diff --git a/api/core/dify_builder/handlers_build.py b/api/core/dify_builder/handlers_build.py
index 380fd64d890..42428857017 100644
--- a/api/core/dify_builder/handlers_build.py
+++ b/api/core/dify_builder/handlers_build.py
@@ -632,17 +632,31 @@ def handle_await_testdata(env: Env, turn: Turn, s: Session, fc: DifyBuilderConte
     return StepResult(next=PcState.BUILD_TEST_AND_REPAIR, context=fc)
 
 
+# Node outputs are only truncated upstream at ~100,000 chars per string, so a
+# report-generating workflow (the Builder's showcase case) can otherwise push
+# hundreds of KB of JSON into the conversation-item row, the SSE frame, and
+# the localizer walk on every successful build. The card is a preview, not a
+# download -- this cap keeps it one.
+_MAX_TERMINAL_OUTPUT_CHARS = 2000
+_TERMINAL_OUTPUT_TRUNCATED_MARKER = "\n… (truncated)"
+
+
 def _terminal_output(per_node: list[NodeOutput]) -> str:
     """The last node that produced anything, as readable JSON, or "".
 
     Deliberately status-agnostic: node status spellings differ by source
     ("success" vs "succeeded"), and a status filter that silently misses is
     worse than showing the output of a run that ended badly -- showing what
-    ran is the point of the card.
+    ran is the point of the card. Capped at ``_MAX_TERMINAL_OUTPUT_CHARS``
+    (see its comment) -- a big JSON blob is capped with a visible marker
+    rather than silently dropped.
     """
     for node in reversed(per_node):
         if node.outputs:
-            return json.dumps(node.outputs, ensure_ascii=False, indent=2)
+            rendered = json.dumps(node.outputs, ensure_ascii=False, indent=2)
+            if len(rendered) > _MAX_TERMINAL_OUTPUT_CHARS:
+                return rendered[:_MAX_TERMINAL_OUTPUT_CHARS] + _TERMINAL_OUTPUT_TRUNCATED_MARKER
+            return rendered
     return ""
 
 
diff --git a/api/tests/unit_tests/core/dify_builder/test_handlers_build.py b/api/tests/unit_tests/core/dify_builder/test_handlers_build.py
index af143d7ca6f..ed783c1db70 100644
--- a/api/tests/unit_tests/core/dify_builder/test_handlers_build.py
+++ b/api/tests/unit_tests/core/dify_builder/test_handlers_build.py
@@ -600,6 +600,25 @@ def test_a_passing_test_shows_what_the_workflow_produced():
     assert '"result": "42"' in test_result.payload["output"]
 
 
+def test_a_passing_test_caps_an_oversized_output_with_a_marker():
+    """Node outputs are only truncated upstream at ~100,000 chars per string,
+    so an uncapped render (e.g. a report-generating workflow, the Builder's
+    showcase case) could push hundreds of KB of JSON into the card, the SSE
+    frame, and the localizer walk on every successful build. The card must
+    cap the rendered output instead, with a visible truncation marker."""
+    from core.dify_builder.handlers_build import _MAX_TERMINAL_OUTPUT_CHARS, handle_test_and_repair
+
+    env, _ = _new_env()  # default FakeDifyPort; verify_pass=True by default
+    env.dify.run_outputs = {"report": "x" * 50_000}  # far beyond the cap once JSON-rendered
+    s = _session(entry_mode=EntryMode.BUILD, current_state=PcState.BUILD_TEST_AND_REPAIR)
+    fc = DifyBuilderContext(built_node_ids=["llm"])
+    result = handle_test_and_repair(env, Turn(actor=_actor()), s, fc)
+    test_result = next(i for i in result.items if i.kind == "test_result")
+    output = test_result.payload["output"]
+    assert len(output) < _MAX_TERMINAL_OUTPUT_CHARS + 100  # capped, not the ~50KB payload
+    assert "truncated" in output
+
+
 def test_a_passing_test_with_no_output_shows_none():
     """No output produced -> the card's output is "", not a stale/placeholder
     value -- a passing test that shows nothing is not evidence of anything,