[codex] Add friendly Python SDK sandbox presets (#24772)

## Why

The Python SDK currently exposes sandbox selection differently depending
on where it is used: thread lifecycle methods accept `SandboxMode`,
while turns accept the lower-level `SandboxPolicy` shape. For the common
case of choosing an access level, that leaks app-server wire details
into otherwise straightforward SDK usage.

This makes the common path explicit and discoverable: callers choose a
named sandbox preset once, using the same keyword on threads and turns.
The preset name `workspace_write` also makes the granted capability
clear at the callsite.

## What changed

- Added a root-level `Sandbox` enum with documented presets:
  - `Sandbox.read_only`: read files without allowing writes.
- `Sandbox.workspace_write`: the normal default for projects with a
recorded trust decision; read files and write inside the workspace and
configured writable roots.
  - `Sandbox.full_access`: run without filesystem access restrictions.
- Documented that omitting `sandbox=` delegates to app-server's
configured default, while explicit turn overrides remain sticky for
subsequent turns.
- Updated sync and async thread lifecycle and turn APIs to consistently
accept `sandbox=Sandbox...`, translating to the existing app-server
thread and turn representations internally.
- Updated the public API artifact generator so regenerated SDK wrappers
retain the friendly enum shape.
- Replaced low-level policy construction in Python docs, examples, and
the walkthrough notebook with the preset API.
- Added focused coverage for root exports, method signatures,
preset-to-wire mapping, and rejection of raw string sandbox inputs.

## API impact

High-level turn calls now use `sandbox=` instead of `sandbox_policy=`:

```python
from openai_codex import Codex, Sandbox

with Codex() as codex:
    thread = codex.thread_start(sandbox=Sandbox.workspace_write)
    result = thread.run("Review the diff only.", sandbox=Sandbox.read_only)
```

`thread_start(...)` already defaults to `ApprovalMode.auto_review`, so
normal writable usage is concise:

```python
with Codex() as codex:
    thread = codex.thread_start(sandbox=Sandbox.workspace_write)
    thread.run("Update the files in this workspace.")
```

With that combination, edits inside `cwd` and configured writable roots
run within the workspace-write sandbox. Operations that require
approval, such as edits outside those roots, are routed through auto
review. When `sandbox=` is omitted, app-server resolves its configured
default. A sandbox supplied to `run(...)` or `turn(...)` applies to that
turn and subsequent turns.

## Test coverage

- `sdk/python/tests/test_public_api_signatures.py` covers the public
export and parameter names, including the default approval mode.
- `sdk/python/tests/test_public_api_runtime_behavior.py` covers preset
mappings to the existing wire types and raw string rejection.

sdk/python/src/openai_codex/api.py

@@ -37,6 +37,7 @@ from ._run import (
     _collect_async_turn_result,
     _collect_turn_result,
 )
+from ._sandbox import Sandbox as Sandbox, _sandbox_mode, _sandbox_policy
 from .async_client import AsyncAppServerClient
 from .client import AppServerClient, AppServerConfig
 from .generated.v2_all import (
@@ -48,8 +49,6 @@ from .generated.v2_all import (
     Personality,
     ReasoningEffort,
     ReasoningSummary,
-    SandboxMode,
-    SandboxPolicy,
     SortDirection,
     ThreadArchiveResponse,
     ThreadCompactStartResponse,
@@ -138,7 +137,7 @@ class Codex:
         model: str | None = None,
         model_provider: str | None = None,
         personality: Personality | None = None,
-        sandbox: SandboxMode | None = None,
+        sandbox: Sandbox | None = None,
         service_name: str | None = None,
         service_tier: str | None = None,
         session_start_source: ThreadStartSource | None = None,
@@ -156,7 +155,7 @@ class Codex:
             model=model,
             model_provider=model_provider,
             personality=personality,
-            sandbox=sandbox,
+            sandbox=_sandbox_mode(sandbox),
             service_name=service_name,
             service_tier=service_tier,
             session_start_source=session_start_source,
@@ -205,7 +204,7 @@ class Codex:
         model: str | None = None,
         model_provider: str | None = None,
         personality: Personality | None = None,
-        sandbox: SandboxMode | None = None,
+        sandbox: Sandbox | None = None,
         service_tier: str | None = None,
     ) -> Thread:
         approval_policy, approvals_reviewer = _approval_mode_override_settings(approval_mode)
@@ -220,7 +219,7 @@ class Codex:
             model=model,
             model_provider=model_provider,
             personality=personality,
-            sandbox=sandbox,
+            sandbox=_sandbox_mode(sandbox),
             service_tier=service_tier,
         )
         resumed = self._client.thread_resume(thread_id, params)
@@ -238,7 +237,7 @@ class Codex:
         ephemeral: bool | None = None,
         model: str | None = None,
         model_provider: str | None = None,
-        sandbox: SandboxMode | None = None,
+        sandbox: Sandbox | None = None,
         service_tier: str | None = None,
         thread_source: ThreadSource | None = None,
     ) -> Thread:
@@ -254,7 +253,7 @@ class Codex:
             ephemeral=ephemeral,
             model=model,
             model_provider=model_provider,
-            sandbox=sandbox,
+            sandbox=_sandbox_mode(sandbox),
             service_tier=service_tier,
             thread_source=thread_source,
         )
@@ -371,7 +370,7 @@ class AsyncCodex:
         model: str | None = None,
         model_provider: str | None = None,
         personality: Personality | None = None,
-        sandbox: SandboxMode | None = None,
+        sandbox: Sandbox | None = None,
         service_name: str | None = None,
         service_tier: str | None = None,
         session_start_source: ThreadStartSource | None = None,
@@ -390,7 +389,7 @@ class AsyncCodex:
             model=model,
             model_provider=model_provider,
             personality=personality,
-            sandbox=sandbox,
+            sandbox=_sandbox_mode(sandbox),
             service_name=service_name,
             service_tier=service_tier,
             session_start_source=session_start_source,
@@ -440,7 +439,7 @@ class AsyncCodex:
         model: str | None = None,
         model_provider: str | None = None,
         personality: Personality | None = None,
-        sandbox: SandboxMode | None = None,
+        sandbox: Sandbox | None = None,
         service_tier: str | None = None,
     ) -> AsyncThread:
         await self._ensure_initialized()
@@ -456,7 +455,7 @@ class AsyncCodex:
             model=model,
             model_provider=model_provider,
             personality=personality,
-            sandbox=sandbox,
+            sandbox=_sandbox_mode(sandbox),
             service_tier=service_tier,
         )
         resumed = await self._client.thread_resume(thread_id, params)
@@ -474,7 +473,7 @@ class AsyncCodex:
         ephemeral: bool | None = None,
         model: str | None = None,
         model_provider: str | None = None,
-        sandbox: SandboxMode | None = None,
+        sandbox: Sandbox | None = None,
         service_tier: str | None = None,
         thread_source: ThreadSource | None = None,
     ) -> AsyncThread:
@@ -491,7 +490,7 @@ class AsyncCodex:
             ephemeral=ephemeral,
             model=model,
             model_provider=model_provider,
-            sandbox=sandbox,
+            sandbox=_sandbox_mode(sandbox),
             service_tier=service_tier,
             thread_source=thread_source,
         )
@@ -529,7 +528,7 @@ class Thread:
         model: str | None = None,
         output_schema: JsonObject | None = None,
         personality: Personality | None = None,
-        sandbox_policy: SandboxPolicy | None = None,
+        sandbox: Sandbox | None = None,
         service_tier: str | None = None,
         summary: ReasoningSummary | None = None,
     ) -> TurnResult:
@@ -541,7 +540,7 @@ class Thread:
             model=model,
             output_schema=output_schema,
             personality=personality,
-            sandbox_policy=sandbox_policy,
+            sandbox=sandbox,
             service_tier=service_tier,
             summary=summary,
         )
@@ -562,7 +561,7 @@ class Thread:
         model: str | None = None,
         output_schema: JsonObject | None = None,
         personality: Personality | None = None,
-        sandbox_policy: SandboxPolicy | None = None,
+        sandbox: Sandbox | None = None,
         service_tier: str | None = None,
         summary: ReasoningSummary | None = None,
     ) -> TurnHandle:
@@ -578,7 +577,7 @@ class Thread:
             model=model,
             output_schema=output_schema,
             personality=personality,
-            sandbox_policy=sandbox_policy,
+            sandbox_policy=_sandbox_policy(sandbox),
             service_tier=service_tier,
             summary=summary,
         )
@@ -612,7 +611,7 @@ class AsyncThread:
         model: str | None = None,
         output_schema: JsonObject | None = None,
         personality: Personality | None = None,
-        sandbox_policy: SandboxPolicy | None = None,
+        sandbox: Sandbox | None = None,
         service_tier: str | None = None,
         summary: ReasoningSummary | None = None,
     ) -> TurnResult:
@@ -624,7 +623,7 @@ class AsyncThread:
             model=model,
             output_schema=output_schema,
             personality=personality,
-            sandbox_policy=sandbox_policy,
+            sandbox=sandbox,
             service_tier=service_tier,
             summary=summary,
         )
@@ -645,7 +644,7 @@ class AsyncThread:
         model: str | None = None,
         output_schema: JsonObject | None = None,
         personality: Personality | None = None,
-        sandbox_policy: SandboxPolicy | None = None,
+        sandbox: Sandbox | None = None,
         service_tier: str | None = None,
         summary: ReasoningSummary | None = None,
     ) -> AsyncTurnHandle:
@@ -662,7 +661,7 @@ class AsyncThread:
             model=model,
             output_schema=output_schema,
             personality=personality,
-            sandbox_policy=sandbox_policy,
+            sandbox_policy=_sandbox_policy(sandbox),
             service_tier=service_tier,
             summary=summary,
         )