Add improvements 2

gateway/README.md

@@ -352,6 +352,25 @@ headers = {
 - **Caching**: Gateway caches validated service tokens for 5 minutes
 - **No Additional HTTP Calls**: Service auth happens locally at gateway
 
+### Unified Header Management System
+
+The gateway uses a **centralized HeaderManager** for consistent header handling across all middleware and proxy layers.
+
+**Key Features:**
+- Standardized header names and conventions
+- Automatic header sanitization to prevent spoofing
+- Unified header injection and forwarding
+- Cross-middleware header access via `request.state.injected_headers`
+- Consistent logging and error handling
+
+**Standard Headers:**
+- `x-user-id`, `x-user-email`, `x-user-role`, `x-user-type`
+- `x-service-name`, `x-tenant-id`
+- `x-subscription-tier`, `x-subscription-status`
+- `x-is-demo`, `x-demo-session-id`, `x-demo-account-type`
+- `x-tenant-access-type`, `x-can-view-children`, `x-parent-tenant-id`
+- `x-forwarded-by`, `x-request-id`
+
 ### Context Header Injection
 
 When a service token is validated, the gateway injects these headers for downstream services: