Nan Gao 8fbf101de3

fix(subagents): inject durable context before compaction (#4040) ...

* fix(subagents): inject durable context before compaction

* fix(subagents): coalesce system messages after durable-context injection

Address #4040 review:
- append SystemMessageCoalescingMiddleware innermost on the subagent chain
  so the SystemMessage(authority) DurableContextMiddleware injects is merged
  into one leading system_message; otherwise the durable fix trades #4039's
  assistant-first 400 for a duplicate-system 400 on strict backends
- add a two-system regression guard driving the real builder output through
  a strict model; assert exactly one leading SystemMessage
- assert single-leading-system in the compaction integration test too
- update the middleware count/last-element assertion (coalescer is now
  unconditionally last, removing the summarization-dependence ambiguity)
- compare _skills_root against posixpath.normpath(container_path)
- document the coalescer on the subagent chain in backend/AGENTS.md

2026-07-11 08:29:42 +08:00

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harness

fix(subagents): inject durable context before compaction (#4040)

2026-07-11 08:29:42 +08:00