revert(langgraph): restore logic to surface interrupts for stream_mod… (#6141)

### Description

Revert change in #5201 that prevented the surfacing of interrupts when
`stream_mode="values"`. [Comment highlighting affected
lines](https://github.com/langchain-ai/langgraph/pull/5201#discussion_r2344884841)

Resolves #5409 

### Test

Add test to verify interrupts are properly surfaced when
`stream_mode="values"` (`test_interrupt_stream_mode_values`)

libs/langgraph/langgraph/pregel/_loop.py

@@ -904,7 +904,11 @@ class PregelLoop:
                         )
                     }
                 ]
-                self._emit("updates", lambda: iter(interrupts))
+                stream_modes = self.stream.modes if self.stream else []
+                if "updates" in stream_modes:
+                    self._emit("updates", lambda: iter(interrupts))
+                elif "values" in stream_modes:
+                    self._emit("values", lambda: iter(interrupts))
             elif writes[0][0] != ERROR:
                 self._emit(
                     "updates",

libs/langgraph/tests/test_pregel.py

@@ -8430,3 +8430,22 @@ def test_null_resume_disallowed_with_multiple_interrupts(
         "text_1": "resume for prompt: original text 1",
         "text_2": "resume for prompt: original text 2",
     }
+
+
+def test_interrupt_stream_mode_values():
+    """Test that interrupts are surfaced when steam_mode='values'"""
+
+    class State(TypedDict):
+        human_input: str
+
+    def human_input_node(state: State) -> Command:
+        human_input = interrupt("interrupt")
+        return Command(update={"human_input": human_input})
+
+    builder = StateGraph(State)
+    builder.add_node(human_input_node)
+    builder.add_edge(START, "human_input_node")
+    app = builder.compile()
+
+    result = [*app.stream(State(), stream_mode="values")]
+    assert "__interrupt__" in result[-1]