fix(mcp-profile-gateway): support inline JSON in MCP_PROFILE_GATEWAY_CONFIG

LoadPipelineConfig treated the env var value as a file path in all cases,
so e2e tests passing inline JSON triggered os.Stat on the JSON string,
causing "no such file or directory" and leaving the filter factory
unregistered. Detect values that start with '{' and parse them directly
via NewStaticConfig, falling back to the file-based pipeline for paths.

Author: dio

examples/mcp-profile-gateway/gateway.go

@@ -114,14 +114,22 @@ func decodeConfig(data []byte) (Config, error) {
 	return cfg, nil
 }
 
-// LoadPipelineConfig returns a PipelineConfig backed by the file path in
-// MCP_PROFILE_GATEWAY_CONFIG. Call RefreshOnce before reading Snapshot().
+// LoadPipelineConfig returns a PipelineConfig backed by MCP_PROFILE_GATEWAY_CONFIG.
+// If the value starts with '{' it is parsed as inline JSON; otherwise it is
+// treated as a file path and read via a cached file source.
 func LoadPipelineConfig() (*up.PipelineConfig[Config], error) {
-	path := strings.TrimSpace(os.Getenv(ConfigEnv))
-	if path == "" {
+	raw := strings.TrimSpace(os.Getenv(ConfigEnv))
+	if raw == "" {
 		return nil, fmt.Errorf("%s is required", ConfigEnv)
 	}
-	pc := up.NewFileConfig[Config](path, decodeConfig, up.PollOptions{})
+	if strings.HasPrefix(raw, "{") {
+		cfg, err := decodeConfig([]byte(raw))
+		if err != nil {
+			return nil, err
+		}
+		return up.NewStaticConfig(cfg), nil
+	}
+	pc := up.NewFileConfig[Config](raw, decodeConfig, up.PollOptions{})
 	if err := pc.RefreshOnce(context.Background()); err != nil {
 		return nil, err
 	}