Sleep gains a depth: the wake threshold rides FLP-11 and the unspent pressure

[YesterdaysLemon]

Closes #204.

What

Arousability across a real sleep bout is graded, not flat — thresholds rise as the bout deepens and fall again near its natural end (Nichols et al. 2017, graded arousability across sleep in C. elegans). The model's arousal was a hard constant: measured before this change, a poke at any strength ≥ 1.0 woke the animal at every instant of a bout, identically.

The mechanism (no new state)

Both halves of the depth curve were already in the homeostat's state:

• FLP-11 is slow to accumulate (flp11_tau), so the bout's start is shallow — the depth on the way in;
• undischarged pressure is spent by the bout's end, so its close is shallow again — the depth on the way out.

depth = flp11 × clip((pressure − threshold_off)/(threshold_on − threshold_off)), and the wake threshold is arousal_touch + arousal_depth·depth. Nothing new is integrated, and depth is exactly zero in an animal that has never slept — the never-slept trajectory stays bit-identical.

Measured

On the shipped clock the threshold runs 0.74 → 1.13 → 0.86 at 2/20/35 s into a bout. The new behaviour test pins the curve and the inversion it buys:

• a gentle prod (1.0, delivering ~0.95 summed touch) wakes the dozing ends of a bout and rolls off its deep middle;
• the canonical hard prod (3.0, delivering ~1.7 within 0.3 s) always wakes — a depth that defended sleep against emergencies would be paralysis. The compressed-clock fixture's operating point was checked too (threshold 1.35 there, crossed at ~0.2 s), so the existing arousal tests keep their margins.

Runtime parity

The depth term is ported into the WASM sleep cascade and arousal_depth rides the payload. The conformance sleep scenario still sleeps and still wakes, and the port reproduces Python to 5e-13 mm / 6e-11 mV, multi-animal included.

On the site: a deeply-asleep worm is now genuinely harder to wake than a dozing one. 💤

🤖 Generated with Claude Code

https://claude.ai/code/session_01CBroMXcYdfkyb5buJPcKvL

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