feat: 短期多轮历史接入 Eino 图 MessagesPlaceholder (⑨)

会话历史(Redis,易失,与长期画像分开)经 MCP 工具进出 Eino 图：
recall 召回历史填 MessagesPlaceholder，写回把本轮 user/assistant 落历史。

- mcp-go: internal/history(go-redis, sundynix:history:<session>, LPUSH+LTRIM 保留近20条,
  24h TTL) + 工具 history_get(返回JSON turns)/history_append; main 开 Redis(降级)
- dispatcher Eino: 模板加 MessagesPlaceholder('history'); recall 调 history_get→转 schema.Message;
  Handle 累积 answer; memorize 异步 history_append(user+assistant)
- shared: contract.MetaSessionID; gateway: SubmitTask 注入 Meta[session_id](X-Session-ID 头,缺省 default)
- demo.sh: 同会话两轮提交，验证第2轮召回第1轮历史
- 验证: 4 模块 build✓ + 3 e2e PASS; live 跑通——轮1=0轮历史→落库, 轮2 history_get 命中→注入

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sundynix-mcp-go/cmd/server/main.go

@@ -10,6 +10,7 @@ import (
 
 	sharedbus "github.com/sundynix/sundynix-shared/bus"
 
+	"github.com/sundynix/sundynix-mcp-go/internal/history"
 	"github.com/sundynix/sundynix-mcp-go/internal/mcp"
 	"github.com/sundynix/sundynix-mcp-go/internal/memory"
 	"github.com/sundynix/sundynix-mcp-go/internal/search"
@@ -18,6 +19,7 @@ import (
 func main() {
 	natsURL := envOr("NATS_URL", "nats://localhost:4222")
 	pgDSN := envOr("POSTGRES_DSN", "postgres://sundynix:sundynix@localhost:5432/sundynix?sslmode=disable")
+	redisAddr := envOr("REDIS_ADDR", "localhost:6379")
 
 	b, err := sharedbus.Connect(natsURL)
 	if err != nil {
@@ -27,9 +29,11 @@ func main() {
 	log.Printf("[mcp_go] connected %s", natsURL)
 
 	engine := search.NewHybrid() // LLM Wiki 混合检索：Bleve + Milvus + Neo4j
-	mem := memory.Open(pgDSN)    // 偏好记忆：sundynix_user_profile（连不上则降级）
+	mem := memory.Open(pgDSN) // 偏好记忆：sundynix_user_profile（连不上则降级）
 	defer mem.Close()
-	gw := mcp.NewGateway(b, engine, mem)
+	hist := history.Open(redisAddr) // 会话短期历史：Redis（连不上则降级）
+	defer hist.Close()
+	gw := mcp.NewGateway(b, engine, mem, hist)
 
 	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
 	defer stop()