Adapted from upstream langchain-ai/open-swe #1684 to the fork's
direct-import middleware registry and middleware stack ordering.
Adds SubdirAgentsReadMiddleware, which appends applicable ancestor
AGENTS.md instructions to read_file results once per run, so scoped
rules are visible before edits. Wired into get_agent immediately after
ToolErrorMiddleware, matching upstream's relative position.
Note: this changes file-read behavior for every main-agent run. The
reviewer graph uses its own leaner middleware stack and is unaffected.
(cherry picked from commit 7f7af71547be2199cea699284676f8ceefba7691)
