_NOW) == "20260729_1430_r-energy8_gum"
+
+
+def test_default_out_dir_name_router_gumbel_omitted_when_router_disabled():
+    cfg = _default_cfg(
+        router={"enabled": False, "type": "energy", "n_experts": 8, "gumbel": True}
+    )
+    assert gconfig.default_out_dir_name(cfg, now=_NOW) == "20260729_1430"
+
+
+def test_default_out_dir_name_router_learn_centers_shown_only_when_disabled():
+    cfg_default = _default_cfg(
+        router={"enabled": True, "type": "energy", "n_experts": 8}
+    )
+    assert (
+        gconfig.default_out_dir_name(cfg_default, now=_NOW) == "20260729_1430_r-energy8"
+    )
+
+    cfg_off = _default_cfg(
+        router={
+            "enabled": True,
+            "type": "energy",
+            "n_experts": 8,
+            "learn_centers": False,
+        }
+    )
+    assert (
+        gconfig.default_out_dir_name(cfg_off, now=_NOW)
+        == "20260729_1430_r-energy8_nolc"
+    )
+
+
+def test_default_out_dir_name_router_learn_width_and_temperature_shown():
+    cfg = _default_cfg(
+        router={
+            "enabled": True,
+            "type": "energy",
+            "n_experts": 8,
+            "learn_width": True,
+        }
+    )
+    assert gconfig.default_out_dir_name(cfg, now=_NOW) == "20260729_1430_r-energy8_lw"
+
+    cfg2 = _default_cfg(
+        router={
+            "enabled": True,
+            "type": "energy",
+            "n_experts": 8,
+            "learn_temperature": True,
+        }
+    )
+    assert gconfig.default_out_dir_name(cfg2, now=_NOW) == "20260729_1430_r-energy8_lt"
+
+
 def test_default_out_dir_name_mode_shown_bare_no_prefix():
     cfg = _default_cfg(mode="wgan")
     assert gconfig.default_out_dir_name(cfg, now=_NOW) == "20260729_1430_wgan"