[devin-ai-integration]

Summary

Closes a code scan coverage gap: _aggregate_episode_stats, _extract_err_msg and ExpResult.status in src/agentlab/experiments/loop.py produce the per-episode summary numbers and completion status behind every report, but were only exercised indirectly on the happy path.

New tests/experiments/test_loop_stats.py (14 tests, no source changes) drives the edge branches directly:

• _aggregate_episode_stats: cum_/max_ values, None -> np.nan skipping, the all-NaN key (cum_ == 0, max_ is None), empty episode ({"cum_steps": 0}), and that every returned value is a builtin int/float rather than an np.generic.
• _extract_err_msg: last non-None (err_msg, stack_trace) wins, missing stack trace yields (msg, None), clean episode yields (None, None), agent_info=None steps are skipped.
• ExpResult.status over a tmp_path: missing file and empty summary_info.json -> incomplete, err_msg set -> error, terminated or truncated -> done, neither -> incomplete.

Devin-Org: engineering

Link to Devin session: https://app.devin.ai/sessions/f9baa5b4abad4a4a849609f075970556
Open in Devin Desktop: https://app.devin.ai/desktop/session/f9baa5b4abad4a4a849609f075970556?variant=devin

[devin-ai-integration]

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