fix(skippy): treat zero-temperature sampling as greedy

[i386]

Problem

OpenAI clients commonly use temperature: 0 when they need reproducible output. Skippy still classified those requests as stochastic whenever sampling was enabled, so it rejected verified linear proposals even when no sampling option could change the winning token.

That meant a deterministic request behaved differently depending on whether the client omitted sampling settings or explicitly requested zero temperature.

Fix

Admission now depends on whether the request can actually change greedy token selection. Zero temperature with neutral penalties and no logit bias is treated as deterministic. Non-zero temperature, grammar-constrained sampling, penalties, and logit bias remain excluded.

This keeps the safety boundary narrow: proposals are admitted only when verification is equivalent to greedy decoding, without special-casing a particular model or client.

Validation

Skippy Server tests pass (353/353), including deterministic and stochastic sampling cases.

Summary by CodeRabbit

• Bug Fixes
  • Improved linear proposal handling for generation requests.
  • Deterministic, zero-temperature sampling is now supported when no penalties or bias adjustments are applied.
  • Requests using stochastic sampling or logit-modifying settings continue to be handled appropriately.

[github-actions]

This pull request is currently a draft. Reviews will not take place until the PR is marked as ready for review.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: c789bda4-a659-4a9b-a96a-7abf7ea4d880

📥 Commits

Reviewing files that changed from the base of the PR and between 4d289b0 and 42b7fdf.

📒 Files selected for processing (2)

• crates/skippy-server/src/frontend/linear_proposal.rs
• crates/skippy-server/src/frontend/local_generation.rs

🚧 Files skipped from review as they are similar to previous changes (2)

• crates/skippy-server/src/frontend/local_generation.rs
• crates/skippy-server/src/frontend/linear_proposal.rs

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📝 Walkthrough

Walkthrough

Linear proposal admission now evaluates the complete SamplingConfig. Greedy-equivalent settings remain eligible, while stochastic or logit-modified settings are rejected. Local generation passes the full configuration to the admission check.

Changes

Sampling-aware linear proposal admission

Layer / File(s)	Summary
Sampling configuration admission crates/skippy-server/src/frontend/linear_proposal.rs	greedy_linear_proposal_admitted evaluates sampling enablement, temperature, penalties, repeat penalty, and logit bias. Tests cover disabled, zero-temperature, stochastic, logit-biased, and grammar metadata configurations.
Local generation integration crates/skippy-server/src/frontend/local_generation.rs	Local generation passes the complete sampling configuration to linear proposal admission.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• Mesh-LLM/mesh-llm#1081: Introduces the same proposal-admission logic that this change refines.

Suggested labels: experimental

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: zero-temperature sampling is treated as greedy for proposal admission.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch agent/skippy-zero-temperature-greedy

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[michaelneale]

Low risk: local speculative-verification admission only, invisible across versions. Zero-temp treated as greedy is a correct, well-scoped change. LGTM.