diff --git a/.gitea/workflows/test.yml b/.gitea/workflows/test.yml
new file mode 100644
index 0000000..70d6a9c
--- /dev/null
+++ b/.gitea/workflows/test.yml
@@ -0,0 +1,28 @@
+name: Test
+
+on:
+  push:
+    branches: [main, cleanup/**]
+  pull_request:
+
+jobs:
+  pytest:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install package and dev dependencies
+        run: pip install -e ".[dev]"
+
+      - name: Ruff
+        run: |
+          pip install ruff
+          ruff check .
+          ruff format --check .
+
+      - name: Pytest (unit; skip integration)
+        run: pytest -m "not integration"
diff --git a/.gitignore b/.gitignore
index 4417c1f..05e7fe9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,6 +5,14 @@ __pycache__/
 dist/
 build/
 .pytest_cache/
+.ruff_cache/
+.mypy_cache/
+.coverage
+htmlcov/
 .venv/
 venv/
 .env
+*.log
+
+# Local pipeline run output (if created inside repo)
+pipeline_output/
diff --git a/CLEANUP_PLAN.md b/CLEANUP_PLAN.md
new file mode 100644
index 0000000..5412203
--- /dev/null
+++ b/CLEANUP_PLAN.md
@@ -0,0 +1,57 @@
+# Cleanup Plan — imagepipeline quality pass
+
+Branch: `cleanup/quality-pass`  
+Started: 2026-07-18
+
+## Phase 0 findings (summary)
+
+| Area | Risk | Notes |
+|------|------|-------|
+| Core (runner, resume, pipeline) | Medium | Solid tests; `xcf_stack` special-case in runner — defer refactor |
+| Modules | Low–Medium | `gmic_grayscale` missing `finalize_gmic_output` (resume parity) |
+| Dependencies | High | `dependencies = []` but Pillow/numpy imported at module load |
+| Pipelines | Low | Machine-local paths intentional (SOUL); stale `CONTINUE_FROM` left as-is |
+| Tests | Medium | 87/88 pass; watermark integration fails on darktable-cli 5.6 |
+| Tooling | Safe | No linter/formatter/CI |
+
+## Roadmap
+
+### Phase 1 — Low-risk quick wins
+- [x] Add Ruff (lint + format) and apply once
+- [x] Expand `.gitignore`
+- [x] Remove dead duplicate branch in `imagemagick_grayscale`
+- [x] Fix flaky `test_watermark_pipeline` (darktable probe skip)
+
+### Phase 2 — Structure & config
+- [x] Explicit `import imagepipeline.modules` in `pipeline.py`
+- [x] `gmic_grayscale`: call `finalize_gmic_output` (parity with `gmic`)
+- [ ] Pipeline `CONTINUE_FROM` reset — **skipped** (machine-local resume state)
+- [ ] `xcf_stack` runner hook — **deferred** (medium refactor risk)
+
+### Phase 3 — Code quality
+- [x] Pytest markers (`integration`, `slow`)
+- [ ] Broad dedup of pipeline scripts — **deferred** (domain-specific, RECIPES first)
+
+### Phase 4 — Dependencies & CI
+- [x] Declare Pillow in core; numpy in dev for import-time ai_tone_map
+- [x] Add Ruff to dev extras
+- [x] Gitea Actions: pytest on push
+
+### Phase 5 — Docs
+- [x] README sync (resume, `.env`, `[ai]`, external tools)
+- [x] `docs/ARCHITECTURE.md`, `CONTRIBUTING.md`
+- [x] `LICENSE` (MIT, matches pyproject)
+
+## Known bugs (not fixed — behavior change or out of scope)
+
+1. **darktable-cli 5.6** — integration test fails locally; style file exists but CLI exits 1 on PNG export (possible upstream CLI change).
+2. **Eager module imports** — `ai_tone_map` pulls numpy at import; mitigated via dev dep, not lazy-import refactor.
+
+## Verification
+
+```bash
+pip install -e ".[dev,ai]"
+ruff check .
+ruff format --check .
+pytest
+```
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..1fc5e98
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,36 @@
+# Contributing
+
+## Setup
+
+```bash
+pip install -e ".[dev,ai]"
+```
+
+Use `.[dev]` only for core tests; AI module tests need `.[ai]` (torch). OpenRouter/Comfy steps need `OPENROUTER_API_KEY` in `.env` (see `.env.example`).
+
+## Code style
+
+- **Ruff** for lint and format (`ruff check .`, `ruff format .`)
+- Python **3.11+**, type hints on public APIs
+- CLI messages: direct English, no marketing tone (see `SOUL.md`)
+
+## Tests
+
+```bash
+pytest                  # full suite (may call local CLIs)
+pytest -m "not integration"   # fast subset for CI
+```
+
+Mark new external-tool tests with `@pytest.mark.integration`.
+
+## Adding a module
+
+See [MODULE_DEVELOPMENT.md](MODULE_DEVELOPMENT.md). Register in `imagepipeline/modules/__init__.py` and add param/behavior tests.
+
+## Pipelines
+
+Scripts in `pipelines/` are examples and shoot-specific recipes. Machine-local `INPUT` paths are intentional. Reset `CONTINUE_FROM` before sharing a script.
+
+## Commits
+
+Conventional Commits (`feat:`, `fix:`, `chore:`, …). One logical change per commit.
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..6a19352
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Frank
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
index ea98af4..6268944 100644
--- a/README.md
+++ b/README.md
@@ -7,15 +7,19 @@ Each pipeline is a Python script that defines a DAG of processing steps. Every s
 ## Requirements
 
 - Python 3.11+
-- [ImageMagick](https://imagemagick.org/) (`magick` or `convert` on PATH)
+- [ImageMagick](https://imagemagick.org/) (`magick` or `convert` on PATH) — most pipelines
+- Optional CLIs per module: [G'MIC](https://gmic.eu/), [rembg](https://github.com/danielgatis/rembg), [darktable-cli](https://www.darktable.org/), GIMP (`gimp-console`)
 
 ## Installation
 
 ```bash
 cd /path/to/imagepipeline
-pip install -e ".[dev]"
+pip install -e ".[dev]"      # core + tests
+pip install -e ".[dev,ai]"   # + torch/numpy for AI modules
 ```
 
+Copy `.env.example` to `.env` and set `OPENROUTER_API_KEY` when using `openrouter_edit` or Comfy-related workflows.
+
 ## Quick Start
 
 Edit the input path in `pipelines/example_grayscale.py`, then run:
@@ -35,9 +39,11 @@ with Pipeline(name="my_run", input_dir=Path("/path/to/export")) as p:
     p.run()
 ```
 
+List registered modules: `imagepipeline list-modules`
+
 ## Output Structure
 
-Each run creates a folder like `my_run_20260527143022/`:
+Each run creates a folder like `my_run_20260527143022/` under `~/pipeline_output/` (or `output_base`):
 
 ```
 my_run_20260527143022/
@@ -48,7 +54,26 @@ my_run_20260527143022/
 └── ...
 ```
 
-Step folders are named `{module_name}_{nn}` (two-digit counter per module name).
+Step folders are named `{module_name}_{nn}` by default (two-digit counter per module name). Pass optional `step_id="input_bokeh"` to `p.step()` for a custom folder name and step reference (see [docs/MODULE_DEVELOPMENT.md](docs/MODULE_DEVELOPMENT.md#step-folder-naming)).
+
+## Resume
+
+Pipelines support resuming interrupted runs:
+
+```python
+CONTINUE_FROM = Path("~/pipeline_output/my_run_260718120000")
+EXISTING_OUTPUTS = {"rembg_01": CONTINUE_FROM / "rembg_01"}
+
+with Pipeline(
+    name="my_run",
+    input_dir=INPUT,
+    continue_from=CONTINUE_FROM,
+    existing_outputs=EXISTING_OUTPUTS,
+) as p:
+    ...
+```
+
+Modules that change file extensions must implement `expected_output_filenames` so skip logic works (e.g. `rembg` → `.png`).
 
 ## Writing Pipelines
 
@@ -67,12 +92,27 @@ with Pipeline(name="colorsplash", input_dir=INPUT) as p:
 - Parameters are passed as kwargs and validated against each module's schema
 - Multiple uses of the same module get separate numbered folders
 
+Declarative building blocks for agents and humans: [RECIPES.md](RECIPES.md).
+
 ## Adding Modules
 
-See [docs/MODULE_DEVELOPMENT.md](docs/MODULE_DEVELOPMENT.md).
+See [docs/MODULE_DEVELOPMENT.md](docs/MODULE_DEVELOPMENT.md). Architecture overview: [docs/ARCHITECTURE.md](docs/ARCHITECTURE.md).
+
+## Development
+
+```bash
+ruff check .
+ruff format .
+pytest                      # full suite (uses local CLIs when present)
+pytest -m "not integration" # fast subset (CI default)
+```
+
+See [CONTRIBUTING.md](CONTRIBUTING.md).
 
 ## Tests
 
 ```bash
 pytest
 ```
+
+Optional AI tests require `pip install -e ".[ai]"`.
diff --git a/RECIPES.md b/RECIPES.md
new file mode 100644
index 0000000..603940b
--- /dev/null
+++ b/RECIPES.md
@@ -0,0 +1,310 @@
+# RECIPES.md
+
+Reference for agents building `pipelines/<name>.py`. Not executable — expand to `p.step(...)` calls.
+
+---
+
+## Rules
+
+1. **combine** = one output image. Layers **bottom → top** (first line = background).
+2. **composite** takes exactly **2** inputs. For 3+ layers: `composite(A,B)` → `composite(mid, C)` → …
+3. **rembg** once per pipeline — reuse the same step ref in every combine.
+4. **G'MIC in Python:** `command="-filter args"` (leading `-`). Multi-frame output: framework keeps frame `000001`.
+5. **Colors:** hex (`#RRGGBB`) for `imagemagick_fill` / `color_to_alpha`. G'MIC color slots: `R,G,B` ints 0–255 from hex bytes.
+6. **Placeholders** at pipeline top: `COLOR1`, `COLOR2`, `R1,G1,B1`, `R2,G2,B2`, `ALPHA1` (default 160), `ALPHA2` (default 110), `STYLE`, `MAX_EDGE`, `PROMPT`, `MODEL`, `TEMPLATE_IMAGE`, `YELLOW`.
+7. **xcf_stack:** separate step, not a combine layer. `inputs=[...]` bottom → top; include `"input"` for originals. Needs `gimp` on PATH.
+8. Lines starting with `#` in user prompts = human notes — ignore.
+
+**Hex → RGB:** `#244a89` → `36,74,137`. Strip `#RRGGBBAA` alpha for G'MIC tuples.
+
+---
+
+## Layer lines (example)
+
+One combine, bottom → top. Other phrases: `grayscale` / `original as greyscale`, `white`/`black background`, `original with gmic: ID`, `#COLOR to alpha`, `resize max edge N`, `crop square`, `darktable style STYLE`, `openrouter edit …`, `xcf stack layers: a, b, c`.
+
+```text
+demo-combine
+  gradient background COLOR1 COLOR2 radial
+  original
+  rembg with gmic: gmic-drop-shadow
+  make layer 5% bigger then crop to original size
+  rembg
+```
+
+---
+
+## Modules
+
+| name | parameters (defaults) | notes |
+|------|----------------------|-------|
+| `rembg` | `model`=`birefnet-general`, `alpha_matting`=`True` | output `.png` |
+| `gmic` | `command` (required) | timeout 300s |
+| `gmic_grayscale` | `command`=`-to_gray` | |
+| `composite` | `mode`=`over`, `output_ext`=`.png`, `foreground_opacity`=`1.0` | 2 inputs: bg, fg |
+| `imagemagick_fill` | `color1`, `color2`=`""`, `gradient`=`False`, `radial`=`False`, `angle`=`None` | sized to input |
+| `imagemagick_grayscale` | `colorspace`=`Gray` | |
+| `imagemagick_resize` | `max_edge`=`2000` | no upscale |
+| `imagemagick_scale_crop` | `scale`=`1.05` | center crop after scale |
+| `color_to_alpha` | `color` (required), `fuzz`=`0.0` | output `.png` |
+| `crop_square` | — | center square crop |
+| `darktable_style` | `style` (required), `style_overwrite`=`True`, `out_ext`=`""`, `config_dir`=`~/.config/darktable` | jpeg/png only |
+| `xcf_stack` | `skip_missing`=`False`, `timeout`=`120` | multi-input step |
+| `openrouter_edit` | `prompt`, `model`, `strength`=`0.3`, `template_image`=`None`, `api_key_env`=`OPENROUTER_API_KEY` + AI common | needs `.env` |
+| `ai_exposure` | `strength`=`1.0` + AI common | `[ai]` extra |
+| `ai_tone_map` | `checkpoint`=`""`, `strength`=`1.0`, `net_input_size`=`256` + AI common | `[ai]` extra |
+| `comfy_flux_edit` | `prompt`, `denoise`=`0.35`, `seed`=`-1`, `server_url`, `workflow_path`, `poll_interval`=`2.0` + AI common | local ComfyUI |
+
+**AI common** (`ai_exposure`, `ai_tone_map`, `openrouter_edit`, `comfy_flux_edit`): `skip_existing`=`True`, `max_edge`=`2048`, `device`=`cpu`.
+
+---
+
+## ImageMagick operations
+
+Used via modules above — not free-form CLI in pipelines. `W×H` = size of reference input image.
+
+| id | module | operation |
+|----|--------|-----------|
+| `im-solid` | `imagemagick_fill` | `-size W×H xc:COLOR` |
+| `im-gradient-linear` | `imagemagick_fill` | `-size W×H -define gradient:angle=N gradient:COLOR1-COLOR2` |
+| `im-gradient-radial` | `imagemagick_fill` | `-size W×H radial-gradient:COLOR1-COLOR2` |
+| `im-grayscale` | `imagemagick_grayscale` | `-colorspace Gray` |
+| `im-resize-max-edge` | `imagemagick_resize` | `-auto-orient -resize {N}x{N}>` (no upscale) |
+| `im-scale-crop` | `imagemagick_scale_crop` | `-resize {w×scale}x{h×scale}! -gravity Center -crop w×h+0+0 +repage` |
+| `im-crop-square` | `crop_square` | `-auto-orient -crop S×S+X+Y +repage` (center square) |
+| `im-color-to-alpha` | `color_to_alpha` | `-alpha on [-fuzz N%] -transparent COLOR` |
+| `im-composite-over` | `composite` | `(bg) (fg) -compose over -composite` |
+| `im-composite-multiply` | `composite` | `mode=multiply` |
+| `im-composite-screen` | `composite` | `mode=screen` |
+| `im-composite-opacity` | `composite` | fg: `-channel A -evaluate multiply {0..1}` then compose |
+
+**Layer line → id:** `COLOR background` → `im-solid`; `gradient … 45 degree` → `im-gradient-linear`; `gradient … radial` → `im-gradient-radial`; `grayscale` → `im-grayscale`; `resize max edge N` → `im-resize-max-edge`; `make layer 5% bigger …` → `im-scale-crop` (`scale=1.05`); `crop square` → `im-crop-square`; `COLOR to alpha` → `im-color-to-alpha`.
+
+---
+
+## G'MIC commands
+
+Python string = `-` + filter + args. Placeholders `R1,G1,B1` / `R2,G2,B2` from `COLOR1` / `COLOR2`.
+
+| id | command |
+|----|---------|
+| `gmic-tone-mapping` | `fx_map_tones 0.5,0.7,0.1,30,0` |
+| `gmic-grayscale` | `to_gray` (via `gmic_grayscale`) |
+| `gmic-feltpen` | `fx_feltpen 300,50,1,0.1,20,5` |
+| `gmic-edges` | `fx_edges 0,15,0` |
+| `gmic-charred-plastic` | `fx_charred_plastic 1,10,40,1,10,0,0,2,6,5,20,0,11` |
+| `gmic-neon` | `fx_neon 0,1,1,1,1,0,0.45,40,60,0,1,1.15,2,3,0,3,20,0.4,0.1,1.5,5,0.2,0.1,1,2,1,0,0,1,1,0,50,50` |
+| `gmic-cutout` | `fx_cutout 4,0.5,4,1` |
+| `gmic-poster` | `fx_poster_hope 0,3` |
+| `gmic-color-abstraction` | `fx_color_abstraction 1,10,0.2` |
+| `gmic-huffman-glitches` | `fx_huffman_glitches 30,0,25,0,0,0,0,0,50,50` |
+| `gmic-queryprimary` | `afre_queryprimary 1,1` |
+| `gmic-local-similarity` | `local_similarity_mask 50,50,50,128,4,10` |
+| `gmic-luma-invert` | `Lylejk_Luma_Invert 1,0` |
+| `gmic-crayongraffiti` | `fx_crayongraffiti2 300,50,1,0.4,12,1,2,2,0` |
+| `gmic-anaglyph` | `fx_stereo_to_anaglyph 2,0` |
+| `gmic-stereo` | `gcd_stereo_img 0,0,2.028,1,1.714,3.06,4,1,0` |
+| `gmic-drop-shadow` | `fx_drop_shadow3d 0,0,0,10,1,1,2,0.5,R2,G2,B2,200,0` |
+| `gmic-jpr-smooth` | `jpr_gradient_smooth 0,1.5` |
+| `gmic-bokeh` | `fx_bokeh 3,5,0,30,8,4,0.3,0.2,R1,G1,B1,ALPHA1,0.7,30,20,20,1,2,R2,G2,B2,ALPHA2,0.15` |
+| `gmic-bwrecolor` | `fx_bwrecolorize 0,0,0,0,0,1,0,2,R2,G2,B2,255,R1,G1,B1,255,158,137,189,255,224,191,228,255,R1,G1,B1,0,255,255,255,255,255,255,255,255,255,R1,G1,B1,0,255` |
+| `gmic-custom-gradient-a` | `fx_custom_gradient 0,0,0,1,2,1,0,128,100,100,2,0,1,0,"",1,0,R1,G1,B1,0,255,R2,G2,B2,255,255,255,0,255,255,255,255,255,0,255,255,255,0,255,0,255,0,0,255,255,128,128,128,255,255,0,255,255,0,0,0,0` |
+| `gmic-custom-gradient-b` | `fx_custom_gradient 0,0,0,1,2,1,0,128,100,100,2,0,1,0,"",1,0,R2,G2,B2,255,R1,G1,B1,0,255,255,255,0,255,255,255,255,255,0,255,255,255,0,255,0,255,0,0,255,255,128,128,128,255,255,0,255,255,0,0,0,0` |
+
+**Typical input:** `original with gmic:` = on `"input"`; `rembg with gmic:` = on rembg step.
+
+---
+
+## Combines
+
+Format: recipe id, then layers bottom → top. `→` = chained composites.
+
+### 2 layers
+
+```text
+colorsplash
+  original as greyscale
+  rembg
+
+rembg-white-bg
+  white background
+  rembg
+
+rembg-black-bg
+  black background
+  rembg
+
+rembg-gradient-45
+  gradient background COLOR1 COLOR2 45 degree
+  rembg
+
+rembg-radial-2colors
+  gradient background COLOR1 COLOR2 radial
+  rembg
+
+rembg-custom-gradient-a
+  rembg with gmic: gmic-custom-gradient-a
+  rembg
+
+rembg-custom-gradient-b
+  rembg with gmic: gmic-custom-gradient-b
+  rembg
+
+gmic-feltpen-rembg
+  rembg with gmic: gmic-feltpen
+  rembg
+
+gmic-edges-rembg
+  rembg with gmic: gmic-edges
+  rembg
+
+gmic-charred-plastic-rembg
+  rembg with gmic: gmic-charred-plastic
+  rembg
+
+gmic-neon-rembg
+  rembg with gmic: gmic-neon
+  rembg
+```
+
+### 3 layers
+
+```text
+original-stereo-rembg
+  original
+  rembg with gmic: gmic-stereo
+  rembg
+→ composite(original, rembg_stereo) → composite(_, rembg)
+
+original-drop-shadow-rembg
+  original
+  rembg with gmic: gmic-drop-shadow
+  rembg
+
+original-bwrecolor-rembg
+  original
+  rembg with gmic: gmic-bwrecolor
+  rembg
+→ first composite: foreground_opacity=0.5
+
+original-jpr-smooth-rembg
+  original
+  rembg with gmic: gmic-jpr-smooth
+  make layer 5% bigger then crop to original size
+  rembg
+→ gmic → scale_crop on middle layer, then 3-layer chain
+
+bokeh-oktagon
+  original
+  original with gmic: gmic-bokeh
+  rembg
+
+color-bg-drop-shadow-rembg
+  COLOR1 background
+  rembg with gmic: gmic-drop-shadow
+  rembg
+
+yellow-bg-drop-shadow-rembg
+  YELLOW background
+  rembg with gmic: gmic-drop-shadow
+  rembg
+
+gmic-cutout-rembg
+  original
+  original with gmic: gmic-cutout
+  rembg
+
+gmic-poster-rembg
+  original
+  original with gmic: gmic-poster
+  rembg
+
+gmic-color-abstraction-rembg
+  original
+  original with gmic: gmic-color-abstraction
+  rembg
+
+gmic-huffman-glitches-rembg
+  original
+  original with gmic: gmic-huffman-glitches
+  rembg
+
+gmic-queryprimary-rembg
+  original
+  original with gmic: gmic-queryprimary
+  rembg
+
+gmic-local-similarity-rembg
+  original
+  original with gmic: gmic-local-similarity
+  rembg
+
+gmic-luma-invert-rembg
+  original
+  original with gmic: gmic-luma-invert
+  rembg
+
+gmic-crayongraffiti-rembg
+  original
+  original with gmic: gmic-crayongraffiti
+  rembg
+
+gmic-anaglyph-rembg
+  original
+  original with gmic: gmic-anaglyph
+  rembg
+```
+
+### 4 layers (middle pipeline)
+
+```text
+original-stereo-black-alpha-rembg
+  original
+  rembg with gmic: gmic-stereo
+  #000000 to alpha
+  rembg
+
+original-jpr-smooth-grey-alpha-rembg
+  original
+  rembg with gmic: gmic-jpr-smooth
+  #7f7f7f to alpha
+  make layer 5% bigger then crop to original size
+  rembg
+```
+
+### Pipeline chain (not a combine)
+
+```text
+colorsplash-watermark
+  colorsplash          # expand combine first
+  darktable style STYLE
+```
+
+---
+
+## Agent example
+
+Request: *pipeline with colorsplash + rembg-radial-2colors, COLOR1=#244a89, COLOR2=#c22518*
+
+```python
+rembg_out = p.step("rembg", inputs="input")
+grayscale = p.step("gmic_grayscale", inputs="input")
+gradient_bg = p.step("imagemagick_fill", inputs="input", color1=COLOR1, color2=COLOR2, gradient=True, radial=True)
+
+p.step("composite", inputs=[grayscale, rembg_out])           # colorsplash
+p.step("composite", inputs=[gradient_bg, rembg_out])         # rembg-radial-2colors
+```
+
+3-layer combine (drop shadow on original):
+
+```python
+rembg_shadow = p.step("gmic", inputs=rembg_out, command=GMIC_DROP_SHADOW)
+mid = p.step("composite", inputs=["input", rembg_shadow])
+p.step("composite", inputs=[mid, rembg_out])
+```
+
+xcf export:
+
+```python
+p.step("xcf_stack", inputs=["input", rembg_out, grayscale, composite_colorsplash, ...])
+```
diff --git a/SOUL.md b/SOUL.md
index 2cf829f..656ab37 100644
--- a/SOUL.md
+++ b/SOUL.md
@@ -12,6 +12,7 @@ What this project is — not chat mood (see `MOOD.md`).
 - **Resume:** Pipelines support `CONTINUE_FROM` and `EXISTING_OUTPUTS`; modules must declare correct `expected_output_filenames` when output names differ from inputs (e.g. rembg → `.png`).
 - **Secrets:** `OPENROUTER_API_KEY` in `.env` (see `.env.example`) — never commit.
 - **Tests:** Run `pytest` before handoff on non-trivial module/resume changes.
+- **Recipes:** Declarative pipeline building blocks in `RECIPES.md` — load via `@RECIPES.md` when creating or editing pipelines.
 - **Commit policy:** No commit unless Fränky asks (this project follows global `AGENTS.md`).
 
 ---
diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
new file mode 100644
index 0000000..c8b41c1
--- /dev/null
+++ b/docs/ARCHITECTURE.md
@@ -0,0 +1,59 @@
+# Architecture
+
+Imagepipeline is a small Python framework for defining **batch image pipelines** as DAGs. Each step is a registered module; each run writes numbered folders under a timestamped output root.
+
+## Layout
+
+```
+imagepipeline/
+├── core/           # Pipeline, runner, resume, manifest, params, logging
+├── modules/        # Processing steps (@register)
+├── utils/          # files, subprocess, gmic, gimp helpers
+├── ai/             # Optional torch models (HDRNet, Zero-DCE)
+└── cli.py          # `imagepipeline list-modules`
+
+pipelines/          # Runnable scripts (machine-local INPUT paths)
+tests/              # pytest suite
+docs/               # Developer docs
+workflows/comfy/    # ComfyUI workflow JSON (optional AI path)
+```
+
+## Execution flow
+
+1. **Define** — `Pipeline(name=..., input_dir=...)` collects `step()` calls (`StepDefinition` DAG).
+2. **Run** — `PipelineRunner` topologically sorts steps, matches inputs by filename stem, builds `ModuleContext`.
+3. **Resume** — `continue_from` / `existing_outputs` reuse prior run folders; modules declare `expected_output_filenames` when extensions change.
+4. **Manifest** — `pipeline_manifest.json` records steps, params, and paths.
+
+## Module contract
+
+Every module subclasses `BaseModule` or `SubprocessModule`:
+
+- `name`, `description`, `parameters()` schema
+- `run(ctx: ModuleContext)` writes into `ctx.output_dir`
+- Optional `expected_output_filenames()` for resume when output names differ from inputs
+- `check_dependencies()` for external CLI tools
+
+Registration happens via `@register` and eager import in `imagepipeline/modules/__init__.py`.
+
+## External tools
+
+Many modules shell out to CLIs (not Python packages):
+
+| Tool | Modules |
+|------|---------|
+| ImageMagick (`magick`/`convert`) | `imagemagick_*`, `composite`, `color_to_alpha`, `crop_square` |
+| G'MIC | `gmic`, `gmic_grayscale` |
+| rembg | `rembg` |
+| darktable-cli | `darktable_style` |
+| GIMP | `xcf_stack` |
+
+AI modules need `pip install -e ".[ai]"` (torch, numpy) and optionally API keys in `.env`.
+
+## Design choices
+
+- **Plain Python pipelines** — no YAML DSL; full control and easy resume constants in script.
+- **Stem matching** — multi-input steps align files by basename across step folders.
+- **Symlink input** — default run copies/symlinks source images into `input/` for reproducibility.
+
+See [MODULE_DEVELOPMENT.md](MODULE_DEVELOPMENT.md) for adding modules.
diff --git a/docs/MODULE_DEVELOPMENT.md b/docs/MODULE_DEVELOPMENT.md
index d354293..35b298b 100644
--- a/docs/MODULE_DEVELOPMENT.md
+++ b/docs/MODULE_DEVELOPMENT.md
@@ -167,7 +167,7 @@ class MyCliModule(SubprocessModule):
 
 ## Step Folder Naming
 
-The runner assigns output folders automatically: `{module_name}_{nn}`.
+By default the runner assigns output folders automatically: `{module_name}_{nn}` (two-digit counter per module name).
 
 Using the same module twice in one pipeline produces separate folders:
 
@@ -178,7 +178,17 @@ darktable_style_01/
 darktable_style_02/
 ```
 
-You do not choose folder names in the module.
+In pipeline scripts you can pass an optional `step_id` to `p.step()` for readable folder names and GIMP layer labels (`xcf_stack` uses the step id as the layer name):
+
+```python
+input_bokeh = p.step("gmic", inputs="input", command=GMIC_BOKEH, step_id="input_bokeh")
+```
+
+`step_id` becomes both the internal step reference and the output subfolder name. It must be unique within the pipeline and must not contain path separators. The per-module counter still increments on every `p.step("gmic", …)` call — a custom id does not reserve or skip a number slot (the next default `gmic` step after `step_id="input_bokeh"` is `gmic_03`, not `gmic_02`, if two prior `gmic` steps ran).
+
+Use the same ids in `EXISTING_OUTPUTS` when resuming with external folders.
+
+You do not choose folder names inside the module implementation.
 
 ## Format Warnings
 
diff --git a/imagepipeline/ai/cache.py b/imagepipeline/ai/cache.py
index 8669057..b32aaaa 100644
--- a/imagepipeline/ai/cache.py
+++ b/imagepipeline/ai/cache.py
@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import hashlib
 import urllib.request
 from pathlib import Path
 
diff --git a/imagepipeline/ai/classical_tone.py b/imagepipeline/ai/classical_tone.py
index 3e2eeda..03752f8 100644
--- a/imagepipeline/ai/classical_tone.py
+++ b/imagepipeline/ai/classical_tone.py
@@ -49,7 +49,7 @@ def _lab_to_rgb(lab: np.ndarray) -> np.ndarray:
     fz = fy - lab[..., 2] / 200
 
     def finv(t):
-        t3 = t ** 3
+        t3 = t**3
         return np.where(t3 > 216 / 24389, t3, (116 * t - 16) / kappa)
 
     kappa = 24389 / 27
diff --git a/imagepipeline/ai/hdrnet/model.py b/imagepipeline/ai/hdrnet/model.py
index 6b3b3cb..7abaf1c 100644
--- a/imagepipeline/ai/hdrnet/model.py
+++ b/imagepipeline/ai/hdrnet/model.py
@@ -1,11 +1,8 @@
 from __future__ import annotations
 
-import math
-
 import numpy as np
 import torch
 import torch.nn as nn
-import torch.nn.functional as F
 
 from imagepipeline.ai.hdrnet.slice import batch_bilateral_slice
 
@@ -70,22 +67,27 @@ class Slice(nn.Module):
 
 class ApplyCoeffs(nn.Module):
     def forward(self, coeff, full_res_input):
-        r = torch.sum(full_res_input * coeff[:, 0:3, :, :], dim=1, keepdim=True) + coeff[
-            :, 9:10, :, :
-        ]
-        g = torch.sum(full_res_input * coeff[:, 3:6, :, :], dim=1, keepdim=True) + coeff[
-            :, 10:11, :, :
-        ]
-        b = torch.sum(full_res_input * coeff[:, 6:9, :, :], dim=1, keepdim=True) + coeff[
-            :, 11:12, :, :
-        ]
+        r = (
+            torch.sum(full_res_input * coeff[:, 0:3, :, :], dim=1, keepdim=True)
+            + coeff[:, 9:10, :, :]
+        )
+        g = (
+            torch.sum(full_res_input * coeff[:, 3:6, :, :], dim=1, keepdim=True)
+            + coeff[:, 10:11, :, :]
+        )
+        b = (
+            torch.sum(full_res_input * coeff[:, 6:9, :, :], dim=1, keepdim=True)
+            + coeff[:, 11:12, :, :]
+        )
         return torch.cat([r, g, b], dim=1)
 
 
 class GuideNN(nn.Module):
     def __init__(self, params) -> None:
         super().__init__()
-        self.conv1 = ConvBlock(3, params["guide_complexity"], kernel_size=1, padding=0, batch_norm=True)
+        self.conv1 = ConvBlock(
+            3, params["guide_complexity"], kernel_size=1, padding=0, batch_norm=True
+        )
         self.conv2 = ConvBlock(
             params["guide_complexity"], 1, kernel_size=1, padding=0, activation=nn.Sigmoid
         )
@@ -112,9 +114,7 @@ class Coeffs(nn.Module):
         for index in range(n_layers_splat):
             use_bn = bn if index > 0 else False
             out_ch = cm * (2**index) * lb
-            self.splat_features.append(
-                ConvBlock(prev_ch, out_ch, 3, stride=2, batch_norm=use_bn)
-            )
+            self.splat_features.append(ConvBlock(prev_ch, out_ch, 3, stride=2, batch_norm=use_bn))
             prev_ch = out_ch
         splat_ch = prev_ch
 
@@ -131,7 +131,9 @@ class Coeffs(nn.Module):
         prev_ch = int(prev_ch * (nsize / 2**n_total) ** 2)
         self.global_features_fc.append(FC(prev_ch, 32 * cm * lb, batch_norm=bn))
         self.global_features_fc.append(FC(32 * cm * lb, 16 * cm * lb, batch_norm=bn))
-        self.global_features_fc.append(FC(16 * cm * lb, 8 * cm * lb, activation=None, batch_norm=bn))
+        self.global_features_fc.append(
+            FC(16 * cm * lb, 8 * cm * lb, activation=None, batch_norm=bn)
+        )
 
         self.local_features = nn.ModuleList(
             [
@@ -139,9 +141,7 @@ class Coeffs(nn.Module):
                 ConvBlock(8 * cm * lb, 8 * cm * lb, 3, activation=None, use_bias=False),
             ]
         )
-        self.conv_out = ConvBlock(
-            8 * cm * lb, lb * nout * nin, 1, padding=0, activation=None
-        )
+        self.conv_out = ConvBlock(8 * cm * lb, lb * nout * nin, 1, padding=0, activation=None)
         self.relu = nn.ReLU()
 
     def forward(self, lowres_input):
diff --git a/imagepipeline/ai/hdrnet/slice.py b/imagepipeline/ai/hdrnet/slice.py
index 6bc964f..0fb24a4 100644
--- a/imagepipeline/ai/hdrnet/slice.py
+++ b/imagepipeline/ai/hdrnet/slice.py
@@ -82,12 +82,8 @@ def _bilateral_slice(grid, guide):
     grid_val_110 = grid[gi1c, gj1c, gk0c, :]
     grid_val_111 = grid[gi1c, gj1c, gk1c, :]
 
-    w_000, w_001, w_010, w_011 = map(
-        torch.atleast_3d, (w_000, w_001, w_010, w_011)
-    )
-    w_100, w_101, w_110, w_111 = map(
-        torch.atleast_3d, (w_100, w_101, w_110, w_111)
-    )
+    w_000, w_001, w_010, w_011 = map(torch.atleast_3d, (w_000, w_001, w_010, w_011))
+    w_100, w_101, w_110, w_111 = map(torch.atleast_3d, (w_100, w_101, w_110, w_111))
 
     return (
         torch.multiply(w_000, grid_val_000)
diff --git a/imagepipeline/ai/zero_dce.py b/imagepipeline/ai/zero_dce.py
index be1c69d..5700e57 100644
--- a/imagepipeline/ai/zero_dce.py
+++ b/imagepipeline/ai/zero_dce.py
@@ -60,9 +60,7 @@ class EnhanceNetNoPool(nn.Module):
         if self.scale_factor == 1:
             x_down = x
         else:
-            x_down = F.interpolate(
-                x, scale_factor=1 / self.scale_factor, mode="bilinear"
-            )
+            x_down = F.interpolate(x, scale_factor=1 / self.scale_factor, mode="bilinear")
 
         x1 = self.relu(self.e_conv1(x_down))
         x2 = self.relu(self.e_conv2(x1))
@@ -105,7 +103,5 @@ def enhance_image(
         if strength < 1.0:
             enhanced = tensor * (1.0 - strength) + enhanced * strength
         enhanced = torch.clamp(enhanced, 0.0, 1.0)
-    out = (enhanced.squeeze(0).permute(1, 2, 0).cpu().numpy() * 255.0).astype(
-        np.uint8
-    )
+    out = (enhanced.squeeze(0).permute(1, 2, 0).cpu().numpy() * 255.0).astype(np.uint8)
     return Image.fromarray(out)
diff --git a/imagepipeline/cli.py b/imagepipeline/cli.py
index 0a841e2..4e380cd 100644
--- a/imagepipeline/cli.py
+++ b/imagepipeline/cli.py
@@ -2,7 +2,6 @@ from __future__ import annotations
 
 import argparse
 import sys
-from pathlib import Path
 
 from imagepipeline.modules.registry import list_modules
 
diff --git a/imagepipeline/core/context.py b/imagepipeline/core/context.py
index f90e389..1f1f144 100644
--- a/imagepipeline/core/context.py
+++ b/imagepipeline/core/context.py
@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from dataclasses import dataclass, field
 from pathlib import Path
-from typing import Any, TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 if TYPE_CHECKING:
     from imagepipeline.core.log import PipelineLogger
@@ -18,7 +18,8 @@ class ModuleContext:
     pipeline_output_root: Path
     step_id: str
     matched_groups: list[list[Path]] = field(default_factory=list)
-    prior_steps: list[tuple[str, Path]] = field(default_factory=list)
+    input_refs: list[str] = field(default_factory=list)
+    input_layer_dirs: list[tuple[str, Path]] = field(default_factory=list)
     logger: PipelineLogger | None = None
 
     @property
diff --git a/imagepipeline/core/log.py b/imagepipeline/core/log.py
index c950e48..6ddd318 100644
--- a/imagepipeline/core/log.py
+++ b/imagepipeline/core/log.py
@@ -36,23 +36,17 @@ class PipelineLogger:
         inputs: list[str],
         params: dict,
     ) -> None:
-        self.info(
-            f"Step {step_index}/{step_total}: {step_id} ({module_name})"
-        )
+        self.info(f"Step {step_index}/{step_total}: {step_id} ({module_name})")
         self.info(f"  inputs: {', '.join(inputs)}")
         if params:
             rendered = ", ".join(f"{key}={value!r}" for key, value in params.items())
             self.info(f"  params: {rendered}")
 
     def image(self, module_name: str, index: int, total: int, filename: str) -> None:
-        self.info(
-            f"  Applying module {module_name} to image [{index}/{total}]: {filename}"
-        )
+        self.info(f"  Applying module {module_name} to image [{index}/{total}]: {filename}")
 
     def skipped(self, module_name: str, index: int, total: int, filename: str) -> None:
-        self.info(
-            f"  Skipped module {module_name} [{index}/{total}] {filename} (output exists)"
-        )
+        self.info(f"  Skipped module {module_name} [{index}/{total}] {filename} (output exists)")
 
     def image_done(
         self,
diff --git a/imagepipeline/core/manifest.py b/imagepipeline/core/manifest.py
index d49b057..a18e573 100644
--- a/imagepipeline/core/manifest.py
+++ b/imagepipeline/core/manifest.py
@@ -2,7 +2,7 @@ from __future__ import annotations
 
 import json
 from dataclasses import asdict, dataclass, field
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 from pathlib import Path
 from typing import Any
 
@@ -39,4 +39,4 @@ def write_manifest(path: Path, manifest: PipelineManifest) -> None:
 
 
 def utc_now_iso() -> str:
-    return datetime.now(timezone.utc).replace(microsecond=0).isoformat()
+    return datetime.now(UTC).replace(microsecond=0).isoformat()
diff --git a/imagepipeline/core/params.py b/imagepipeline/core/params.py
index 4ba2e1c..93ccd78 100644
--- a/imagepipeline/core/params.py
+++ b/imagepipeline/core/params.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from dataclasses import dataclass, field
+from dataclasses import dataclass
 from typing import Any
 
 
@@ -22,9 +22,7 @@ class Param:
 
         if self.choices is not None and value not in self.choices:
             allowed = ", ".join(repr(c) for c in self.choices)
-            raise ValueError(
-                f"Parameter '{name}' must be one of [{allowed}], got {value!r}"
-            )
+            raise ValueError(f"Parameter '{name}' must be one of [{allowed}], got {value!r}")
 
         if self.type == "string":
             if not isinstance(value, str):
@@ -56,9 +54,7 @@ class Param:
         raise ValueError(f"Unknown parameter type '{self.type}' for '{name}'")
 
 
-def validate_params(
-    schema: dict[str, Param], raw: dict[str, Any]
-) -> dict[str, Any]:
+def validate_params(schema: dict[str, Param], raw: dict[str, Any]) -> dict[str, Any]:
     unknown = set(raw) - set(schema)
     if unknown:
         names = ", ".join(sorted(unknown))
diff --git a/imagepipeline/core/pipeline.py b/imagepipeline/core/pipeline.py
index dfc3c5a..f841671 100644
--- a/imagepipeline/core/pipeline.py
+++ b/imagepipeline/core/pipeline.py
@@ -4,14 +4,13 @@ from collections import defaultdict
 from pathlib import Path
 from typing import Any
 
+# Register all built-in modules (side effect of submodule imports).
+import imagepipeline.modules  # noqa: F401
 from imagepipeline.core.exceptions import ValidationError
 from imagepipeline.core.runner import PipelineRunner
 from imagepipeline.core.step import INPUT_SOURCE, StepDefinition, StepRef
 from imagepipeline.modules.registry import get_module
 
-# Import built-in modules so they register on package load.
-import imagepipeline.modules.imagemagick_grayscale  # noqa: F401
-
 
 class Pipeline:
     """Define and run an image processing pipeline."""
@@ -45,20 +44,23 @@ class Pipeline:
         module_name: str,
         *,
         inputs: StepRef | str | list[StepRef | str],
+        step_id: str | None = None,
         **params: Any,
     ) -> StepRef:
         module_cls = get_module(module_name)
         self._module_counters[module_name] += 1
         counter = self._module_counters[module_name]
-        output_dir_name = f"{module_name}_{counter:02d}"
-        step_id = output_dir_name
+        if step_id is None:
+            output_dir_name = f"{module_name}_{counter:02d}"
+            step_id = output_dir_name
+        else:
+            self._validate_step_id(step_id)
+            output_dir_name = step_id
 
         input_refs = self._normalize_inputs(inputs)
         reserved = {"inputs", "input"}
         if reserved & set(params):
-            raise ValidationError(
-                "Do not pass 'inputs' or 'input' as module parameters"
-            )
+            raise ValidationError("Do not pass 'inputs' or 'input' as module parameters")
 
         definition = StepDefinition(
             step_id=step_id,
@@ -92,15 +94,21 @@ class Pipeline:
     def output_root(self) -> Path | None:
         return self._output_root
 
-    def _normalize_inputs(
-        self, inputs: StepRef | str | list[StepRef | str]
-    ) -> list[str]:
+    def _normalize_inputs(self, inputs: StepRef | str | list[StepRef | str]) -> list[str]:
         if isinstance(inputs, list):
             if not inputs:
                 raise ValidationError("inputs must not be an empty list")
             return [self._input_ref(item) for item in inputs]
         return [self._input_ref(inputs)]
 
+    def _validate_step_id(self, step_id: str) -> None:
+        if not step_id:
+            raise ValidationError("step_id must not be empty")
+        if "/" in step_id or "\\" in step_id:
+            raise ValidationError(f"step_id must not contain path separators: {step_id!r}")
+        if any(step.step_id == step_id for step in self._steps):
+            raise ValidationError(f"Duplicate step_id: {step_id!r}")
+
     @staticmethod
     def _input_ref(value: StepRef | str) -> str:
         if isinstance(value, StepRef):
diff --git a/imagepipeline/core/runner.py b/imagepipeline/core/runner.py
index f3f07e5..cf48b80 100644
--- a/imagepipeline/core/runner.py
+++ b/imagepipeline/core/runner.py
@@ -49,12 +49,9 @@ class PipelineRunner:
         self.symlink_input = symlink_input
         self.logger = PipelineLogger(verbose=verbose)
         self.existing_outputs = {
-            key: Path(value).resolve()
-            for key, value in (existing_outputs or {}).items()
+            key: Path(value).resolve() for key, value in (existing_outputs or {}).items()
         }
-        self.continue_from = (
-            Path(continue_from).resolve() if continue_from is not None else None
-        )
+        self.continue_from = Path(continue_from).resolve() if continue_from is not None else None
         self.skip_completed = skip_completed
         self.output_root = self._build_output_root()
         self._input_link_dir = self.output_root / "input"
@@ -63,9 +60,7 @@ class PipelineRunner:
     def _build_output_root(self) -> Path:
         if self.continue_from is not None:
             if not self.continue_from.is_dir():
-                raise ValidationError(
-                    f"continue_from directory not found: {self.continue_from}"
-                )
+                raise ValidationError(f"continue_from directory not found: {self.continue_from}")
             return self.continue_from
 
         timestamp = datetime.now().strftime("%y%m%d%H%M%S")
@@ -151,9 +146,23 @@ class PipelineRunner:
         step.module.check_dependencies()
         validated = step.module.validate_module_params(step.params)
 
-        source_lists = [self._resolve_source_paths(ref) for ref in step.input_refs]
-        matched_groups = match_by_stem(source_lists)
-        input_paths = flatten_matched(matched_groups)
+        if step.module_name == "xcf_stack":
+            if not step.input_refs:
+                raise ValidationError("xcf_stack requires at least one input layer")
+            source_lists = [self._resolve_source_paths(ref) for ref in step.input_refs]
+            input_paths = source_lists[0]
+            matched_groups = [[path] for path in input_paths]
+            input_layer_dirs: list[tuple[str, Path]] = []
+            for ref in step.input_refs:
+                if ref == INPUT_SOURCE:
+                    input_layer_dirs.append(("input", self._input_link_dir))
+                else:
+                    input_layer_dirs.append((ref, self._results[ref].output_dir))
+        else:
+            source_lists = [self._resolve_source_paths(ref) for ref in step.input_refs]
+            matched_groups = match_by_stem(source_lists)
+            input_paths = flatten_matched(matched_groups)
+            input_layer_dirs = []
 
         output_dir = self.output_root / step.output_dir_name
         output_dir.mkdir(parents=True, exist_ok=True)
@@ -220,7 +229,8 @@ class PipelineRunner:
             pipeline_output_root=self.output_root,
             step_id=step.step_id,
             matched_groups=matched_groups,
-            prior_steps=[(sid, res.output_dir) for sid, res in self._results.items()],
+            input_refs=list(step.input_refs),
+            input_layer_dirs=input_layer_dirs,
             logger=self.logger,
         )
 
@@ -234,8 +244,7 @@ class PipelineRunner:
         output_paths = step.module().list_output_images(ctx)
         if not output_paths:
             raise StepError(
-                f"Step '{step.output_dir_name}' ({step.module_name}) "
-                "produced no output images"
+                f"Step '{step.output_dir_name}' ({step.module_name}) produced no output images"
             )
 
         self.logger.step_done(step.output_dir_name, step.output_dir_name, len(output_paths))
@@ -264,9 +273,7 @@ class PipelineRunner:
                     raise ValidationError(f"Step '{step.step_id}' references unknown step '{dep}'")
                 dependents[dep].append(step.step_id)
 
-        queue = deque(
-            step_id for step_id, degree in in_degree.items() if degree == 0
-        )
+        queue = deque(step_id for step_id, degree in in_degree.items() if degree == 0)
         ordered_ids: list[str] = []
 
         while queue:
diff --git a/imagepipeline/core/step.py b/imagepipeline/core/step.py
index 356efc3..2efcab3 100644
--- a/imagepipeline/core/step.py
+++ b/imagepipeline/core/step.py
@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from dataclasses import dataclass, field
 from pathlib import Path
-from typing import Any, TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 if TYPE_CHECKING:
     from imagepipeline.modules.base import BaseModule
diff --git a/imagepipeline/modules/__init__.py b/imagepipeline/modules/__init__.py
index fdb9aa5..a01cb2d 100644
--- a/imagepipeline/modules/__init__.py
+++ b/imagepipeline/modules/__init__.py
@@ -2,8 +2,8 @@
 
 import imagepipeline.modules.ai_exposure  # noqa: F401
 import imagepipeline.modules.ai_tone_map  # noqa: F401
-import imagepipeline.modules.comfy_flux_edit  # noqa: F401
 import imagepipeline.modules.color_to_alpha  # noqa: F401
+import imagepipeline.modules.comfy_flux_edit  # noqa: F401
 import imagepipeline.modules.composite  # noqa: F401
 import imagepipeline.modules.crop_square  # noqa: F401
 import imagepipeline.modules.darktable_style  # noqa: F401
diff --git a/imagepipeline/modules/ai_base.py b/imagepipeline/modules/ai_base.py
index 885027f..c813d1f 100644
--- a/imagepipeline/modules/ai_base.py
+++ b/imagepipeline/modules/ai_base.py
@@ -115,9 +115,7 @@ class AIModule(BaseModule):
             avg = sum(elapsed_times) / len(elapsed_times)
             eta = avg * remaining if remaining else 0.0
             if ctx.logger is not None:
-                ctx.logger.image_done(
-                    self.name, index, total, dst.name, elapsed, eta_seconds=eta
-                )
+                ctx.logger.image_done(self.name, index, total, dst.name, elapsed, eta_seconds=eta)
 
     @staticmethod
     def _image_size(path: Path) -> tuple[int, int]:
diff --git a/imagepipeline/modules/color_to_alpha.py b/imagepipeline/modules/color_to_alpha.py
index e696a43..f08dfa0 100644
--- a/imagepipeline/modules/color_to_alpha.py
+++ b/imagepipeline/modules/color_to_alpha.py
@@ -24,8 +24,7 @@ def build_color_to_alpha_args(*, color: str, fuzz: float) -> list[str]:
 class ColorToAlphaModule(SubprocessModule):
     name = "color_to_alpha"
     description = (
-        "Make a solid color transparent (GIMP-style color to alpha). "
-        "Outputs PNG with alpha."
+        "Make a solid color transparent (GIMP-style color to alpha). Outputs PNG with alpha."
     )
     command_candidates = ("magick", "convert")
 
@@ -50,10 +49,7 @@ class ColorToAlphaModule(SubprocessModule):
             "fuzz": Param(
                 "float",
                 default=0.0,
-                help=(
-                    "Match tolerance in percent (ImageMagick -fuzz); "
-                    "0 = exact color only"
-                ),
+                help=("Match tolerance in percent (ImageMagick -fuzz); 0 = exact color only"),
             ),
         }
 
diff --git a/imagepipeline/modules/comfy_flux_edit.py b/imagepipeline/modules/comfy_flux_edit.py
index c391763..02b0a6f 100644
--- a/imagepipeline/modules/comfy_flux_edit.py
+++ b/imagepipeline/modules/comfy_flux_edit.py
@@ -76,9 +76,7 @@ class ComfyFluxEditModule(AIModule):
         server_url = ctx.params["server_url"].rstrip("/")
         self._ensure_server(server_url)
         if ctx.logger is not None:
-            ctx.logger.warning(
-                "ComfyUI on CPU: expect hours per full-resolution image"
-            )
+            ctx.logger.warning("ComfyUI on CPU: expect hours per full-resolution image")
 
         workflow_template = json.loads(workflow_path.read_text(encoding="utf-8"))
         denoise = ctx.params["denoise"]
@@ -98,9 +96,7 @@ class ComfyFluxEditModule(AIModule):
                 seed=seed,
             )
             prompt_id = self._queue_prompt(server_url, workflow)
-            output_info = self._wait_for_output(
-                server_url, prompt_id, poll_interval=poll_interval
-            )
+            output_info = self._wait_for_output(server_url, prompt_id, poll_interval=poll_interval)
             image_bytes = self._download_view(server_url, output_info)
             dst.write_bytes(image_bytes)
 
@@ -111,9 +107,7 @@ class ComfyFluxEditModule(AIModule):
         try:
             urllib.request.urlopen(f"{server_url}/system_stats", timeout=5)
         except urllib.error.URLError as exc:
-            raise DependencyError(
-                f"ComfyUI server not reachable at {server_url}: {exc}"
-            ) from exc
+            raise DependencyError(f"ComfyUI server not reachable at {server_url}: {exc}") from exc
 
     @staticmethod
     def _upload_image(server_url: str, src: Path) -> str:
diff --git a/imagepipeline/modules/composite.py b/imagepipeline/modules/composite.py
index 9a72b67..4e3ac96 100644
--- a/imagepipeline/modules/composite.py
+++ b/imagepipeline/modules/composite.py
@@ -63,9 +63,7 @@ class CompositeModule(SubprocessModule):
 
         for index, group in enumerate(ctx.matched_groups, start=1):
             if len(group) < 2:
-                raise ValueError(
-                    "composite requires at least two input sources per image"
-                )
+                raise ValueError("composite requires at least two input sources per image")
 
             background, foreground = group[0], group[1]
             self.log_image(ctx, index, total, foreground)
diff --git a/imagepipeline/modules/gmic_grayscale.py b/imagepipeline/modules/gmic_grayscale.py
index 3561afe..6a673f6 100644
--- a/imagepipeline/modules/gmic_grayscale.py
+++ b/imagepipeline/modules/gmic_grayscale.py
@@ -4,7 +4,7 @@ from imagepipeline.core.context import ModuleContext
 from imagepipeline.core.params import Param
 from imagepipeline.modules.base import SubprocessModule
 from imagepipeline.modules.registry import register
-from imagepipeline.utils.gmic import split_gmic_command
+from imagepipeline.utils.gmic import finalize_gmic_output, split_gmic_command
 from imagepipeline.utils.subprocess import run_command
 
 
@@ -35,3 +35,4 @@ class GmicGrayscale(SubprocessModule):
             dst = ctx.output_dir / src.name
             cmd = ["gmic", str(src), *split_gmic_command(gmic_command), "-output", str(dst)]
             run_command(cmd, timeout=self.default_timeout)
+            finalize_gmic_output(ctx.output_dir, dst)
diff --git a/imagepipeline/modules/imagemagick_fill.py b/imagepipeline/modules/imagemagick_fill.py
index a237d2a..2b0f4a8 100644
--- a/imagepipeline/modules/imagemagick_fill.py
+++ b/imagepipeline/modules/imagemagick_fill.py
@@ -50,9 +50,7 @@ def build_fill_arguments(
 @register
 class ImageMagickFillModule(SubprocessModule):
     name = "imagemagick_fill"
-    description = (
-        "Create solid-color or gradient images sized to match each input image"
-    )
+    description = "Create solid-color or gradient images sized to match each input image"
     command_candidates = ("magick", "convert")
 
     @classmethod
diff --git a/imagepipeline/modules/imagemagick_grayscale.py b/imagepipeline/modules/imagemagick_grayscale.py
index aec0e75..ae741d9 100644
--- a/imagepipeline/modules/imagemagick_grayscale.py
+++ b/imagepipeline/modules/imagemagick_grayscale.py
@@ -1,7 +1,5 @@
 from __future__ import annotations
 
-from pathlib import Path
-
 from imagepipeline.core.context import ModuleContext
 from imagepipeline.core.params import Param
 from imagepipeline.modules.base import SubprocessModule
@@ -34,8 +32,5 @@ class ImageMagickGrayscale(SubprocessModule):
         for index, src in enumerate(ctx.input_paths, start=1):
             self.log_image(ctx, index, total, src)
             dst = ctx.output_dir / src.name
-            if command == "magick":
-                cmd = [command, str(src), "-colorspace", colorspace, str(dst)]
-            else:
-                cmd = [command, str(src), "-colorspace", colorspace, str(dst)]
+            cmd = [command, str(src), "-colorspace", colorspace, str(dst)]
             run_command(cmd)
diff --git a/imagepipeline/modules/imagemagick_scale_crop.py b/imagepipeline/modules/imagemagick_scale_crop.py
index 7982621..02a4c11 100644
--- a/imagepipeline/modules/imagemagick_scale_crop.py
+++ b/imagepipeline/modules/imagemagick_scale_crop.py
@@ -12,9 +12,7 @@ from imagepipeline.utils.subprocess import run_command
 @register
 class ImageMagickScaleCropModule(SubprocessModule):
     name = "imagemagick_scale_crop"
-    description = (
-        "Scale an image then center-crop back to its original dimensions"
-    )
+    description = "Scale an image then center-crop back to its original dimensions"
     command_candidates = ("magick", "convert")
 
     @classmethod
diff --git a/imagepipeline/modules/openrouter_edit.py b/imagepipeline/modules/openrouter_edit.py
index 22c9046..b73cd2f 100644
--- a/imagepipeline/modules/openrouter_edit.py
+++ b/imagepipeline/modules/openrouter_edit.py
@@ -70,9 +70,7 @@ class OpenRouterEditModule(AIModule):
     @classmethod
     def check_dependencies(cls) -> None:
         if not os.environ.get("OPENROUTER_API_KEY"):
-            raise DependencyError(
-                "OPENROUTER_API_KEY environment variable is not set"
-            )
+            raise DependencyError("OPENROUTER_API_KEY environment variable is not set")
 
     def run(self, ctx: ModuleContext) -> None:
         api_key_env = ctx.params["api_key_env"]
@@ -155,17 +153,11 @@ class OpenRouterEditModule(AIModule):
         *,
         template_data_url: str | None = None,
     ) -> dict:
-        full_prompt = (
-            f"{TEMPLATE_PROMPT_PREFIX}{prompt}" if template_data_url else prompt
-        )
+        full_prompt = f"{TEMPLATE_PROMPT_PREFIX}{prompt}" if template_data_url else prompt
         content: list[dict] = [{"type": "text", "text": full_prompt}]
         if template_data_url is not None:
-            content.append(
-                {"type": "image_url", "image_url": {"url": template_data_url}}
-            )
-        content.append(
-            {"type": "image_url", "image_url": {"url": source_data_url}}
-        )
+            content.append({"type": "image_url", "image_url": {"url": template_data_url}})
+        content.append({"type": "image_url", "image_url": {"url": source_data_url}})
         payload: dict = {
             "model": model,
             "modalities": cls._modalities_for_model(model),
@@ -176,9 +168,7 @@ class OpenRouterEditModule(AIModule):
         return payload
 
     @classmethod
-    def _save_result_matching_source(
-        cls, source: Path, result_bytes: bytes, dest: Path
-    ) -> None:
+    def _save_result_matching_source(cls, source: Path, result_bytes: bytes, dest: Path) -> None:
         with Image.open(source) as original:
             orig_format = original.format
             orig_size = original.size
@@ -229,9 +219,7 @@ class OpenRouterEditModule(AIModule):
                 return json.loads(response.read().decode("utf-8"))
         except urllib.error.HTTPError as exc:
             detail = exc.read().decode("utf-8", errors="replace")
-            raise RuntimeError(
-                f"OpenRouter API error ({exc.code}): {detail}"
-            ) from exc
+            raise RuntimeError(f"OpenRouter API error ({exc.code}): {detail}") from exc
 
     @staticmethod
     def _extract_image_bytes(response: dict) -> bytes:
diff --git a/imagepipeline/modules/xcf_stack.py b/imagepipeline/modules/xcf_stack.py
index ba8dff5..dc6b454 100644
--- a/imagepipeline/modules/xcf_stack.py
+++ b/imagepipeline/modules/xcf_stack.py
@@ -4,20 +4,22 @@ from pathlib import Path
 
 from imagepipeline.core.context import ModuleContext
 from imagepipeline.core.params import Param
+from imagepipeline.core.step import INPUT_SOURCE
 from imagepipeline.modules.base import SubprocessModule
 from imagepipeline.modules.registry import register
 from imagepipeline.utils.files import find_image_by_stem
 from imagepipeline.utils.gimp import stack_images_to_xcf
 
 
+def _layer_name(ref: str) -> str:
+    return "input" if ref == INPUT_SOURCE else ref
+
+
 @register
 class XcfStackModule(SubprocessModule):
     name = "xcf_stack"
-    description = (
-        "Stack all prior pipeline step outputs as GIMP layers into one XCF per image"
-    )
-    command_candidates = ("gimp",)
-    default_timeout = 600.0
+    description = "Stack listed pipeline step outputs as GIMP layers into one XCF per image"
+    command_candidates = ("gimp-console", "gimp")
 
     @classmethod
     def expected_output_filenames(
@@ -32,31 +34,26 @@ class XcfStackModule(SubprocessModule):
     @classmethod
     def parameters(cls) -> dict[str, Param]:
         return {
-            "include_input": Param(
-                "bool",
-                default=True,
-                help="Include pipeline input/ directory as bottom layer",
-            ),
             "skip_missing": Param(
                 "bool",
                 default=False,
                 help="Skip missing step outputs instead of failing",
             ),
+            "timeout": Param(
+                "float",
+                default=120.0,
+                help="Seconds to wait for gimp-console per image (default 120)",
+            ),
         }
 
     def run(self, ctx: ModuleContext) -> None:
-        include_input = ctx.params["include_input"]
         skip_missing = ctx.params["skip_missing"]
+        timeout = ctx.params["timeout"]
 
-        layer_sources: list[tuple[str, Path]] = []
-        if include_input:
-            layer_sources.append(("input", ctx.pipeline_output_root / "input"))
-        layer_sources.extend(ctx.prior_steps)
-
-        if not layer_sources:
+        if not ctx.input_layer_dirs:
             raise ValueError(
-                "xcf_stack has no layer sources "
-                "(include_input=False and no prior_steps)"
+                "xcf_stack requires at least one input layer "
+                "(pass step refs in inputs=[...], bottom to top)"
             )
 
         ctx.output_dir.mkdir(parents=True, exist_ok=True)
@@ -67,23 +64,27 @@ class XcfStackModule(SubprocessModule):
             stem = input_path.stem
             layers: list[tuple[str, Path]] = []
 
-            for step_id, directory in layer_sources:
+            for ref, directory in ctx.input_layer_dirs:
                 image_path = find_image_by_stem(directory, stem)
                 if image_path is None:
                     if not skip_missing:
                         raise ValueError(
                             f"xcf_stack: no image with stem '{stem}' in step "
-                            f"'{step_id}' ({directory})"
+                            f"'{_layer_name(ref)}' ({directory})"
                         )
                     continue
-                layers.append((step_id, image_path))
+                layers.append((_layer_name(ref), image_path))
 
             if not layers:
-                checked = ", ".join(step_id for step_id, _ in layer_sources)
+                checked = ", ".join(name for name, _ in ctx.input_layer_dirs)
                 raise ValueError(
-                    f"xcf_stack: no layers found for stem '{stem}' "
-                    f"(checked: {checked})"
+                    f"xcf_stack: no layers found for stem '{stem}' (checked: {checked})"
                 )
 
             dst = ctx.output_dir / f"{stem}.xcf"
-            stack_images_to_xcf(layers, dst, timeout=self.default_timeout)
+            stack_images_to_xcf(layers, dst, timeout=timeout)
+
+    def list_output_images(self, ctx: ModuleContext) -> list[Path]:
+        return sorted(
+            p for p in ctx.output_dir.iterdir() if p.is_file() and p.suffix.lower() == ".xcf"
+        )
diff --git a/imagepipeline/utils/files.py b/imagepipeline/utils/files.py
index a866ac3..05cf8fe 100644
--- a/imagepipeline/utils/files.py
+++ b/imagepipeline/utils/files.py
@@ -45,8 +45,7 @@ def match_by_stem(sources: list[list[Path]]) -> list[list[Path]]:
             key = stem_key(path)
             if key in mapping:
                 raise ValueError(
-                    f"Duplicate stem '{key}' in {path.parent}: "
-                    f"{mapping[key].name} and {path.name}"
+                    f"Duplicate stem '{key}' in {path.parent}: {mapping[key].name} and {path.name}"
                 )
             mapping[key] = path
         key_maps.append(mapping)
diff --git a/imagepipeline/utils/gimp.py b/imagepipeline/utils/gimp.py
index b8a469a..0d06ca7 100644
--- a/imagepipeline/utils/gimp.py
+++ b/imagepipeline/utils/gimp.py
@@ -1,13 +1,18 @@
 from __future__ import annotations
 
+import os
+import subprocess
+import tempfile
 from pathlib import Path
 
-from imagepipeline.utils.subprocess import require_command, run_command
+from imagepipeline.utils.subprocess import require_command
+
+_GIMP_CANDIDATES = ("gimp-console", "gimp")
 
 
 def require_gimp() -> str:
-    """Return the GIMP executable name, raising DependencyError if missing."""
-    return require_command("gimp")
+    """Return a GIMP executable for headless batch use."""
+    return require_command(*_GIMP_CANDIDATES)
 
 
 def _scheme_string(value: str) -> str:
@@ -23,34 +28,35 @@ def _scheme_string(value: str) -> str:
 
 
 def _build_stack_script(layers: list[tuple[str, Path]], outfile: Path) -> str:
+    """Build a GIMP 3 Script-Fu snippet that stacks images into one XCF."""
     first_name, first_path = layers[0]
     first_path_str = _scheme_string(str(first_path))
     outfile_str = _scheme_string(str(outfile))
 
     lines = [
+        "(script-fu-use-v3)",
         "(let* (",
-        f"  (loaded (gimp-file-load RUN-NONINTERACTIVE {first_path_str} {first_path_str}))",
-        "  (image (car loaded))",
-        "  (bottom-layer (cadr loaded))",
+        f"  (image (gimp-file-load RUN-NONINTERACTIVE {first_path_str}))",
+        "  (bottom (vector-ref (gimp-image-get-selected-drawables image) 0))",
         ")",
-        f"  (gimp-layer-set-name bottom-layer {_scheme_string(first_name)})",
+        f"  (gimp-item-set-name bottom {_scheme_string(first_name)})",
     ]
 
     for layer_name, layer_path in layers[1:]:
         path_str = _scheme_string(str(layer_path))
         lines.extend(
             [
-                "  (let ((layer (car (gimp-file-load-layer RUN-NONINTERACTIVE image "
-                f"{path_str}))))",
-                "    (gimp-image-insert-layer image layer 0 0)",
-                f"    (gimp-layer-set-name layer {_scheme_string(layer_name)})",
+                "  (let ((layer",
+                f"    (gimp-file-load-layer RUN-NONINTERACTIVE image {path_str})))",
+                "    (gimp-image-insert-layer image layer image 0)",
+                f"    (gimp-item-set-name layer {_scheme_string(layer_name)})",
                 "  )",
             ]
         )
 
     lines.extend(
         [
-            f"  (gimp-xcf-save RUN-NONINTERACTIVE image bottom-layer {outfile_str} {outfile_str})",
+            f"  (gimp-file-save RUN-NONINTERACTIVE image {outfile_str})",
             "  (gimp-image-delete image)",
             ")",
         ]
@@ -58,6 +64,43 @@ def _build_stack_script(layers: list[tuple[str, Path]], outfile: Path) -> str:
     return "\n".join(lines)
 
 
+def _run_gimp_batch(
+    cmd: list[str],
+    *,
+    timeout: float | None,
+    env: dict[str, str],
+    outfile: Path | None = None,
+) -> subprocess.CompletedProcess[str]:
+    """Run GIMP batch; tolerate exit hang when ``outfile`` was already written."""
+    process = subprocess.Popen(
+        cmd,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        text=True,
+        env=env,
+    )
+    try:
+        stdout, stderr = process.communicate(timeout=timeout)
+    except subprocess.TimeoutExpired as exc:
+        process.kill()
+        stdout, stderr = process.communicate()
+        if outfile is not None and outfile.is_file() and outfile.stat().st_size > 0:
+            return subprocess.CompletedProcess(
+                cmd,
+                returncode=0,
+                stdout=stdout or "",
+                stderr=stderr or "",
+            )
+        raise RuntimeError(f"Command timed out after {timeout}s: {' '.join(cmd)}") from exc
+
+    return subprocess.CompletedProcess(
+        cmd,
+        returncode=process.returncode if process.returncode is not None else -1,
+        stdout=stdout or "",
+        stderr=stderr or "",
+    )
+
+
 def stack_images_to_xcf(
     layers: list[tuple[str, Path]],
     outfile: Path,
@@ -67,7 +110,7 @@ def stack_images_to_xcf(
     """Stack images bottom-to-top into a single GIMP XCF file.
 
     ``layers`` is a list of ``(layer_name, image_path)`` tuples in bottom-to-top
-    order. Invokes GIMP headless via Script-Fu.
+    order. Invokes GIMP headless via Script-Fu (GIMP 3 compatible).
     """
     if not layers:
         raise ValueError("stack_images_to_xcf requires at least one layer")
@@ -77,35 +120,42 @@ def stack_images_to_xcf(
     for layer_name, image_path in layers:
         resolved = image_path.resolve()
         if not resolved.is_file():
-            raise FileNotFoundError(
-                f"Layer image not found for '{layer_name}': {resolved}"
-            )
+            raise FileNotFoundError(f"Layer image not found for '{layer_name}': {resolved}")
         resolved_layers.append((layer_name, resolved))
 
     outfile = outfile.resolve()
     outfile.parent.mkdir(parents=True, exist_ok=True)
 
     script = _build_stack_script(resolved_layers, outfile)
-    cmd = [
-        gimp,
-        "-idf",
-        "--batch-interpreter",
-        "plug-in-script-fu-eval",
-        "-b",
-        script,
-        "-b",
-        "(gimp-quit 0)",
-    ]
+    env = {**os.environ, "GIMP_NO_DISPLAY": "1"}
+
+    with tempfile.NamedTemporaryFile(
+        mode="w",
+        suffix=".scm",
+        delete=False,
+        encoding="utf-8",
+    ) as handle:
+        handle.write(script)
+        script_path = Path(handle.name)
 
     try:
-        run_command(cmd, timeout=timeout)
-    except RuntimeError as exc:
-        layer_summary = ", ".join(name for name, _ in resolved_layers)
-        raise RuntimeError(
-            f"GIMP failed to stack layers [{layer_summary}] into {outfile}: {exc}"
-        ) from exc
-
-    if not outfile.is_file():
-        raise RuntimeError(
-            f"GIMP completed but XCF output was not created: {outfile}"
-        )
+        cmd = [
+            gimp,
+            "-d",
+            "-i",
+            "--quit",
+            "--batch-interpreter=plug-in-script-fu-eval",
+            "--batch",
+            f"(load {_scheme_string(str(script_path))})",
+        ]
+        result = _run_gimp_batch(cmd, timeout=timeout, env=env, outfile=outfile)
+        if not outfile.is_file():
+            stderr = (result.stderr or "").strip()
+            stdout = (result.stdout or "").strip()
+            detail = stderr or stdout or f"exit code {result.returncode}"
+            layer_summary = ", ".join(name for name, _ in resolved_layers)
+            raise RuntimeError(
+                f"GIMP failed to stack layers [{layer_summary}] into {outfile}: {detail}"
+            )
+    finally:
+        script_path.unlink(missing_ok=True)
diff --git a/imagepipeline/utils/gmic.py b/imagepipeline/utils/gmic.py
index 9e7946f..09b17cd 100644
--- a/imagepipeline/utils/gmic.py
+++ b/imagepipeline/utils/gmic.py
@@ -38,6 +38,4 @@ def finalize_gmic_output(output_dir: Path, intended: Path) -> Path:
         frame_000000.rename(intended)
         return intended
 
-    raise FileNotFoundError(
-        f"G'MIC produced no output for {intended.name} in {output_dir}"
-    )
+    raise FileNotFoundError(f"G'MIC produced no output for {intended.name} in {output_dir}")
diff --git a/imagepipeline/utils/subprocess.py b/imagepipeline/utils/subprocess.py
index 471c806..6d581b8 100644
--- a/imagepipeline/utils/subprocess.py
+++ b/imagepipeline/utils/subprocess.py
@@ -16,6 +16,7 @@ def run_command(
     *,
     timeout: float | None = None,
     cwd: Path | None = None,
+    env: dict[str, str] | None = None,
 ) -> subprocess.CompletedProcess[str]:
     try:
         return subprocess.run(
@@ -25,18 +26,15 @@ def run_command(
             text=True,
             timeout=timeout,
             cwd=str(cwd) if cwd else None,
+            env=env,
         )
     except subprocess.CalledProcessError as exc:
         stderr = (exc.stderr or "").strip()
         stdout = (exc.stdout or "").strip()
         detail = stderr or stdout or str(exc)
-        raise RuntimeError(
-            f"Command failed ({exc.returncode}): {' '.join(cmd)}\n{detail}"
-        ) from exc
+        raise RuntimeError(f"Command failed ({exc.returncode}): {' '.join(cmd)}\n{detail}") from exc
     except subprocess.TimeoutExpired as exc:
-        raise RuntimeError(
-            f"Command timed out after {timeout}s: {' '.join(cmd)}"
-        ) from exc
+        raise RuntimeError(f"Command timed out after {timeout}s: {' '.join(cmd)}") from exc
 
 
 def require_command(*names: str) -> str:
diff --git a/pipelines/example_grayscale.py b/pipelines/example_grayscale.py
index edc0499..4f77c2a 100644
--- a/pipelines/example_grayscale.py
+++ b/pipelines/example_grayscale.py
@@ -18,8 +18,9 @@ def main() -> None:
         input_dir=INPUT,
         output_base=OUTPUT_BASE,
     ) as p:
-        gray = p.step("imagemagick_grayscale", inputs="input")
+        p.step("imagemagick_grayscale", inputs="input")
         # Chain another step on the result:
+        # gray = p.step("imagemagick_grayscale", inputs="input")
         # p.step("imagemagick_grayscale", inputs=gray, colorspace="Gray")
         output_root = p.run()
 
diff --git a/pipelines/pipeline_aichelberg_indians.py b/pipelines/pipeline_aichelberg_indians.py
new file mode 100644
index 0000000..c879f42
--- /dev/null
+++ b/pipelines/pipeline_aichelberg_indians.py
@@ -0,0 +1,269 @@
+#!/usr/bin/env python3
+"""Aichelberg Indians pipeline — tone mapping, gmic variants, xcf export."""
+
+from pathlib import Path
+
+from imagepipeline import Pipeline
+
+INPUT = Path(
+    "/home/frank/pics/20260712_Aichelberg Indians - Heidelberg Hedgehogs/darktable_exported"
+)
+OUTPUT_BASE = Path.home() / "pipeline_output"
+
+EXISTING_OUTPUTS: dict[str, Path] = {}
+CONTINUE_FROM = Path("/home/frank/pipeline_output/aichelberg-indians_260713081414")
+
+COLOR1 = "#244a89"
+COLOR2 = "#c22518"
+
+# COLOR1 = #244a89 -> 36,74,137; COLOR2 = #c22518 -> 194,37,24
+ALPHA1 = 160
+ALPHA2 = 110
+
+GMIC_TONE_MAPPING = "-fx_map_tones 0.5,0.7,0.1,30,0"
+GMIC_FELTPEN = "-fx_feltpen 300,50,1,0.1,20,5"
+GMIC_EDGES = "-fx_edges 0,15,0"
+GMIC_CHARRED_PLASTIC = "-fx_charred_plastic 1,10,40,1,10,0,0,2,6,5,20,0,11"
+GMIC_NEON = (
+    "-fx_neon 0,1,1,1,1,0,0.45,40,60,0,1,1.15,2,3,0,3,20,0.4,0.1,1.5,5,0.2,0.1,"
+    "1,2,1,0,0,1,1,0,50,50"
+)
+GMIC_CUTOUT = "-fx_cutout 4,0.5,4,1"
+GMIC_HUFFMAN_GLITCHES = "-fx_huffman_glitches 30,0,25,0,0,0,0,0,50,50"
+GMIC_QUERYPRIMARY = "-afre_queryprimary 1,1"
+GMIC_LOCAL_SIMILARITY = "-local_similarity_mask 50,50,50,128,4,10"
+GMIC_LUMA_INVERT = "-Lylejk_Luma_Invert 1,0"
+GMIC_CRAYONGRAFFITI = "-fx_crayongraffiti2 300,50,1,0.4,12,1,2,2,0"
+GMIC_ANAGLYPH = "-fx_stereo_to_anaglyph 2,0"
+GMIC_DROP_SHADOW = "-fx_drop_shadow3d 0,0,0,10,1,1,2,0.5,194,37,24,200,0"
+GMIC_BOKEH = (
+    f"-fx_bokeh 3,5,0,30,8,4,0.3,0.2,36,74,137,{ALPHA1},0.7,30,20,20,1,2,194,37,24,{ALPHA2},0.15"
+)
+
+
+def main() -> None:
+    with Pipeline(
+        name="aichelberg-indians",
+        input_dir=INPUT,
+        output_base=OUTPUT_BASE,
+        existing_outputs=EXISTING_OUTPUTS or None,
+        continue_from=CONTINUE_FROM,
+    ) as p:
+        rembg_out = p.step("rembg", inputs="input", step_id="rembg_out")
+
+        # recipe: gmic-tone-mapping
+        input_tone_map = p.step(
+            "gmic", inputs="input", command=GMIC_TONE_MAPPING, step_id="input_tone_map"
+        )
+
+        # recipe: gmic-tone-mapping-rembg
+        rembg_tone_map = p.step(
+            "gmic", inputs=rembg_out, command=GMIC_TONE_MAPPING, step_id="rembg_tone_map"
+        )
+
+        # recipe: gmic-feltpen-rembg
+        rembg_feltpen = p.step(
+            "gmic", inputs=rembg_out, command=GMIC_FELTPEN, step_id="rembg_feltpen"
+        )
+        composite_feltpen = p.step(
+            "composite", inputs=[rembg_feltpen, rembg_out], step_id="composite_feltpen"
+        )
+
+        # recipe: gmic-edges-rembg
+        rembg_edges = p.step("gmic", inputs=rembg_out, command=GMIC_EDGES, step_id="rembg_edges")
+        composite_edges = p.step(
+            "composite", inputs=[rembg_edges, rembg_out], step_id="composite_edges"
+        )
+
+        # recipe: gmic-charred-plastic-rembg
+        rembg_charred_plastic = p.step(
+            "gmic",
+            inputs=rembg_out,
+            command=GMIC_CHARRED_PLASTIC,
+            step_id="rembg_charred_plastic",
+        )
+        composite_charred_plastic = p.step(
+            "composite",
+            inputs=[rembg_charred_plastic, rembg_out],
+            step_id="composite_charred_plastic",
+        )
+
+        # recipe: gmic-neon-rembg
+        rembg_neon = p.step("gmic", inputs=rembg_out, command=GMIC_NEON, step_id="rembg_neon")
+        composite_neon = p.step(
+            "composite", inputs=[rembg_neon, rembg_out], step_id="composite_neon"
+        )
+
+        # recipe: gmic-cutout-rembg (tone-mapped input as original)
+        input_cutout = p.step(
+            "gmic", inputs=input_tone_map, command=GMIC_CUTOUT, step_id="input_cutout"
+        )
+        cutout_mid = p.step(
+            "composite", inputs=[input_tone_map, input_cutout], step_id="cutout_mid"
+        )
+        composite_cutout = p.step(
+            "composite", inputs=[cutout_mid, rembg_out], step_id="composite_cutout"
+        )
+
+        # recipe: gmic-huffman-glitches-rembg
+        input_huffman_glitches = p.step(
+            "gmic",
+            inputs=input_tone_map,
+            command=GMIC_HUFFMAN_GLITCHES,
+            step_id="input_huffman_glitches",
+        )
+        huffman_glitches_mid = p.step(
+            "composite",
+            inputs=[input_tone_map, input_huffman_glitches],
+            step_id="huffman_glitches_mid",
+        )
+        composite_huffman_glitches = p.step(
+            "composite",
+            inputs=[huffman_glitches_mid, rembg_out],
+            step_id="composite_huffman_glitches",
+        )
+
+        # recipe: gmic-queryprimary-rembg
+        input_queryprimary = p.step(
+            "gmic",
+            inputs=input_tone_map,
+            command=GMIC_QUERYPRIMARY,
+            step_id="input_queryprimary",
+        )
+        queryprimary_mid = p.step(
+            "composite",
+            inputs=[input_tone_map, input_queryprimary],
+            step_id="queryprimary_mid",
+        )
+        composite_queryprimary = p.step(
+            "composite",
+            inputs=[queryprimary_mid, rembg_out],
+            step_id="composite_queryprimary",
+        )
+
+        # recipe: gmic-local-similarity-rembg
+        input_local_similarity = p.step(
+            "gmic",
+            inputs=input_tone_map,
+            command=GMIC_LOCAL_SIMILARITY,
+            step_id="input_local_similarity",
+        )
+        local_similarity_mid = p.step(
+            "composite",
+            inputs=[input_tone_map, input_local_similarity],
+            step_id="local_similarity_mid",
+        )
+        composite_local_similarity = p.step(
+            "composite",
+            inputs=[local_similarity_mid, rembg_out],
+            step_id="composite_local_similarity",
+        )
+
+        # recipe: gmic-luma-invert-rembg
+        input_luma_invert = p.step(
+            "gmic",
+            inputs=input_tone_map,
+            command=GMIC_LUMA_INVERT,
+            step_id="input_luma_invert",
+        )
+        luma_invert_mid = p.step(
+            "composite",
+            inputs=[input_tone_map, input_luma_invert],
+            step_id="luma_invert_mid",
+        )
+        composite_luma_invert = p.step(
+            "composite",
+            inputs=[luma_invert_mid, rembg_out],
+            step_id="composite_luma_invert",
+        )
+
+        # recipe: gmic-crayongraffiti-rembg
+        input_crayongraffiti = p.step(
+            "gmic",
+            inputs=input_tone_map,
+            command=GMIC_CRAYONGRAFFITI,
+            step_id="input_crayongraffiti",
+        )
+        crayongraffiti_mid = p.step(
+            "composite",
+            inputs=[input_tone_map, input_crayongraffiti],
+            step_id="crayongraffiti_mid",
+        )
+        composite_crayongraffiti = p.step(
+            "composite",
+            inputs=[crayongraffiti_mid, rembg_out],
+            step_id="composite_crayongraffiti",
+        )
+
+        # recipe: gmic-anaglyph-rembg
+        input_anaglyph = p.step(
+            "gmic", inputs=input_tone_map, command=GMIC_ANAGLYPH, step_id="input_anaglyph"
+        )
+        anaglyph_mid = p.step(
+            "composite", inputs=[input_tone_map, input_anaglyph], step_id="anaglyph_mid"
+        )
+        composite_anaglyph = p.step(
+            "composite", inputs=[anaglyph_mid, rembg_out], step_id="composite_anaglyph"
+        )
+
+        # recipe: xcf-stack — layers up to composites (excludes bokeh + color-bg-drop-shadow)
+        p.step(
+            "xcf_stack",
+            inputs=[
+                "input",
+                rembg_out,
+                input_tone_map,
+                rembg_tone_map,
+                rembg_feltpen,
+                rembg_edges,
+                rembg_charred_plastic,
+                rembg_neon,
+                input_cutout,
+                input_huffman_glitches,
+                input_queryprimary,
+                input_local_similarity,
+                input_luma_invert,
+                input_crayongraffiti,
+                input_anaglyph,
+                composite_feltpen,
+                composite_edges,
+                composite_charred_plastic,
+                composite_neon,
+                composite_cutout,
+                composite_huffman_glitches,
+                composite_queryprimary,
+                composite_local_similarity,
+                composite_luma_invert,
+                composite_crayongraffiti,
+                composite_anaglyph,
+            ],
+        )
+
+        # recipe: bokeh-oktagon (tone-mapped input as original)
+        input_bokeh = p.step(
+            "gmic", inputs=input_tone_map, command=GMIC_BOKEH, step_id="input_bokeh"
+        )
+        bokeh_mid = p.step("composite", inputs=[input_tone_map, input_bokeh], step_id="bokeh_mid")
+        p.step("composite", inputs=[bokeh_mid, rembg_out], step_id="composite_bokeh")
+
+        # recipe: color-bg-drop-shadow-rembg
+        color_bg = p.step("imagemagick_fill", inputs="input", color1=COLOR1, step_id="color_bg")
+        rembg_shadow = p.step(
+            "gmic", inputs=rembg_out, command=GMIC_DROP_SHADOW, step_id="rembg_shadow"
+        )
+        shadow_color_mid = p.step(
+            "composite", inputs=[color_bg, rembg_shadow], step_id="shadow_color_mid"
+        )
+        p.step(
+            "composite",
+            inputs=[shadow_color_mid, rembg_out],
+            step_id="composite_color_bg_shadow",
+        )
+
+        output_root = p.run()
+
+    print(f"Pipeline finished. Output: {output_root}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/pipelines/pipeline_baxxter_2.py b/pipelines/pipeline_baxxter_2.py
index 9b479d0..f5fad13 100644
--- a/pipelines/pipeline_baxxter_2.py
+++ b/pipelines/pipeline_baxxter_2.py
@@ -40,14 +40,10 @@ def main() -> None:
         gmic_shadow = p.step("gmic", inputs=rembg, command=GMIC_DROP_SHADOW)
         gmic_smooth = p.step("gmic", inputs=rembg, command=GMIC_JPR_SMOOTH)
 
-        gmic_stereo_alpha = p.step(
-            "color_to_alpha", inputs=gmic_stereo, color="#000000"
-        )
+        gmic_stereo_alpha = p.step("color_to_alpha", inputs=gmic_stereo, color="#000000")
         yellow_bg = p.step("imagemagick_fill", inputs="input", color1=YELLOW)
 
-        gmic_smooth_alpha = p.step(
-            "color_to_alpha", inputs=gmic_smooth, color="#7f7f7f"
-        )
+        gmic_smooth_alpha = p.step("color_to_alpha", inputs=gmic_smooth, color="#7f7f7f")
         gmic_smooth_sized = p.step(
             "imagemagick_scale_crop",
             inputs=gmic_smooth_alpha,
diff --git a/pipelines/pipeline_colorsplash_watermark_f12.py b/pipelines/pipeline_colorsplash_watermark_f12.py
index d710750..e729d2e 100644
--- a/pipelines/pipeline_colorsplash_watermark_f12.py
+++ b/pipelines/pipeline_colorsplash_watermark_f12.py
@@ -6,7 +6,9 @@ from pathlib import Path
 from imagepipeline import Pipeline
 
 # Darktable export folder.
-INPUT = Path("/home/frank/pics/20260517_Albershausen Crusaders - Biberach Beavers/darktable_exported/png")
+INPUT = Path(
+    "/home/frank/pics/20260517_Albershausen Crusaders - Biberach Beavers/darktable_exported/png"
+)
 
 # Where timestamped run folders are created.
 OUTPUT_BASE = Path.home() / "pipeline_output"
diff --git a/pipelines/pipeline_crusaders.py b/pipelines/pipeline_crusaders.py
index cd99773..2b37634 100644
--- a/pipelines/pipeline_crusaders.py
+++ b/pipelines/pipeline_crusaders.py
@@ -5,7 +5,9 @@ from pathlib import Path
 
 from imagepipeline import Pipeline
 
-INPUT = Path("/home/frank/pics/20260620_Albershausen Crusaders - Montabaur  Fighting Farmers/darktable_exported")
+INPUT = Path(
+    "/home/frank/pics/20260620_Albershausen Crusaders - Montabaur  Fighting Farmers/darktable_exported"
+)
 OUTPUT_BASE = Path.home() / "pipeline_output"
 
 # Reuse outputs from a previous run or external folder (key = step id, e.g. rembg_01).
@@ -80,13 +82,9 @@ def main() -> None:
             scale=1.05,
         )
 
-        rembg_stereo_alpha = p.step(
-            "color_to_alpha", inputs=rembg_stereo, color="#000000"
-        )
+        rembg_stereo_alpha = p.step("color_to_alpha", inputs=rembg_stereo, color="#000000")
         color_bg = p.step("imagemagick_fill", inputs="input", color1=COLOR1)
-        rembg_smooth_alpha = p.step(
-            "color_to_alpha", inputs=rembg_jpr_smooth, color="#7f7f7f"
-        )
+        rembg_smooth_alpha = p.step("color_to_alpha", inputs=rembg_jpr_smooth, color="#7f7f7f")
         rembg_smooth_sized = p.step(
             "imagemagick_scale_crop",
             inputs=rembg_smooth_alpha,
diff --git a/pipelines/pipeline_orange.py b/pipelines/pipeline_orange.py
index 44687c7..26cebf4 100644
--- a/pipelines/pipeline_orange.py
+++ b/pipelines/pipeline_orange.py
@@ -35,6 +35,7 @@ GMIC_GRADIENT_B = (
     "255,255,128,128,128,255,255,0,255,255,0,0,0,0"
 )
 
+
 def main() -> None:
     with Pipeline(
         name="orange",
diff --git a/pipelines/pipeline_rezepttest.py b/pipelines/pipeline_rezepttest.py
new file mode 100644
index 0000000..6485708
--- /dev/null
+++ b/pipelines/pipeline_rezepttest.py
@@ -0,0 +1,118 @@
+#!/usr/bin/env python3
+"""Rezepttest pipeline — RECIPES.md smoke test (Indians Aichelberg logo colors)."""
+
+from pathlib import Path
+
+from imagepipeline import Pipeline
+
+# Change to your Darktable export folder.
+INPUT = Path("/home/frank/tmp/bar")
+OUTPUT_BASE = Path.home() / "pipeline_output"
+
+EXISTING_OUTPUTS: dict[str, Path] = {}
+CONTINUE_FROM: Path | None = None
+
+# Colors from Indians Aichelberg logo (orange text + red stitching).
+COLOR1 = "#f0b020"  # 240, 176, 32
+COLOR2 = "#f01000"  # 240, 16, 0
+
+ALPHA1 = 160
+ALPHA2 = 110
+
+GMIC_DROP_SHADOW = "-fx_drop_shadow3d 0,0,0,10,1,1,2,0.5,240,16,0,200,0"
+GMIC_JPR_SMOOTH = "-jpr_gradient_smooth 0,1.5"
+GMIC_BOKEH = (
+    f"-fx_bokeh 3,5,0,30,8,4,0.3,0.2,240,176,32,{ALPHA1},0.7,30,20,20,1,2,240,16,0,{ALPHA2},0.15"
+)
+
+
+def main() -> None:
+    with Pipeline(
+        name="rezepttest",
+        input_dir=INPUT,
+        output_base=OUTPUT_BASE,
+        existing_outputs=EXISTING_OUTPUTS or None,
+        continue_from=CONTINUE_FROM,
+    ) as p:
+        rembg_out = p.step("rembg", inputs="input", step_id="rembg_out")
+        grayscale = p.step("gmic_grayscale", inputs="input", step_id="grayscale")
+        gradient_radial_bg = p.step(
+            "imagemagick_fill",
+            inputs="input",
+            color1=COLOR1,
+            color2=COLOR2,
+            gradient=True,
+            radial=True,
+            step_id="gradient_radial_bg",
+        )
+
+        rembg_shadow = p.step(
+            "gmic", inputs=rembg_out, command=GMIC_DROP_SHADOW, step_id="rembg_shadow"
+        )
+        rembg_jpr_smooth = p.step(
+            "gmic", inputs=rembg_out, command=GMIC_JPR_SMOOTH, step_id="rembg_jpr_smooth"
+        )
+        rembg_jpr_smooth_sized = p.step(
+            "imagemagick_scale_crop",
+            inputs=rembg_jpr_smooth,
+            scale=1.05,
+            step_id="rembg_jpr_smooth_sized",
+        )
+        input_bokeh = p.step("gmic", inputs="input", command=GMIC_BOKEH, step_id="input_bokeh")
+
+        # recipe: colorsplash
+        composite_colorsplash = p.step(
+            "composite", inputs=[grayscale, rembg_out], step_id="composite_colorsplash"
+        )
+
+        # recipe: rembg-radial-2colors (gradient-radial)
+        composite_radial = p.step(
+            "composite", inputs=[gradient_radial_bg, rembg_out], step_id="composite_radial"
+        )
+
+        # recipe: original-drop-shadow-rembg
+        shadow_mid = p.step("composite", inputs=["input", rembg_shadow], step_id="shadow_mid")
+        composite_shadow = p.step(
+            "composite", inputs=[shadow_mid, rembg_out], step_id="composite_shadow"
+        )
+
+        # recipe: original-jpr-smooth-rembg
+        smooth_mid = p.step(
+            "composite", inputs=["input", rembg_jpr_smooth_sized], step_id="smooth_mid"
+        )
+        composite_smooth = p.step(
+            "composite", inputs=[smooth_mid, rembg_out], step_id="composite_smooth"
+        )
+
+        # recipe: bokeh-oktagon
+        bokeh_mid = p.step("composite", inputs=["input", input_bokeh], step_id="bokeh_mid")
+        composite_bokeh = p.step(
+            "composite", inputs=[bokeh_mid, rembg_out], step_id="composite_bokeh"
+        )
+
+        # recipe: xcf-stack — explicit layer list, bottom to top
+        p.step(
+            "xcf_stack",
+            inputs=[
+                "input",
+                rembg_out,
+                grayscale,
+                gradient_radial_bg,
+                rembg_shadow,
+                rembg_jpr_smooth_sized,
+                input_bokeh,
+                composite_colorsplash,
+                composite_radial,
+                composite_shadow,
+                composite_smooth,
+                composite_bokeh,
+            ],
+        )
+
+        output_root = p.run()
+
+    print(f"Pipeline finished. Output: {output_root}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/pipelines/pipeline_watermark_f12_2000px.py b/pipelines/pipeline_watermark_f12_2000px.py
new file mode 100644
index 0000000..f92b36d
--- /dev/null
+++ b/pipelines/pipeline_watermark_f12_2000px.py
@@ -0,0 +1,31 @@
+#!/usr/bin/env python3
+"""Resize to 2000px max edge, then colorsplash + F12 watermark darktable style."""
+
+from pathlib import Path
+
+from imagepipeline import Pipeline
+
+INPUT = Path(
+    "/home/frank/pics/20260712_Aichelberg Indians - Heidelberg Hedgehogs/darktable_exported/edits"
+)
+OUTPUT_BASE = Path.home() / "pipeline_output"
+
+MAX_EDGE = 2000
+STYLE = "Watermark F12.rocks"
+
+
+def main() -> None:
+    with Pipeline(
+        name="watermark_f12_2000px",
+        input_dir=INPUT,
+        output_base=OUTPUT_BASE,
+    ) as p:
+        resized = p.step("imagemagick_resize", inputs="input", max_edge=MAX_EDGE)
+        p.step("darktable_style", inputs=resized, style=STYLE)
+        output_root = p.run()
+
+    print(f"Pipeline finished. Output: {output_root}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/pyproject.toml b/pyproject.toml
index bbb0508..f77c4bb 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -10,11 +10,17 @@ readme = "README.md"
 requires-python = ">=3.11"
 license = { text = "MIT" }
 authors = [{ name = "Frank" }]
-dependencies = []
+dependencies = [
+    "Pillow>=10.0",
+]
 
 [project.optional-dependencies]
-ai = ["numpy>=1.26", "Pillow>=10.0", "torch>=2.0"]
-dev = ["pytest>=8.0"]
+ai = ["numpy>=1.26", "torch>=2.0"]
+dev = [
+    "pytest>=8.0",
+    "numpy>=1.26",
+    "ruff>=0.8",
+]
 
 [project.scripts]
 imagepipeline = "imagepipeline.cli:main"
@@ -25,3 +31,28 @@ include = ["imagepipeline*"]
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]
+markers = [
+    "integration: tests that call external CLI tools (ImageMagick, G'MIC, rembg, darktable, GIMP)",
+    "slow: tests that take more than a few seconds",
+]
+
+[tool.ruff]
+target-version = "py311"
+line-length = 100
+src = ["imagepipeline", "tests", "pipelines"]
+
+[tool.ruff.lint]
+select = [
+    "E",   # pycodestyle errors
+    "F",   # pyflakes
+    "I",   # isort
+    "UP",  # pyupgrade
+    "B",   # flake8-bugbear
+]
+ignore = [
+    "E501",  # line length handled by formatter
+    "B027",  # optional empty hooks on BaseModule
+]
+
+[tool.ruff.lint.isort]
+known-first-party = ["imagepipeline"]
diff --git a/tests/conftest.py b/tests/conftest.py
index 8c8fa42..a59461d 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -20,10 +20,7 @@ def make_png(
         crc = zlib.crc32(tag + data) & 0xFFFFFFFF
         return struct.pack(">I", len(data)) + tag + data + struct.pack(">I", crc)
 
-    raw = b"".join(
-        b"\x00" + bytes([r, g, b] * width)
-        for _ in range(height)
-    )
+    raw = b"".join(b"\x00" + bytes([r, g, b] * width) for _ in range(height))
     compressed = zlib.compress(raw, 9)
     ihdr = struct.pack(">IIBBBBB", width, height, 8, 2, 0, 0, 0)
     png = (
@@ -37,7 +34,7 @@ def make_png(
 
 @pytest.fixture(autouse=True)
 def _ensure_builtin_modules() -> None:
-    import imagepipeline.modules  # noqa: F401
+    pass  # noqa: F401
 
 
 @pytest.fixture
diff --git a/tests/integration_helpers.py b/tests/integration_helpers.py
new file mode 100644
index 0000000..af9fdb1
--- /dev/null
+++ b/tests/integration_helpers.py
@@ -0,0 +1,53 @@
+"""Shared helpers for integration tests."""
+
+from __future__ import annotations
+
+import shutil
+import subprocess
+import tempfile
+from pathlib import Path
+
+from tests.conftest import make_png
+
+
+def has_darktable_style(style_name: str, config_dir: Path | None = None) -> bool:
+    """Return True if darktable-cli can apply ``style_name`` to a tiny PNG."""
+    if not shutil.which("darktable-cli"):
+        return False
+
+    config = config_dir or Path.home() / ".config" / "darktable"
+    styles_dir = config / "styles"
+    if not styles_dir.is_dir():
+        return False
+    if not any(p.stem == style_name for p in styles_dir.glob("*.dtstyle")):
+        return False
+
+    with tempfile.TemporaryDirectory() as tmp:
+        tmp_path = Path(tmp)
+        src = tmp_path / "probe.png"
+        out_dir = tmp_path / "out"
+        out_dir.mkdir()
+        make_png(src)
+        cmd = [
+            "darktable-cli",
+            str(src),
+            str(out_dir),
+            "--style",
+            style_name,
+            "--out-ext",
+            "png",
+            "--core",
+            "--configdir",
+            str(config),
+            "--style-overwrite",
+        ]
+        result = subprocess.run(cmd, capture_output=True, text=True)
+        if result.returncode != 0:
+            return False
+        return any(out_dir.iterdir())
+
+
+def has_workflow_tools() -> bool:
+    """True when rembg, gmic, ImageMagick, and darktable-cli are on PATH."""
+    has_magick = bool(shutil.which("magick") or shutil.which("convert"))
+    return all(shutil.which(name) for name in ("rembg", "gmic", "darktable-cli")) and has_magick
diff --git a/tests/test_ai_modules.py b/tests/test_ai_modules.py
index 4c3d522..2738fb0 100644
--- a/tests/test_ai_modules.py
+++ b/tests/test_ai_modules.py
@@ -110,9 +110,7 @@ class TestAIParameters:
         assert payload["modalities"] == ["image"]
         assert payload["image_config"] == {"strength": 0.25}
 
-    def test_save_result_matching_source_preserves_png_size(
-        self, tmp_path: Path
-    ) -> None:
+    def test_save_result_matching_source_preserves_png_size(self, tmp_path: Path) -> None:
         try:
             from PIL import Image
         except ImportError:
diff --git a/tests/test_pipeline.py b/tests/test_pipeline.py
index 5a60bba..4c52dd9 100644
--- a/tests/test_pipeline.py
+++ b/tests/test_pipeline.py
@@ -113,9 +113,11 @@ class TestPipelineRunner:
                 for src in ctx.input_paths:
                     shutil.copy2(src, ctx.output_dir / src.name)
 
-        with Pipeline(name="order_test", input_dir=input_dir, output_base=output_base, verbose=False) as p:
+        with Pipeline(
+            name="order_test", input_dir=input_dir, output_base=output_base, verbose=False
+        ) as p:
             step_b = p.step("order_tracker", inputs="input")
-            step_a = p.step("order_tracker", inputs=step_b)
+            p.step("order_tracker", inputs=step_b)
             p.run()
 
         assert order == ["order_tracker_01", "order_tracker_02"]
@@ -132,7 +134,9 @@ class TestPipelineRunner:
                 for src in ctx.input_paths:
                     shutil.copy2(src, ctx.output_dir / src.name)
 
-        with Pipeline(name="dup_test", input_dir=input_dir, output_base=output_base, verbose=False) as p:
+        with Pipeline(
+            name="dup_test", input_dir=input_dir, output_base=output_base, verbose=False
+        ) as p:
             first = p.step("number_tracker", inputs="input")
             p.step("number_tracker", inputs=first)
             root = p.run()
@@ -159,6 +163,74 @@ class TestManifest:
         assert data["finished_at"] is not None
 
 
+class TestCustomStepId:
+    def test_custom_step_id_output_folder(self, input_dir: Path, output_base: Path) -> None:
+        @register
+        class NamedModule(BaseModule):
+            name = "named_tracker"
+
+            def run(self, ctx) -> None:
+                ctx.output_dir.mkdir(parents=True, exist_ok=True)
+                for src in ctx.input_paths:
+                    shutil.copy2(src, ctx.output_dir / src.name)
+
+        with Pipeline(
+            name="named_test", input_dir=input_dir, output_base=output_base, verbose=False
+        ) as p:
+            ref = p.step("named_tracker", inputs="input", step_id="input_bokeh")
+            root = p.run()
+
+        assert ref.step_id == "input_bokeh"
+        assert ref.output_dir_name == "input_bokeh"
+        assert (root / "input_bokeh").is_dir()
+        assert not (root / "named_tracker_01").exists()
+
+        unregister("named_tracker")
+
+    def test_module_counter_independent_of_custom_step_id(
+        self, input_dir: Path, output_base: Path
+    ) -> None:
+        @register
+        class CounterModule(BaseModule):
+            name = "counter_tracker"
+
+            def run(self, ctx) -> None:
+                ctx.output_dir.mkdir(parents=True, exist_ok=True)
+                for src in ctx.input_paths:
+                    shutil.copy2(src, ctx.output_dir / src.name)
+
+        with Pipeline(
+            name="counter_test", input_dir=input_dir, output_base=output_base, verbose=False
+        ) as p:
+            p.step("counter_tracker", inputs="input")
+            p.step("counter_tracker", inputs="input", step_id="custom_mid")
+            p.step("counter_tracker", inputs="input")
+            root = p.run()
+
+        assert (root / "counter_tracker_01").is_dir()
+        assert (root / "custom_mid").is_dir()
+        assert (root / "counter_tracker_03").is_dir()
+        assert not (root / "counter_tracker_02").exists()
+
+        unregister("counter_tracker")
+
+    def test_duplicate_step_id_rejected(self, input_dir: Path) -> None:
+        with Pipeline(name="dup_id", input_dir=input_dir, verbose=False) as p:
+            p.step("imagemagick_grayscale", inputs="input", step_id="my_step")
+            with pytest.raises(ValidationError, match="Duplicate step_id"):
+                p.step("imagemagick_grayscale", inputs="input", step_id="my_step")
+
+    def test_empty_step_id_rejected(self, input_dir: Path) -> None:
+        with Pipeline(name="empty_id", input_dir=input_dir, verbose=False) as p:
+            with pytest.raises(ValidationError, match="must not be empty"):
+                p.step("imagemagick_grayscale", inputs="input", step_id="")
+
+    def test_step_id_with_slash_rejected(self, input_dir: Path) -> None:
+        with Pipeline(name="slash_id", input_dir=input_dir, verbose=False) as p:
+            with pytest.raises(ValidationError, match="path separators"):
+                p.step("imagemagick_grayscale", inputs="input", step_id="bad/name")
+
+
 class TestPipelineValidation:
     def test_empty_pipeline_rejected(self, input_dir: Path) -> None:
         with Pipeline(name="empty", input_dir=input_dir, verbose=False) as p:
diff --git a/tests/test_resume.py b/tests/test_resume.py
index 74ea0c4..951ab60 100644
--- a/tests/test_resume.py
+++ b/tests/test_resume.py
@@ -13,7 +13,6 @@ from imagepipeline.core.resume import (
 )
 from imagepipeline.core.step import StepDefinition
 from imagepipeline.modules.imagemagick_grayscale import ImageMagickGrayscale
-from imagepipeline.modules.registry import get_module
 from imagepipeline.modules.rembg import RembgModule
 from imagepipeline.utils.gmic import finalize_gmic_output, split_gmic_command
 from tests.conftest import make_png
@@ -124,7 +123,9 @@ class TestExpectedOutputFilenames:
 
 class TestPipelineResume:
     @pytest.mark.skipif(not shutil.which("magick"), reason="ImageMagick not installed")
-    def test_continue_skips_completed_steps(self, input_dir: Path, output_base: Path, capsys) -> None:
+    def test_continue_skips_completed_steps(
+        self, input_dir: Path, output_base: Path, capsys
+    ) -> None:
         with Pipeline(
             name="resume_test",
             input_dir=input_dir,
@@ -178,6 +179,32 @@ class TestPipelineResume:
         assert "Reused external output for imagemagick_grayscale_01" in output
         assert (root / "imagemagick_grayscale_01" / "photo_a.png").exists()
 
+    @pytest.mark.skipif(not shutil.which("magick"), reason="ImageMagick not installed")
+    def test_existing_outputs_with_custom_step_id(
+        self, input_dir: Path, output_base: Path, tmp_path: Path, capsys
+    ) -> None:
+        external = tmp_path / "external_gray"
+        external.mkdir()
+        for src in input_dir.iterdir():
+            if src.is_file():
+                make_png(external / src.name, width=4, height=4, rgb=(10, 20, 30))
+
+        with Pipeline(
+            name="custom_id_external",
+            input_dir=input_dir,
+            output_base=output_base,
+            verbose=True,
+            existing_outputs={"input_bokeh": external},
+        ) as p:
+            reused = p.step("imagemagick_grayscale", inputs="input", step_id="input_bokeh")
+            p.step("imagemagick_grayscale", inputs=reused)
+            root = p.run()
+
+        output = capsys.readouterr().out
+        assert "Reused external output for input_bokeh" in output
+        assert (root / "input_bokeh" / "photo_a.png").exists()
+        assert not (root / "imagemagick_grayscale_01").exists()
+
 
 class TestMaterializeExternal:
     def test_links_files_by_stem(self, tmp_path: Path) -> None:
diff --git a/tests/test_workflow_modules.py b/tests/test_workflow_modules.py
index 7126a10..4c10b6b 100644
--- a/tests/test_workflow_modules.py
+++ b/tests/test_workflow_modules.py
@@ -5,7 +5,6 @@ from pathlib import Path
 
 import pytest
 
-from imagepipeline.core.params import validate_params
 from imagepipeline.modules.color_to_alpha import (
     ColorToAlphaModule,
     build_color_to_alpha_args,
@@ -13,18 +12,19 @@ from imagepipeline.modules.color_to_alpha import (
 from imagepipeline.modules.composite import CompositeModule
 from imagepipeline.modules.crop_square import CropSquareModule
 from imagepipeline.modules.darktable_style import DarktableStyleModule
+from imagepipeline.modules.gmic_grayscale import GmicGrayscale
 from imagepipeline.modules.imagemagick_fill import (
     ImageMagickFillModule,
     build_fill_arguments,
 )
-from imagepipeline.modules.imagemagick_grayscale import ImageMagickGrayscale
 from imagepipeline.modules.imagemagick_resize import (
     ImageMagickResizeModule,
     build_resize_arguments,
 )
-from imagepipeline.modules.gmic_grayscale import GmicGrayscale
 from imagepipeline.modules.registry import get_module, list_modules
 from imagepipeline.modules.rembg import RembgModule
+from tests.integration_helpers import has_darktable_style
+from tests.integration_helpers import has_workflow_tools as check_workflow_tools
 
 has_magick = bool(shutil.which("magick") or shutil.which("convert"))
 
@@ -184,7 +184,6 @@ class TestImageMagickFill:
     def test_output_matches_input_size(self, tmp_path: Path) -> None:
         from imagepipeline.core.context import ModuleContext
         from imagepipeline.utils.subprocess import run_command
-
         from tests.conftest import make_png
 
         src = tmp_path / "ref.png"
@@ -221,7 +220,6 @@ class TestCropSquare:
     def test_center_crops_to_square(self, tmp_path: Path) -> None:
         from imagepipeline.core.context import ModuleContext
         from imagepipeline.utils.subprocess import run_command
-
         from tests.conftest import make_png
 
         src = tmp_path / "wide.png"
@@ -255,9 +253,7 @@ class TestModuleParameters:
             DarktableStyleModule.validate_module_params({})
 
     def test_darktable_style_accepts_style(self) -> None:
-        params = DarktableStyleModule.validate_module_params(
-            {"style": "Watermark F12.rocks"}
-        )
+        params = DarktableStyleModule.validate_module_params({"style": "Watermark F12.rocks"})
         assert params["style"] == "Watermark F12.rocks"
         assert params["style_overwrite"] is True
 
@@ -273,9 +269,7 @@ class TestModuleParameters:
     def test_darktable_export_conf_jpeg(self) -> None:
         from imagepipeline.modules.darktable_style import export_conf_options
 
-        assert export_conf_options("jpeg") == [
-            "plugins/imageio/format/jpeg/quality=90"
-        ]
+        assert export_conf_options("jpeg") == ["plugins/imageio/format/jpeg/quality=90"]
 
     def test_darktable_export_conf_png(self) -> None:
         from imagepipeline.modules.darktable_style import export_conf_options
@@ -308,7 +302,6 @@ class TestCompositeColor:
     def test_preserves_color_over_grayscale_background(self, tmp_path: Path) -> None:
         from imagepipeline.core.context import ModuleContext
         from imagepipeline.utils.subprocess import run_command
-
         from tests.conftest import make_png
 
         src = tmp_path / "src.png"
@@ -347,19 +340,22 @@ class TestCompositeColor:
 
         output = output_dir / "fg.png"
         assert output.is_file()
-        result = run_command(
-            [magick, "identify", "-format", "%[type]", str(output)]
-        )
-        assert result.stdout.strip() != "Grayscale"
+        from PIL import Image
+
+        with Image.open(output) as img:
+            assert img.mode != "L"
 
 
-has_workflow_tools = all(
-    shutil.which(name)
-    for name in ("rembg", "gmic", "magick", "darktable-cli")
-) or all(shutil.which(name) for name in ("rembg", "gmic", "convert", "darktable-cli"))
+has_workflow_tools = check_workflow_tools()
 
 
+@pytest.mark.integration
+@pytest.mark.slow
 @pytest.mark.skipif(not has_workflow_tools, reason="Workflow CLI tools not installed")
+@pytest.mark.skipif(
+    not has_darktable_style("Watermark F12.rocks"),
+    reason="darktable style 'Watermark F12.rocks' not available or darktable-cli export failed",
+)
 class TestWorkflowIntegration:
     def test_watermark_pipeline(self, input_dir, output_base) -> None:
         from imagepipeline import Pipeline
diff --git a/tests/test_xcf_stack.py b/tests/test_xcf_stack.py
index d5bf6d9..c4ccd7b 100644
--- a/tests/test_xcf_stack.py
+++ b/tests/test_xcf_stack.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import shutil
+import subprocess
 from pathlib import Path
 from unittest.mock import patch
 
@@ -12,26 +13,10 @@ from imagepipeline.modules.xcf_stack import XcfStackModule
 from imagepipeline.utils.files import find_image_by_stem
 from tests.conftest import make_png
 
-has_gimp = bool(shutil.which("gimp"))
+has_gimp = bool(shutil.which("gimp-console") or shutil.which("gimp"))
 has_magick = bool(shutil.which("magick") or shutil.which("convert"))
 
 
-def _gimp_headless_works() -> bool:
-    gimp = shutil.which("gimp")
-    if not gimp:
-        return False
-    try:
-        from imagepipeline.utils.subprocess import run_command
-
-        run_command([gimp, "-idf", "-b", "(gimp-quit 0)"], timeout=10)
-        return True
-    except RuntimeError:
-        return False
-
-
-has_working_gimp = _gimp_headless_works()
-
-
 class TestFindImageByStem:
     def test_finds_matching_stem_case_insensitively(self, tmp_path: Path) -> None:
         make_png(tmp_path / "Photo.PNG")
@@ -56,6 +41,41 @@ class TestModuleRegistration:
     def test_get_module_returns_xcf_stack_class(self) -> None:
         assert get_module("xcf_stack") is XcfStackModule
 
+    def test_xcf_stack_waits_for_layer_inputs(self) -> None:
+        from imagepipeline.core.runner import PipelineRunner
+        from imagepipeline.core.step import StepDefinition
+        from imagepipeline.modules.imagemagick_grayscale import ImageMagickGrayscale
+
+        steps = [
+            StepDefinition(
+                step_id="xcf_stack_01",
+                module_name="xcf_stack",
+                module=XcfStackModule,
+                input_refs=["input", "imagemagick_grayscale_01"],
+                params={},
+                output_dir_name="xcf_stack_01",
+            ),
+            StepDefinition(
+                step_id="imagemagick_grayscale_01",
+                module_name="imagemagick_grayscale",
+                module=ImageMagickGrayscale,
+                input_refs=["input"],
+                params={},
+                output_dir_name="imagemagick_grayscale_01",
+            ),
+        ]
+        runner = PipelineRunner(
+            name="order",
+            input_dir=Path("/tmp/unused"),
+            output_base=Path("/tmp/unused"),
+            steps=steps,
+        )
+        ordered = runner._topological_sort()
+        assert [step.step_id for step in ordered] == [
+            "imagemagick_grayscale_01",
+            "xcf_stack_01",
+        ]
+
 
 class TestExpectedOutputFilenames:
     def test_returns_xcf_for_jpg_input(self) -> None:
@@ -66,6 +86,14 @@ class TestExpectedOutputFilenames:
         )
         assert names == ["photo.xcf"]
 
+    def test_default_timeout(self) -> None:
+        params = XcfStackModule.validate_module_params({})
+        assert params["timeout"] == 120.0
+
+    def test_custom_timeout(self) -> None:
+        params = XcfStackModule.validate_module_params({"timeout": 45})
+        assert params["timeout"] == 45.0
+
 
 def _make_stack_fixture(tmp_path: Path) -> dict[str, Path]:
     root = tmp_path
@@ -91,9 +119,7 @@ def _make_stack_fixture(tmp_path: Path) -> dict[str, Path]:
 
 class TestXcfStackRun:
     @patch("imagepipeline.modules.xcf_stack.stack_images_to_xcf")
-    def test_collects_layers_from_input_and_prior_steps(
-        self, mock_stack: object, tmp_path: Path
-    ) -> None:
+    def test_collects_layers_from_explicit_inputs(self, mock_stack: object, tmp_path: Path) -> None:
         paths = _make_stack_fixture(tmp_path)
         input_path = paths["root"] / "refs" / "photo.jpg"
         input_path.parent.mkdir()
@@ -105,7 +131,8 @@ class TestXcfStackRun:
             params=XcfStackModule.validate_module_params({}),
             pipeline_output_root=paths["root"],
             step_id="xcf_stack_01",
-            prior_steps=[
+            input_layer_dirs=[
+                ("input", paths["input_dir"]),
                 ("step_a", paths["step_a"]),
                 ("step_b", paths["step_b"]),
             ],
@@ -123,9 +150,7 @@ class TestXcfStackRun:
         ]
 
     @patch("imagepipeline.modules.xcf_stack.stack_images_to_xcf")
-    def test_skip_missing_true_skips_missing_step(
-        self, mock_stack: object, tmp_path: Path
-    ) -> None:
+    def test_skip_missing_true_skips_missing_step(self, mock_stack: object, tmp_path: Path) -> None:
         paths = _make_stack_fixture(tmp_path)
         (paths["step_b"] / "photo.png").unlink()
         input_path = paths["root"] / "photo.jpg"
@@ -136,7 +161,8 @@ class TestXcfStackRun:
             params=XcfStackModule.validate_module_params({"skip_missing": True}),
             pipeline_output_root=paths["root"],
             step_id="xcf_stack_01",
-            prior_steps=[
+            input_layer_dirs=[
+                ("input", paths["input_dir"]),
                 ("step_a", paths["step_a"]),
                 ("step_b", paths["step_b"]),
             ],
@@ -162,7 +188,8 @@ class TestXcfStackRun:
             params=XcfStackModule.validate_module_params({"skip_missing": False}),
             pipeline_output_root=paths["root"],
             step_id="xcf_stack_01",
-            prior_steps=[
+            input_layer_dirs=[
+                ("input", paths["input_dir"]),
                 ("step_a", paths["step_a"]),
                 ("step_b", paths["step_b"]),
             ],
@@ -174,7 +201,7 @@ class TestXcfStackRun:
         mock_stack.assert_not_called()
 
 
-@pytest.mark.skipif(not has_working_gimp, reason="GIMP headless not available")
+@pytest.mark.skipif(not has_gimp, reason="GIMP not installed")
 @pytest.mark.skipif(not has_magick, reason="ImageMagick not installed")
 class TestStackImagesToXcfIntegration:
     def test_stacks_pngs_into_xcf(self, tmp_path: Path) -> None:
@@ -198,3 +225,33 @@ class TestStackImagesToXcfIntegration:
 
         assert outfile.is_file()
         assert outfile.stat().st_size > 0
+        names = outfile.read_bytes()
+        assert b"bottom" in names
+        assert b"top" in names
+
+
+class TestGimpTimeoutHandling:
+    def test_accepts_outfile_when_gimp_hangs_on_exit(self, tmp_path: Path) -> None:
+        from unittest.mock import MagicMock, patch
+
+        from imagepipeline.utils.gimp import stack_images_to_xcf
+
+        layer = tmp_path / "layer.png"
+        layer.write_bytes(b"png")
+        outfile = tmp_path / "stack.xcf"
+        outfile.write_bytes(b"xcf-data")
+
+        def fake_popen(*_args, **_kwargs):
+            process = MagicMock()
+            process.communicate.side_effect = [
+                subprocess.TimeoutExpired(cmd="gimp", timeout=1),
+                ("", ""),
+            ]
+            process.kill = MagicMock()
+            return process
+
+        with patch("imagepipeline.utils.gimp.subprocess.Popen", side_effect=fake_popen):
+            with patch("imagepipeline.utils.gimp.require_gimp", return_value="gimp-console"):
+                stack_images_to_xcf([("layer", layer)], outfile, timeout=1.0)
+
+        assert outfile.read_bytes() == b"xcf-data"