README.md

@@ -48,7 +48,7 @@ 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)).
 
 ## Writing Pipelines
 

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
 

imagepipeline/core/pipeline.py

@@ -45,13 +45,18 @@ 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]
+        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"}
@@ -101,6 +106,16 @@ class Pipeline:
             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):

pipelines/pipeline_rezepttest.py

@@ -35,8 +35,8 @@ def main() -> None:
         existing_outputs=EXISTING_OUTPUTS or None,
         continue_from=CONTINUE_FROM,
     ) as p:
-        rembg_out = p.step("rembg", inputs="input")
+        rembg_out = p.step("rembg", inputs="input", step_id="rembg_out")
-        grayscale = p.step("gmic_grayscale", inputs="input")
+        grayscale = p.step("gmic_grayscale", inputs="input", step_id="grayscale")
         gradient_radial_bg = p.step(
             "imagemagick_fill",
             inputs="input",
@@ -44,34 +44,56 @@ def main() -> None:
             color2=COLOR2,
             gradient=True,
             radial=True,
+            step_id="gradient_radial_bg",
         )
 
-        rembg_shadow = p.step("gmic", inputs=rembg_out, command=GMIC_DROP_SHADOW)
+        rembg_shadow = p.step(
-        rembg_jpr_smooth = p.step("gmic", inputs=rembg_out, command=GMIC_JPR_SMOOTH)
+            "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"
         )
-        input_bokeh = p.step("gmic", inputs="input", command=GMIC_BOKEH)
 
         # recipe: colorsplash
-        composite_colorsplash = p.step("composite", inputs=[grayscale, rembg_out])
+        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])
+        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])
+        shadow_mid = p.step(
-        composite_shadow = p.step("composite", inputs=[shadow_mid, rembg_out])
+            "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])
+        smooth_mid = p.step(
-        composite_smooth = p.step("composite", inputs=[smooth_mid, rembg_out])
+            "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])
+        bokeh_mid = p.step("composite", inputs=["input", input_bokeh], step_id="bokeh_mid")
-        composite_bokeh = p.step("composite", inputs=[bokeh_mid, rembg_out])
+        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(

tests/test_pipeline.py

@@ -159,6 +159,70 @@ 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:

tests/test_resume.py

@@ -178,6 +178,34 @@ 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: