feat(P1-2): 预算三法并存落地 — 增量/零基/弹性均可应用

按任总观点: 三个方法都体现功能, 具体用哪个取决于用户场景
- 后端: POST /budget/apply-method 把所选方法结果写入预算计划(version标注方法)
  增量95.5万(上月×1.05) / 零基71.4万(成本砍半压缩) / 弹性58.7万(收入联动)
- 前端: 确认选择改为真正调用apply-method(原来只弹提示不落地)
- 场景提示: 增量=稳定快速编 / 零基=成本优化 / 弹性=收入波动大

backend/app/api/budget.py

@@ -1056,6 +1056,103 @@ def budget_method_comparison(data: dict):
     }
 
 
+@router.post("/apply-method")
+def apply_budget_method(
+    data: dict,
+    db: Session = Depends(get_db),
+    current_user=Depends(require_auth),
+):
+    """应用所选预算编制方法到预算计划（2026-08-26：三法并存，按用户场景选择后落地）
+    接收: { method: 'incremental'|'zero_based'|'flexible', year: 2026, entity: 'hanke', ... }
+    说明: 方法计算结果 → 写入/更新预算计划（version标注方法名，便于追溯）
+    """
+    method = data.get("method", "zero_based")
+    year = data.get("year", datetime.now().year)
+    entity = data.get("entity", "hanke")
+    entity_id = data.get("entity_id", 1)
+
+    # 复用method-comparison计算（获得三法结果）
+    comp = budget_method_comparison({
+        "entity": entity,
+        "last_month_budget": data.get("last_month_budget", 91),
+        "current_revenue": data.get("current_revenue", 122),
+        "fixed_costs": data.get("fixed_costs", {
+            "rent": 15, "labor": 40, "entertainment": 16, "misc": 12,
+        }),
+        "variable_cost_rate": data.get("variable_cost_rate", 0.4862),
+        "increment_rate": data.get("increment_rate", 0.05),
+    })
+
+    # 找所选方法的结果
+    selected = None
+    for m in comp["methods"]:
+        if m["id"] == method:
+            selected = m
+            break
+    if not selected:
+        raise HTTPException(400, "未知预算方法: " + method)
+
+    # 找到该年的核心KPI（营业收入/净利润/费用率等）
+    # 取该年已有预算的KPI，或默认核心4个
+    kpis = db.query(KPIDefinition).filter(
+        KPIDefinition.entity_id == entity_id,
+        KPIDefinition.status == "active",
+        KPIDefinition.kpi_code.in_(["F_REVENUE", "F_NET_PROFIT", "F_COST_RATIO", "F_GROSS_MARGIN"]),
+    ).all()
+    if not kpis:
+        raise HTTPException(400, "未找到可应用的KPI")
+
+    # 方法结果解释为收入预算（核心KPI应用）
+    # incremental/flexible/zero_based 的 result_value 均为"预算总额(万)"
+    # 写入F_REVENUE年度预算（period=YYYY-00 表示年度）
+    version = f"{method}-{datetime.now().strftime('%Y%m%d')}"
+    applied = []
+    for kpi in kpis:
+        period = f"{year}-00"
+        # 删除旧版本的同KPI年度预算
+        db.query(BudgetPlan).filter(
+            BudgetPlan.kpi_id == kpi.id,
+            BudgetPlan.period == period,
+            BudgetPlan.version.like(f"{method}-%"),
+        ).delete()
+
+        # 各KPI的应用值（简化：收入用方法结果，其他按比例）
+        if kpi.kpi_code == "F_REVENUE":
+            budget_val = selected["result_value"]
+        elif kpi.kpi_code == "F_NET_PROFIT":
+            budget_val = round(selected["result_value"] * 0.02, 1)  # 净利率约2%
+        elif kpi.kpi_code == "F_COST_RATIO":
+            budget_val = round(selected["result_value"] * 0.22, 1)  # 费用率约22%
+        else:  # F_GROSS_MARGIN
+            budget_val = round(selected["result_value"] * 0.18, 1)  # 毛利率约18%
+
+        bp = BudgetPlan(
+            entity_id=entity_id,
+            kpi_id=kpi.id,
+            period=period,
+            budget_value=budget_val,
+            budget_year=year,
+            budget_month=0,
+            version=version,
+            status="active",
+            remark=f"{selected['name']}应用({selected['result_value']}万) 来源{method}",
+        )
+        db.add(bp)
+        applied.append({"kpi_code": kpi.kpi_code, "budget_value": budget_val})
+
+    db.commit()
+    return {
+        "message": f"已应用「{selected['name']}」到预算计划",
+        "method": method,
+        "method_name": selected["name"],
+        "version": version,
+        "total_budget": selected["result_value"],
+        "detail": selected["detail"],
+        "applied": applied,
+        "note": "选择哪种方法取决于场景：增量=稳定业务快速编；零基=成本优化专项；弹性=收入波动大。方法结果写入年度预算(period=YYYY-00)，可在版本管理中查看。",
+    }
+
+
 # ============ 预算版本管理 API（2026-08-25 补充，修复前端"加载版本失败"） ============
 
 @router.get("/versions")

frontend/src/api/index.ts

@@ -178,6 +178,7 @@ export const budgetApi = {
   autoDecompose: (data: any) => api.post('/budget/auto-decompose', data),
   deviationReport: (params?: any) => api.get('/budget/deviation-report', { params }),
   methodComparison: (data: any) => api.post('/budget/method-comparison', data),
+  applyMethod: (data: any) => api.post('/budget/apply-method', data),
   // 版本管理
   versions: (params?: any) => api.get('/budget/versions', { params }),
   versionSubmit: (data: any) => api.post('/budget/versions/submit', data),

frontend/src/views/BudgetManagement.vue

@@ -669,10 +669,23 @@ async function refreshMethodComparison() {
   } catch { ElMessage.error('加载预算方法对比失败') }
 }
 
-function confirmMethod() {
+async function confirmMethod() {
   const m = selectedMethodDetail.value
-  if (m) {
-    ElMessage.success(`已选择「${m.name}」，预算结果：${m.result_value} 万`)
+  if (!m) return
+  try {
+    const r: any = await budgetApi.applyMethod({
+      method: m.id,
+      year: currentYear,
+      entity: 'hanke',
+      entity_id: getEntityId(),
+      last_month_budget: 91,
+      current_revenue: 122,
+    })
+    ElMessage.success(r.message || `已应用「${m.name}」`)
+    // 刷新预算列表
+    loadBudget()
+  } catch (e: any) {
+    ElMessage.error(e?.response?.data?.detail || e?.message || '应用失败')
   }
 }