Aari b7933d18e4
fix(safety): backfill empty content-filter responses so they don't poison the thread (#4394)
An empty assistant message from a provider safety filter (content_filter with
no content, no tool calls) was persisted into thread history and replayed to
strict OpenAI-compatible providers, which reject it with HTTP 400 ("message ...
with role 'assistant' must not be empty") — breaking every later turn until a
new chat is started.

SafetyFinishReasonMiddleware only handled the tool-call case (#3028) and
TerminalResponseMiddleware only the post-tool case (#4027), so a plain empty
content-filter response fell through both. Extend the safety middleware to
backfill a user-facing explanation when a safety-terminated message is
otherwise blank, so the persisted turn is non-empty (and the user sees why it
was blocked).

Fixes #4393
2026-07-23 16:59:34 +08:00
..