fix: name the module relative to the MLproject in the export header

docs/guides/mlproject-export.md

@@ -70,6 +70,14 @@ Custom health checks cannot be detected from the built app and are not warned ab
 
 The generated file starts with a `Generated from ... by chapkit mlproject export` header. `export` refuses to overwrite an MLproject without it, so a hand-written file is not lost. Pass `--force` to replace it once; from then on it is regenerated freely.
 
+The header names the module relative to the MLproject's folder, so it holds no machine-specific path and `--check` gives the same result on every machine. A service in a package (a `src/` layout) can be exported straight to the project root:
+
+```bash
+chapkit mlproject export src/my_model/service.py -o MLproject
+```
+
+The header then reads `Generated from src/my_model/service.py`, and its regenerate command includes `-o MLproject`, because `export` otherwise writes next to the module.
+
 ## Options
 
 | Option | Effect |

src/chapkit/cli/export.py

@@ -332,11 +332,12 @@ def build_mlproject(parts: ServiceParts) -> dict[str, Any]:
     return document
 
 
-def render_mlproject(parts: ServiceParts, source: str) -> str:
+def render_mlproject(parts: ServiceParts, source: str, output: str | None = None) -> str:
     """Render the MLproject file, with a header saying where it comes from and how to regenerate it."""
+    command = f"chapkit mlproject export {source}" + (f" -o {output}" if output else "")
     header = [
         f"# Generated from {source} {GENERATED_MARKER} -- do not edit by hand.",
-        f"# Regenerate with `chapkit mlproject export {source}`; add --check to fail when it is stale.",
+        f"# Regenerate with `{command}`; add --check to fail when it is stale.",
     ]
     body = yaml.safe_dump(build_mlproject(parts), sort_keys=False, allow_unicode=True, width=100)
     return "\n".join(header) + "\n\n" + body
@@ -464,6 +465,14 @@ def _print_dropped(dropped: list[str]) -> None:
         typer.echo(f"WARNING: not carried over to the MLproject: {setting}", err=True)
 
 
+def _source_label(module_path: Path, target: Path) -> str:
+    """Name the module relative to the MLproject's folder, so the header holds no machine-specific path."""
+    try:
+        return Path(os.path.relpath(module_path, target.parent)).as_posix()
+    except ValueError:  # On Windows, a module on another drive has no relative path.
+        return str(module_path)
+
+
 def _default_output(module_path: Path) -> Path:
     """Return the existing MLproject next to the module, or where a new one goes."""
     for filename in MLPROJECT_FILENAMES:
@@ -522,8 +531,10 @@ def export_command(
         typer.echo(f"Error: {error}", err=True)
         raise typer.Exit(code=1) from error
 
-    source = module_path.name if target.parent == module_path.parent else str(module_path)
-    wanted = render_mlproject(parts, source)
+    source = _source_label(module_path, target)
+    # Export writes next to the module by default, so a module in another folder needs -o to land here again.
+    output_flag = None if target.parent == module_path.parent else target.name
+    wanted = render_mlproject(parts, source, output_flag)
     current = target.read_text(encoding="utf-8") if target.is_file() else None
 
     if check:

tests/test_cli_mlproject_export.py

@@ -219,6 +219,28 @@ def test_export_refuses_to_overwrite_a_hand_written_mlproject(tmp_path: Path) ->
     assert "chapkit mlproject export" in (tmp_path / "MLproject").read_text()
 
 
+def test_export_names_a_module_in_a_subfolder_relative_to_the_mlproject(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """A src-layout service gets a portable header that regenerates the same file."""
+    package = tmp_path / "src" / "pkg"
+    package.mkdir(parents=True)
+    module = package / "service.py"
+    module.write_text(SERVICE_MODULE)
+    target = tmp_path / "MLproject"
+
+    assert CliRunner().invoke(app, ["mlproject", "export", str(module), "-o", str(target)]).exit_code == 0
+    header = target.read_text().splitlines()[:2]
+    assert header[0] == "# Generated from src/pkg/service.py by `chapkit mlproject export` -- do not edit by hand."
+    assert "`chapkit mlproject export src/pkg/service.py -o MLproject`" in header[1]
+    assert str(tmp_path) not in target.read_text()
+
+    # The command in the header, run from the MLproject's folder, reproduces the same file.
+    monkeypatch.chdir(tmp_path)
+    check = CliRunner().invoke(app, ["mlproject", "export", "src/pkg/service.py", "-o", "MLproject", "--check"])
+    assert check.exit_code == 0, check.output
+
+
 def test_export_writes_to_output_and_updates_an_existing_mlproject_yaml(tmp_path: Path) -> None:
     module = _write_service(tmp_path)
     other = tmp_path / "out" / "MLproject"