fix: accept rounded Jev probability distributions

[jmlago]

A valid Jev response such as [0.33, 0.33, 0.33] was rejected because decision validation required probability mass within 0.000001 of one. TypeSafe displays probabilities to two decimal places. Accept distributions whose rounding intervals contain unit mass for Jev model IDs, while keeping strict validation for other models and rejecting invalid values, missing options and non-argmax choices.

Apply the same validation to Choice, Score, the direct Jev adapter and automatic policy selection. Preserve reported probabilities; normalize only the derived entropy. The public endpoint regression tests cover both OpenRouter and AntSeed adapters.

Validation: 53 focused tests passed locally; public adapter integration tests require PostgreSQL and run in CI. Includes a randomized rounding property check. Documentation links the upstream precision contract and explains the validation bounds.

Observed production bad_response failures are consistent with this bug, but rejected upstream bodies were not retained, so this does not claim to explain every observed 502. This does not change generation deadlines or address separate generation-body timeouts. No deployment performed.

Summary by CodeRabbit

• New Features

  • Improved handling of rounded probability distributions for supported JEV models, including valid values that sum to 0.99 after display rounding.
  • Normalized entropy calculations while preserving reported probabilities, scores, confidence, and usage values.
  • Maintained strict probability validation for other model families and invalid distributions.

• Documentation

  • Added guidance on probability rounding, validation rules, and model-specific behavior.

• Tests

  • Expanded coverage for rounded choices, scores, routing, fallback behavior, and automatic revalidation.

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Reviewing files that changed from the base of the PR and between 05e98b1 and a16f470.

📒 Files selected for processing (1)

• docs/decision-rounding.md

📝 Walkthrough

Walkthrough

The change adds model-aware probability validation. Two-decimal Jev distributions can pass rounded-mass checks, while other models and invalid distributions retain strict validation. Normalized values are used only for entropy.

Changes

Model-aware probability validation

Layer / File(s)	Summary
Probability validation rules decision_providers/__init__.py	Adds model precision detection and rounded probability-sum validation. validate_answer preserves reported probabilities and normalizes values only for entropy.
Response and routing integration decision_protocol.py, decision_providers/jev.py, policy_selection.py	Passes model-specific precision through response validation, direct Jev parsing, score validation, and policy-result revalidation.
Rounding and routing coverage tests/test_decision_rounding.py, tests/test_automatic_routing.py, tests/test_decision_routing.py, docs/decision-rounding.md	Adds coverage and documentation for accepted Jev rounding, rejected invalid or non-Jev distributions, entropy normalization, and routing fallback behavior.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant DecisionResponse
  participant ResponseValidator
  participant JevProvider
  participant PolicySelector
  DecisionResponse->>ResponseValidator: submit model and probabilities
  ResponseValidator->>ResponseValidator: apply model-specific precision
  JevProvider->>ResponseValidator: validate parsed answer
  ResponseValidator-->>JevProvider: preserve probabilities and normalize entropy
  PolicySelector->>ResponseValidator: revalidate provider result
  ResponseValidator-->>PolicySelector: accept result or trigger fallback

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Merge Risk: 🔵 Low · up to 05e98

The mutable jev-latest alias receives rounded-probability handling but is absent from the documented contract. Update the documentation before merge.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 8.70% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 23 functions across 7 files. (1 skipped: 1…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: accepting rounded Jev probability distributions.
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.

Full details: Docstring Coverage

Explanation

Docstring coverage is 8.70% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 23 functions across 7 files. (1 skipped: 1 unsupported.)

✨ Finishing Touches 💡 1

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
In `@docs/decision-rounding.md`:
- Line 14: Update the sentence describing accepted Jev model identifiers to
include the mutable jev-latest alias, including vendor-prefixed forms, alongside
versioned identifiers.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 9d67a26b-bb13-4bce-8a48-e5692241c88a

📥 Commits

Reviewing files that changed from the base of the PR and between 3bb36ad and 05e98b1.

📒 Files selected for processing (8)

• decision_protocol.py
• decision_providers/__init__.py
• decision_providers/jev.py
• docs/decision-rounding.md
• policy_selection.py
• tests/test_automatic_routing.py
• tests/test_decision_rounding.py
• tests/test_decision_routing.py

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