feat: model Codex subagent workflows

frontend/src/lib/utils/messages.test.ts

@@ -49,6 +49,7 @@ describe("isSystemMessage", () => {
     ["continuation", "This session is being continued from a previous..."],
     ["interrupted", "[Request interrupted by user]"],
     ["task-notification", "<task-notification>done</task-notification>"],
+    ["subagent-notification", "<subagent_notification>{\"agent_id\":\"abc\"}</subagent_notification>"],
     ["command-message", "<command-message>commit</command-message>"],
     ["command-name", "<command-name>/commit</command-name>"],
     ["local-command", "<local-command-output>ok</local-command-output>"],

frontend/src/lib/utils/messages.ts

@@ -4,6 +4,7 @@ const SYSTEM_MSG_PREFIXES = [
   "This session is being continued",
   "[Request interrupted",
   "<task-notification>",
+  "<subagent_notification>",
   "<command-message>",
   "<command-name>",
   "<local-command-",

internal/db/db.go

@@ -23,7 +23,7 @@ import (
 // formatting changes). Old databases with a lower user_version
 // trigger a non-destructive re-sync (mtime reset + skip cache
 // clear) so existing session data is preserved.
-const dataVersion = 6
+const dataVersion = 7
 
 //go:embed schema.sql
 var schemaSQL string