[PortPather] add default_spacing (.at(..., spacing=...))

examples/tutorial/README.md

@@ -22,7 +22,7 @@ Contents
 - [library](library.py)
     * Continue from `devices.py` by declaring a mixed library with `BuildLibrary`
     * Import source-backed GDS cells and register python-generated recipes together
-    * Call `build()` to produce a normal library for downstream `Pather` usage and writing
+    * Call `build()` to produce a normal library and report for downstream `Pather` usage and writing
     * Explore alternate ways of specifying a pattern for `.plug()` and `.place()`
 - [pather](pather.py)
     * Use `Pather` to route individual wires and wire bundles

examples/tutorial/library.py

@@ -81,8 +81,9 @@ def main() -> None:
     # Build the declaration set into a normal library.
     #
 
-    built = builder.build()
+    built, report = builder.build()
     print('Built library contains:\n' + pformat(list(built.keys())))
+    print('Build dependency graph:\n' + pformat(report.dependency_graph))
 
     #
     # Continue designing against the built library.

examples/tutorial/port_pather.py

@@ -54,9 +54,10 @@ def main() -> None:
     (rpather.at(['GND', 'VCC'])
         .trace(True, xmax=-10_000, spacing=5_000)   # Move West to -10k, turn South
         .retool(M1_tool)                            # Retools both GND and VCC
-        .trace(True, emax=50_000, spacing=1_200)    # Turn East, moves 50um extension
+        .set_spacing(1_200)                         # Default bundle spacing for later bends
-        .trace(False, emin=1_000, spacing=1_200)    # U-turn back South
+        .trace(True, emax=50_000)                   # Turn East, moves 50um extension
-        .trace(False, emin=2_000, spacing=4_500)    # U-turn back West
+        .trace(False, emin=1_000)                   # U-turn back South
+        .trace(False, emin=2_000, spacing=4_500)    # U-turn back West, overriding the default spacing
         )
 
     # Retool VCC back to M2 and move both to x=-28k

masque/__init__.py

@@ -63,7 +63,6 @@ from .library import (
     ILibrary as ILibrary,
     LibraryView as LibraryView,
     Library as Library,
-    BuiltLibrary as BuiltLibrary,
     BuildLibrary as BuildLibrary,
     BuildReport as BuildReport,
     CellProvenance as CellProvenance,

masque/builder/pather.py

@@ -1173,30 +1173,50 @@ class Pather(PortList):
         self.pattern.flatten(self.library)
         return self
 
-    def at(self, portspec: str | Iterable[str]) -> 'PortPather':
+    def at(
-        return PortPather(portspec, self)
+            self,
+            portspec: str | Iterable[str],
+            *,
+            spacing: float | ArrayLike | None = None,
+            ) -> 'PortPather':
+        return PortPather(portspec, self, default_spacing=spacing)
 
 
 class PortPather:
     """ Port state manager for fluent pathing. """
-    def __init__(self, ports: str | Iterable[str], pather: Pather) -> None:
+    def __init__(
+            self,
+            ports: str | Iterable[str],
+            pather: Pather,
+            *,
+            default_spacing: float | ArrayLike | None = None,
+            ) -> None:
         self.ports = [ports] if isinstance(ports, str) else list(ports)
         self.pather = pather
+        self.default_spacing = default_spacing
 
     def retool(self, tool: Tool) -> Self:
         self.pather.retool(tool, self.ports)
         return self
 
+    def set_spacing(self, spacing: float | ArrayLike | None) -> Self:
+        self.default_spacing = spacing
+        return self
+
     @contextmanager
     def toolctx(self, tool: Tool) -> Iterator[Self]:
         with self.pather.toolctx(tool, keys=self.ports):
             yield self
 
     def trace(self, ccw: SupportsBool | None, length: float | None = None, **kw: Any) -> Self:
+        if 'spacing' not in kw and self.default_spacing is not None and len(self.ports) > 1 and ccw is not None:
+            kw['spacing'] = self.default_spacing
         self.pather.trace(self.ports, ccw, length, **kw)
         return self
 
     def trace_to(self, ccw: SupportsBool | None, **kw: Any) -> Self:
+        if 'spacing' not in kw and self.default_spacing is not None and len(self.ports) > 1 and ccw is not None:
+            kw['spacing'] = self.default_spacing
         self.pather.trace_to(self.ports, ccw, **kw)
         return self
 

masque/file/gdsii_lazy_core.py

@@ -17,7 +17,7 @@ Both the classic and Arrow-backed lazy GDS readers rely on these helpers.
 from __future__ import annotations
 
 from dataclasses import dataclass
-from typing import IO, Any, cast
+from typing import IO, Any, Literal, cast
 from collections import defaultdict
 from collections.abc import Callable, Iterator, Mapping, Sequence
 import copy
@@ -32,7 +32,7 @@ from numpy.typing import NDArray
 from . import gdsii
 from .utils import tmpfile
 from ..error import LibraryError
-from ..library import ILibrary, ILibraryView, LibraryView, dangling_mode_t
+from ..library import ILibrary, ILibraryView, LibraryView, _plan_source_names, _source_rename_map, dangling_mode_t
 from ..pattern import Pattern, map_targets
 from ..utils import apply_transforms
 from ..utils.ports2data import data_to_ports
@@ -303,26 +303,30 @@ class OverlayLibrary(ILibrary):
             source: Mapping[str, Pattern] | ILibraryView,
             *,
             rename_theirs: Callable[[ILibraryView, str], str] | None = None,
+            rename_when: Literal['conflict', 'always'] = 'conflict',
             ) -> dict[str, str]:
+        """
+        Add a source-backed library layer.
+
+        Args:
+            rename_theirs: Function used to choose visible names for imported
+                source cells.
+            rename_when: If `'conflict'`, only conflicting names are renamed.
+                If `'always'`, every imported source name is passed through
+                `rename_theirs`.
+        """
         view = _coerce_library_view(source)
         source_order = list(view.source_order())
         child_graph = view.child_graph(dangling='include')
 
-        source_to_visible: dict[str, str] = {}
+        source_to_visible = _plan_source_names(
-        visible_to_source: dict[str, str] = {}
+            self,
-        rename_map: dict[str, str] = {}
+            source_order,
-
+            self._entries,
-        for name in source_order:
+            rename_theirs = rename_theirs,
-            visible = name
+            rename_when = rename_when,
-            if visible in self._entries or visible in visible_to_source:
+            )
-                if rename_theirs is None:
+        visible_to_source = {visible: source_name for source_name, visible in source_to_visible.items()}
-                    raise LibraryError(f'Conflicting name while adding source: {name!r}')
-                visible = rename_theirs(self, name)
-                if visible in self._entries or visible in visible_to_source:
-                    raise LibraryError(f'Unresolved duplicate key encountered while adding source: {name!r} -> {visible!r}')
-                rename_map[name] = visible
-            source_to_visible[name] = visible
-            visible_to_source[visible] = name
 
         layer = _SourceLayer(
             library=view,
@@ -339,7 +343,7 @@ class OverlayLibrary(ILibrary):
             if visible_name not in self._order:
                 self._order.append(visible_name)
 
-        return rename_map
+        return _source_rename_map(source_to_visible)
 
     def rename(
             self,
@@ -549,20 +553,6 @@ class OverlayLibrary(ILibrary):
         return tuple(name for name in self._order if name in self._entries)
 
 
-class BuiltOverlayLibrary(OverlayLibrary):
-    """
-    Internal overlay output returned by `BuildLibrary.build(output='overlay')`.
-
-    The type is intentionally not part of the public API. It exists so build
-    outputs can carry a `build_report` while still behaving like an
-    `OverlayLibrary`.
-    """
-
-    def __init__(self, *, build_report: Any | None = None) -> None:
-        super().__init__()
-        self.build_report = build_report
-
-
 def _iter_library_infos(library: Mapping[str, Pattern] | ILibraryView) -> Iterator[dict[str, Any]]:
     info = getattr(library, 'library_info', None)
     if isinstance(info, dict):

masque/library.py

@@ -15,10 +15,11 @@ Classes include:
     library. Generated with `ILibraryView.abstract_view()`.
 """
 from typing import Self, TYPE_CHECKING, Any, cast, TypeAlias, Protocol, Literal
-from collections.abc import Iterator, Mapping, MutableMapping, Sequence, Callable
+from collections.abc import Container, Iterator, Mapping, MutableMapping, Sequence, Callable
 import logging
 import re
 import copy
+from functools import wraps
 from pprint import pformat
 from collections import defaultdict
 from abc import ABCMeta, abstractmethod
@@ -69,9 +70,6 @@ Tree: TypeAlias = MutableMapping[str, 'Pattern']
 dangling_mode_t: TypeAlias = Literal['error', 'ignore', 'include']
 """ How helpers should handle refs whose targets are not present in the library. """
 
-emitted_via_t: TypeAlias = Literal['declaration', 'helper_write', 'tree_merge', 'source_import']
-""" Build-provenance origin tags for emitted cells. """
-
 
 @dataclass(frozen=True)
 class CellProvenance:
@@ -83,29 +81,18 @@ class CellProvenance:
     chosen.
 
     Attributes:
-        final_name: Name exposed by the completed library.
         requested_name: First name requested for this cell during the build.
         kind: Whether the cell came from a declaration, helper emission, or an
             imported source library.
         owner_declared_name: Declared cell responsible for this output cell, if
             any. Imported source cells leave this as `None`.
-        emitted_via: High-level path by which the cell entered the output.
         build_chain: Declared-cell dependency chain that was active when the
             cell was emitted.
-        renamed_from: Original requested name when the final name differs.
-        source_name: Original on-source name for imported cells.
-        source_metadata: Optional source-library metadata copied through from
-            lazy GDS readers.
     """
-    final_name: str
     requested_name: str
     kind: Literal['declared', 'helper', 'source']
     owner_declared_name: str | None
-    emitted_via: emitted_via_t
     build_chain: tuple[str, ...]
-    renamed_from: str | None = None
-    source_name: str | None = None
-    source_metadata: dict[str, Any] | None = None
 
 
 @dataclass(frozen=True)
@@ -121,15 +108,11 @@ class BuildReport:
         requested_roots: Roots explicitly requested for the run. A full
             `build()` uses all declared cells.
         provenance: Mapping from final output name to provenance metadata.
-        owned_cells: Mapping from declared cell name to all final output cell
-            names it owns, including helper cells emitted while that declared
-            cell was building.
         dependency_graph: Declared-cell dependency graph discovered through
             library-mediated reads and explicit recipe hints.
     """
     requested_roots: tuple[str, ...]
     provenance: Mapping[str, CellProvenance]
-    owned_cells: Mapping[str, tuple[str, ...]]
     dependency_graph: Mapping[str, frozenset[str]]
 
 
@@ -166,6 +149,47 @@ def _rename_patterns(lib: 'ILibraryView', name: str) -> str:
     return lib.get_name(SINGLE_USE_PREFIX + stem)
 
 
+def _plan_source_names(
+        target: 'ILibraryView',
+        source_order: Sequence[str],
+        existing_names: Container[str],
+        *,
+        rename_theirs: Callable[['ILibraryView', str], str] | None = None,
+        rename_when: Literal['conflict', 'always'] = 'conflict',
+        ) -> dict[str, str]:
+    if rename_when not in ('conflict', 'always'):
+        raise ValueError(f'Unknown source rename mode: {rename_when!r}')
+    if rename_when == 'always' and rename_theirs is None:
+        raise TypeError('rename_theirs is required when rename_when="always"')
+
+    source_to_visible: dict[str, str] = {}
+    visible_names: set[str] = set()
+
+    for name in source_order:
+        visible = name
+        if rename_when == 'always':
+            assert rename_theirs is not None
+            visible = rename_theirs(target, name)
+        elif visible in existing_names or visible in visible_names:
+            if rename_theirs is None:
+                raise LibraryError(f'Conflicting name while adding source: {name!r}')
+            visible = rename_theirs(target, name)
+        if visible in existing_names or visible in visible_names:
+            raise LibraryError(f'Unresolved duplicate key encountered while adding source: {name!r} -> {visible!r}')
+        source_to_visible[name] = visible
+        visible_names.add(visible)
+
+    return source_to_visible
+
+
+def _source_rename_map(source_to_visible: Mapping[str, str]) -> dict[str, str]:
+    return {
+        source_name: visible_name
+        for source_name, visible_name in source_to_visible.items()
+        if source_name != visible_name
+        }
+
+
 class ILibraryView(Mapping[str, 'Pattern'], metaclass=ABCMeta):
     """
     Interface for a read-only library.
@@ -598,12 +622,12 @@ class ILibraryView(Mapping[str, 'Pattern'], metaclass=ABCMeta):
 
                 for ref_transform in ref_transforms:
                     self.dfs(
-                        pattern=self[target],
+                        pattern = self[target],
-                        visit_before=visit_before,
+                        visit_before = visit_before,
-                        visit_after=visit_after,
+                        visit_after = visit_after,
-                        hierarchy=hierarchy + (target,),
+                        hierarchy = hierarchy + (target,),
-                        transform=ref_transform,
+                        transform = ref_transform,
-                        memo=memo,
+                        memo = memo,
                         )
 
         if visit_after is not None:
@@ -1467,42 +1491,6 @@ class Library(ILibrary):
         return tree, pat
 
 
-class BuiltLibrary(Library):
-    """
-    Eager library returned by `BuildLibrary.build(output='library')`.
-
-    This is a normal materialized `Library` with one additional attribute,
-    `build_report`, which records how the library was assembled from
-    declarations, helper emissions, and imported source-backed cells.
-    """
-
-    def __init__(
-            self,
-            mapping: MutableMapping[str, 'Pattern'] | None = None,
-            *,
-            build_report: BuildReport | None = None,
-            ) -> None:
-        super().__init__(mapping=mapping)
-        self.build_report = build_report
-
-
-class _CellFactory:
-    """
-    Adapter that turns a plain pattern factory into a deferred recipe factory.
-
-    Calling the wrapper captures arguments and returns a `_BuildRecipe`
-    instead of executing the function immediately.
-    """
-
-    def __init__(self, func: Callable[..., 'Pattern']) -> None:
-        self.func = func
-        self.__name__ = getattr(func, '__name__', type(self).__name__)
-        self.__doc__ = getattr(func, '__doc__')
-
-    def __call__(self, *args: Any, **kwargs: Any) -> '_BuildRecipe':
-        return _BuildRecipe(func=self.func, args=args, kwargs=kwargs)
-
-
 @dataclass
 class _BuildRecipe:
     """ Captured deferred call to a pattern factory. """
@@ -1516,41 +1504,17 @@ class _BuildRecipe:
         return self
 
 
-@dataclass(frozen=True)
+def cell(func: Callable[..., 'Pattern']) -> Callable[..., _BuildRecipe]:
-class _PatternDeclaration:
-    """ Declared cell backed by an already-built `Pattern`. """
-    pattern: 'Pattern'
-
-
-@dataclass(frozen=True)
-class _RecipeDeclaration:
-    """ Declared cell backed by a deferred recipe. """
-    recipe: _BuildRecipe
-
-
-@dataclass(frozen=True)
-class _SourceDeclaration:
-    """
-    Imported source-backed names registered with a `BuildLibrary`.
-
-    The declaration stores visible-name remapping plus pre-scanned graph
-    metadata. Underlying source cells stay lazy until a build session
-    materializes or copies them through.
-    """
-    library: ILibraryView
-    source_to_visible: Mapping[str, str]
-    visible_to_source: Mapping[str, str]
-    child_graph: Mapping[str, set[str]]
-    order: tuple[str, ...]
-
-
-def cell(func: Callable[..., 'Pattern']) -> _CellFactory:
     """
     Wrap a plain pattern factory so calls return deferred build recipes.
 
     Use as either `cell(fn)(...)` or `@cell`.
     """
-    return _CellFactory(func)
+    @wraps(func)
+    def wrapper(*args: Any, **kwargs: Any) -> _BuildRecipe:
+        return _BuildRecipe(func=func, args=args, kwargs=kwargs)
+
+    return wrapper
 
 
 class BuildCellsView:
@@ -1596,19 +1560,16 @@ class BuildLibrary(ILibrary):
     The builder itself is not a normal readable library during authoring.
     Instead, `validate()` and `build()` create a temporary build-session library
     that recipes can read from and write helper cells into while dependencies
-    are resolved. `build()` then freezes the builder on success and returns a
+    are resolved. `build()` then freezes the builder on success and returns the
-    normal library-like object carrying a `build_report`.
+    built library plus a `BuildReport`.
     """
 
-    def __init__(self, *, check_on_register: bool = False) -> None:
+    def __init__(self) -> None:
-        self.check_on_register = check_on_register
         self.cells = BuildCellsView(self)
-        self.last_build_report: BuildReport | None = None
         self._frozen = False
-        self._declarations: dict[str, _PatternDeclaration | _RecipeDeclaration] = {}
+        self._declarations: dict[str, Pattern | _BuildRecipe] = {}
-        self._sources: list[_SourceDeclaration] = []
+        self._sources: list[tuple[ILibraryView, dict[str, str]]] = []
-        self._names: set[str] = set()
+        self._names: dict[str, None] = {}
-        self._order: list[str] = []
 
     def _active_session(self) -> '_BuildSessionLibrary | None':
         sessions = _ACTIVE_BUILD_SESSIONS.get()
@@ -1622,7 +1583,7 @@ class BuildLibrary(ILibrary):
             raise BuildError(
                 f'BuildLibrary.{operation}() is only available while validate() or build() is running. '
                 'Use the built output library for reads.'
-            )
+                )
         return session
 
     def _assert_editable(self) -> None:
@@ -1633,7 +1594,7 @@ class BuildLibrary(ILibrary):
         session = self._active_session()
         if session is not None:
             return iter(session)
-        return iter(self._order)
+        return iter(self._names)
 
     def __len__(self) -> int:
         session = self._active_session()
@@ -1653,7 +1614,7 @@ class BuildLibrary(ILibrary):
     def __setitem__(
             self,
             key: str,
-            value: 'Pattern | _BuildRecipe | Callable[[], Pattern]',
+            value: 'Pattern | _BuildRecipe',
             ) -> None:
         session = self._active_session()
         if session is not None:
@@ -1664,26 +1625,15 @@ class BuildLibrary(ILibrary):
         if key in self._names:
             raise LibraryError(f'"{key}" already exists in the builder. Overwriting is not allowed!')
 
-        declaration: _PatternDeclaration | _RecipeDeclaration
         if isinstance(value, _BuildRecipe):
-            declaration = _RecipeDeclaration(value)
+            declaration = value
         else:
             if callable(value):
                 raise TypeError('BuildLibrary recipes must be wrapped with cell(fn)(...) or @cell.')
-            declaration = _PatternDeclaration(value)
+            declaration = value
 
         self._declarations[key] = declaration
-        self._names.add(key)
+        self._names[key] = None
-        self._order.append(key)
-
-        if self.check_on_register:
-            try:
-                self.validate(names=(key,))
-            except Exception:
-                del self._declarations[key]
-                self._names.remove(key)
-                self._order.remove(key)
-                raise
 
     def __delitem__(self, key: str) -> None:
         session = self._active_session()
@@ -1695,8 +1645,7 @@ class BuildLibrary(ILibrary):
         if key not in self._declarations:
             raise KeyError(key)
         del self._declarations[key]
-        self._names.remove(key)
+        del self._names[key]
-        self._order.remove(key)
 
     def _merge(self, key_self: str, other: Mapping[str, 'Pattern'], key_other: str) -> None:
         session = self._active_session()
@@ -1711,10 +1660,77 @@ class BuildLibrary(ILibrary):
             rename_theirs: Callable[['ILibraryView', str], str] = _rename_patterns,
             mutate_other: bool = False,
             ) -> dict[str, str]:
+        from .pattern import map_targets        # noqa: PLC0415
+
         session = self._active_session()
         if session is not None:
             return session.add(other, rename_theirs=rename_theirs, mutate_other=mutate_other)
-        return super().add(other, rename_theirs=rename_theirs, mutate_other=mutate_other)
+
+        self._assert_editable()
+
+        source_backed = isinstance(other, ILibraryView) and not isinstance(other, Library | LibraryView)
+        if source_backed:
+            if mutate_other:
+                raise BuildError('BuildLibrary.add(..., mutate_other=True) is not supported for source-backed inputs.')
+            return self.add_source(
+                other,
+                rename_theirs = rename_theirs,
+                rename_when = 'conflict',
+                )
+
+        source_order = tuple(other.keys())
+        source_to_visible = _plan_source_names(
+            self,
+            source_order,
+            self._names,
+            rename_theirs = rename_theirs,
+            rename_when = 'conflict',
+            )
+        rename_map = _source_rename_map(source_to_visible)
+
+        if mutate_other:
+            temp = other
+        else:
+            temp = Library(copy.deepcopy(dict(other)))
+
+        for source_name in source_order:
+            visible_name = source_to_visible[source_name]
+            pattern = temp[source_name]
+            if rename_map:
+                pattern.refs = map_targets(
+                    pattern.refs,
+                    lambda target: cast('dict[str | None, str | None]', rename_map).get(target, target),
+                    )
+            self[visible_name] = pattern
+
+        return rename_map
+
+    def __lshift__(self, other: TreeView) -> str:
+        session = self._active_session()
+        if session is not None:
+            return session << other
+
+        self._assert_editable()
+        if len(other) == 1:
+            name = next(iter(other))
+        elif isinstance(other, ILibraryView) and not isinstance(other, Library | LibraryView):
+            source_order = other.source_order()
+            child_graph = other.child_graph(dangling='include')
+            referenced = set().union(*child_graph.values()) if child_graph else set()
+            tops = [candidate for candidate in source_order if candidate not in referenced]
+            if len(tops) != 1:
+                raise LibraryError(f'Asked for the single topcell, but found the following: {pformat(tops)}')
+            name = tops[0]
+        else:
+            return super().__lshift__(other)
+
+        rename_map = self.add(other)
+        return rename_map.get(name, name)
+
+    def __le__(self, other: Mapping[str, 'Pattern']) -> Abstract:
+        if self._active_session() is not None:
+            return super().__le__(other)
+        raise BuildError('BuildLibrary.__le__() is only available while validate() or build() is running.')
 
     def rename(
             self,
@@ -1723,12 +1739,11 @@ class BuildLibrary(ILibrary):
             move_references: bool = False,
             ) -> Self:
         """
-        Rename an imported source-backed visible name during authoring.
+        Rename a helper cell during an active build session.
 
-        Only imported source-backed cells may be renamed on the builder itself.
+        During authoring, declared cells must be registered under their
-        Declared/generated cells must be registered under their intended final
+        intended final names and imported source cells must be renamed through
-        names. `move_references=True` is intentionally unsupported here because
+        `add_source(...)`.
-        deferred recipes and declaration internals cannot be rewritten safely.
         """
         session = self._active_session()
         if session is not None:
@@ -1742,49 +1757,14 @@ class BuildLibrary(ILibrary):
             raise BuildError(
                 f'Cannot rename declared build cell "{old_name}" during authoring. '
                 'Register it under the intended final name instead.'
-            )
+                )
         if old_name not in self._names:
             raise LibraryError(f'"{old_name}" does not exist in the builder.')
-        if new_name in self._names:
+        raise BuildError(
-            raise LibraryError(f'"{new_name}" already exists in the builder.')
+            f'Cannot rename imported source cell "{old_name}" during authoring. '
-        if move_references:
+            'Choose visible source names with add_source(..., rename_theirs=..., rename_when=...).'
-            raise BuildError(
-                'BuildLibrary.rename(..., move_references=True) is not supported for imported source cells. '
-                'Builder-level renames only change the visible imported name.'
             )
 
-        source_index = next(
-            (idx for idx, spec in enumerate(self._sources) if old_name in spec.visible_to_source),
-            None,
-        )
-        if source_index is None:
-            raise BuildError(
-                f'Cannot rename "{old_name}" during authoring because only imported source-backed '
-                'cells may be renamed on a BuildLibrary.'
-            )
-
-        spec = self._sources[source_index]
-        source_name = spec.visible_to_source[old_name]
-        source_to_visible = dict(spec.source_to_visible)
-        visible_to_source = dict(spec.visible_to_source)
-        order = list(spec.order)
-
-        source_to_visible[source_name] = new_name
-        del visible_to_source[old_name]
-        visible_to_source[new_name] = source_name
-        order[order.index(old_name)] = new_name
-
-        self._sources[source_index] = replace(
-            spec,
-            source_to_visible=source_to_visible,
-            visible_to_source=visible_to_source,
-            order=tuple(order),
-        )
-        self._names.remove(old_name)
-        self._names.add(new_name)
-        self._order[self._order.index(old_name)] = new_name
-        return self
-
     def abstract(self, name: str) -> Abstract:
         return self._require_active_session('abstract').abstract(name)
 
@@ -1800,54 +1780,48 @@ class BuildLibrary(ILibrary):
             source: Mapping[str, 'Pattern'] | ILibraryView,
             *,
             rename_theirs: Callable[[ILibraryView, str], str] | None = None,
+            rename_when: Literal['conflict', 'always'] = 'conflict',
             ) -> dict[str, str]:
         """
         Register an imported source-backed library with the builder.
 
-        The source is not materialized immediately. Instead, its names and
+        The source is not materialized immediately. Its names are scanned once
-        child graph are scanned once and stored as an import declaration. The
+        to reserve visible builder names, then the source is read again when a
-        source may be renamed on entry to avoid collisions with existing
+        build session starts. The source's cell membership must not be
+        structurally mutated between `add_source()` and `build()`/`validate()`.
+        Source cells may be renamed on entry to avoid collisions with existing
         declarations or other imported sources.
 
+        Args:
+            rename_theirs: Function used to choose visible names for imported
+                source cells.
+            rename_when: If `'conflict'`, only conflicting names are renamed.
+                If `'always'`, every imported source name is passed through
+                `rename_theirs`.
+
         Returns:
             Mapping of `{source_name: visible_name}` for imported names that
             were renamed while being added.
         """
+        if self._active_session() is not None:
+            raise BuildError('BuildLibrary.add_source() is only available while authoring, not during validate() or build().')
         self._assert_editable()
 
         view = source if isinstance(source, ILibraryView) else LibraryView(source)
         source_order = tuple(view.source_order())
-        child_graph = view.child_graph(dangling='include')
+        source_to_visible = _plan_source_names(
+            self,
+            source_order,
+            self._names,
+            rename_theirs = rename_theirs,
+            rename_when = rename_when,
+            )
 
-        source_to_visible: dict[str, str] = {}
+        self._sources.append((view, dict(source_to_visible)))
-        visible_to_source: dict[str, str] = {}
+        for source_name in source_order:
-        rename_map: dict[str, str] = {}
+            visible = source_to_visible[source_name]
-        new_names: list[str] = []
+            self._names[visible] = None
-
+        return _source_rename_map(source_to_visible)
-        for name in source_order:
-            visible = name
-            if visible in self._names or visible in visible_to_source:
-                if rename_theirs is None:
-                    raise LibraryError(f'Conflicting name while adding source: {name!r}')
-                visible = rename_theirs(self, name)
-                if visible in self._names or visible in visible_to_source:
-                    raise LibraryError(f'Unresolved duplicate key encountered while adding source: {name!r} -> {visible!r}')
-                rename_map[name] = visible
-            source_to_visible[name] = visible
-            visible_to_source[visible] = name
-            new_names.append(visible)
-
-        self._sources.append(_SourceDeclaration(
-            library=view,
-            source_to_visible=dict(source_to_visible),
-            visible_to_source=dict(visible_to_source),
-            child_graph={name: set(children) for name, children in child_graph.items()},
-            order=tuple(source_to_visible[name] for name in source_order),
-        ))
-        for visible in new_names:
-            self._names.add(visible)
-            self._order.append(visible)
-        return rename_map
 
     def validate(
             self,
@@ -1862,8 +1836,7 @@ class BuildLibrary(ILibrary):
         execution path used by `build()`. Any generated library is discarded
         after validation completes.
         """
-        report, _output = self._run_build(names=names, output='overlay', allow_dangling=allow_dangling, persist_output=False)
+        _session, report = self._run_build(names=names, allow_dangling=allow_dangling)
-        self.last_build_report = report
         return report
 
     def build(
@@ -1871,9 +1844,9 @@ class BuildLibrary(ILibrary):
             *,
             output: Literal['overlay', 'library'] = 'overlay',
             allow_dangling: bool = False,
-            ) -> 'BuiltLibrary | ILibrary':
+            ) -> tuple[ILibrary, BuildReport]:
         """
-        Materialize declarations and return a usable output library.
+        Materialize declarations and return a usable output library plus report.
 
         Args:
             output: `'overlay'` preserves imported source-backed cells where
@@ -1882,20 +1855,23 @@ class BuildLibrary(ILibrary):
             allow_dangling: If `False`, fail the build when the completed
                 library still contains dangling references.
         """
+        if output not in ('overlay', 'library'):
+            raise ValueError(f'Unknown build output mode: {output!r}')
         self._assert_editable()
-        report, built_output = self._run_build(names=None, output=output, allow_dangling=allow_dangling, persist_output=True)
+        session, report = self._run_build(names=None, allow_dangling=allow_dangling)
+        if output == 'library':
+            built_output = session.to_library()
+        else:
+            built_output = session.to_overlay()
         self._frozen = True
-        self.last_build_report = report
+        return built_output, report
-        return built_output
 
     def _run_build(
             self,
             *,
             names: Sequence[str] | None,
-            output: Literal['overlay', 'library'],
             allow_dangling: bool,
-            persist_output: bool,
+            ) -> tuple['_BuildSessionLibrary', BuildReport]:
-            ) -> tuple[BuildReport, BuiltLibrary | ILibrary | None]:
         roots = tuple(dict.fromkeys(names if names is not None else self._declarations.keys()))
         unknown = [name for name in roots if name not in self._names]
         if unknown:
@@ -1909,19 +1885,11 @@ class BuildLibrary(ILibrary):
             session.materialize_many(roots)
             if not allow_dangling:
                 session.child_graph(dangling='error')
-            if output == 'library':
-                built_output = session.to_library() if persist_output else None
-            elif persist_output:
-                built_output = session.to_overlay()
-            else:
-                built_output = None
         finally:
             _ACTIVE_BUILD_SESSIONS.reset(token)
 
         report = session.build_report(roots)
-        if built_output is not None:
+        return session, report
-            built_output.build_report = report
-        return report, built_output
 
 
 class _BuildSessionLibrary(ILibrary):
@@ -1935,71 +1903,62 @@ class _BuildSessionLibrary(ILibrary):
     """
 
     def __init__(self, builder: BuildLibrary) -> None:
-        from .file.gdsii_lazy_core import BuiltOverlayLibrary, _SourceEntry, _SourceLayer      # noqa: PLC0415
+        from .file.gdsii_lazy_core import OverlayLibrary      # noqa: PLC0415
 
         self._builder = builder
-        self._overlay = BuiltOverlayLibrary()
+        self._overlay = OverlayLibrary()
-        self._source_entry_type = _SourceEntry
+        self._built: set[str] = set()
-        self._source_layer_type = _SourceLayer
-        self._states: dict[str, Literal['unbuilt', 'building', 'built']] = {
-            name: 'unbuilt' for name in builder._declarations
-        }
         self._declared_stack: list[str] = []
-        self._emission_stack: list[str] = []
+        self._names = dict(builder._names)
-        self._emission_via_stack: list[emitted_via_t] = []
-        self._names = set(builder._names)
-        self._order = list(builder._order)
         self._provenance: dict[str, CellProvenance] = {}
-        self._owned_cells: defaultdict[str, list[str]] = defaultdict(list)
         self._dependency_graph: defaultdict[str, set[str]] = defaultdict(set)
         self._install_sources()
 
     def _install_sources(self) -> None:
-        for spec in self._builder._sources:
+        for source_library, source_to_visible in self._builder._sources:
-            layer = self._source_layer_type(
+            source_order = source_library.source_order()
-                library=spec.library,
+            expected_names = set(source_to_visible)
-                source_to_visible=dict(spec.source_to_visible),
+            actual_names = set(source_order)
-                visible_to_source=dict(spec.visible_to_source),
+            if actual_names != expected_names:
-                child_graph={name: set(children) for name, children in spec.child_graph.items()},
+                added_names = sorted(actual_names - expected_names)
-                order=list(spec.order),
+                removed_names = sorted(expected_names - actual_names)
-            )
+                detail = []
-            layer_index = len(self._overlay._layers)
+                if added_names:
-            self._overlay._layers.append(layer)
+                    detail.append(f'added={added_names}')
-            source_info = getattr(spec.library, 'library_info', None)
+                if removed_names:
-            source_meta = dict(source_info) if isinstance(source_info, dict) else None
+                    detail.append(f'removed={removed_names}')
+                raise BuildError(
+                    'Imported source library changed after add_source() was called '
+                    f'({", ".join(detail)}). '
+                    'Do not structurally mutate source libraries between add_source() and build()/validate().'
+                    )
 
-            for source_name, visible_name in spec.source_to_visible.items():
+            def rename_source(_lib: ILibraryView, name: str, *, mapping: Mapping[str, str] = source_to_visible) -> str:
-                self._overlay._entries[visible_name] = self._source_entry_type(
+                return mapping[name]
-                    layer_index=layer_index,
+
-                    source_name=source_name,
+            self._overlay.add_source(
-                )
+                source_library,
-                if visible_name not in self._overlay._order:
+                rename_theirs = rename_source,
-                    self._overlay._order.append(visible_name)
+                rename_when = 'always',
+            )
+
+            for source_name in source_order:
+                visible_name = source_to_visible[source_name]
                 self._provenance[visible_name] = CellProvenance(
-                    final_name=visible_name,
+                    requested_name = source_name,
-                    requested_name=source_name,
+                    kind = 'source',
-                    kind='source',
+                    owner_declared_name = None,
-                    owner_declared_name=None,
+                    build_chain = (),
-                    emitted_via='source_import',
+                    )
-                    build_chain=(),
-                    renamed_from=source_name if visible_name != source_name else None,
-                    source_name=source_name,
-                    source_metadata=source_meta,
-                )
 
     def __iter__(self) -> Iterator[str]:
-        return (name for name in self._order if name in self._names)
+        return iter(self._names)
 
     def __len__(self) -> int:
         return len(self._names)
 
     def __contains__(self, key: object) -> bool:
-        return key in self._names or key in self._overlay
+        return key in self._names
-
-    def _touch_name(self, key: str) -> None:
-        if key not in self._names:
-            self._names.add(key)
-            self._order.append(key)
 
     def _current_declared(self) -> str | None:
         if not self._declared_stack:
@@ -2020,14 +1979,6 @@ class _BuildSessionLibrary(ILibrary):
         if provenance is not None and provenance.kind == 'source':
             raise BuildError(f'Cannot {operation} imported source cell "{key}" during an active build session.')
 
-    def _remove_owned_cell(self, owner: str | None, name: str) -> None:
-        if owner is None or owner not in self._owned_cells:
-            return
-        cells = self._owned_cells[owner]
-        self._owned_cells[owner] = [cell for cell in cells if cell != name]
-        if not self._owned_cells[owner]:
-            del self._owned_cells[owner]
-
     def rename(
             self,
             old_name: str,
@@ -2046,26 +1997,13 @@ class _BuildSessionLibrary(ILibrary):
             raise LibraryError(f'"{new_name}" already exists in the library.')
 
         self._overlay.rename(old_name, new_name, move_references=move_references)
-        self._names.discard(old_name)
+        self._names = {
-        self._names.add(new_name)
+            new_name if name == old_name else name: None
-        if old_name in self._order:
+            for name in self._names
-            idx = self._order.index(old_name)
+            }
-            self._order[idx] = new_name
 
         provenance = self._provenance.pop(old_name)
-        requested_name = provenance.requested_name
+        self._provenance[new_name] = provenance
-        self._provenance[new_name] = replace(
-            provenance,
-            final_name=new_name,
-            renamed_from=requested_name if new_name != requested_name else None,
-        )
-
-        owner = provenance.owner_declared_name
-        if owner is not None and owner in self._owned_cells:
-            self._owned_cells[owner] = [
-                new_name if cell_name == old_name else cell_name
-                for cell_name in self._owned_cells[owner]
-            ]
         return self
 
     def __getitem__(self, key: str) -> 'Pattern':
@@ -2087,31 +2025,20 @@ class _BuildSessionLibrary(ILibrary):
 
         pattern = value() if callable(value) else value
         self._overlay[key] = pattern
-        self._touch_name(key)
+        self._names.setdefault(key, None)
 
         kind: Literal['declared', 'helper']
-        via = self._emission_via_stack[-1] if self._emission_via_stack else 'helper_write'
         if current is not None and key == current:
             kind = 'declared'
-            via = 'declaration'
         else:
             kind = 'helper'
-            if not self._emission_via_stack:
-                via = 'helper_write'
 
-        self._emission_stack.append(key)
+        self._provenance[key] = CellProvenance(
-        try:
+            requested_name = key,
-            self._record_provenance(
+            kind = kind,
-                final_name=key,
+            owner_declared_name = current if kind == 'helper' else key,
-                requested_name=key,
+            build_chain = tuple(self._declared_stack),
-                kind=kind,
-                owner_declared_name=current if kind == 'helper' else key,
-                emitted_via=via,
-                build_chain=tuple(self._declared_stack),
-                renamed_from=None,
             )
-        finally:
-            self._emission_stack.pop()
 
     def __delitem__(self, key: str) -> None:
         if key not in self._overlay:
@@ -2120,15 +2047,10 @@ class _BuildSessionLibrary(ILibrary):
             raise KeyError(key)
 
         self._guard_mutable_output_name(key, operation='delete')
-        provenance = self._provenance.get(key)
         if key in self._overlay:
             del self._overlay[key]
-        self._names.discard(key)
+        self._names.pop(key, None)
-        if key in self._order:
-            self._order.remove(key)
         self._provenance.pop(key, None)
-        if provenance is not None:
-            self._remove_owned_cell(provenance.owner_declared_name, key)
 
     def _merge(self, key_self: str, other: Mapping[str, 'Pattern'], key_other: str) -> None:
         self[key_self] = copy.deepcopy(other[key_other])
@@ -2139,52 +2061,21 @@ class _BuildSessionLibrary(ILibrary):
             rename_theirs: Callable[['ILibraryView', str], str] = _rename_patterns,
             mutate_other: bool = False,
             ) -> dict[str, str]:
-        self._emission_via_stack.append('tree_merge')
+        rename_map = super().add(other, rename_theirs=rename_theirs, mutate_other=mutate_other)
-        try:
-            rename_map = super().add(other, rename_theirs=rename_theirs, mutate_other=mutate_other)
-        finally:
-            self._emission_via_stack.pop()
 
         current = self._current_declared()
         for old_name, new_name in rename_map.items():
             if new_name in self._provenance:
                 self._provenance[new_name] = replace(
                     self._provenance[new_name],
-                    requested_name=old_name,
+                    requested_name = old_name,
-                    renamed_from=old_name,
+                    owner_declared_name = current if current is not None else self._provenance[new_name].owner_declared_name,
-                    owner_declared_name=current if current is not None else self._provenance[new_name].owner_declared_name,
+                    )
-                )
         return rename_map
 
-    def _record_provenance(
-            self,
-            *,
-            final_name: str,
-            requested_name: str,
-            kind: Literal['declared', 'helper'],
-            owner_declared_name: str | None,
-            emitted_via: emitted_via_t,
-            build_chain: tuple[str, ...],
-            renamed_from: str | None,
-            ) -> None:
-        self._provenance[final_name] = CellProvenance(
-            final_name=final_name,
-            requested_name=requested_name,
-            kind=kind,
-            owner_declared_name=owner_declared_name,
-            emitted_via=emitted_via,
-            build_chain=build_chain,
-            renamed_from=renamed_from,
-        )
-        if owner_declared_name is not None and final_name not in self._owned_cells[owner_declared_name]:
-            self._owned_cells[owner_declared_name].append(final_name)
-
     def _wrap_error(self, name: str, exc: Exception) -> BuildError:
-        helper = self._emission_stack[-1] if self._emission_stack else None
         chain = tuple(self._declared_stack)
         msg = [f'Failed while building declared cell "{name}"']
-        if helper is not None and helper != name:
-            msg.append(f'while materializing helper/output "{helper}"')
         if chain:
             msg.append(f'Dependency chain: {" -> ".join(chain)}')
         msg.append(f'Cause: {exc}')
@@ -2202,36 +2093,33 @@ class _BuildSessionLibrary(ILibrary):
     def _ensure_declared(self, name: str) -> None:
         from .pattern import Pattern        # noqa: PLC0415
 
-        state = self._states[name]
+        if name in self._built:
-        if state == 'built':
             return
-        if state == 'building':
+        if name in self._declared_stack:
             chain = ' -> '.join(self._declared_stack + [name])
             raise BuildError(f'Cycle detected while building declared cells: {chain}')
 
         declaration = self._builder._declarations[name]
-        self._states[name] = 'building'
         self._declared_stack.append(name)
         try:
-            if isinstance(declaration, _PatternDeclaration):
+            if isinstance(declaration, _BuildRecipe):
-                pattern = declaration.pattern.deepcopy()
+                for dep in declaration.explicit_dependencies:
-            else:
-                for dep in declaration.recipe.explicit_dependencies:
                     self._ensure_named(dep)
-                pattern = declaration.recipe.func(*declaration.recipe.args, **declaration.recipe.kwargs)
+                pattern = declaration.func(*declaration.args, **declaration.kwargs)
                 if not isinstance(pattern, Pattern):
                     raise BuildError(f'Recipe for "{name}" returned {type(pattern).__name__}, expected Pattern')
+            else:
+                pattern = declaration.deepcopy()
 
             if name in self._overlay:
                 if self._overlay[name] is not pattern:
                     raise BuildError(
                         f'Recipe for "{name}" wrote a different pattern into the session under its own name.'
-                    )
+                        )
             else:
                 self[name] = pattern
-            self._states[name] = 'built'
+            self._built.add(name)
         except Exception as exc:
-            self._states[name] = 'unbuilt'
             raise self._wrap_error(name, exc) from exc
         finally:
             self._declared_stack.pop()
@@ -2260,24 +2148,19 @@ class _BuildSessionLibrary(ILibrary):
             name: frozenset(self._dependency_graph.get(name, set()))
             for name in self._builder._declarations
             if name in self._dependency_graph or name in requested_roots
-        }
+            }
-        owned_cells = {
-            name: tuple(cells)
-            for name, cells in self._owned_cells.items()
-        }
         return BuildReport(
-            requested_roots=tuple(dict.fromkeys(requested_roots)),
+            requested_roots = tuple(dict.fromkeys(requested_roots)),
-            provenance=dict(self._provenance),
+            provenance = dict(self._provenance),
-            owned_cells=owned_cells,
+            dependency_graph = dependency_graph,
-            dependency_graph=dependency_graph,
+            )
-        )
 
     def to_overlay(self) -> ILibrary:
         return self._overlay
 
-    def to_library(self) -> BuiltLibrary:
+    def to_library(self) -> Library:
         mapping = {name: self._overlay[name] for name in self._overlay.source_order()}
-        return BuiltLibrary(mapping)
+        return Library(mapping)
 
 
 class LazyLibrary(ILibrary):

masque/test/test_build_library.py

@@ -1,12 +1,47 @@
+from collections.abc import Iterator
+
 import pytest
 
 from ..builder import Pather
 from ..error import BuildError
-from ..library import BuildLibrary, BuiltLibrary, Library, cell
+from ..library import BuildLibrary, BuildReport, ILibraryView, Library, cell, dangling_mode_t
 from ..pattern import Pattern
 from ..ports import Port
 
 
+def _owned_by(report: BuildReport, owner: str) -> set[str]:
+    return {
+        name for name, prov in report.provenance.items()
+        if prov.owner_declared_name == owner
+    }
+
+
+class _MetadataSource(ILibraryView):
+    def __init__(self, mapping: dict[str, Pattern], child_graph: dict[str, set[str]]) -> None:
+        self.mapping = mapping
+        self._child_graph = child_graph
+        self.loads = 0
+
+    def __getitem__(self, key: str) -> Pattern:
+        self.loads += 1
+        return self.mapping[key]
+
+    def __iter__(self) -> Iterator[str]:
+        return iter(self.mapping)
+
+    def __len__(self) -> int:
+        return len(self.mapping)
+
+    def __contains__(self, key: object) -> bool:
+        return key in self.mapping
+
+    def source_order(self) -> tuple[str, ...]:
+        return tuple(self.mapping)
+
+    def child_graph(self, dangling: dangling_mode_t = 'error') -> dict[str, set[str]]:     # noqa: ARG002
+        return self._child_graph
+
+
 def test_build_library_traces_declared_dependencies_out_of_order() -> None:
     builder = BuildLibrary()
 
@@ -19,12 +54,12 @@ def test_build_library_traces_declared_dependencies_out_of_order() -> None:
     builder.cells.parent = cell(make_parent)(builder)
     builder["child"] = Pattern(ports={"p": Port((0, 0), 0)})
 
-    built = builder.build()
+    built, report = builder.build()
 
     assert "parent" in built
     assert "child" in built
-    assert built.build_report.dependency_graph["parent"] == frozenset({"child"})
+    assert report.dependency_graph["parent"] == frozenset({"child"})
-    assert built.build_report.provenance["parent"].kind == "declared"
+    assert report.provenance["parent"].kind == "declared"
 
 
 def test_build_library_tracks_helper_provenance_and_tree_merge_renames() -> None:
@@ -40,18 +75,46 @@ def test_build_library_tracks_helper_provenance_and_tree_merge_renames() -> None
         return top
 
     builder.cells.top = cell(make_top)(builder)
-    built = builder.build()
+    _built, report = builder.build()
-    report = built.build_report
 
     helpers = [
-        prov for prov in report.provenance.values()
+        (name, prov) for name, prov in report.provenance.items()
         if prov.owner_declared_name == "top" and prov.kind == "helper"
     ]
 
-    assert "top" in report.owned_cells["top"]
+    assert "top" in _owned_by(report, "top")
     assert len(helpers) == 2
-    assert all(prov.emitted_via == "tree_merge" for prov in helpers)
+    assert any(name != prov.requested_name for name, prov in helpers)
-    assert any(prov.renamed_from == "_helper" for prov in helpers)
+
+
+def test_build_library_authoring_tree_merge_renames_repeated_single_use_names() -> None:
+    builder = BuildLibrary()
+    tree = Library({"_helper": Pattern()})
+
+    name_a = builder << tree
+    name_b = builder << tree
+    built, report = builder.build()
+
+    assert name_a == "_helper"
+    assert name_b != "_helper"
+    assert name_a in built
+    assert name_b in built
+    assert report.provenance[name_b].requested_name == name_b
+
+
+def test_build_library_authoring_tree_merge_remaps_internal_refs() -> None:
+    builder = BuildLibrary()
+    builder["_helper"] = Pattern()
+    helper = Pattern()
+    top = Pattern()
+    top.ref("_helper")
+
+    top_name = builder << Library({"_helper": helper, "top": top})
+    built, _report = builder.build()
+
+    assert top_name == "top"
+    assert "_helper" not in built[top_name].refs
+    assert any(name != "_helper" for name in built[top_name].refs)
 
 
 def test_build_library_requires_build_session_for_reads_and_freezes_after_build() -> None:
@@ -64,10 +127,10 @@ def test_build_library_requires_build_session_for_reads_and_freezes_after_build(
     with pytest.raises(BuildError, match="write-only"):
         _ = builder.cells.leaf
 
-    built = builder.build(output="library")
+    built, report = builder.build(output="library")
 
-    assert isinstance(built, BuiltLibrary)
+    assert isinstance(built, Library)
-    assert built.build_report.requested_roots == ("leaf",)
+    assert report.requested_roots == ("leaf",)
 
     with pytest.raises(BuildError, match="frozen"):
         builder["later"] = Pattern()
@@ -95,21 +158,6 @@ def test_build_library_validate_is_retryable_after_failure() -> None:
     assert report.dependency_graph["parent"] == frozenset({"child"})
 
 
-def test_build_library_check_on_register_rolls_back_failed_declarations() -> None:
-    builder = BuildLibrary(check_on_register=True)
-
-    def make_parent(lib: BuildLibrary) -> Pattern:
-        pat = Pattern()
-        pat.ref("child")
-        lib.abstract("child")
-        return pat
-
-    with pytest.raises(BuildError, match='Failed while building declared cell "parent"'):
-        builder.cells.parent = cell(make_parent)(builder)
-
-    assert "parent" not in builder
-
-
 def test_build_library_depends_on_supports_hidden_dependencies_for_partial_validation() -> None:
     builder = BuildLibrary()
     builder["child"] = Pattern()
@@ -134,6 +182,14 @@ def test_build_library_validate_rejects_removed_output_argument() -> None:
         builder.validate(output="library")   # type: ignore[call-arg]
 
 
+def test_build_library_rejects_unknown_build_output_mode() -> None:
+    builder = BuildLibrary()
+    builder["leaf"] = Pattern()
+
+    with pytest.raises(ValueError, match="Unknown build output mode"):
+        builder.build(output="bad")   # type: ignore[arg-type]
+
+
 def test_build_library_allows_helper_writes_via_pather() -> None:
     builder = BuildLibrary()
     builder["leaf"] = Pattern(ports={"a": Port((0, 0), 0)})
@@ -147,50 +203,169 @@ def test_build_library_allows_helper_writes_via_pather() -> None:
         return top
 
     builder.cells.top = cell(make_top)(builder)
-    built = builder.build()
+    _built, report = builder.build()
 
-    helper_prov = built.build_report.provenance["_route"]
+    helper_prov = report.provenance["_route"]
     assert helper_prov.kind == "helper"
     assert helper_prov.owner_declared_name == "top"
 
 
+def test_build_library_contains_tracks_active_session_names() -> None:
+    builder = BuildLibrary()
+    builder["leaf"] = Pattern()
+    builder.add_source(Library({"src": Pattern()}))
+
+    def make_top(lib: BuildLibrary) -> Pattern:
+        assert "leaf" in lib
+        assert "src" in lib
+        assert "_helper" not in lib
+        lib["_helper"] = Pattern()
+        assert "_helper" in lib
+        return Pattern()
+
+    builder.cells.top = cell(make_top)(builder)
+    built, _report = builder.build()
+
+    assert "_helper" in built
+
+
 def test_build_library_preserves_source_cells_and_records_source_provenance() -> None:
     source = Library({"src": Pattern()})
     builder = BuildLibrary()
     builder.add_source(source)
     builder.cells.top = cell(lambda: Pattern())()
 
-    built = builder.build()
+    built, report = builder.build()
 
     assert "src" in built
-    assert built.build_report.provenance["src"].kind == "source"
+    assert report.provenance["src"].kind == "source"
-    assert built.build_report.provenance["src"].emitted_via == "source_import"
 
 
-def test_build_library_can_rename_imported_source_cells_during_authoring() -> None:
+def test_build_library_add_source_can_rename_every_source_cell() -> None:
     source = Library()
     source["child"] = Pattern()
     parent = Pattern()
     parent.ref("child")
     source["parent"] = parent
 
+    builder = BuildLibrary()
+    rename_map = builder.add_source(
+        source,
+        rename_theirs=lambda _lib, name: f"mapped_{name}",
+        rename_when="always",
+    )
+    built, report = builder.build()
+
+    assert rename_map == {
+        "child": "mapped_child",
+        "parent": "mapped_parent",
+    }
+    assert "mapped_child" in built["mapped_parent"].refs
+    assert report.provenance["mapped_child"].requested_name == "child"
+
+
+def test_build_library_authoring_tree_merge_keeps_source_view_lazy() -> None:
+    child = Pattern()
+    top = Pattern()
+    top.ref("child")
+    source = _MetadataSource(
+        {"child": child, "top": top},
+        {"child": set(), "top": {"child"}},
+    )
+
+    builder = BuildLibrary()
+    top_name = builder << source
+    built, _report = builder.build()
+
+    assert top_name == "top"
+    assert "top" in built
+    assert source.loads == 0
+
+
+def test_build_library_authoring_source_tree_merge_returns_renamed_top() -> None:
+    existing = Pattern()
+    source_top = Pattern()
+    source = _MetadataSource(
+        {"_helper": source_top},
+        {"_helper": set()},
+    )
+
+    builder = BuildLibrary()
+    builder["_helper"] = existing
+    top_name = builder << source
+    built, _report = builder.build()
+
+    assert top_name != "_helper"
+    assert top_name in built
+    assert source.loads == 0
+
+
+def test_build_library_authoring_source_tree_merge_remaps_renamed_child_on_materialization() -> None:
+    source_helper = Pattern()
+    source_top = Pattern()
+    source_top.ref("_helper")
+    source = _MetadataSource(
+        {"_helper": source_helper, "top": source_top},
+        {"_helper": set(), "top": {"_helper"}},
+    )
+
+    builder = BuildLibrary()
+    builder["_helper"] = Pattern()
+    top_name = builder << source
+    built, _report = builder.build(output="library")
+
+    assert top_name == "top"
+    assert "_helper" not in built[top_name].refs
+    assert source.loads == 2
+
+
+def test_build_library_rejects_authoring_tree_le_before_mutating() -> None:
+    builder = BuildLibrary()
+
+    with pytest.raises(BuildError, match="__le__"):
+        _abstract = builder <= Library({"leaf": Pattern()})
+
+    assert list(builder) == []
+
+
+def test_build_library_rejects_source_cells_added_after_add_source() -> None:
+    source = Library({"src": Pattern()})
     builder = BuildLibrary()
     builder.add_source(source)
-    builder.rename("child", "renamed_child")
+    source["late"] = Pattern()
 
-    built = builder.build()
+    with pytest.raises(BuildError, match="Do not structurally mutate source libraries"):
-
+        builder.build()
-    assert "renamed_child" in built
-    assert "child" not in built
-    assert "renamed_child" in built["parent"].refs
-    assert built.build_report.provenance["renamed_child"].source_name == "child"
 
 
-def test_build_library_rejects_move_references_for_source_rename() -> None:
+def test_build_library_rejects_source_cells_removed_after_add_source() -> None:
+    source = Library({"src": Pattern()})
+    builder = BuildLibrary()
+    builder.add_source(source)
+    del source["src"]
+
+    with pytest.raises(BuildError, match="Do not structurally mutate source libraries"):
+        builder.build()
+
+
+def test_build_library_rejects_add_source_during_build() -> None:
+    builder = BuildLibrary()
+
+    def make_top(lib: BuildLibrary) -> Pattern:
+        lib.add_source(Library({"src": Pattern()}))
+        return Pattern()
+
+    builder.cells.top = cell(make_top)(builder)
+
+    with pytest.raises(BuildError, match="add_source"):
+        builder.build()
+
+
+def test_build_library_rejects_renaming_imported_source_cells_during_authoring() -> None:
     builder = BuildLibrary()
     builder.add_source(Library({"src": Pattern()}))
 
-    with pytest.raises(BuildError, match="move_references=True"):
+    with pytest.raises(BuildError, match="add_source"):
         builder.rename("src", "renamed_src", move_references=True)
 
 
@@ -202,7 +377,7 @@ def test_build_library_rejects_renaming_declared_cells_during_authoring() -> Non
         builder.rename("declared", "renamed_declared")
 
 
-def test_build_library_helper_rename_updates_provenance_and_owned_cells() -> None:
+def test_build_library_helper_rename_updates_provenance_owner() -> None:
     builder = BuildLibrary()
 
     def make_top(lib: BuildLibrary) -> Pattern:
@@ -213,18 +388,16 @@ def test_build_library_helper_rename_updates_provenance_and_owned_cells() -> Non
         return top
 
     builder.cells.top = cell(make_top)(builder)
-    built = builder.build()
+    built, report = builder.build()
-    report = built.build_report
 
     assert "final_helper" in built
     assert "_helper" not in built
-    assert "final_helper" in report.owned_cells["top"]
+    owned = _owned_by(report, "top")
-    assert "_helper" not in report.owned_cells["top"]
+    assert "final_helper" in owned
+    assert "_helper" not in owned
     prov = report.provenance["final_helper"]
     assert prov.kind == "helper"
     assert prov.requested_name == "_helper"
-    assert prov.renamed_from == "_helper"
-    assert prov.final_name == "final_helper"
 
 
 def test_build_library_helper_delete_removes_provenance_and_ownership() -> None:
@@ -236,12 +409,11 @@ def test_build_library_helper_delete_removes_provenance_and_ownership() -> None:
         return Pattern()
 
     builder.cells.top = cell(make_top)(builder)
-    built = builder.build()
+    built, report = builder.build()
-    report = built.build_report
 
     assert "_helper" not in built
     assert "_helper" not in report.provenance
-    assert report.owned_cells["top"] == ("top",)
+    assert _owned_by(report, "top") == {"top"}
 
 
 def test_build_library_helper_rename_after_auto_rename_preserves_requested_name() -> None:
@@ -258,13 +430,11 @@ def test_build_library_helper_rename_after_auto_rename_preserves_requested_name(
         return top
 
     builder.cells.top = cell(make_top)(builder)
-    built = builder.build()
+    built, report = builder.build()
-    report = built.build_report
 
     assert "final_helper" in built
     prov = report.provenance["final_helper"]
     assert prov.requested_name == "_helper"
-    assert prov.renamed_from == "_helper"
 
 
 def test_build_library_rejects_renaming_declared_or_source_cells_during_build() -> None:

masque/test/test_gdsii_lazy.py

@@ -1,6 +1,7 @@
 from pathlib import Path
 
 import numpy
+import pytest
 from numpy.testing import assert_allclose
 
 from ..file import gdsii, gdsii_lazy
@@ -82,6 +83,35 @@ def test_gdsii_lazy_overlay_add_source_stays_lazy_for_processed_view(tmp_path: P
     assert set(abstract.ports) == {'A'}
 
 
+def test_gdsii_lazy_overlay_add_source_can_rename_every_source_cell() -> None:
+    src = _make_lazy_port_library()
+    overlay = gdsii_lazy.OverlayLibrary()
+
+    rename_map = overlay.add_source(
+        src,
+        rename_theirs=lambda _lib, name: f'mapped_{name}',
+        rename_when='always',
+    )
+
+    assert rename_map == {
+        'leaf': 'mapped_leaf',
+        'child': 'mapped_child',
+        'top': 'mapped_top',
+    }
+    assert tuple(overlay.keys()) == ('mapped_leaf', 'mapped_child', 'mapped_top')
+    assert 'mapped_leaf' in overlay['mapped_child'].refs
+
+
+def test_gdsii_lazy_overlay_add_source_rename_when_validation() -> None:
+    src = _make_lazy_port_library()
+
+    with pytest.raises(TypeError, match='rename_theirs'):
+        gdsii_lazy.OverlayLibrary().add_source(src, rename_when='always')
+
+    with pytest.raises(ValueError, match='rename mode'):
+        gdsii_lazy.OverlayLibrary().add_source(src, rename_when='sometimes')   # type: ignore[arg-type]
+
+
 def test_gdsii_lazy_processed_write_roundtrips_without_explicit_units(tmp_path: Path) -> None:
     gds_file = tmp_path / 'lazy_roundtrip.gds'
     src = _make_lazy_port_library()

masque/test/test_pather_core.py

@@ -1,13 +1,11 @@
-from typing import Any
-
 import pytest
 import numpy
 from numpy import pi
 from numpy.testing import assert_allclose, assert_equal
 
 from masque import Pather, Library, Pattern, Port
-from masque.builder.tools import PathTool, Tool
+from masque.builder.tools import PathTool
-from masque.error import BuildError, PortError, PatternError
+from masque.error import BuildError, PortError
 
 
 @pytest.fixture
@@ -117,6 +115,82 @@ def test_pather_bundle_trace() -> None:
     assert numpy.isclose(p.pattern.ports['A'].offset[0], -20000)
     assert numpy.isclose(p.pattern.ports['B'].offset[0], -22000)
 
+def test_portpather_default_spacing_matches_explicit_spacing() -> None:
+    lib_default = Library()
+    tool_default = PathTool(layer='M1', width=1000)
+    p_default = Pather(lib_default, tools=tool_default, auto_render=False)
+    p_default.pattern.ports['A'] = Port((0, 0), rotation=0)
+    p_default.pattern.ports['B'] = Port((0, 2000), rotation=0)
+
+    lib_explicit = Library()
+    tool_explicit = PathTool(layer='M1', width=1000)
+    p_explicit = Pather(lib_explicit, tools=tool_explicit, auto_render=False)
+    p_explicit.pattern.ports['A'] = Port((0, 0), rotation=0)
+    p_explicit.pattern.ports['B'] = Port((0, 2000), rotation=0)
+
+    p_default.at(['A', 'B'], spacing=2000).ccw(xmin=-20000)
+    p_explicit.at(['A', 'B']).ccw(xmin=-20000, spacing=2000)
+
+    assert_allclose(p_default.pattern.ports['A'].offset, p_explicit.pattern.ports['A'].offset)
+    assert_allclose(p_default.pattern.ports['B'].offset, p_explicit.pattern.ports['B'].offset)
+
+def test_portpather_default_spacing_reused_and_overridden() -> None:
+    p_default = Pather(Library(), tools=PathTool(layer='M1', width=1000), auto_render=False)
+    p_default.pattern.ports['A'] = Port((0, 0), rotation=0)
+    p_default.pattern.ports['B'] = Port((0, 2000), rotation=0)
+
+    p_explicit = Pather(Library(), tools=PathTool(layer='M1', width=1000), auto_render=False)
+    p_explicit.pattern.ports['A'] = Port((0, 0), rotation=0)
+    p_explicit.pattern.ports['B'] = Port((0, 2000), rotation=0)
+
+    pp_default = p_default.at(['A', 'B'], spacing=2000)
+    pp_default.ccw(xmin=-20000)
+    pp_default.cw(emin=1000)
+    p_explicit.at(['A', 'B']).ccw(xmin=-20000, spacing=2000).cw(emin=1000, spacing=2000)
+
+    assert_allclose(p_default.pattern.ports['A'].offset, p_explicit.pattern.ports['A'].offset)
+    assert_allclose(p_default.pattern.ports['B'].offset, p_explicit.pattern.ports['B'].offset)
+
+    p_override = Pather(Library(), tools=PathTool(layer='M1', width=1000), auto_render=False)
+    p_override.pattern.ports['A'] = Port((0, 0), rotation=0)
+    p_override.pattern.ports['B'] = Port((0, 2000), rotation=0)
+
+    p_override_explicit = Pather(Library(), tools=PathTool(layer='M1', width=1000), auto_render=False)
+    p_override_explicit.pattern.ports['A'] = Port((0, 0), rotation=0)
+    p_override_explicit.pattern.ports['B'] = Port((0, 2000), rotation=0)
+
+    p_override.at(['A', 'B'], spacing=2000).ccw(xmin=-20000, spacing=3000)
+    p_override_explicit.at(['A', 'B']).ccw(xmin=-20000, spacing=3000)
+
+    assert_allclose(p_override.pattern.ports['A'].offset, p_override_explicit.pattern.ports['A'].offset)
+    assert_allclose(p_override.pattern.ports['B'].offset, p_override_explicit.pattern.ports['B'].offset)
+
+def test_portpather_default_spacing_not_injected_for_straight_bundle() -> None:
+    lib = Library()
+    tool = PathTool(layer='M1', width=1000)
+    p = Pather(lib, tools=tool, auto_render=False)
+    p.pattern.ports['A'] = Port((0, 0), rotation=0)
+    p.pattern.ports['B'] = Port((0, 2000), rotation=0)
+
+    p.at(['A', 'B'], spacing=2000).straight(xmin=-10000)
+
+    assert numpy.isclose(p.pattern.ports['A'].offset[0], -10000)
+    assert numpy.isclose(p.pattern.ports['B'].offset[0], -10000)
+
+def test_portpather_default_spacing_vector_revalidated_after_selection_change() -> None:
+    lib = Library()
+    tool = PathTool(layer='M1', width=1000)
+    p = Pather(lib, tools=tool, auto_render=False)
+    p.pattern.ports['A'] = Port((0, 0), rotation=0)
+    p.pattern.ports['B'] = Port((0, 2000), rotation=0)
+    p.pattern.ports['C'] = Port((0, 4000), rotation=0)
+
+    pp = p.at(['A', 'B', 'C'], spacing=[2000, 3000])
+    pp.deselect('C')
+
+    with pytest.raises(BuildError, match='spacing must be scalar or have length 1'):
+        pp.ccw(xmin=-20000)
+
 def test_pather_each_bound() -> None:
     lib = Library()
     tool = PathTool(layer='M1', width=1000)