Expose CP shared-KV allocation fallback as a warning

The compute-owner allocation path is an intended hot path for CP shared KV. Falling back to legacy page allocation changes the behavior profile enough that INFO/no-marker logging is too easy to miss during profiling.

This makes the fallback warning-visible and gives it the standard CP shared-KV fallback marker while preserving the existing behavior of logging every fallback event.

Constraint: Production fallbacks from intended CP shared-KV hot paths must be visible and grep-able.

Rejected: Keep INFO logging | historical silent or low-visibility fallbacks hid inactive optimized paths.

Confidence: medium

Scope-risk: narrow

Directive: Keep fallback logs warning-level unless the path is proven to be expected steady state and separately observable.

Tested: Local py_compile for common.py and test_cp_shared_kv_layout.py.

Tested: Local extracted assertLogs check for _log_cp_shared_kv_alloc_fallback warning prefix and reason formatting.

Tested: Remote g0034 py_compile for common.py and test_cp_shared_kv_layout.py.

Not-tested: Full remote pytest for test_cp_shared_kv_layout.py; current g0034 container aborts while importing installed sgl_kernel common_ops before test execution.

Co-authored-by: OmX <omx@oh-my-codex.dev>

python/sglang/srt/mem_cache/common.py

@@ -58,8 +58,8 @@ def _log_cp_shared_kv_alloc_fallback(
     message: str,
     *args,
 ) -> None:
-    logger.info(
-        "CP shared KV compute-owner allocation fallback (%s): " + message,
+    logger.warning(
+        "[CP_SHARED_KV_FALLBACK][compute_owner_alloc] reason=%s " + message,
         reason,
         *args,
     )