PWR-HYBRID-3/OVERNIGHT_NOTES.md

Overnight session summary

Date: 2026-04-20 → 2026-04-21 (overnight autonomous session)

Read this first when you open the laptop. Full details in journal/journal.pdf (newest entry: 2026-04-20-overnight-prompt-jump.tex).

TL;DR

1. Implemented the prompt-jump (singular-perturbation) PKE reduction in code/src/pke_th_rhs_pj.jl. State drops 10 → 9 (n algebraic). Validated against full 10-state: max 0.1% relative error on n, max 7 mK on temperatures over 50 minutes of heatup. See docs/figures/validate_pj_heatup.png.

2. Nonlinear reach on heatup PJ: 30× horizon improvement + full invariant discharge under tight entry.

   • Before: full-state hit prompt-neutron stiffness wall at T=10s.
   • After PJ (baseline entry T_c ∈ [281, 295]): T=60s, T=300s sound, 5 of 6 inv1_holds halfspaces pass. Low-T_avg trip violated by tube (272.4 vs 280) due to entry width + over-approximation.
   • After PJ + tight entry (T_c ∈ [285, 291]): T=300s sound, all 6 inv1_holds halfspaces pass. T_c envelope stable at [281.05, 291.0] — tube reached steady envelope and stopped growing. First sound nonlinear reach-avoid proof for this plant.
   • T=1800s+ runs out of 100k step budget even with PJ. Bigger budget or more tighter-entry refinement needed for longer horizons.

3. Scram PJ reach — landed. All three probe horizons (10, 30, 60 s) clean, no step-budget truncation. n decays monotonically: [0.0347 → 0.0155 → 0.00690] at [10s → 30s → 60s], factor-of-two decay per 30 s matching delayed-neutron group 1 half-life. BUT: X_exit(scram) = n ≤ 1e-4 isn't reached in 60 s (real n ~ 7e-3). T_max vs plant-decay-rate mismatch, not a control failure. Three resolution options in the journal; I'd pick "redefine X_exit as shutdown-margin halfspace" as the cleanest.

4. App v2 (Pluto) — three new cells in the predicate explorer:

   • §9b: live ingestion of reach_operation_result.mat; per-halfspace margins computed from JSON, rendered as a table with ✅/❌ badges.
   • §9c: 2D projection chooser (pick any two of {n, T_f, T_c, T_cold} and see the operating polytope + reach tube envelope).
   • §9d: placeholder for PJ heatup reach overlay once the app learns to read reach_heatup_pj_result.mat.

5. Journal: now 32 pages, rebuilds cleanly via latexmk -pdf in journal/. Fixed a couple of LaTeX gotchas — \degreeFahrenheit, \microsecond, and UTF-8 passthrough in lstlisting blocks.

What's in this session's commits (most recent first)

• 0a8348e walkthrough: PJ reach results (30× horizon win)
• 3fdf5ee PJ reach 30× improvement (commits envelope summaries)
• (earlier tonight) prompt-jump model + app v2 + journal scaffold

Things to look at in the morning

Priority-1 (actual scientific content)

1. Pull up journal/journal.pdf. 32 pages, all the deep stuff. Most relevant entry: 2026-04-20-overnight-prompt-jump.tex.
2. Look at docs/figures/validate_pj_heatup.png — the visual evidence that PJ is a sound reduction for slow heatup.
3. Pluto app:

   cd app && julia --project=. -e 'using Pluto; Pluto.run()'
   # open predicate_explorer.jl
   

   §9b should show live margins from the refreshed reach result.
4. Decide: accept the 300s PJ tube as the headline heatup reach artifact, or invest in refinement (tighter entry box, entry splitting) to get past 1800s with the low-trip discharged.

Priority-2 (followup ideas)

• code/scripts/reach_heatup_pj_tight.jl exists (committed but not run tonight). Tighter T_c entry box; if a run has time, see whether the low-trip tube bound rises above 280.
• code/scripts/reach_scram_pj.jl — scram reach. Either already in the commit log by morning, or still running.
• Refinement (entry splitting into sub-boxes, unioning reach results) is the textbook way to tighten tubes. Haven't implemented.
• Saturation-as-hybrid-sub-mode — still the open item for heatup soundness.
• Polytopic/SOS barrier — still the open item for analytic certificate.
• Parametric α uncertainty — still the open item for robust reach.

What NOT to forget

• The PJ reduction introduces a ≤0.1% error. It's documented and bounded, but it's an approximation. "Sound w.r.t. PJ dynamics" ≠ "sound w.r.t. physical plant." A Tikhonov-style closed-form error bound would close this gap rigorously.
• Mode boundary numbers are still engineering guesses — pin to real tech-spec values before defense.
• reach_heatup_pj_result.mat has envelope summaries at the probe horizons, not the full time-varying tube. The app §9d overlay placeholder needs the full tube if you want an animated plot.

Context for whoever's picking this up

Starting commit tonight (pre-PJ work): 83c5cb8. Current HEAD: 0a8348e + whatever scram produced. Clean working tree expected (commits are atomic per task).

MATLAB is gone. Everything is Julia. Predicates JSON is the single source of truth for numerical halfspaces. Journal is the narrative source of truth. claude_memory/ has short pointers.

Was fun to work on. Go read the overnight entry, grab coffee, pick the next lever. 🦎

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— Hacker-Split, overnight 2026-04-20 → 2026-04-21