# Opt-in observation-window ledger in the DFG runner

This test-only integration adds `--exchange-window` to `run_refined_dfg.py`. It uses the
existing production ledger; no collision, boundary, transfer, physical setup, reference,
periodicity gate or acceptance threshold changes. Default remains the historical
per-base-step observation path. Uniform stepping/force accumulation is unchanged.

For the refined case, each existing observation interval opens a new ledger at completed
base step `begin`, advances exactly the same `n` base intervals, and reads the integrated
root-lattice impulse for `[begin, begin+n]`. The contract requires root units, `window`
kind, `2*n` fine samples, matching endpoints, and fine dt=.5. The existing coefficient
calculation still divides this impulse by `n` and `.5*U_lattice**2*D_root`; force timestamps
remain `(begin+n/2)*U_lattice/D_root`. It does not divide an already averaged force again.
Pressure/macro/physical-leaf mass measurements and safety checks remain at the original
interval end. Pilot interval is 80 root steps; early full-run intervals remain 2000, and
any final shortened interval uses its actual `n`.

The opt-in uses one `step(n)` call and one window read per observation, rather than `n`
Python calls/readbacks. Internal subcycling and per-base synchronization remain owned by
the same backend. Cooperative deadline checks surround that complete interval; unlike
the default path they cannot interrupt between base steps inside `step(n)`. The existing
external hard watchdog is still required. The full-run cadence/cap is documented here,
but this preparation does not admit a full run or a GPU operation.

## Provenance and receipt separation

`source_manifest_window.json` pins the reviewed a233c9032487a6006e950d1e327079b00466c410
snapshot (production ledger origin d930) plus existing helper/reference files. Both SRT
and MRT are supported by this explicit opt-in source pin; collision selection remains
independent and shared by the two cases. Existing SRT and MRT manifests are untouched.
Default mode continues to reject the changed candidate under those historical pins;
use a matching historical `--source` checkout to run its default path. There is no
silent repinning, source fallback, or reuse of historical outputs as candidate evidence.

Plan, READY, summaries, timeout/comparison receipts now record `observation_mode` as
`last_base_step` or `window`, alongside collision and actual checkout provenance. On a
uniform receipt this labels its **paired campaign's refined observation mode**, not a
change to uniform observation. Full-mode pilot validation rejects missing or mismatched
mode labels in the plan, either case summary, and either READY receipt. Source/runner
hash, collision, completeness and health checks remain. Cross-mode pilot reuse is denied.

The earlier short A/W/W1 timing/capability evidence is not a full-run speedup or accuracy
claim. Mathematical impulse integration/units are unchanged; floating-point reduction
order can differ, so bitwise equality of force sums is not promised. Physics acceptance
continues to use the existing frozen gates. Historical failures/results are untouched.

CPU preparation commands, from the repository root:

```sh
python tests/unit/test_refined_dfg.py
PYTHONPATH=src python -m unittest tests.unit.test_raw_exchange_window tests.unit.test_time_window_dfg -v
python tests/validation/run_refined_dfg.py --collision MRT --exchange-window --mode plan --output /tmp/new-window-dfg-plan
```

Root must independently review and admit any execution. An admitted paired pilot uses
the existing watchdog, device selection, `--gpu-gates-approved`, positive
`--max-wall-seconds` and a new output directory, adding only `--exchange-window` to the
selected collision's pilot command. No GPU or remote action was performed for this patch.

## Wide fine storage allocation

The wide runner uses `FINE_BLOCK = (240, 568)`: one block containing the whole
fine allocation, including the four-cell refinement ghost band on each side.
The active `232 x 560` region alone is not a valid substitute. Physical bounds,
resolution, numerical kernels, 256-thread launches, per-root synchronization
and all scientific gates are unchanged. The plan records this storage block.

This is a wide-only configuration backport; no compact-placement or public-Jet
API is added. Existing source hashes remain checked, and the separate runner
hash requires a fresh completed pilot before a full run. Earlier short-layout
timings do not establish a full-run speedup or change historical failed verdicts.