Fix flaky decode cache-hit check in Inkling test (#34405)

test/registered/models_e2e/test_inkling_small_nvfp4.py

@@ -58,6 +58,12 @@ KL_DIV_THRESHOLD = 1e-9
 # checkpoint or a mis-restored prefix would surface.
 KL_MAX_NEW_TOKENS = 1024
 
+# Equal to the page size below. Out-of-window SWA slots are freed a page at a
+# time, so only a checkpoint sitting on a page boundary still has a full window
+# of SWA data below it -- at the default 256 half the sequence lengths land off
+# that boundary and lose their decode prefix entirely.
+KL_TRACK_INTERVAL = 128
+
 
 class TestInklingSmallNvfp4(CustomTestCase):
     @classmethod
@@ -162,6 +168,8 @@ class TestInklingSmallNvfp4Deterministic(CustomTestCase):
                 "0.1",
                 "--mem-fraction-static",
                 "0.85",
+                "--mamba-track-interval",
+                str(KL_TRACK_INTERVAL),
                 "--enable-deterministic-inference",
             ],
             env={**os.environ, "SGLANG_ENABLE_UNIFIED_RADIX_TREE": "1"},
@@ -172,7 +180,7 @@ class TestInklingSmallNvfp4Deterministic(CustomTestCase):
         if getattr(cls, "process", None) is not None:
             kill_process_tree(cls.process.pid)
 
-    def _run(self, helper):
+    def _run(self, helper, **kwargs):
         helper(
             self.base_url,
             {self.model: {"kl_div": KL_DIV_THRESHOLD}},
@@ -180,6 +188,7 @@ class TestInklingSmallNvfp4Deterministic(CustomTestCase):
             max_samples=32,
             max_new_tokens=KL_MAX_NEW_TOKENS,
             trust_remote_code=True,
+            **kwargs,
         )
 
     def test_input_output_logprobs_match(self):
@@ -189,7 +198,9 @@ class TestInklingSmallNvfp4Deterministic(CustomTestCase):
         self._run(assert_logprobs_match_prefill_cache_hit)
 
     def test_input_output_logprobs_match_decode_cache_hit(self):
-        self._run(assert_logprobs_match_decode_cache_hit)
+        # 0.99 is every prompt: the interval above makes the reuse unconditional, so
+        # a single miss is a state-reuse regression rather than a geometry coincidence.
+        self._run(assert_logprobs_match_decode_cache_hit, min_cache_hit_ratio=0.99)
 
 
 if __name__ == "__main__":