me.woach.feed, add activity unit lexicon

lexicons/me/woach/feed/activity.json

@@ -0,0 +1,33 @@
+{
+  "lexicon": 1,
+  "id": "me.woach.feed.activity",
+  "defs": {
+    "main": {
+      "type": "record",
+      "description": "A single activity log for a specific show",
+      "key": "tid",
+      "record": {
+        "type": "object",
+        "required": ["session", "progress", "createdAt"],
+        "nullable": ["performedAt"],
+        "properties": {
+          "session": { "type": "ref", "ref": "com.atproto.repo.strongRef" },
+          "progress": {
+            "type": "integer",
+            "description": "The episode/chapter number for the content consumed."
+          },
+          "performedAt": {
+            "type": "string",
+            "format": "datetime",
+            "description": "User-declared timestamp for when they performed the activity."
+          },
+          "createdAt": {
+            "type": "string",
+            "format": "datetime",
+            "description": "Client-declared timestamp for when this activity was created"
+          }
+        }
+      }
+    }
+  }
+}