Add a sandbox sample and snipsync markers for the OpenAI Agents docs guide

[brianstrauch]

What changed

New openai_agents/sandbox sample. Covers SandboxAgent through the plugin: SandboxClientProvider on the worker, temporal_sandbox_client() in the workflow, and a run that writes a file in the sandbox, reads it back, and reports what it found.

It uses UnixLocalSandboxClient, so it runs with only OPENAI_API_KEY and no Daytona/E2B account — at the cost of giving the agent a shell on the worker host, which the sample README calls out and points at the remote clients for production. Worth knowing: that class lives in agents.sandbox.sandboxes.unix_local, not the agents.extensions.sandbox.unix_local path the contrib README shows (fixed in temporalio/sdk-python#1764).

Snipsync markers on the 16 existing samples the docs guide walks through.

Why?

Python is currently the only Temporal OpenAI Agents integration with no guide on docs.temporal.io — the SDK index and the integrations grid both send readers to the contrib README on GitHub. The companion docs PR adds that guide, and it needs code to pull from here rather than hand-maintaining inline copies. Sandbox is the one section with no sample to pull from, hence the new one.

Two details worth flagging for review:

• Markers are scoped to exactly the code the guide shows, so no docs block needs selectedLines and none renders a leading # ... elision.
• Markers that wrap indented code sit at that code's indent level rather than column 0, keeping snipsync's dedenting working — the same fix as Scope google_genai snippet markers to the excerpted code #346.

Checklist

1. Closes

2. How was this tested:

The sandbox sample was run end to end against temporal server start-dev. With no OpenAI key available, the model was driven by the plugin's own temporalio.contrib.openai_agents.testing.TestModel scripting one exec_command tool call; the sandbox itself was real. The workflow returned its output and history confirms the sandbox activities executed:

invoke_model_activity
local-sandbox_client_create
local-sandbox_session_start
local-sandbox_session_running
local-sandbox_session_pty_exec_start
local-sandbox_session_stop
local-sandbox_session_shutdown
local-sandbox_client_delete

Also confirmed the worker registers all 16 activities under the local- provider prefix, and that it boots and polls the task queue.

ruff check --select I, ruff format --check, and mypy --check-untyped-defs --namespace-packages all pass across openai_agents/ (120 files).

Snippet resolution was verified by pointing a local snipsync.config.yaml at this working tree and running yarn snipsync from the documentation repo: all 18 IDs resolve and every excerpt dedents to column 0.

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