test: preserve structured Codex CLI errors

test/fixtures/codex_cli.sh

@@ -12,6 +12,9 @@ printf '%s\n' "$@" > "$fixture_dir/$mode.args"
 printf '%s\n' "${GEN_AGENT_FIXTURE-unset}" > "$fixture_dir/$mode.env"
 
 case "${*}" in
+  *typed-fail*)
+    fixture_mode=typed_failure
+    ;;
   *fail*)
     fixture_mode=failure
     ;;
@@ -24,6 +27,11 @@ case "${*}" in
 esac
 
 case "$fixture_mode" in
+  typed_failure)
+    printf '%s\n' '{"type":"thread.started","thread_id":"fixture-thread"}'
+    printf '%s\n' '{"type":"turn.failed","error":{"code":"fixture_error","message":"typed fixture failure"}}'
+    ;;
+
   failure)
     printf '%s\n' '{"type":"thread.started","thread_id":"fixture-thread"}'
     printf '%s\n' '{"type":"turn.failed","error":"fixture failure"}'

test/gen_agent/backends/codex_executable_conformance_test.exs

@@ -146,6 +146,15 @@ defmodule GenAgent.Backends.CodexExecutableConformanceTest do
     assert "fail" == List.last(args(context.directory, :fresh))
   end
 
+  test "structured CLI failure reaches GenAgent without flattening its fields", context do
+    name = start_agent(context)
+
+    assert {:error, %{"code" => "fixture_error", "message" => "typed fixture failure"}} =
+             GenAgent.ask(name, "typed-fail")
+
+    assert [%{"code" => "fixture_error"}] = GenAgent.status(name).agent_state.errors
+  end
+
   for action <- [:interrupt, :watchdog, :stop, :kill] do
     @tag action: action
     test "#{action} stops the BEAM task on the executable streaming path", context do