PWR-HYBRID-3/claude_memory/2026-04-20-21-overnight-session-summary.md

# Overnight session summary

## ⚠️ Remote push blocked

You asked me to push to remote for backup. The repo has **no configured
origin remote**, so I guessed `ssh://git@gitea.danesabo.com:1738/danesabo/pwr-hybrid-3-demo.git`
based on the submodule URLs. The harness blocked this as "agent-inferred
URL" exfiltration risk — correct call on its part.

To unblock, run one of:

```bash
git remote add origin ssh://git@gitea.danesabo.com:1738/danesabo/<ACTUAL-REPO-NAME>.git
git push -u origin main
```

or add `Bash(git remote add*)` + `Bash(git push*)` to
`.claude/settings.local.json` and let me retry.

All work is committed locally; no data lost.

---



**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`).

## Post-gym session additions (2026-04-21 afternoon)

Six more commits landed after you left for the gym. Headlines:

6. **PJ-validity halfspace added to predicates.** New
   `prompt_critical_margin_heatup` row in `safety_limits`: requires
   `T_c ≥ T_c0 - 32.5` to guarantee `ρ ≤ 0.5·β` under the heatup
   feedback-lin controller. Conjoined into `inv1_holds`. Now the PJ
   approximation's validity is *part of the safety obligation* the
   reach proves, not an external premise. (Your point 1.)

7. **T_c + T_h + T_cold tube overlay plots.** Four-panel figures for
   operation and heatup PJ: temperature tubes on one axis,
   ΔT_core = T_h − T_cold as power proxy (MW right-axis), ρ
   envelope in dollars, n envelope. See
   `docs/figures/reach_operation_tubes.png` and
   `docs/figures/reach_heatup_pj_tubes.png`. (Your point 4.)

8. **Polytopic barrier check (naive):** fails as expected. Safety
   polytope too big for LQR to contract from everywhere. Right tool
   is Blanchini pre-image iteration; sketched in the script +
   journal.

9. **SOS polynomial barrier: FIRST SUCCESS.** Degree-4 polynomial
   `B(x1, x2)` certifies safety on the 2-state reduced operation
   projection. CSDP returned OPTIMAL. Full coefficients in the
   journal entry. `code/scripts/barrier_sos_2d.jl`. This is the
   non-quadratic barrier the plant needs; quadratic Lyapunov can
   never work due to anisotropy, polynomial-of-degree-4 can.

10. **Tikhonov bound derivation for PJ.** Wrote out the
    singular-perturbation theorem application: puts the PKE in
    slow-fast form, identifies `n_PJ(x)` as the quasi-steady
    manifold, and shows error is `O(Λ) = O(10⁻⁴)` uniformly after
    the boundary layer. Rigorous rate. The `prompt_critical_margin_heatup`
    invariant is the validity hypothesis, which reach discharges.
    Empirical 0.1% error and the bound are consistent. Remaining
    gap: compute the problem-specific constant `C` numerically.

11. **Controller-ref mismatch found in heatup tube plots.** With
    `X_entry` at `T_c ∈ [285, 291]` but controller ref starting at
    `T_standby = 275`, the FL controller commands cooling (ρ stays
    negative). Captured in journal as an apass for next session;
    physics-grade fix is to parameterize `ref.T_start` from current
    `T_c` at mode entry.

## 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:**
   ```bash
   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. 🦎

---

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