# A8 — ETR (Existential Temporality Relief) — torus

## 1. Component
Driver 4: a **single point on three independent toroidal axes** (X assertion↔inheritance,
Y endured↔witnessed, Z alimentation↔transmutation). Handles the stress PS+/Eth-Int generate;
Z-sign selects maintain-vs-evolve at migration.

## 2. Status / certainty
**SCAFFOLD — built and tested this session** (`run_etr_tests.sh` → 12 PASS / 2 FAIL-by-design /
2 PEND). Full law + status in `../../src/endocrine/etr/etr_invariants.md` (this spec defers to it).

## 3. Language & location
GNU Octave · `src/endocrine/etr/` (`etr.m`, `test_etr.m`, `run_etr_tests.sh`, `etr_invariants.md`).
R wrapper `src/endocrine/driver_etr.R` bridges into the Drive-Box.

## 4. Does / does-not
- **Does:** hold the point; wrap each axis at ±50; apply per-axis restoring toward [17,35]; take
  AI-originated drift; classify per-axis band; (future) cross-axis coupling via stress.
- **Does-not:** generate its own drift (caller-fed, L4) or compute coupling yet (open seam).

## 5. Interface contract
- `etr_init(coord) -> s` · `etr_axis_wrap(v)` · `etr_axis_restoring_dir(v)` ·
  `etr_step(s, drift, stress) -> s'` · `etr_status(s) -> per-axis {BELOW|IN_BAND|ABOVE}`.
- Inputs: **drift** (from A3/A6 via G1, AI-originated) + **stress** (G1 mediator). Output: coord + status,
  surfaced through A1 `drive_snapshot`.

## 6. Dependencies & stubs
Drift + stress are fed in — *stub:* `etr_step(s, [dx dy dz], 0)` (already how tests run). Fully standalone today.

## 7. Invariants / laws
Defer to `etr_invariants.md` (L1 wrap ±50 C5 · L2 bands [17,35] C5 · L3 opposition C5 · L4 AI-drift C4 ·
L5 cross-axis coupling via stress C1 · L6 Z-path C3 · L7 no-zero-cross C2 · L8 mechanism C2).

## 8. Build steps (remaining)
1. **Fit `RESTORE_GAIN`** → the 2 red tests (magnitude + band-convergence) go green.
2. Confirm **L8** (restoring = force vs cost) and **L7** (no-zero-crossing) → promote from PEND.
3. Define **L5** coupling (the stress→cross-axis mapping; G1) → replace the identity stub.
4. Wire R↔Octave (driver_etr.R ↔ etr.m) for the Drive-Box (A1) — and the larger medium (D2).

## 9. Tests
`bash src/endocrine/etr/run_etr_tests.sh` (currently 12/2/2 — the 2 reds are the to-fit work).

## 10. Open items
- `RESTORE_GAIN` curve (C1) · L5 coupling mapping (C1, shared with G1) · L7/L8 confirmation (C2)
  · R↔Octave bridge transport (C1, shared with A1/C3/D2).