feat(invisible): sliding-window tiled diffusion for large inputs (--tile)

Add a lossless alternative to the --max-resolution downscale for large
images that OOM on MPS/GPU: regenerate in overlapping, feather-blended
tiles at native resolution.

- noai/tiling.py: pure plan_tiles (uniform tiles, last flush to edge) +
  feather_weights (strictly-positive separable taper -> partition-of-unity
  blend) + run_tiled (per-tile generate callable, decoupled from the
  pipeline). Unit-tested without the model.
- WatermarkRemover.remove_watermark: refactor _generate into _generate_one
  + a tiled branch that engages only when --tile is set and the long side
  exceeds tile_size (ControlNet canny is rebuilt per tile).
- Thread tile/tile_size/tile_overlap through InvisibleEngine and the
  invisible/all/batch CLI commands via a shared _tile_options decorator.

Verified end-to-end on the real SDXL pipeline (forced 2x2 tiling on a
1024px sample, MPS): non-degenerate output, no gross seam at tile borders.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/module-internals.md

@@ -191,6 +191,12 @@ At the shared low removal strength the canny edge-conditioning keeps the regener
 
 **But the reverse also holds: a flat-graphic logo/poster SURVIVED `default` while clearing controlnet** -- removal at the low strength is content×pipeline dependent and neither pipeline is universally safe; the real lever is a higher strength. See the controlnet Known-limitations bullet for the full table + root cause. Canny holds face STRUCTURE but NOT identity (the regenerated face drifts in likeness -- canny carries edges, not identity). The drifted cleaned face is the LEAST-AI state we can reach without re-introducing SynthID; the library does NOT ship a face-restore extra. Every restore approach we evaluated (GFPGAN-on-cleaned, PhotoMaker-V2 txt2img, InstantID txt2img, InstantID img2img-on-cleaned at three parameter sweeps, 2026-06-04 - 2026-06-08 Modal cert sweeps) regenerated the face from an ArcFace embedding via SDXL diffusion -- which makes the output face look MORE AI-generated, not less. Empirical conclusion in `docs/synthid-robust-identity-research-2026-06-08.md` "Empirical follow-up". For production face preservation, ship the cleaned image as-is. `controlnet_conditioning_scale` (ctor arg, default 1.0) is the structure-preservation knob. Same dtype rule as `default` (fp32 on cpu/mps, fp16 only on cuda/xpu; the fp16-fixed SDXL VAE `_SDXL_FP16_VAE_ID` is swapped in on fp16 GPUs -- issue #29) and the same MPS->CPU fallback (reload on cpu/fp32, drop a non-cpu generator, retry once).
 
+**Tiled diffusion (`tile`/`tile_size`/`tile_overlap` ctor-path args, CLI `--tile`, issue #10):** for large inputs that OOM at native resolution, `remove_watermark` can process the diffusion pass in overlapping sliding-window tiles instead of one forward pass — the lossless alternative to a `--max-resolution` downscale. The single-image generation closure was refactored into `_generate_one(img)` (dispatches controlnet/img2img, generator shared so the seed advances deterministically across tiles), and `_generate()` routes it through `noai.tiling.run_tiled` when `tile` is set AND `max(init_image.size) > tile_size` (a sub-tile image runs one pass unchanged). The ControlNet canny edge map is rebuilt per tile inside `_generate_one`, so structure preservation is tile-local. See `noai/tiling.py` below and the tiled-diffusion subsection in `docs/known-limitations.md` for the geometry, the partition-of-unity blend, and the quality caveat.
+
+## `noai/tiling.py`
+
+Pure sliding-window tiling for the diffusion path (no torch import; numpy/PIL only). `plan_tiles(w, h, tile_size, overlap)` returns a row-major grid of uniform-size `Tile` boxes — every tile is exactly `tile_size` (the SDXL training size), with the last tile on each axis pulled back flush to the far edge (`_axis_positions` clamps a pathological `overlap >= tile` to `tile - 1` so the step stays >= 1). `feather_weights(w, h, overlap)` is a separable linear taper (1 in the interior, ramping toward each edge) floored at `_WEIGHT_EPS` so it is **strictly positive everywhere** — that makes the normalised `accum / weight_sum` blend a partition of unity, so identical/unchanged tiles reconstruct the input exactly (the seam-free guarantee). `run_tiled(generate_tile, image, tile_size, overlap, set_progress)` is the orchestration loop: crop each planned tile, call `generate_tile` (one diffusion pass on a single PIL tile — injected, so this stays decoupled from the pipeline), resize a latent-grid-rounded result back to the exact tile size, and feather-accumulate. All three are unit-tested without the model (`tests/test_tiling.py`: axis math, grid coverage, taper shape/symmetry/positivity, identity reconstruction, per-tile call count, and the resize-back path). New blend tuning belongs in these pure helpers, not inlined into the runner.
+
 ## `auto_config.py` (REMOVED 2026-06-09)
 
 **`auto_config.py` + the content-detection layer were REMOVED 2026-06-09.**