test(e2e): let the cache-rebuild gate run on reasoning checkpoints

tests/e2e/test_cache_rebuild.py

@@ -90,8 +90,16 @@ def _wait_until_serving(base: str, proc: subprocess.Popen, deadline: float) -> N
     raise TimeoutError("server never reached the serving state")
 
 
-def _generate(base: str) -> str:
-    """A short non-thinking completion — the point is that the engine still runs, not what it says."""
+def _generate(base: str) -> int:
+    """Tokens the engine decoded -- the point is that it still runs, not what it says.
+
+    Counts rather than reads the reply. Which field the text lands in depends on the
+    checkpoint: ``enable_thinking`` is read by the qwen/glm/gemma/dsv4 templates and is
+    inert for gpt-oss, whose Harmony channels are not gated by it, so its trace goes to
+    ``reasoning_content`` and ``content`` can be empty on a perfectly healthy engine.
+    ``usage.completion_tokens`` is accumulated from the scheduler's own acks, upstream of
+    every reasoning parser, so it says decode ran without depending on any of that.
+    """
     code, body = _post(
         base,
         "/v1/chat/completions",
@@ -104,7 +112,7 @@ def _generate(base: str) -> str:
         },
     )
     assert code == 200, body
-    return str(body["choices"][0]["message"]["content"])
+    return int(body["usage"]["completion_tokens"])
 
 
 @pytest.mark.skipif(not torch.cuda.is_available(), reason="cache rebuild e2e needs CUDA")
@@ -142,7 +150,7 @@ def test_cache_rebuild_resizes_a_live_engine_and_keeps_serving(tmp_path):
 
         geometry = _get(base, "/v1/cache/status")["geometry"]
         assert geometry["num_pages"] == BOOT_PAGES
-        assert _generate(base)  # a baseline generation, before anything is torn down
+        assert _generate(base) > 0  # a baseline generation, before anything is torn down
 
         # 1. Grow the KV pool. The reply carries the geometry the engine actually landed on.
         code, reply = _post(base, "/v1/cache/rebuild", {"num_pages": GROWN_PAGES})
@@ -153,7 +161,7 @@ def test_cache_rebuild_resizes_a_live_engine_and_keeps_serving(tmp_path):
         assert status["geometry"]["num_pages"] == GROWN_PAGES
         assert status["last_rebuild"]["status"] == "ok"
         # Graphs were re-captured against the new pool: decoding still works.
-        assert _generate(base)
+        assert _generate(base) > 0
 
         # 2. The second axis, if this checkpoint has a GDN state pool. Resizing it moves a
         #    different pool through the same teardown/re-capture path.
@@ -166,7 +174,7 @@ def test_cache_rebuild_resizes_a_live_engine_and_keeps_serving(tmp_path):
             assert geometry["num_mamba_slots"] == grown_slots
             # A pool-only resize must not disturb the pool the previous rebuild grew.
             assert geometry["num_pages"] == GROWN_PAGES
-            assert _generate(base)
+            assert _generate(base) > 0
 
         # 3. An unfittable target is rejected BEFORE anything is freed, and the engine that was
         #    serving a moment ago keeps serving on its old cache.
@@ -177,7 +185,7 @@ def test_cache_rebuild_resizes_a_live_engine_and_keeps_serving(tmp_path):
         status = _get(base, "/v1/cache/status")
         assert status["state"] == "serving"
         assert status["geometry"]["num_pages"] == GROWN_PAGES  # untouched by the rejection
-        assert _generate(base)
+        assert _generate(base) > 0
     finally:
         proc.terminate()
         try: