## Why
The SDK had behavioral tests that replaced SDK client internals. Those
tests could catch wrapper mistakes, but they did not prove the pinned
app-server runtime, generated notification models, request routing, and
sync/async public clients worked together.
This PR adds deterministic integration coverage that starts the pinned
`codex app-server` process and mocks only the upstream Responses HTTP
boundary.
## What
- Add `AppServerHarness` and `MockResponsesServer` helpers for isolated
`CODEX_HOME`, mock-provider config, queued SSE responses, and captured
`/v1/responses` requests.
- Add shared helpers for SSE construction, stream assertions,
approval-policy inspection, and image fixtures.
- Split integration coverage into focused modules for run behavior,
inputs, streaming, turn controls, approvals, and thread lifecycle.
- Cover sync and async `Thread.run`, `TurnHandle.stream`, interleaved
streams, approval-mode persistence, lifecycle helpers, final-answer
phase handling, image inputs, loaded skill input injection, steering,
interruption, listing, history reads, run overrides, and token usage
mapping.
- Replace public-wrapper tests that duplicated integration-test behavior
with lower-level client tests only where direct client behavior is the
thing under test.
## Stack
1. #21891 `[1/8]` Pin Python SDK runtime dependency
2. #21893 `[2/8]` Generate Python SDK types from pinned runtime
3. #21895 `[3/8]` Run Python SDK tests in CI
4. #21896 `[4/8]` Define Python SDK public API surface
5. #21905 `[5/8]` Rename Python SDK package to `openai-codex`
6. #21910 `[6/8]` Add high-level Python SDK approval mode
7. This PR `[7/8]` Add Python SDK app-server integration harness
8. #22021 `[8/8]` Add Python SDK Ruff formatting
## Verification
- Added pinned app-server integration tests under
`sdk/python/tests/test_app_server_*.py` and
`test_real_app_server_integration.py`.
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Co-authored-by: Codex <noreply@openai.com>
