fix(flows): end invocation on a deferred long-running tool call

core/src/main/java/com/google/adk/agents/LlmAgent.java

@@ -611,41 +611,47 @@ protected BaseLlmFlow determineLlmFlow() {
   }
 
   private void maybeSaveOutputToState(Event event) {
-    if (outputKey().isPresent() && event.finalResponse() && event.content().isPresent()) {
-      // Concatenate text from all parts, excluding thoughts.
-      Object output;
-      String rawResult =
-          event.content().flatMap(Content::parts).orElseGet(ImmutableList::of).stream()
-              .filter(part -> !isThought(part))
-              .map(part -> part.text().orElse(""))
-              .collect(joining());
-
-      Optional<Schema> outputSchema = outputSchema();
-      if (outputSchema.isPresent()) {
-        try {
-          Map<String, Object> validatedMap =
-              SchemaUtils.validateOutputSchema(rawResult, outputSchema.get());
-          output = validatedMap;
-        } catch (JsonProcessingException e) {
-          logger.error(
-              "LlmAgent output for outputKey '{}' was not valid JSON, despite an outputSchema being"
-                  + " present. Saving raw output to state.",
-              outputKey().get(),
-              e);
-          output = rawResult;
-        } catch (IllegalArgumentException e) {
-          logger.error(
-              "LlmAgent output for outputKey '{}' did not match the outputSchema. Saving raw output"
-                  + " to state.",
-              outputKey().get(),
-              e);
-          output = rawResult;
-        }
-      } else {
-        output = rawResult;
+    if (outputKey().isEmpty() || !event.finalResponse() || event.content().isEmpty()) {
+      return;
+    }
+    List<Part> parts = event.content().flatMap(Content::parts).orElseGet(ImmutableList::of);
+
+    // Skip events with no non-thought text part (e.g. a function-call-only long-running call, or a
+    // function-response-only event) so an output value already in state is not overwritten with an
+    // empty string. Mirrors ADK Python's output_key handling.
+    boolean hasTextPart =
+        parts.stream().anyMatch(part -> !isThought(part) && part.text().isPresent());
+    if (!hasTextPart) {
+      return;
+    }
+
+    // Concatenate text from all parts, excluding thoughts.
+    String rawResult =
+        parts.stream()
+            .filter(part -> !isThought(part))
+            .map(part -> part.text().orElse(""))
+            .collect(joining());
+
+    Object output = rawResult;
+    Optional<Schema> outputSchema = outputSchema();
+    if (outputSchema.isPresent()) {
+      try {
+        output = SchemaUtils.validateOutputSchema(rawResult, outputSchema.get());
+      } catch (JsonProcessingException e) {
+        logger.error(
+            "LlmAgent output for outputKey '{}' was not valid JSON, despite an outputSchema being"
+                + " present. Saving raw output to state.",
+            outputKey().get(),
+            e);
+      } catch (IllegalArgumentException e) {
+        logger.error(
+            "LlmAgent output for outputKey '{}' did not match the outputSchema. Saving raw output"
+                + " to state.",
+            outputKey().get(),
+            e);
       }
-      event.actions().stateDelta().put(outputKey().get(), output);
     }
+    event.actions().stateDelta().put(outputKey().get(), output);
   }
 
   private static boolean isThought(Part part) {

core/src/main/java/com/google/adk/events/Event.java

@@ -336,10 +336,21 @@ public final boolean hasTrailingCodeExecutionResult() {
         .isPresent();
   }
 
+  /**
+   * Returns whether this event carries a pending long-running tool call (e.g. a human-in-the-loop
+   * request) whose result is deferred until the caller supplies it later.
+   */
+  @JsonIgnore
+  public final boolean hasPendingLongRunningToolCall() {
+    return longRunningToolIds().map(ids -> !ids.isEmpty()).orElse(false);
+  }
+
   /** Returns true if this is a final response. */
   @JsonIgnore
   public final boolean finalResponse() {
-    if (actions().skipSummarization().orElse(false)) {
+    // A pending long-running tool call ends the invocation: control returns to the caller, who
+    // supplies the deferred response later. This mirrors Python ADK's is_final_response.
+    if (actions().skipSummarization().orElse(false) || hasPendingLongRunningToolCall()) {
       return true;
     }
     return functionCalls().isEmpty()

core/src/main/java/com/google/adk/flows/llmflows/Functions.java

@@ -540,7 +540,14 @@ private static Maybe<Event> processFunctionResult(
                   .flatMapMaybe(
                       finalOptionalResult -> {
                         Map<String, Object> finalFunctionResult = finalOptionalResult.orElse(null);
-                        if (tool.longRunning() && finalFunctionResult == null) {
+                        boolean hasNoResult =
+                            finalFunctionResult == null || finalFunctionResult.isEmpty();
+                        if (tool.longRunning() && hasNoResult) {
+                          // A long-running tool with no result yet defers its response, so skip the
+                          // function-response event to avoid re-invoking the model with a
+                          // placeholder. The empty-map case is included because FunctionTool
+                          // coerces
+                          // an absent return into an empty map.
                           return Maybe.empty();
                         }
                         Event event =

core/src/test/java/com/google/adk/events/EventTest.java

@@ -300,13 +300,12 @@ public void finalResponse_isTrueForEventWithTextContent() {
             .invocationId("i1")
             .author("agent")
             .content(Content.fromParts(Part.fromText("hello")))
-            .longRunningToolIds(ImmutableSet.of("tool1"))
             .build();
     assertThat(event.finalResponse()).isTrue();
   }
 
   @Test
-  public void finalResponse_isFalseForEventWithToolCallAndLongRunningToolId() {
+  public void finalResponse_isTrueForEventWithToolCallAndLongRunningToolId() {
     Event event =
         Event.builder()
             .id("e1")
@@ -315,7 +314,8 @@ public void finalResponse_isFalseForEventWithToolCallAndLongRunningToolId() {
             .content(Content.fromParts(Part.fromFunctionCall("tool", ImmutableMap.of("k", "v"))))
             .longRunningToolIds(ImmutableSet.of("tool1"))
             .build();
-    assertThat(event.finalResponse()).isFalse();
+    // A pending long-running tool call ends the invocation, so the event is a final response.
+    assertThat(event.finalResponse()).isTrue();
   }
 
   @Test

core/src/test/java/com/google/adk/runner/RunnerTest.java

@@ -2301,6 +2301,159 @@ public void runAsync_withLongRunningCall_resumabilityDisabled_doesNotPause() {
     assertThat(simplifyEvents(events)).contains("agent: after pending call");
   }
 
+  // A long-running tool awaiting an external result (real HITL, e.g. human input) returns nothing
+  // yet. The invocation must end after the single model call rather than re-invoking the model with
+  // a placeholder response and looping until the call limit. Matches Python ADK v1: the function
+  // response is skipped and the long-running call event is treated as final.
+  @Test
+  public void runAsync_withLongRunningCall_noImmediateResult_endsAfterSingleModelCall() {
+    TestLlm testLlm =
+        createTestLlm(
+            createFunctionCallLlmResponse(
+                "lro_call_id", "pendingTool", ImmutableMap.of("message", "hello")),
+            // Extra response the flow must NOT consume; reaching it means it looped.
+            createTextLlmResponse("should not be reached"));
+    LlmAgent agent =
+        createTestAgentBuilder(testLlm)
+            .name("agent")
+            .tools(
+                FunctionTool.create(
+                    Tools.class,
+                    "pendingTool",
+                    /* requireConfirmation= */ false,
+                    /* isLongRunning= */ true))
+            .build();
+    Runner runner =
+        Runner.builder().app(App.builder().name("test").rootAgent(agent).build()).build();
+    Session session = runner.sessionService().createSession("test", "user").blockingGet();
+
+    List<Event> events =
+        runner
+            .runAsync("user", session.id(), Content.fromParts(Part.fromText("from user")))
+            .toList()
+            .blockingGet();
+
+    // Ended after the single long-running call: no function response, no second model call.
+    assertThat(testLlm.getRequests()).hasSize(1);
+    assertThat(simplifyEvents(events)).doesNotContain("agent: should not be reached");
+  }
+
+  // The long-running call event is now a final response, but it carries no text. An agent with an
+  // outputKey must not overwrite that key with an empty string. Matches ADK Python's output_key
+  // guard, which skips final events that have no text part.
+  @Test
+  public void runAsync_withLongRunningCall_andOutputKey_doesNotWriteEmptyOutput() {
+    TestLlm testLlm =
+        createTestLlm(
+            createFunctionCallLlmResponse(
+                "lro_call_id", "pendingTool", ImmutableMap.of("message", "hello")));
+    LlmAgent agent =
+        createTestAgentBuilder(testLlm)
+            .name("agent")
+            .outputKey("result")
+            .tools(
+                FunctionTool.create(
+                    Tools.class,
+                    "pendingTool",
+                    /* requireConfirmation= */ false,
+                    /* isLongRunning= */ true))
+            .build();
+    Runner runner =
+        Runner.builder().app(App.builder().name("test").rootAgent(agent).build()).build();
+    Session session = runner.sessionService().createSession("test", "user").blockingGet();
+
+    List<Event> events =
+        runner
+            .runAsync("user", session.id(), Content.fromParts(Part.fromText("from user")))
+            .toList()
+            .blockingGet();
+
+    assertThat(events).hasSize(1);
+    assertThat(events.get(0).actions().stateDelta()).doesNotContainKey("result");
+  }
+
+  // Mirrors ADK Python's test_functions_long_running.test_async_function: a long-running tool that
+  // reports a non-empty "pending" status drives a multi-turn lifecycle. The initial pending result
+  // is summarized, then the caller injects progress/result function responses over later turns,
+  // each summarized by the model, and the tool executes exactly once across the whole lifecycle.
+  @Test
+  public void runAsync_longRunningCall_multiTurnLifecycle_executesToolOnce() {
+    Tools.pendingProgressToolCalls.set(0);
+    TestLlm testLlm =
+        createTestLlm(
+            createFunctionCallLlmResponse(
+                "lro_call_id", "pendingProgressTool", ImmutableMap.of("message", "hi")),
+            createTextLlmResponse("response1"),
+            createTextLlmResponse("response2"),
+            createTextLlmResponse("response3"),
+            createTextLlmResponse("response4"));
+    LlmAgent agent =
+        createTestAgentBuilder(testLlm)
+            .name("agent")
+            .tools(
+                FunctionTool.create(
+                    Tools.class,
+                    "pendingProgressTool",
+                    /* requireConfirmation= */ false,
+                    /* isLongRunning= */ true))
+            .build();
+    Runner runner =
+        Runner.builder().app(App.builder().name("test").rootAgent(agent).build()).build();
+    Session session = runner.sessionService().createSession("test", "user").blockingGet();
+
+    // Turn 1: the model calls the long-running tool; the pending result is summarized.
+    List<Event> turn1 =
+        runner
+            .runAsync("user", session.id(), Content.fromParts(Part.fromText("test1")))
+            .toList()
+            .blockingGet();
+    assertThat(testLlm.getRequests()).hasSize(2);
+    assertThat(turn1.get(0).longRunningToolIds().get())
+        .contains(turn1.get(0).functionCalls().get(0).id().get());
+    assertThat(simplifyEvents(turn1))
+        .containsExactly(
+            "agent: FunctionCall(name=pendingProgressTool, args={message=hi})",
+            "agent: FunctionResponse(name=pendingProgressTool, response={status=pending})",
+            "agent: response1")
+        .inOrder();
+    assertThat(Tools.pendingProgressToolCalls.get()).isEqualTo(1);
+
+    // Turn 2: the caller injects a progress update; the model summarizes, tool not re-run.
+    assertThat(simplifyEvents(resumeWithStatus(runner, session, "still waiting")))
+        .containsExactly("agent: response2");
+    assertThat(testLlm.getRequests()).hasSize(3);
+
+    // Turn 3: the caller injects the result.
+    assertThat(simplifyEvents(resumeWithStatus(runner, session, "done")))
+        .containsExactly("agent: response3");
+    assertThat(testLlm.getRequests()).hasSize(4);
+
+    // Turn 4: a further result is still accepted and summarized.
+    assertThat(simplifyEvents(resumeWithStatus(runner, session, "done again")))
+        .containsExactly("agent: response4");
+    assertThat(testLlm.getRequests()).hasSize(5);
+
+    // The tool executed exactly once across the whole lifecycle.
+    assertThat(Tools.pendingProgressToolCalls.get()).isEqualTo(1);
+  }
+
+  private static List<Event> resumeWithStatus(Runner runner, Session session, String status) {
+    return runner
+        .runAsync(
+            "user",
+            session.id(),
+            Content.fromParts(
+                Part.builder()
+                    .functionResponse(
+                        FunctionResponse.builder()
+                            .id("lro_call_id")
+                            .name("pendingProgressTool")
+                            .response(ImmutableMap.of("status", status)))
+                    .build()))
+        .toList()
+        .blockingGet();
+  }
+
   // A pending long-running call must stop a resumable LoopAgent after the current iteration rather
   // than looping again (re-calling the model every iteration), matching Python ADK v1.
   @Test
@@ -2564,6 +2717,23 @@ private Tools() {}
     public static ImmutableMap<String, Object> echoTool(String message) {
       return ImmutableMap.of("message", message);
     }
+
+    // A long-running tool awaiting an external result has nothing to return yet; FunctionTool
+    // coerces the absent return into an empty response.
+    @SuppressWarnings("unused") // Invoked reflectively by FunctionTool.
+    public static @Nullable ImmutableMap<String, Object> pendingTool(String message) {
+      return null;
+    }
+
+    static final AtomicInteger pendingProgressToolCalls = new AtomicInteger(0);
+
+    // A long-running tool that reports progress: it returns a non-empty "pending" status on the
+    // initial call. Counts executions so a test can assert it runs exactly once across turns.
+    @SuppressWarnings("unused") // Invoked reflectively by FunctionTool.
+    public static ImmutableMap<String, Object> pendingProgressTool(String message) {
+      pendingProgressToolCalls.incrementAndGet();
+      return ImmutableMap.of("status", "pending");
+    }
   }
 
   @Test