fix(api): defer streaming response until referenced variables are updated (#30832)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/core/workflow/nodes/variable_assigner/v1/node.py

@@ -33,6 +33,15 @@ class VariableAssignerNode(Node[VariableAssignerData]):
             graph_runtime_state=graph_runtime_state,
         )
 
+    def blocks_variable_output(self, variable_selectors: set[tuple[str, ...]]) -> bool:
+        """
+        Check if this Variable Assigner node blocks the output of specific variables.
+
+        Returns True if this node updates any of the requested conversation variables.
+        """
+        assigned_selector = tuple(self.node_data.assigned_variable_selector)
+        return assigned_selector in variable_selectors
+
     @classmethod
     def version(cls) -> str:
         return "1"

api/tests/fixtures/workflow/test_streaming_conversation_variables_v1_overwrite.yml

@@ -0,0 +1,158 @@
+app:
+  description: Validate v1 Variable Assigner blocks streaming until conversation variable is updated.
+  icon: 🤖
+  icon_background: '#FFEAD5'
+  mode: advanced-chat
+  name: test_streaming_conversation_variables_v1_overwrite
+  use_icon_as_answer_icon: false
+dependencies: []
+kind: app
+version: 0.5.0
+workflow:
+  conversation_variables:
+  - description: ''
+    id: 6ddf2d7f-3d1b-4bb0-9a5e-9b0c87c7b5e6
+    name: conv_var
+    selector:
+    - conversation
+    - conv_var
+    value: default
+    value_type: string
+  environment_variables: []
+  features:
+    file_upload:
+      allowed_file_extensions:
+      - .JPG
+      - .JPEG
+      - .PNG
+      - .GIF
+      - .WEBP
+      - .SVG
+      allowed_file_types:
+      - image
+      allowed_file_upload_methods:
+      - local_file
+      - remote_url
+      enabled: false
+      fileUploadConfig:
+        audio_file_size_limit: 50
+        batch_count_limit: 5
+        file_size_limit: 15
+        image_file_size_limit: 10
+        video_file_size_limit: 100
+        workflow_file_upload_limit: 10
+      image:
+        enabled: false
+        number_limits: 3
+        transfer_methods:
+        - local_file
+        - remote_url
+      number_limits: 3
+    opening_statement: ''
+    retriever_resource:
+      enabled: true
+    sensitive_word_avoidance:
+      enabled: false
+    speech_to_text:
+      enabled: false
+    suggested_questions: []
+    suggested_questions_after_answer:
+      enabled: false
+    text_to_speech:
+      enabled: false
+      language: ''
+      voice: ''
+  graph:
+    edges:
+    - data:
+        isInIteration: false
+        isInLoop: false
+        sourceType: start
+        targetType: assigner
+      id: start-source-assigner-target
+      source: start
+      sourceHandle: source
+      target: assigner
+      targetHandle: target
+      type: custom
+      zIndex: 0
+    - data:
+        isInLoop: false
+        sourceType: assigner
+        targetType: answer
+      id: assigner-source-answer-target
+      source: assigner
+      sourceHandle: source
+      target: answer
+      targetHandle: target
+      type: custom
+      zIndex: 0
+    nodes:
+    - data:
+        desc: ''
+        selected: false
+        title: Start
+        type: start
+        variables: []
+      height: 54
+      id: start
+      position:
+        x: 30
+        y: 253
+      positionAbsolute:
+        x: 30
+        y: 253
+      selected: false
+      sourcePosition: right
+      targetPosition: left
+      type: custom
+      width: 244
+    - data:
+        answer: 'Current Value Of `conv_var` is:{{#conversation.conv_var#}}'
+        desc: ''
+        selected: false
+        title: Answer
+        type: answer
+        variables: []
+      height: 106
+      id: answer
+      position:
+        x: 638
+        y: 253
+      positionAbsolute:
+        x: 638
+        y: 253
+      selected: true
+      sourcePosition: right
+      targetPosition: left
+      type: custom
+      width: 244
+    - data:
+        assigned_variable_selector:
+        - conversation
+        - conv_var
+        desc: ''
+        input_variable_selector:
+        - sys
+        - query
+        selected: false
+        title: Variable Assigner
+        type: assigner
+        write_mode: over-write
+      height: 84
+      id: assigner
+      position:
+        x: 334
+        y: 253
+      positionAbsolute:
+        x: 334
+        y: 253
+      selected: false
+      sourcePosition: right
+      targetPosition: left
+      type: custom
+      width: 244
+    viewport:
+      x: 0
+      y: 0
+      zoom: 0.7

api/tests/unit_tests/core/workflow/graph_engine/test_streaming_conversation_variables.py

@@ -45,3 +45,33 @@ def test_streaming_conversation_variables():
     runner = TableTestRunner()
     result = runner.run_test_case(case)
     assert result.success, f"Test failed: {result.error}"
+
+
+def test_streaming_conversation_variables_v1_overwrite_waits_for_assignment():
+    fixture_name = "test_streaming_conversation_variables_v1_overwrite"
+    input_query = "overwrite-value"
+
+    case = WorkflowTestCase(
+        fixture_path=fixture_name,
+        use_auto_mock=False,
+        mock_config=MockConfigBuilder().build(),
+        query=input_query,
+        inputs={},
+        expected_outputs={"answer": f"Current Value Of `conv_var` is:{input_query}"},
+    )
+
+    runner = TableTestRunner()
+    result = runner.run_test_case(case)
+    assert result.success, f"Test failed: {result.error}"
+
+    events = result.events
+    conv_var_chunk_events = [
+        event
+        for event in events
+        if isinstance(event, NodeRunStreamChunkEvent) and tuple(event.selector) == ("conversation", "conv_var")
+    ]
+
+    assert conv_var_chunk_events, "Expected conversation variable chunk events to be emitted"
+    assert all(event.chunk == input_query for event in conv_var_chunk_events), (
+        "Expected streamed conversation variable value to match the input query"
+    )