docs: Add hooks to the-agent-format.md

Author: chaynabors

docs/the-agent-format.md

@@ -145,6 +145,23 @@ Resources are data and content that your agent has access to. As of today, only
 }
 ```
 
+### The `hooks` field
+
+The `hooks` field invokes functions at specific trigger points. The output of these functions is persisted into context according to the lifetime rules of the trigger. Hooks that run once, on `agentSpawn` for example, will be added to persistant context while shorter lived hooks like `userPromptSubmit` exist inside of the rolling context window.  
+
+```json
+{
+  "hooks": {
+    "agentSpawn": {
+      "command": "git status",
+    },
+    "userPromptSubmit": {
+      "command": "ls",
+    }
+  }
+}
+```
+
 ## Complete Example
 
 Here's a complete example of an agent manifest: