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
* fix(runtime): suppress tool execution when provider safety-terminates with tool_calls
When a provider stops generation for safety reasons (OpenAI/Moonshot
finish_reason=content_filter, Anthropic stop_reason=refusal, Gemini
finish_reason=SAFETY/BLOCKLIST/PROHIBITED_CONTENT/SPII/RECITATION/
IMAGE_SAFETY/...), the response may still carry truncated tool_calls.
LangChain's tool router treats any non-empty tool_calls as executable,
so partial arguments (e.g. write_file with a half-finished markdown)
get dispatched and the agent loops on retry.
Add SafetyFinishReasonMiddleware at after_model: detect safety
termination via a pluggable detector registry, clear both structured
tool_calls and raw additional_kwargs.tool_calls / function_call,
preserve response_metadata.finish_reason for downstream observers,
stamp additional_kwargs.safety_termination for traces, append a
user-facing explanation to message content (list-aware for thinking
blocks), and emit a safety_termination custom stream event so SSE
consumers can reconcile any "tool starting..." UI.
Default detectors cover OpenAI-compatible content_filter, Anthropic
refusal, and Gemini safety enums (text + image). Custom providers are
added via reflection (same pattern as guardrails). Wired into both
lead-agent and subagent runtimes.
Closes#3028
* fix(runtime): persist safety_termination as a middleware audit event
Address review on #3035: the SSE custom event is great for live
consumers but invisible to post-run audit. RunEventStore should carry
its own row so operators can answer "which runs were safety-suppressed
today?" from a single SQL query without joining the message body.
Worker now exposes the run-scoped RunJournal via
runtime.context["__run_journal"] (sentinel key, internal channel).
SafetyFinishReasonMiddleware calls the previously-unused
RunJournal.record_middleware, which emits
event_type = "middleware:safety_termination"
category = "middleware"
content = {name, hook, action, changes={
detector, reason_field, reason_value,
suppressed_tool_call_count,
suppressed_tool_call_names,
suppressed_tool_call_ids,
message_id, extras}}
Tool *arguments* are deliberately excluded — those are the very content
the provider filtered and persisting them would defeat the purpose of
the safety filter (per review note in #3035).
Graceful skips when journal is absent (subagent runtime, unit tests,
no-event-store local dev). Journal exceptions never propagate into the
agent loop.
Refs #3028
* fix(runtime): satisfy ruff format + address Copilot review
- ruff format on safety_finish_reason_config.py and e2e demo (CI lint
failed on ruff format --check; backend Makefile lint target runs
ruff check AND ruff format --check).
- Docstring on SafetyFinishReasonConfig now says resolve_variable to
match the actual loader used in from_config (the wording was
resolve_class previously; behavior is unchanged — resolve_variable
mirrors how guardrails.provider is loaded).
- Switch the AIMessage type check in SafetyFinishReasonMiddleware._apply
from getattr(last, "type") == "ai" to isinstance(last, AIMessage),
matching TokenUsageMiddleware / TodoMiddleware / ViewImageMiddleware
/ SummarizationMiddleware which are the dominant pattern.
Refs #3028
