feat: jev 接入，判断创建、修改、问答、不明确四类意图

app/schemas/requirement.py

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+"""需求理解的输出协议，描述用户诉求，不包含前端执行动作。"""
+
+from typing import Literal, Self
+
+from pydantic import Field, model_validator
+
+from .base import ExtensibleModel, JsonObject, NonBlankString
+
+Intent = Literal["create_screen", "modify_screen", "qa", "unclear"]
+TargetScope = Literal["nodes", "canvas", "screen", "unresolved"]
+
+
+class RequirementChange(ExtensibleModel):
+    """一项需求变更。目标范围显式声明，避免空 ID 被理解成修改整个大屏。"""
+
+    target_scope: TargetScope = Field(
+        description="nodes=已有节点；canvas=画布属性；screen=整体或新增内容；unresolved=目标待确认"
+    )
+    target_ids: list[NonBlankString] = Field(
+        default_factory=list, description="已有节点的 ID；新增组件不能虚构 ID"
+    )
+    target_description: NonBlankString | None = Field(
+        default=None, description="目标的自然语言描述，例如右侧区域、用户所说的那个图"
+    )
+    operation: NonBlankString = Field(
+        description="需求操作，例如 move、resize、add、delete、restyle；允许后续扩展"
+    )
+    parameters: JsonObject = Field(
+        default_factory=dict,
+        description="需求参数，例如 delta_x=50；保留用户要求的单位与相对变化语义",
+    )
+
+    @model_validator(mode="after")
+    def validate_target(self) -> Self:
+        if len(self.target_ids) != len(set(self.target_ids)):
+            raise ValueError("target_ids 不能包含重复 ID")
+        if self.target_scope == "nodes":
+            if not self.target_ids:
+                raise ValueError("nodes 范围必须提供 target_ids")
+        elif self.target_ids:
+            raise ValueError("只有 nodes 范围可以提供 target_ids")
+        if self.target_scope == "unresolved" and self.target_description is None:
+            raise ValueError("目标待确认时必须提供 target_description")
+        return self
+
+
+class Requirement(ExtensibleModel):
+    intent: Intent
+    goal: NonBlankString = Field(description="忠实概括用户目标，不能擅自扩大修改范围")
+    changes: list[RequirementChange] = Field(default_factory=list)
+    needs_clarification: bool
+    clarification_question: NonBlankString | None = None
+    needs_planning: bool = Field(description="是否需要布局或设计规划，与修改范围分别判断")
+    needs_resources: bool = Field(description="是否需要补充查询组件、数据、模板或素材")
+    assumptions: list[NonBlankString] = Field(
+        default_factory=list, description="非阻塞信息采用的默认假设，不可用来猜测删除目标"
+    )
+    constraints: list[NonBlankString] = Field(
+        default_factory=list, description="用户明确提出的约束，例如只修改右侧、保留其他组件"
+    )
+
+    @model_validator(mode="after")
+    def validate_consistency(self) -> Self:
+        if self.needs_clarification != (self.clarification_question is not None):
+            raise ValueError("需要澄清时必须提供问题，不需要澄清时问题应为 null")
+        if self.intent == "unclear" and not self.needs_clarification:
+            raise ValueError("意图不明确时必须澄清")
+        if any(change.target_scope == "unresolved" for change in self.changes):
+            if not self.needs_clarification:
+                raise ValueError("存在待确认目标时必须澄清")
+        if self.intent == "qa" and self.changes:
+            raise ValueError("纯问答需求不应包含大屏变更")
+        return self