feat(model_runner): remove pool/backend refs from ForwardBatch via ForwardContext (#25983)

Co-authored-by: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

test/registered/kernels/test_dsa_indexer.py

@@ -360,7 +360,6 @@ class TestDSAIndexer(CustomTestCase):
                 ),
                 extend_seq_lens=torch.tensor([q_len] * batch_size, device=self.device),
                 extend_seq_lens_cpu=torch.tensor([q_len] * batch_size, device="cpu"),
-                attn_backend=self.backend,
             )
         else:  # ForwardMode.DECODE
             decode_len = 1
@@ -379,12 +378,18 @@ class TestDSAIndexer(CustomTestCase):
                 req_pool_indices=torch.arange(batch_size, device=self.device),
                 seq_lens=torch.tensor([total_len] * batch_size, device=self.device),
                 seq_lens_cpu=torch.tensor([total_len] * batch_size, device="cpu"),
-                attn_backend=self.backend,
             )
 
-        # Add token pools
-        forward_batch.req_to_token_pool = self.model_runner.req_to_token_pool
-        forward_batch.token_to_kv_pool = self.model_runner.token_to_kv_pool
+        # Pool refs + attn_backend are now resolved via the ForwardContext;
+        # publish ``self.backend`` for the duration of this fixture call so
+        # ``get_attn_backend()`` / ``get_token_to_kv_pool()`` /
+        # ``get_req_to_token_pool()`` resolve correctly.
+        from sglang.srt.model_executor.forward_context import (
+            ForwardContext,
+            set_forward_context,
+        )
+
+        set_forward_context(ForwardContext(attn_backend=self.backend))
 
         # Mock write to req_to_token_pool
         page_size = self.model_runner.page_size