Session Validation

Remote behavioral data is vulnerable to bots, distraction, and superficial engagement. The engine embeds a validation pipeline that runs automatically inside score_bart() and is also callable on its own via validate_bart_session().

Validation never raises on a playable session; instead it sets a boolean is_valid and accumulates human-readable warnings. Only structurally broken input (an empty log, or no balloons) raises.

What validate_bart_session returns

{
    "is_valid": bool,                  # False if any hard check fails
    "warnings": list[str],             # all soft + hard findings
    "balloon_count": int,
    "color_distribution": dict,        # {"purple": 10, "teal": 10, "orange": 10}
}

Checks

Check	Effect	Rule
Completeness	invalidates	Fewer than 15 of 30 balloons → is_valid = False.
Attrition	warns	15–29 balloons → retained but flagged incomplete.
Color balance	warns	Fewer than 5 balloons of a color → “too few”; 5–9 → “partial” (target is 10 each).
Monotonicity	invalidates	Any out-of-order timestamp → is_valid = False (browser lag, desync, or tampering).
Pacing	warns	A ≥15-balloon session finished in under 30 s.
Pump uniformity	warns	Across ≥10 balloons, pump-count standard deviation < 0.5 → possible automated play.

Auto-repeat detection

Separately from validate_bart_session, the scorer detects OS key-repeat: holding the pump key produces a burst of pumps at ~30–80 ms intervals rather than discrete decisions. _is_autorepeat_balloon() flags a balloon when the median inter-pump interval (over intervals < 2000 ms) is below 80 ms. Auto-repeat balloons are:

• excluded from all behavioral-intention metrics (pumps, learning, consistency, latency), and

• reported in session_warnings with the count of affected balloons.

They still count toward total_balloons, explosion_rate, and money_collected.

The RNG fallback

When a color has fewer than MIN_COLLECTED_FALLBACK (2) collected balloons, the engine cannot estimate behavioral intention from collected trials alone. It then falls back to using all trials of that color for that color’s behavioral mean and emits an RNG fallback warning. The EV-referenced efficiency for such a color is instead set to zero, because the participant secured essentially no payoff at that hazard level.

Interpreting validity

session_valid = False does not necessarily mean the data is worthless — it means at least one hard check failed (too few balloons, or non-monotonic timestamps). Treat session_warnings as a triage list: decide per study whether to exclude, retain, or manually review each flagged session. The reference study retained 15–29-balloon sessions with warnings and excluded sub-15 sessions entirely.