Compression could produce a transcript with ZERO user-role messages,
which OpenAI-compatible backends (vLLM/Qwen) reject with a non-retryable
`400 No user query found in messages`. This crashes `hermes kanban`
workers unrecoverably: every resume replays the same poisoned history and
fails on the very first request after a successful compaction.
The existing #52160 guard pins the handoff summary to role="user" only
when `last_head_role == "system"` — i.e. when the system prompt sits
inside `messages` (the gateway `/compress` path). The main
auto-compression path prepends the system prompt at request-build time,
so the list handed to `compress()` starts with a user/assistant turn,
`last_head_role` defaults to "user", and the summary is emitted as
role="assistant". A kanban worker seeded with a single short
`"work kanban task <id>"` prompt followed by nothing but assistant/tool
turns therefore ends up user-less once that early turn is summarised.
Generalise the guard: when no user-role message survives in the protected
head or the preserved tail, force the summary to carry role="user" so the
request always has at least one user turn. When a user does survive
(e.g. in the tail), the guard does not fire, so alternation is preserved.
Fixes#58753.
HexLab98
24add1db74