Harden the affinity wiring per opus review (F-1, F-2)

- A chunked-led batch now seeds affinity_batch_warm_led from the CHUNK's
  class instead of the first loop candidate: a 65536 first chunk is
  cold-led (later colds are free density, caps bound them); latching
  from a warm follower inverted cold-led-admits-everything and could
  spuriously STOP the scan, under-filling the forward.
- The policy additionally requires no LoRA and no L3 hicache-storage:
  their pre-classification continues make "first classified candidate"
  drift from the true FCFS head, mis-routing the defer accounting.

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

python/sglang/srt/managers/scheduler.py

@@ -2572,12 +2572,29 @@ class Scheduler(
         affinity_on = (
             envs.SGLANG_CP_PREFILL_AFFINITY_GROUP.get()
             and not self.enable_priority_scheduling
+            # The pre-classification continues (LoRA compatibility, L3
+            # prefetch pending) would make "first classified candidate" drift
+            # from the true FCFS head and mis-route the defer accounting —
+            # the policy is only exact (and only validated) without them.
+            and not self.enable_lora
+            and not self.enable_hicache_storage
             and self.server_args.enable_cp_shared_kv_prefill_bs_gt1
             and is_nsa_prefill_cp_in_seq_split()
         )
         affinity_window_used = 0
         affinity_head_pending = True  # first classified candidate = FCFS head
         affinity_batch_warm_led: Optional[bool] = None
+        if affinity_on and adder._chunked_req_in_batch is not None:
+            # A chunked-led batch must carry the CHUNK's class: a 65536 first
+            # chunk is cold-led (further colds are free density and the caps
+            # bound them); a tail chunk over a big cached prefix is warm-led.
+            # Latching from the first loop candidate instead would invert
+            # cold-led-admits-everything and spuriously STOP the scan.
+            chunked = adder._chunked_req_in_batch
+            affinity_batch_warm_led = (
+                len(chunked.prefix_indices)
+                + int(getattr(chunked, "host_hit_length", 0) or 0)
+            ) >= int(envs.SGLANG_CP_PREFILL_AFFINITY_WARM_FLOOR.get())
 
         for req in self.waiting_queue:
             if self.enable_lora and req.lora_id not in running_loras:
@@ -2642,6 +2659,9 @@ class Scheduler(
                         - (1 if adder._chunked_req_in_batch is not None else 0)
                         == 0
                     ),
+                    # None = nothing admitted yet; only reachable together
+                    # with batch_empty_for_affinity=True (which decides
+                    # first), so False is never read as a real class here.
                     batch_warm_led=bool(affinity_batch_warm_led),
                     is_head=is_head,
                     head_defer_count=req.affinity_defer_count,