Add Qwen3.5-397B INT4-AutoRound TP=4 recipe and Marlin fix

Production-tested recipe for running Qwen3.5-397B-A17B with INT4 AutoRound
quantization across 4 DGX Spark nodes using tensor parallelism.

Performance (4× DGX Spark, driver 580.126.09):
- Single user: 37 tok/s
- 4 concurrent: ~26 tok/s per user, ~103 tok/s aggregate

The Marlin TP fix resolves the MIN_THREAD_N=64 constraint that breaks
in_proj_ba layers at TP=4 (output_size=128/4=32 < 64). Solution:
ReplicatedLinear for B/A projections, applied via diff patches.

Key config:
- VLLM_MARLIN_USE_ATOMIC_ADD=1 (required for Marlin correctness)
- KV cache FP8, prefix caching enabled
- gpu_memory_utilization 0.78 (UMA safe margin)
- CUDAGraphs enabled (default, requires driver 580.x)

Note: Driver 590.x has CUDAGraph capture deadlock on GB10 unified memory.
Stay on driver 580.126.09.

mods/fix-qwen35-tp4-marlin/qwen3_5.patch

@@ -0,0 +1,46 @@
+--- qwen3_5.py.orig	2026-03-03 00:00:00.000000000 +0000
++++ qwen3_5.py	2026-03-03 00:00:00.000000000 +0000
+@@ -166,11 +166,13 @@
+         z_size = self.value_dim // self.tp_size
+         mixed_qkv, z = mixed_qkvz.split([qkv_size, z_size], dim=-1)
+         z = z.reshape(z.size(0), -1, self.head_v_dim)
+-        ba, _ = self.in_proj_ba(hidden_states)
+-        b, a = ba.chunk(2, dim=-1)
+-
+-        b = b.contiguous()
+-        a = a.contiguous()
++        # Replicated B/A projections — full output, sliced to local TP partition
++        b_full, _ = self.in_proj_b(hidden_states)
++        a_full, _ = self.in_proj_a(hidden_states)
++        _ba_chunk = self.num_v_heads // self.tp_size
++        _ba_start = self.tp_rank * _ba_chunk
++        b = b_full[:, _ba_start:_ba_start+_ba_chunk].contiguous()
++        a = a_full[:, _ba_start:_ba_start+_ba_chunk].contiguous()
+
+         # ============================================================
+         # Part 2: Core Attention (Custom Op)
+@@ -374,8 +376,6 @@
+             # GDN
+             ("in_proj_qkvz", "in_proj_qkv", (0, 1, 2)),
+             ("in_proj_qkvz", "in_proj_z", 3),
+-            ("in_proj_ba", "in_proj_b", 0),
+-            ("in_proj_ba", "in_proj_a", 1),
+         ]
+
+         params_dict = dict(self.named_parameters())
+@@ -530,7 +530,6 @@
+         "gate_up_proj": ["gate_proj", "up_proj"],
+         # GDN fused projections.
+         "in_proj_qkvz": ["in_proj_qkv", "in_proj_z"],
+-        "in_proj_ba": ["in_proj_b", "in_proj_a"],
+     }
+
+     def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
+@@ -630,7 +629,6 @@
+ class Qwen3_5ForConditionalGeneration(Qwen3VLForConditionalGeneration, IsHybrid):
+     packed_modules_mapping = Qwen3VLForConditionalGeneration.packed_modules_mapping | {
+         "in_proj_qkvz": ["in_proj_qkv", "in_proj_z"],
+-        "in_proj_ba": ["in_proj_b", "in_proj_a"],
+     }
+
+     def __init__(self, *, vllm_config: VllmConfig, prefix: str = "model"):