Build composite subscription bucket two

docs/COMPOSITE_GROUPS.md

@@ -73,13 +73,53 @@ guessing a provider.
 - Composite groups can copy accounts from concrete provider groups.
 - Concrete provider accounts can be assigned directly to composite groups from
   account create/edit and bulk account workflows.
+- Subscription payment plans can bind to a composite group when that group's
+  `subscription_type` is `subscription`. The plan grants access to the
+  composite group; each request is still billed and quota-checked against the
+  resolved concrete provider platform.
 - Channel configuration exposes composite groups in concrete provider sections.
   The channel `group_ids` payload is still flat; provider-specific model
   mapping and pricing remain keyed by concrete platform.
 
+## Bucket 2 Setup: OpenAI + Claude + Gemini + Grok
+
+Use one composite subscription group when one customer-facing plan should expose
+model aliases across OpenAI, Claude, Gemini, and Grok without issuing separate
+keys per provider.
+
+1. Create concrete provider groups for the upstream account pools, for example
+   `OpenAI Paid`, `Claude Paid`, `Gemini Paid`, and `Grok Paid`.
+2. Create a `composite` group with `subscription_type` set to `subscription`.
+3. Assign provider accounts directly to the composite group, or copy accounts
+   from the concrete provider groups during group creation.
+4. Add explicit routes for public aliases that should not rely on built-in
+   model detection:
+
+   | Public model | Endpoint | Target platform | Upstream model |
+   | --- | --- | --- | --- |
+   | `all/gpt-5` | `responses` | `openai` | `gpt-5` |
+   | `all/claude-sonnet` | `messages` | `anthropic` | `claude-sonnet-4-6` |
+   | `all/gemini-pro` | `gemini` | `gemini` | `gemini-2.5-pro` |
+   | `all/grok` | `responses` | `grok` | `grok-4` |
+
+5. Configure channel pricing and model mapping under the concrete platforms
+   named in each route. Composite routing does not create pricing records.
+6. Create a subscription payment plan for the composite group.
+
+The same composite group can also rely on built-in detection for standard model
+names such as `gpt-*`, `claude-*`, `gemini-*`, and `grok-*`. Explicit routes are
+recommended for bundled plan aliases because they make endpoint, provider, and
+upstream model attribution reviewable in the admin UI.
+
 ## Limits
 
 Composite routes choose a concrete provider and upstream model; they do not
 create synthetic model metadata, pricing, or upstream capability records by
 themselves. Keep channel pricing/model mapping configured for the concrete
 provider platforms that the routes target.
+
+This PR intentionally does not implement:
+
+- AUTO smart-routing among multiple providers for the same abstract task.
+- Direct API-key binding to several existing groups without a composite group.
+- Protocol-agnostic provider decoupling or a LiteLLM-style adapter rewrite.