# `turn1-state → turn2` is not a deterministic pair

Lane L5, 2026-09-08, VM146. A by-product of a rule-19 control, and a caution for any lane that
reaches for this pair as an oracle.

## What was measured

Three End Turns from the same input save, through the identical UI path, in three freshly launched
processes:

| run | shim | `(Autosave).sav` sha256[0:16] | `Player[512 "Singularity"]/ResTNm` |
|---|---|---|---|
| control | `hooks=off` (no MinHook at all) | `62061918176e3441` | `XNC_TrnsLir2` |
| A | `ComputeBudget=compare` | `7fc9e6ab46b47794` | `XNC_TrnsHvr2` |
| B | same hooks, different arithmetic on OUR side only | `ab4ac2d7e2977260` | `BIO_GnMod` |

Every pairwise diff is **exactly four leaves**: that research-target name, two of that player's
tech-tree status words, and the derived `/Summary/Checksum`. Nothing else in the state moves.

## Why this is not the instrument

* Runs A and B carry **identical hooks**. They differ only in a constant on our side of the
  compare, and compare mode runs `ours` on scratch copies and never lets it touch game memory. A
  hook-induced perturbation cannot produce A ≠ B.
* The `hooks=off` control is a **third** value, not one of the other two.
* Run B reproduced `ab4ac2d7e2977260…`, which is the hash `running-the-game.md` records for the
  original live session's `Autosave - turn2.sav`. So the un-instrumented behaviour is inside the
  observed spread.
* All three runs wrote a **byte-identical pre-turn autosave** (`a3f9dc4b49fc669c…`). The loader and
  the writer are deterministic; only the turn's AI decision is not.

## Why it matters

`determinism-oracle.md` established byte-reproducibility on **`ref-turn2 → turn3`** — five runs,
two processes, one pair of hashes. That result is sound and is not contradicted here. What is new
is that **it does not generalise**: the neighbouring pair in the same game is unstable, in one
shadow empire's AI research pick.

Consequences:

* Do not use `turn1-state → turn2` as a byte-match oracle. Use `ref-turn2 → turn3`.
* A standalone comparison against a `turn1-state → turn2` post-save is comparing against one draw
  from a distribution. The four unstable leaves are `ResTNm` and two `St[n]` words on
  `Player[512]`, plus `Checksum`.
* This corroborates lane PL's placement of `ResTNm` / `ResErrRoll` on Rung B for the Singularity
  shadow empires: those leaves are not merely AI-dependent, they are **not reproducible**, so no
  amount of modelling the AI's *rules* will close them without also reproducing whatever the pick
  is actually keyed on.

## What was not established

The cause. The candidates are the shadow empires' `ResErrRoll` (a research error roll that lane PL
saw flip `False → True`, i.e. an RNG consumer on exactly this player class) and anything in the AI
path keyed on wall-clock time or frame count rather than on the saved generator. Distinguishing
them is a probe on the pick site, not another End Turn.