[Feature] Add Winnow read strategy to the Decisions API

[Txoka]

Overview

Add an explicit Winnow read strategy to the Decisions API, preserving the model’s trained prompt and candidate-token protocol.

This PR depends on the still-open #60465, pinned at 4f5fd1e2f93ff16e8fec2b731fbed61eceb77f66, and reuses the shared structured decision backend from #59299.

Claims

• Render canonical Winnow state, questions, and options instead of a generic chat prompt.
• Support predicate, choice, and score answers through existing Decisions response types.
• Apply external conditional temperature while preserving raw full-vocabulary confidence.

Validation

October 10 rebase: updated onto upstream 2bea220 and refreshed the pending #60465 implementation from a8867eab, retaining upstream DiffusionGemma routing and shared tracing. The image branch remains stacked on the text branch. All 86 affected CPU/HTTP tests and all contribution-file pre-commit hooks passed. GPU/model evaluations were not rerun for this rebase.

Rebased onto upstream 9adba10f3f4bb3bb756f9de53fbf6820668157db on October 9. Preserved upstream cache-salt and tracing behavior in the relocated shared backend, and forwarded both through Winnow reads. The three affected CPU/HTTP suites passed 84 tests; after adding cache-salt/tracing coverage, the strategy suite passed 36 tests. Contribution-file pre-commit hooks, including mypy, passed.

Local checks

Check	Result
Focused CPU/HTTP tests	70 passed after rebase
Full-repository pre-commit hooks	Passed
Entrypoint CPU unit tests	189 passed
API generation tests	78 passed; 18 GPU-memory skips
Broader launcher tests	232 passed; memory skips and remaining environment failures

The focused tests cover exact prompts, candidate mappings, model restrictions, malformed requests, and temperature/confidence semantics.

Remaining launcher failures included CUDA device-busy/unavailable errors and device-wide memory-release timeouts. A one-element PyTorch CUDA allocation outside vLLM reproduced the device-busy error. Complete upstream Buildkite and hardware CI has not been run; this PR does not claim a full CI pass.

To reproduce the focused tests in a test-enabled environment:

.venv/bin/python -m pytest \
  tests/entrypoints/generate/structured_decisions/test_question_types.py \
  tests/entrypoints/generate/structured_decisions/test_strategies.py \
  tests/entrypoints/generate/structured_decisions/test_decisions.py \
  -q

Quantized runtime checks

Resident mixed-scope AWQ4 and AWQ8 checks exercised all three API types, public and typed benchmarks, and concurrency sweeps without CPU offload.

AWQ4 quality regressed substantially. AWQ8 retained approximately the native reference’s public accuracy, with mixed typed results:

Metric	Native reference	AWQ8
Public accuracy	~74.10%	~74.10%
Typed accuracy	71.90%	72.35%
Typed ECE	5.33%	6.13%

These results provide compatibility evidence, not a claim of universal quantization quality or speedup. Full measurements remain in the separate research packet.

Details

The generic strategy JSON-quotes choice values and uses a chat prompt, which differs from Winnow’s trained serialization. Explicit strategy selection isolates this model-specific behavior while retaining existing generic routing and response semantics.

Temperature rescales conditional candidate probabilities. Confidence remains the raw engine probability of the selected candidate. A checkpoint-specific residual calibration is external, rather than baked into these weights.

This PR does not duplicate #60465’s endpoint implementation or #60676’s LiquidAI/Jev image work. AI assistance was used to implement, test, and document the contribution. The submitting human confirmed review of every changed line and execution of the relevant tests.

Stacked review

Review only the Winnow changes.

The full PR diff includes the pending predecessor until #60465 merges and will need rebasing afterward. Vision support remains on a separate stacked branch.

---

Pull Request Checklist

• I used vLLM’s /pr-checklist skill.
• AI assistance was used during the creation of this PR.
• Design Fit: Reuses the existing backend and isolates model-specific serialization.
• Testing and Validation: Local CPU/API checks pass with documented memory skips. Launcher environment failures and upstream hardware CI limitations are disclosed. Human review and relevant test execution are confirmed.
• Code Quality and Style: Full-repository hooks pass; documentation is included.
• Pull Request Contents: Human review is confirmed; dependencies and test limitations are disclosed.

Rebased on the updated #60465 head on October 9. Affected text tests: 70 passed; contribution-file pre-commit hooks passed. The rebased Winnow branch merges cleanly with the fetched upstream main (ab905a8). Earlier full-repository and GPU validation results above predate this rebase; no new full-hardware CI pass is claimed.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[mergify]

Documentation preview: https://vllm--60713.org.readthedocs.build/en/60713/

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @Txoka.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @Txoka.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @Txoka.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @Txoka.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork