[Test][Frontend] Cover resume cancellation during takeover

[LOGO127]

Purpose

Test-only follow-up to #7429 after #7413 landed the production rollback behavior. The older conflicting implementation PR is closed; this PR changes no production code.

Parameterize the existing cancellation regression for attached takeover and detached reconnect, at both activation and replay (four combinations). Retain the attachment rollback and old-token recovery assertions. The inspected Oct-5 main snapshot 0b0d2d700 still covers only the detached reconnect combinations in this regression, so the attached takeover coverage is not duplicated.

Validation

Signed PR head: 4003916cb3bce0be56b985a40db3da745b5a262a.

• git diff --check and applicable pre-commit hooks previously passed; the signed test source is unchanged.
• Native CPU source-checkout execution at this PR head: 25 passed, 0 skipped, using normal Omni/vLLM initialization and repository conftests, with vLLM v0.30.0 source ced6857afa0ea7b2e3f0846a62e1394e90f15607.
• Oct-5 pinned-main compatibility execution: the exact signed PR test file against Omni 0b0d2d70090e1df820de95ef599e109981bf06d0 and vLLM v0.31.0 source db9527a46873454610df6dbedf79a36d6bf1a7f6 also passed 25 tests, 0 skipped, including all four cancellation combinations. Post-run verification confirmed the tested attachment registry was imported from that main snapshot. This is a compatibility run, not a rebase or a merged candidate tree. The two runs cover the same cases and are not additive.

Environment: WSL Python 3.12.3, PyTorch 2.11.0+cpu, Transformers 5.14.1. Installed vLLM distribution metadata remains 0.28.0; Python source imports were explicitly pinned as above. Only the CPU host's NVML discovery was adapted. Each run had one pytest/anyio import-rewrite warning. These results supersede the earlier initialization-bypassing supplemental run; they do not certify a rebuilt wheel, native kernels, the complete CI image, GPU, live serving, network transport or PersonaPlex resume support.

With compatible dependencies, from the PR checkout's tests directory:

python -m pytest entrypoints/openai/test_duplex_session_attachment.py \
  -m 'core_model and cpu' --run-level core_model -q

Status

At the Oct-5 status check, DCO, Python 3.11/3.12 wheel builds and pre-commit are successful for this head. GitHub still shows docs Pending, but the Read the Docs API reports exact-commit build 34894885 as cancelled, with success=false and no error text. The commit-filtered listing contains only that build; no replacement/live documentation job is evidenced, and no cancellation cause is inferred. No retrigger has been performed.

Keeping this Draft pending final readiness review and the documentation check. Codex assisted with the test-only change, local verification and this description; this does not replace personal review or DCO attestation.

[LOGO127]

Update: I fixed the CI formatting-only failure on the existing test-only change and pushed refreshed head eb46d06e. ruff format --check, py_compile, and git diff --check pass locally on the changed test file. The remaining DCO check requires contributor sign-off; I am not representing that as completed. No production code or test semantics changed.