fix: add legacy /app/config.json fallback for container upgrades

docs/DEPLOY.en.md

@@ -131,6 +131,7 @@ docker-compose logs -f
 
 The default `docker-compose.yml` directly uses `ghcr.io/cjackhwang/ds2api:latest` and maps host port `6011` to container port `5001`. If you want `5001` exposed directly, set `DS2API_HOST_PORT=5001` (or adjust the `ports` mapping).
 The compose template also defaults to `DS2API_CONFIG_PATH=/data/config.json` with `./config.json:/data/config.json` mounted, so deployments avoid read-only `/app` persistence issues by default.
+Compatibility note: when `DS2API_CONFIG_PATH` is unset and runtime base dir is `/app`, newer versions prefer `/data/config.json`; if that file is missing but legacy `/app/config.json` exists, DS2API automatically falls back to the legacy path to avoid post-upgrade config loss.
 
 If you want a pinned version instead of `latest`, you can also pull a specific tag directly:
 

docs/DEPLOY.md

@@ -131,6 +131,7 @@ docker-compose logs -f
 
 默认 `docker-compose.yml` 直接使用 `ghcr.io/cjackhwang/ds2api:latest`，并把宿主机 `6011` 映射到容器内的 `5001`。如果你希望直接对外暴露 `5001`，请设置 `DS2API_HOST_PORT=5001`（或者手动调整 `ports` 配置）。
 Compose 模板还会默认设置 `DS2API_CONFIG_PATH=/data/config.json` 并挂载 `./config.json:/data/config.json`，优先避免 `/app` 只读带来的配置持久化问题。
+兼容说明：若未设置 `DS2API_CONFIG_PATH` 且运行目录是 `/app`，新版本会优先使用 `/data/config.json`；当该文件不存在但检测到历史 `/app/config.json` 时，会自动回退读取旧路径，避免升级后“配置丢失”。
 
 如需固定版本，也可以直接拉取指定 tag：
 

internal/config/paths.go

@@ -38,6 +38,14 @@ func ConfigPath() string {
 	return ResolvePath("DS2API_CONFIG_PATH", "config.json")
 }
 
+func legacyContainerConfigPath() string {
+	return "/app/config.json"
+}
+
+func shouldTryLegacyContainerConfigPath() bool {
+	return strings.TrimSpace(os.Getenv("DS2API_CONFIG_PATH")) == "" && BaseDir() == "/app"
+}
+
 func RawStreamSampleRoot() string {
 	return ResolvePath("DS2API_RAW_STREAM_SAMPLE_ROOT", "tests/raw_stream_samples")
 }

internal/config/store.go

@@ -87,12 +87,17 @@ func loadConfig() (Config, bool, error) {
 		}
 		return cfg, true, err
 	}
-
 	cfg, err := loadConfigFromFile(ConfigPath())
 	if err != nil {
+		if shouldTryLegacyContainerConfigPath() {
+			legacyPath := legacyContainerConfigPath()
+			if legacyCfg, legacyErr := loadConfigFromFile(legacyPath); legacyErr == nil {
+				Logger.Info("[config] loaded legacy container config path", "path", legacyPath)
+				return legacyCfg, false, nil
+			}
+		}
 		if IsVercel() {
-			// Vercel one-click deploy may start without a writable/present config file.
-			// Keep an in-memory config so users can bootstrap via WebUI then sync env.
+			// Vercel may start without writable/present config; keep in-memory bootstrap config.
 			return Config{}, true, nil
 		}
 		return Config{}, false, err