Examples+Docs: add FileEditor GPT-5.1 example and update ApplyPatch Responses notes

- FileEditor example mirrors ApplyPatch for log comparison
- Notes: restore reasoning passthrough; pair assistant calls with tool outputs

Co-authored-by: openhands <[email protected]>

Author: enyst

docs/dev/apply_patch_responses_notes.md

@@ -17,8 +17,8 @@ We integrated an ApplyPatch tool modeled after OpenAI's cookbook for GPT-5.1 "se
 
 ## Responses pipeline adjustments
 
-- Do not echo prior-turn `reasoning` items in input; this can violate ordering constraints.
-- Include assistant `function_call` items in the input and the paired `function_call_output` items produced by tools. This satisfies the server's validation that an output must correspond to a previous call in the same input batch.
+- Reasoning passthrough: we DO include the prior-turn `reasoning` item in input (test `test_assistant_includes_reasoning_passthrough` depends on this). It must not be the last input item; it should be followed by at least one other item (message or function_call), which our serializer ensures by ordering.
+- Assistant tool calls: we include assistant `function_call` items in input and pair them with `function_call_output` items produced by tools in the same request. This satisfies the server's validation that an output must correspond to a previous call in the same input batch.
 
 ## Remaining issue
 

examples/01_standalone_sdk/29_file_editor_with_gpt5_1.py

@@ -0,0 +1,63 @@
+"""Example: Using FileEditor tool with GPT-5.1 models via direct OpenAI API.
+
+This mirrors the ApplyPatch example but uses FileEditor to create/modify/delete
+FACTS.txt. Useful for comparing Responses input/output behavior and logs.
+
+Requirements:
+- OPENAI_API_KEY in the environment (or LLM_API_KEY)
+- Model: any openai/gpt-5.1* variant; default uses openai/gpt-5.1-codex-mini
+"""
+
+from __future__ import annotations
+
+import os
+
+from pydantic import SecretStr
+
+from openhands.sdk import LLM, Agent, Conversation, get_logger
+from openhands.sdk.tool import Tool
+from openhands.tools.file_editor import FileEditorTool
+from openhands.tools.task_tracker import TaskTrackerTool
+from openhands.tools.terminal import TerminalTool
+
+
+logger = get_logger(__name__)
+
+api_key = os.getenv("OPENAI_API_KEY") or os.getenv("LLM_API_KEY")
+assert api_key, "Set OPENAI_API_KEY (or LLM_API_KEY) in your environment."
+
+model = os.getenv("LLM_MODEL", "openai/gpt-5.1-codex-mini")
+assert model.startswith("openai/gpt-5.1"), "Model must be an openai gpt-5.1 variant"
+
+llm = LLM(
+    model=model,
+    api_key=SecretStr(api_key),
+    native_tool_calling=True,
+    reasoning_summary=None,
+    log_completions=True,
+)
+
+# Ensure registration
+_ = (TerminalTool, TaskTrackerTool, FileEditorTool)
+
+agent = Agent(
+    llm=llm,
+    tools=[Tool(name="terminal"), Tool(name="task_tracker"), Tool(name="file_editor")],
+    system_prompt_kwargs={"cli_mode": True},
+)
+
+conversation = Conversation(agent=agent, workspace=os.getcwd())
+
+prompt = (
+    "You must use tools to perform all actions. Do not merely describe actions. "
+    "Use the FileEditor tool to: "
+    "1) create a FACTS.txt with a single line 'OpenHands SDK integrates tools.'; "
+    "2) modify FACTS.txt by appending a second line 'FileEditor works.'; "
+    "3) delete FACTS.txt using the terminal tool with: rm FACTS.txt."
+)
+
+conversation.send_message(prompt)
+conversation.run()
+
+print("Conversation finished.")
+print(f"EXAMPLE_COST: {llm.metrics.accumulated_cost}")