新增 HHD 场加权标定模型与加权空载基线

field_gain/1 用坐标增益图对无旋向量场做 L1 场加权，以连续 30 帧加权中位数替代旧 raw 零点，实时入口暂不支持。目标测试 102 项与 lint_gate 通过；契约见 orisys-sdk/docs/field-gain-model.zh.md。

src/orisys/calibration_context.py

@@ -53,8 +53,13 @@ def domain_fingerprint(domain) -> str:
 
 def build_context(config, filters=None, *, geometry_sha256=None, source_scale=None,
                   coordinates=None, output_domain_sha256=None, processing_backend=None,
-                  preprocessing=None) -> dict:
-    """Build the closed v1 feature identity from effective values, excluding readout filters."""
+                  preprocessing=None, field=None) -> dict:
+    """Build the closed v1 feature identity from effective values, excluding readout filters.
+
+    ``field`` carries the closed profile identity for field models (shape, dtype,
+    unit, mask and lifecycle). It is omitted for scalar profiles so their
+    signatures stay byte-identical to previously exported files.
+    """
     camera = config.get("camera", {})
     tracker = dict(config.get("tracker", {}))
     raw_downsample = tracker.get("hhd_downsample", 1)
@@ -94,5 +99,8 @@ def build_context(config, filters=None, *, geometry_sha256=None, source_scale=No
         "source_scale": source_scale,
         "preprocessing": preprocessing or {},
     }
+    if field is not None:
+        result["field"] = deepcopy(field)
+        effective["field"] = deepcopy(field)
     result["feature_signature_sha256"] = _feature_signature(effective)
     return CalibrationContext(result, effective)