[2/N][Mixed] Mixed chunk prefill with spec enabled (#36933)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

test/registered/unit/spec/test_decode_bookkeeping_ownership.py

@@ -78,6 +78,13 @@ _OWNER_SITES = {
     ): 1,
     (*_RESOLVE, "kv_committed_len"): 1,
     (*_RESOLVE, "spec_verify_ct"): 1,
+    # Mixed-chunk spec tails: the mixed prefill step commits the pending
+    # bonus token, advancing the watermark by exactly that one token.
+    (
+        "managers/scheduler_components/batch_result_processor.py",
+        "SchedulerBatchResultProcessor.process_batch_result_prefill",
+        "kv_committed_len",
+    ): 1,
     # disaggregation decode prealloc: kv_allocated_len is settled inside the
     # owned-kv alloc_for_decode_prealloc(_hisparse) functions (op42).
     (