fix(muh_dispatch): add verify_against_headers() to close the loop

Adds verification that hand-written values in muh_dispatch.py
(reduce_threads=512, reduce_items=16, etc.) match the C++ headers
(bi100_float32_plus_o4 in tuning_reduce.cuh).

Previously: muh_dispatch.py had hand-coded values with no link to
the C++ source of truth. gen_patch.py reads from C++ headers,
but muh_dispatch.py was a separate copy that could diverge.

Now: verify_against_headers() calls gen_patch.extract_bi100_structs()
and compares. Self-test prints mismatches if any exist.

muh_dispatch.py

@@ -224,6 +224,60 @@ def qwen36_config() -> AttentionConfig:
     )
 
 
+
+
+# ============================================================
+# Verification: check hand-written values match C++ headers
+# Closes the loop: muh_dispatch.py values must come from tuning_*.cuh
+# ============================================================
+
+def verify_against_headers(header_dir: str = "muh/include/muh/tuning") -> list:
+    """Verify that muh_dispatch.py's hand-written values match C++ headers.
+    
+    Returns list of mismatches. Empty list = all values verified.
+    This is the closed-loop check that prevents the gen_patch pipeline
+    from diverging from the runtime dispatch values.
+    """
+    mismatches = []
+    
+    try:
+        # Import from sibling module
+        sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+        from gen_patch import extract_bi100_structs
+    except ImportError:
+        return [("IMPORT_ERROR", "Cannot import gen_patch.extract_bi100_structs")]
+    
+    header_map = {
+        "tuning_reduce.cuh": {
+            "bi100_float32_plus_o4": {"items": 16, "threads": 512},  # must match reduce_items, reduce_threads
+        },
+    }
+    
+    reduce_header = os.path.join(header_dir, "tuning_reduce.cuh")
+    if os.path.exists(reduce_header):
+        structs = extract_bi100_structs(reduce_header)
+        for name, fields in structs:
+            if name == "bi100_float32_plus_o4":
+                cpp_threads = fields.get("threads", fields.get("threads_per_block"))
+                cpp_items = fields.get("items", fields.get("items_per_thread"))
+                
+                # Compare against AttentionConfig defaults
+                cfg = qwen36_config()
+                if cfg.reduce_threads != cpp_threads:
+                    mismatches.append((
+                        "reduce_threads",
+                        f"muh_dispatch={cfg.reduce_threads} vs tuning_reduce.cuh={cpp_threads}"
+                    ))
+                if cfg.reduce_items != cpp_items:
+                    mismatches.append((
+                        "reduce_items",
+                        f"muh_dispatch={cfg.reduce_items} vs tuning_reduce.cuh={cpp_items}"
+                    ))
+    else:
+        mismatches.append(("HEADER_MISSING", reduce_header))
+    
+    return mismatches
+
 # ============================================================
 # Self-test
 # ============================================================
@@ -246,3 +300,13 @@ if __name__ == "__main__":
         print(f"    decode: partition={cfg.partition_size} v1_thresh={cfg.v1_v2_threshold}")
         print(f"    reduce: threads={cfg.reduce_threads} items={cfg.reduce_items} vec={cfg.vec_size}")
         print()
+    # Verification: check values match C++ headers
+    print("\n=== Verification against C++ headers ===")
+    mismatches = verify_against_headers()
+    if mismatches:
+        for field, msg in mismatches:
+            print(f"  ✗ MISMATCH {field}: {msg}")
+        print(f"\n  {len(mismatches)} mismatches found — update muh_dispatch.py!")
+    else:
+        print("  ✓ All hand-written values match C++ headers")
+