chore: 恢复旧布局基线（迁移改动丢失后重建，apps/packages 布局暂存）

server/internal/ai/stub.go

@@ -0,0 +1,93 @@
+package ai
+
+import (
+	"context"
+	"fmt"
+	"strings"
+)
+
+// stubProvider 离线占位实现:未配置真实模型时的兜底,内容为字符串模板。
+type stubProvider struct{}
+
+func (stubProvider) Name() string { return "stub" }
+
+func (stubProvider) Complete(_ context.Context, req ChatReq) (ChatRes, error) {
+	return chatStub(req), nil
+}
+
+func chatStub(req ChatReq) ChatRes {
+	driver := req.Driver
+	if driver == "" {
+		driver = "mysql"
+	}
+	db := req.Database
+	if db == "" {
+		db = "your_db"
+	}
+	sql := strings.TrimSpace(req.SQL)
+	prompt := strings.TrimSpace(req.Prompt)
+
+	switch strings.ToLower(req.Action) {
+	case "generate", "ask":
+		q := prompt
+		if q == "" {
+			q = "示例查询"
+		}
+		gen := fmt.Sprintf("-- 根据描述生成（%s / %s）\n-- 需求: %s\nSELECT *\nFROM `%s`.some_table\nWHERE 1=1\nLIMIT 100;", driver, db, q, db)
+		return ChatRes{
+			Content: fmt.Sprintf("已根据「%s」生成 SQL（stub，可替换为真实模型）。\n\n```sql\n%s\n```", q, gen),
+			SQL:     gen,
+		}
+	case "explain":
+		if sql == "" {
+			sql = "SELECT 1"
+		}
+		return ChatRes{Content: fmt.Sprintf("## 解释 SQL\n\n```sql\n%s\n```\n\n- 这是一条在 **%s** 上执行的查询。\n- 建议检查 WHERE 条件是否走索引，避免 `SELECT *` 拉取过大结果集。\n- （stub 回复）", sql, driver)}
+	case "optimize":
+		opt := sql
+		if opt == "" {
+			opt = "SELECT id, name FROM users WHERE status = 1 LIMIT 100;"
+		} else if strings.Contains(strings.ToUpper(opt), "SELECT *") {
+			opt = strings.Replace(opt, "*", "id /* TODO: 显式列 */", 1)
+		}
+		opt = strings.TrimSpace(opt)
+		if !strings.Contains(strings.ToUpper(opt), "LIMIT") {
+			opt = opt + "\nLIMIT 100;"
+		}
+		return ChatRes{
+			Content: fmt.Sprintf("## 优化建议\n\n1. 避免不必要的全表扫描\n2. 显式列出列名\n3. 加合理 LIMIT\n\n```sql\n%s\n```", opt),
+			SQL:     opt,
+		}
+	case "fix":
+		fixed := sql
+		if fixed == "" {
+			fixed = "SELECT 1 AS ok;"
+		}
+		msg := req.Error
+		if msg == "" {
+			msg = "未知错误"
+		}
+		return ChatRes{
+			Content: fmt.Sprintf("## 修复错误\n\n原错误：`%s`\n\n尝试修正后的 SQL：\n\n```sql\n%s\n```\n\n（stub：请结合真实报错继续调整）", msg, fixed),
+			SQL:     fixed,
+		}
+	case "dialect":
+		out := sql
+		if out == "" {
+			out = "SELECT * FROM dual"
+		}
+		out = strings.ReplaceAll(out, "`", "\"")
+		return ChatRes{
+			Content: fmt.Sprintf("## 方言转换 → PostgreSQL 风格（示例）\n\n```sql\n%s\n```", out),
+			SQL:     out,
+		}
+	case "sample":
+		sample := fmt.Sprintf("SELECT id, name, created_at\nFROM `%s`.users\nORDER BY id DESC\nLIMIT 20;", db)
+		return ChatRes{
+			Content: fmt.Sprintf("## 样例 SQL（%s）\n\n```sql\n%s\n```", driver, sample),
+			SQL:     sample,
+		}
+	default:
+		return ChatRes{Content: "未知 AI 动作。可用：ask / generate / explain / optimize / fix / dialect / sample"}
+	}
+}