Document collaboration capability contract

README.md

@@ -27,6 +27,10 @@ Guest Star channel settings are described by
 token is a server-to-authenticated-client value and fixtures use a synthetic
 placeholder only.
 
+The Twitch-authoritative collaboration capability probe is described by
+`collaboration-capabilities-response.json`; unavailable beta surfaces include
+a machine-readable reason without exposing Twitch tokens.
+
 Destructive backup recovery uses the explicit `backup-restore-request.json`
 and `backup-restore-response.json` contracts; test fixtures contain no real
 database paths or credentials.

contracts/v1/collaboration-capabilities-response.json

@@ -0,0 +1,14 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://trixie.local/contracts/v1/collaboration-capabilities-response.json",
+  "title": "Collaboration capabilities response",
+  "type": "object",
+  "required": ["guest_star_available", "shared_chat_available"],
+  "properties": {
+    "guest_star_available": { "type": "boolean" },
+    "guest_star_reason": { "type": ["string", "null"] },
+    "shared_chat_available": { "type": "boolean" },
+    "shared_chat_reason": { "type": ["string", "null"] }
+  },
+  "additionalProperties": false
+}

fixtures/v1/collaboration-capabilities.response.json

@@ -0,0 +1,6 @@
+{
+  "guest_star_available": true,
+  "guest_star_reason": null,
+  "shared_chat_available": true,
+  "shared_chat_reason": null
+}