fix: guard _classify_completed_outcomes against non-dict rewards

[VaisakhiMishra]

Previously, a truthy non-dict value in the 'rewards' field of result.json (e.g. bare float 1.0, int, bool, list) caused an uncaught AttributeError in _classify_completed_outcomes, crashing the entire evaluation run before any new tasks could execute.

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How to reproduce the crash (pre-fix)

# 1. Create a jobs directory with a result.json whose rewards is a bare float
mkdir -p /tmp/bf_repro/my-job/my-task__abc123
cat > /tmp/bf_repro/my-job/my-task__abc123/result.json <<'EOF'
{
  "task_name": "my-task",
  "rollout_name": "my-task__abc123",
  "rewards": 1.0,
  "agent": "oracle",
  "model": null,
  "n_tool_calls": 5
}
EOF

# 2. Resume — crashes before any tasks run
bench eval run --tasks-dir tasks/my-task --jobs-dir /tmp/bf_repro
# AttributeError: 'float' object has no attribute 'get'

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Can we make this bug fix as part of https://github.com/benchflow-ai/FrontierPhysics/issues/125 or should I open a separate issue to track this fix?

Root cause:

    rewards = r.get('rewards') if isinstance(r, dict) else None
    reward = rewards.get('reward') if rewards else None

only guards against falsy values; a truthy non-dict (e.g. 1.0) passes the if rewards check and then fails on .get().

Fixes:

1. Import extract_reward from benchflow._utils.scoring — it already handles None, dict, and non-dict values safely.
2. Replace the two-liner in _classify_completed_outcomes with:

reward = extract_reward(r) 
if isinstance(r, dict) else None

3. Add a logger.warning in _get_completed_tasks when rewards is a non-dict truthy value, so operators can identify malformed result files without a crash. The fix is backwards-compatible: valid dict-shaped rewards are unchanged; falsy non-dict values were already silently treated as errored and still are (with a warning now); truthy non-dict values no longer crash.

4. Minimal fix for uvx ruff check . failure for src/benchflow/contracts/user.py

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[devin-ai-integration]

Devin Review found 1 potential issue.

[VaisakhiMishra]

/devin review