Add subagent identity to hook inputs (#22882)

# What

When a normal hook fires inside a thread-spawned subagent, Codex now
includes these optional top-level fields in the hook input:

- `agent_id`: the child thread id
- `agent_type`: the subagent role

Root-agent hook inputs omit these fields. `SubagentStart` and
`SubagentStop` keep their existing required `agent_id` and `agent_type`
fields because those events are inherently subagent-scoped.

This does not change matcher behavior. Tool hooks still match on tool
name, compact hooks still match on trigger, and `UserPromptSubmit` still
ignores matchers. Only `SubagentStart` and `SubagentStop` match on
`agent_type`.

codex-rs/hooks/schema/generated/pre-tool-use.command.input.schema.json

@@ -10,6 +10,12 @@
     }
   },
   "properties": {
+    "agent_id": {
+      "type": "string"
+    },
+    "agent_type": {
+      "type": "string"
+    },
     "cwd": {
       "type": "string"
     },