TODO.md

# TODO (Prioritised)

## ✅ σ=0 ACHIEVED — Solver works!

The solver now finds `Id∘KroneckerSelfSimilar` at depth 1 and achieves **σ=0** on all 6 pairs of ARC task 007bbfb7.

### What was wrong
1. **Wrong target** — the repo's example1 target had 4 incorrect cells (row 7). Discovered by cross-referencing against the real ARC dataset (`data/training/007bbfb7.json`). Fixed.
2. **Limited transform library** — the beam only had vanilla tile, fill_enclosed, rotate90, reflect_h. None could express the Kronecker self-similar pattern. Fixed: added 19 new transforms.
3. **Beam only tried resized input** — shape-changing transforms (Kronecker: 3×3→9×9) need the original input, not the tiled 9×9 intermediate. The beam now uses a dual-strategy: each transform is tried on both the resized field AND the original input.

### The actual transformation (ARC task 007bbfb7)
`output = np.kron((input != 0).astype(int), input)` — a Kronecker product where the input's own nonzero mask determines the meta-layout for placing copies of itself.

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## Immediate (blockers) — ALL RESOLVED
- ~~**Add candidate snapshot to beam logs**~~ ✅ Done.
- ~~**Ensure gate values are booleans**~~ ✅ Done.
- ~~**Make tile transform nontrivial**~~ ✅ Done — `ShiftedTile` wired in + 19 new transforms including `KroneckerSelfSimilar`.
- ~~**Implement robust fill_enclosed**~~ ✅ Done — BFS in `solver_core.py`.
- ~~**Fix σ=98 flatline**~~ ✅ Done — σ=0 on all 6 pairs.

## Short term
- ~~Add CLI entrypoint with `--use_wandb` flag~~ ✅ Done — `scripts/entrypoint.py`.
- ~~Add unit tests for transforms~~ ✅ Done — `tests/test_transforms.py` (40 tests, all pass).
- Add small visualization notebook for `phi_best`, diff maps, and Layer‑1 masks.

## Medium term
- ~~Improve Layer‑1 mask generation~~ ✅ Done.
- Add a toggle to include/exclude `candidate_array` in logs to control log size.
- ~~Create a reproducible benchmark harness~~ ✅ Done — `experiment_driver.sweep()` + `results.csv`.
- **Expand to more ARC tasks** — test on other 3×3→9×9 tasks and different task families.
- **Benchmark the enriched library** — run sweep across multiple ARC tasks, measure solve rate.

## Long term
- ~~Integrate a safe external W&B uploader~~ ✅ Done.
- **Build task loader for full ARC dataset** — load any task from `fchollet/ARC-AGI` by ID.
- **Add more transform families** — connected components, object extraction, voronoi fill (see Icecuber DSL: arxiv:2402.03507).
- **Automated evaluation harness** — run solver on all 400 ARC training tasks, report solve rate.
- Document reproducibility steps and expected outputs for each example task.

## Code hygiene (completed)
- ~~Duplicate `Transform` class in `transforms.py`~~ ✅ Fixed.
- ~~Duplicate imports/paste blocks in `solver_core.py`~~ ✅ Fixed.
- ~~Lambda closure bug in `default_atomic_factory`~~ ✅ Fixed.
- ~~`wandb_runner.py` `int(generate_id(), 36)` crash~~ ✅ Fixed.
- ~~`minimal_runner.py` TARGET was all‑zeros~~ ✅ Fixed.
- ~~README.md referenced non‑existent paths~~ ✅ Fixed.
- ~~Committed `.pyc` files~~ ✅ Fixed.
- ~~`itt_solver/README.md.md` double extension~~ ✅ Fixed.
- ~~Wrong target in example1 (4 cells off)~~ ✅ Fixed — corrected in entrypoint.py, experiments_analysis.py, fix_and_inspect_logs.py, minimal_runner.py.
- ~~Beam search only applied transforms to resized field~~ ✅ Fixed — dual-strategy (resized + original).

## New transforms added (19 total)
| Transform | Description |
|---|---|
| `KroneckerSelfSimilar` | `kron((I≠0), I)` — self-similar meta-layout |
| `KroneckerSelfSimilarInv` | `kron(I, (I≠0))` — mirror variant |
| `MirrorTileH` | `[abc\|cba]` horizontal mirror |
| `MirrorTileV` | Vertical mirror stack |
| `MirrorTile4Way` | Full kaleidoscope (D4) |
| `Upscale(2)` / `Upscale(3)` | Pixel-repeat zoom |
| `Downscale(2)` | Subsample (inverse of upscale) |
| `StackH(3)` / `StackV(3)` | Tile horizontally/vertically |
| `RetainColor(c)` | Keep only color c |
| `RemoveColor(c)` | Zero out color c |
| `InvertColors` | Swap black ↔ top color |
| `GravityDown` / `GravityUp` | Pixels fall/rise in columns |
| `OverlayTransparent(bg)` | Transparent overlay on background |
| `CropToContent` | Crop to non-zero bounding box |
| `Transpose` | Matrix transpose |
| `ShiftedTile` | Tile with roll offset |