Python: [BREAKING] Request concise Harness progress without private reasoning

python/packages/core/agent_framework/_harness/_agent.py

@@ -52,16 +52,17 @@
 
 logger = logging.getLogger(__name__)
 
 DEFAULT_HARNESS_INSTRUCTIONS = """\
 You are a helpful AI assistant that uses tools to complete tasks.
 
 ## General guidelines
 
 - Think through the task before acting. Break complex work into clear steps.
 - Use the tools available to you to gather information, perform actions, and verify results.
-- Explain your reasoning and thought process as you work through tasks.
-- Explain what you learned and what you are going to do next between tool calls, \
-so the user can follow along with your thought process.
+- Explain decisions, actions, results, and important trade-offs at a high level. \
+Do not expose private chain-of-thought or hidden reasoning.
+- Keep the user informed with concise progress updates between tool calls, \
+summarizing what you learned and what you will do next.
 - Avoid making more than 4 tool calls in a row without explaining what you are doing.
 - If a tool call fails or returns unexpected results, adapt your approach rather than \
 repeating the same call.

python/packages/core/tests/core/test_harness_agent.py

@@ -94,6 +94,16 @@ def test_create_harness_agent_with_defaults() -> None:
     assert agent.id is not None
 
 
+def test_default_harness_instructions_keep_reasoning_private() -> None:
+    """Default guidance should request useful progress without private reasoning."""
+    instructions = _assemble_instructions(None, None)
+    assert instructions is not None
+    assert "Explain decisions, actions, results, and important trade-offs at a high level." in instructions
+    assert "Do not expose private chain-of-thought or hidden reasoning." in instructions
+    assert "concise progress updates between tool calls" in instructions
+    assert "thought process" not in instructions
+
+
 def test_create_harness_agent_includes_all_default_providers(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
     """Default assembly should include history, compaction, todo, mode, and file memory."""
     monkeypatch.chdir(tmp_path)

python/samples/02-agents/harness/harness_data_processing.py

@@ -74,7 +74,7 @@
 ## Working with data
 - When asked to analyze data, read the relevant files first, then perform the analysis.
 - Show your analysis clearly with tables, summaries, and key insights.
-- When calculations are needed, work through them step by step and show your reasoning.
+- When calculations are needed, show the formulas, inputs, and results so the user can verify them.
 
 ## Writing output
 - When asked to produce output files (e.g., reports, summaries, filtered data), use file_access_write to write them.
@@ -84,9 +84,10 @@
 ## Important
 - Never modify or delete the original input data files unless explicitly asked to do so.
 - If asked about data you haven't read yet, read it first before answering.
-- Always explain your reasoning and thought process as you work through tasks.
-- Always explain what you learned and what you are going to do next between tool calls, so the user can
-  follow along with your thought process.
+- Explain decisions, actions, results, and important trade-offs at a high level. \
+Do not expose private chain-of-thought or hidden reasoning.
+- Keep the user informed with concise progress updates between tool calls, \
+summarizing what you learned and what you will do next.
 """
 
 MAX_CONTEXT_WINDOW_TOKENS = 1_050_000