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fix(react): continue after empty model responses #2355

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297dbbe
fix(react): continue after empty model responses
Zbhbb Jul 22, 2026
6383b84
fix(react): retry only empty responses
Zbhbb Jul 22, 2026
995dcbf
fix(react): avoid duplicate post reasoning
Zbhbb Jul 22, 2026
ac0ecb2
test(core): cover empty model response retries
Zbhbb Jul 23, 2026
38f943b
fix(react): cover empty response loop edges
Zbhbb Jul 23, 2026
4e33938
test(react): align thinking-only retry expectation
Zbhbb Aug 24, 2026
87aad29
ci: rerun flaky Windows test
Zbhbb Aug 24, 2026
44241bc
ci: rerun harness cleanup check
Zbhbb Aug 24, 2026
4d060b7
ci: retry harness suite once more
Zbhbb Aug 24, 2026
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46 changes: 43 additions & 3 deletions agentscope-core/src/main/java/io/agentscope/core/ReActAgent.java
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Original file line number Diff line number Diff line change
Expand Up @@ -2306,6 +2306,7 @@ private Mono<Msg> reasoning(int iter, boolean ignoreMaxIters) {
}

ReasoningContext context = new ReasoningContext(getName());
AtomicBoolean retryEmptyResponse = new AtomicBoolean(false);

return checkInterrupted()
.then(
Expand Down Expand Up @@ -2380,7 +2381,10 @@ private Mono<Msg> reasoning(int iter, boolean ignoreMaxIters) {
context.buildFinalMessage();
RequestStopEvent rs =
stopRequested.get();
if (rs != null && finalMsg != null) {
if (rs != null) {
if (finalMsg == null) {
return Mono.empty();
}
// Persist the reasoning message
// before
// returning so the next call can
Expand All @@ -2393,7 +2397,11 @@ private Mono<Msg> reasoning(int iter, boolean ignoreMaxIters) {
rs
.getGenerateReason()));
}
return Mono.justOrEmpty(finalMsg);
if (finalMsg == null) {
retryEmptyResponse.set(true);
return Mono.empty();
}
return Mono.just(finalMsg);
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}));
})
.onErrorResume(
Expand Down Expand Up @@ -2427,7 +2435,15 @@ private Mono<Msg> reasoning(int iter, boolean ignoreMaxIters) {
return Mono.just(msg);
}
return runPostReasoningPipeline(msg, iter);
});
})
.switchIfEmpty(
Mono.defer(
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() -> {
if (retryEmptyResponse.get()) {
return executeIteration(iter + 1);
}
return Mono.empty();
}));
}

@SuppressWarnings("deprecation")
Expand Down Expand Up @@ -2460,6 +2476,12 @@ private Mono<Msg> runPostReasoningPipeline(Msg msg, int iter) {
return reasoning(iter + 1, true);
}

// Continue the bounded ReAct loop when the model produced only
// blank text. The message has already been persisted above.
if (hasBlankTextResponse(eventMsg)) {
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return executeIteration(iter + 1);
}

// Check finish conditions
if (isFinished(eventMsg)) {
return Mono.justOrEmpty(eventMsg);
Expand Down Expand Up @@ -3778,6 +3800,24 @@ private static Msg buildEmptyResponseReminder() {
.build();
}

/**
* Check whether a model response contains only blank text and no tool calls.
*
* @param msg The reasoning message
* @return true if the response contains one or more blank text blocks
*/
private boolean hasBlankTextResponse(Msg msg) {
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if (msg == null || !msg.getContentBlocks(ToolUseBlock.class).isEmpty()) {
return false;
}

List<TextBlock> textBlocks = msg.getContentBlocks(TextBlock.class);
return !textBlocks.isEmpty()
&& textBlocks.stream()
.map(TextBlock::getText)
.noneMatch(text -> !text.isBlank());
}

/**
* Check whether every tool call in the given list has a DENIED result in context.
*/
Expand Down
229 changes: 229 additions & 0 deletions agentscope-core/src/test/java/io/agentscope/core/agent/ReActAgentNewLoopE2ETest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -24,19 +24,25 @@
import io.agentscope.core.event.AgentEvent;
import io.agentscope.core.event.AgentStartEvent;
import io.agentscope.core.event.ModelCallEndEvent;
import io.agentscope.core.event.RequestStopEvent;
import io.agentscope.core.event.ToolCallEndEvent;
import io.agentscope.core.event.ToolResultEndEvent;
import io.agentscope.core.event.ToolResultTextDeltaEvent;
import io.agentscope.core.hook.Hook;
import io.agentscope.core.hook.HookEvent;
import io.agentscope.core.hook.PostReasoningEvent;
import io.agentscope.core.message.ContentBlock;
import io.agentscope.core.message.Msg;
import io.agentscope.core.message.MsgRole;
import io.agentscope.core.message.TextBlock;
import io.agentscope.core.message.ThinkingBlock;
import io.agentscope.core.message.ToolResultBlock;
import io.agentscope.core.message.ToolResultState;
import io.agentscope.core.message.ToolUseBlock;
import io.agentscope.core.middleware.ActingInput;
import io.agentscope.core.middleware.AgentInput;
import io.agentscope.core.middleware.MiddlewareBase;
import io.agentscope.core.middleware.ReasoningInput;
import io.agentscope.core.model.ChatModelBase;
import io.agentscope.core.model.ChatResponse;
import io.agentscope.core.model.GenerateOptions;
Expand Down Expand Up @@ -324,6 +330,229 @@ void toolReturningErrorBlockEmitsErrorResultEndState() {
assertEquals(ToolResultState.ERROR, end.getState());
}

@Test
void retriesAfterModelStreamCompletesWithoutAResponse() {
ScriptedModel model =
new ScriptedModel(
List.of(() -> Flux.empty(), () -> Flux.just(textResponse("recovered"))));
ReActAgent agent =
ReActAgent.builder().name("asst").sysPrompt("you are helpful").model(model).build();

List<AgentEvent> events =
agent.streamEvents(
List.of(
Msg.builder()
.role(MsgRole.USER)
.textContent("continue after an empty response")
.build()))
.collectList()
.block();

assertNotNull(events);
assertEquals(2, model.calls.get());
assertTrue(
agent.getAgentState().getContext().stream()
.flatMap(message -> message.getContentBlocks(TextBlock.class).stream())
.anyMatch(text -> "recovered".equals(text.getText())));
}

@Test
void retriesAfterModelReturnsOnlyBlankText() {
ScriptedModel model =
new ScriptedModel(
List.of(
() -> Flux.just(textResponse(" ")),
() -> Flux.just(textResponse("recovered"))));
ReActAgent agent =
ReActAgent.builder().name("asst").sysPrompt("you are helpful").model(model).build();

List<AgentEvent> events =
agent.streamEvents(
List.of(
Msg.builder()
.role(MsgRole.USER)
.textContent("continue after a blank response")
.build()))
.collectList()
.block();

assertNotNull(events);
assertEquals(2, model.calls.get());
assertTrue(
agent.getAgentState().getContext().stream()
.flatMap(message -> message.getContentBlocks(TextBlock.class).stream())
.anyMatch(text -> "recovered".equals(text.getText())));
}

@Test
void stopsWithoutRetryWhenMiddlewareStopsAnEmptyResponse() {
ScriptedModel model = new ScriptedModel(List.of(Flux::empty));
MiddlewareBase stoppingMiddleware =
new MiddlewareBase() {
@Override
public Flux<AgentEvent> onReasoning(
Agent agent,
RuntimeContext ctx,
ReasoningInput input,
Function<ReasoningInput, Flux<AgentEvent>> next) {
return Flux.concat(
next.apply(input), Flux.just(new RequestStopEvent("test stop")));
}
};
ReActAgent agent =
ReActAgent.builder()
.name("asst")
.sysPrompt("you are helpful")
.model(model)
.middleware(stoppingMiddleware)
.build();

List<AgentEvent> events =
agent.streamEvents(
List.of(
Msg.builder()
.role(MsgRole.USER)
.textContent("stop the empty response")
.build()))
.collectList()
.block();

assertNotNull(events);
assertEquals(1, model.calls.get());
assertTrue(events.stream().anyMatch(RequestStopEvent.class::isInstance));
}

@Test
void retriesAfterModelReturnsEmptyText() {
ScriptedModel model =
new ScriptedModel(
List.of(
() -> Flux.just(textResponse("")),
() -> Flux.just(textResponse("recovered"))));
ReActAgent agent =
ReActAgent.builder().name("asst").sysPrompt("you are helpful").model(model).build();

agent.streamEvents(
List.of(
Msg.builder()
.role(MsgRole.USER)
.textContent("continue after a null text response")
.build()))
.collectList()
.block();

assertEquals(2, model.calls.get());
assertTrue(
agent.getAgentState().getContext().stream()
.flatMap(message -> message.getContentBlocks(TextBlock.class).stream())
.anyMatch(text -> "recovered".equals(text.getText())));
}

@Test
void preservesModelResponseWhenMiddlewareRequestsStop() {
ScriptedModel model = new ScriptedModel(List.of(() -> Flux.just(textResponse("paused"))));
MiddlewareBase stoppingMiddleware =
new MiddlewareBase() {
@Override
public Flux<AgentEvent> onReasoning(
Agent agent,
RuntimeContext ctx,
ReasoningInput input,
Function<ReasoningInput, Flux<AgentEvent>> next) {
return Flux.concat(
next.apply(input), Flux.just(new RequestStopEvent("test stop")));
}
};
ReActAgent agent =
ReActAgent.builder()
.name("asst")
.sysPrompt("you are helpful")
.model(model)
.middleware(stoppingMiddleware)
.build();

List<AgentEvent> events =
agent.streamEvents(
List.of(
Msg.builder()
.role(MsgRole.USER)
.textContent("stop with a response")
.build()))
.collectList()
.block();

assertNotNull(events);
assertEquals(1, model.calls.get());
assertTrue(events.stream().anyMatch(RequestStopEvent.class::isInstance));
assertTrue(
agent.getAgentState().getContext().stream()
.flatMap(message -> message.getContentBlocks(TextBlock.class).stream())
.anyMatch(text -> "paused".equals(text.getText())));
}

@Test
void retriesAfterModelReturnsOnlyThinking() {
ChatResponse thinkingResponse =
ChatResponse.builder()
.content(
List.<ContentBlock>of(
ThinkingBlock.builder()
.thinking("internal thought")
.build()))
.build();
ScriptedModel model = new ScriptedModel(List.of(() -> Flux.just(thinkingResponse)));
ReActAgent agent =
ReActAgent.builder()
.name("asst")
.sysPrompt("you are helpful")
.model(model)
.maxIters(2)
.build();

List<AgentEvent> events =
agent.streamEvents(
List.of(
Msg.builder()
.role(MsgRole.USER)
.textContent("continue after a thinking response")
.build()))
.collectList()
.block();

assertNotNull(events);
// Main treats a thinking-only response as an empty final response. Two reasoning attempts
// are followed by one bounded summary call instead of silently completing with no reply.
assertEquals(3, model.calls.get());
}

@Test
void doesNotRetryWhenPostReasoningHookDiscardsTheMessage() {
ScriptedModel model =
new ScriptedModel(List.of(() -> Flux.just(textResponse("discarded"))));
Hook discardingHook =
new Hook() {
@Override
public <T extends HookEvent> Mono<T> onEvent(T event) {
if (event instanceof PostReasoningEvent postReasoningEvent) {
postReasoningEvent.setReasoningMessage(null);
}
return Mono.just(event);
}
};
ReActAgent agent =
ReActAgent.builder()
.name("asst")
.sysPrompt("you are helpful")
.model(model)
.hook(discardingHook)
.build();

List<AgentEvent> events = agent.streamEvents(List.of()).collectList().block();

assertNotNull(events);
assertEquals(1, model.calls.get());
}

@Test
void toolResultMetadataPropagatesToEvents() {
ScriptedModel model =
Expand Down
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