modify proxy handler

specs/005-proxy-module-delegation/data-model.md

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+# Data Model: Proxy Module Delegation
+
+## Entities
+
+- **Hub Module**
+  - Attributes: `module_key`, `description`, `supported_protocols`, `cache_strategy` (ttl_hint, validation_mode, disk_layout, supports_streaming_write), `locator_rewrite`
+  - Behavior: Registers into global registry; binds to a module handler.
+  - Constraints: module_key unique; handler must be registered.
+
+- **Module Handler**
+  - Attributes: `module_key`, `handle(request, route)` entrypoint; owns cache policy/rewrites; error mapping.
+  - Relationships: One-to-one with Hub Module; invoked by Proxy Dispatcher.
+  - Constraints: Must produce structured logs (hub, domain, module_key, cache_hit, upstream_status, request_id).
+
+- **Proxy Dispatcher**
+  - Attributes: handler map (module_key → handler), default handler fallback.
+  - Behavior: Lookup by route.ModuleKey and invoke handler; wraps errors/logging.
+  - Constraints: If handler missing, return 5xx with observable logging.
+
+- **Cache Policy**
+  - Attributes: `ttl_hint`, `validation_mode`, `disk_layout`, `requires_metadata_file`, `supports_streaming_write`, module-specific locator rewrite.
+  - Behavior: Used by module handlers to govern caching and revalidation.
+
+## Relationships
+
+- Hub Module 1:1 Module Handler (per module_key).
+- Proxy Dispatcher 1:N Module Handler (registered handlers).
+- Module Handler uses Cache Policy defined by its Hub Module.
+
+## Identity & Uniqueness
+
+- `module_key` is the unique identifier for module registration and dispatch.
+- Handler map keys must not collide; duplicates cause startup failure.
+
+## State & Lifecycle
+
+- Registration (init/startup) → Handler binding → Runtime dispatch.
+- Missing handler or duplicate registration causes startup rejection.
+
+## Volume/Scale Assumptions
+
+- Number of modules small (handful of warehouse types). Handler map fits in memory.
+- Cache size/TTL managed per module; relies on existing filesystem cache layout.