From f9611933acfd003076d5f11e27a38c288eca6bba Mon Sep 17 00:00:00 2001
From: Jan Petykiewicz <jan@mpxd.net>
Date: Mon, 13 Jul 2026 14:44:39 -0700
Subject: [PATCH] [Pather / Tool] more unification work and fixes

---
 MIGRATION.md                                |  75 +++-
 examples/tutorial/pather.py                 |  16 +-
 masque/__init__.py                          |   1 +
 masque/builder/__init__.py                  |   6 +
 masque/builder/_tolerances.py               |  48 +++
 masque/builder/error.py                     |   4 +
 masque/builder/pather.py                    |  51 +--
 masque/builder/planner/bounds.py            |  10 +-
 masque/builder/planner/interface.py         |   4 +-
 masque/builder/planner/planner.py           |  93 +++--
 masque/builder/tool_testing.py              | 368 ++++++++++++++++++++
 masque/builder/tools.py                     | 186 +++++++---
 masque/builder/utils.py                     |   9 +-
 masque/test/helpers.py                      |   2 +-
 masque/test/test_autotool_planning.py       |  73 +++-
 masque/test/test_pather_constraints.py      |  43 ++-
 masque/test/test_pather_core.py             |  16 +
 masque/test/test_pather_primitive_offers.py |  94 ++++-
 masque/test/test_pather_rendering.py        |  60 +++-
 19 files changed, 1022 insertions(+), 137 deletions(-)
 create mode 100644 masque/builder/_tolerances.py
 create mode 100644 masque/builder/tool_testing.py

diff --git a/MIGRATION.md b/MIGRATION.md
index 1a54793..3fb545f 100644
--- a/MIGRATION.md
+++ b/MIGRATION.md
@@ -288,7 +288,25 @@ you are exposing:
 common callback behavior. It is not the normal class users should instantiate.
 The concrete offer classes carry the semantic fields (`length_domain`,
 `jog_domain`, `ccw`) so tools do not need to encode primitive identity in
-strings.
+strings. Each concrete offer now also exposes a class-level canonical `kind`.
+Tools must return the matching offer kind for the discovery query; for example,
+`primitive_offers('s', ...)` must return only `SOffer` instances. Mismatches are
+reported as fatal `ToolContractError`s rather than silently ignored.
+
+`RenderStep` now stores that same canonical kind. Code that constructs render
+steps directly must use the kind rather than a legacy opcode:
+
+```python
+# old
+RenderStep('L', tool, start, end, data)
+
+# new
+RenderStep('straight', tool, start, end, data)
+```
+
+Use `'bend'`, `'s'`, `'u'`, or `'plug'` for the other step types. The read-only
+`RenderStep.opcode` and `PrimitiveOffer.opcode` properties remain available for
+code that only consumes steps, but opcodes are now derived rather than stored.
 
 Minimal straight-only example:
 
@@ -341,9 +359,11 @@ The mapping is unpacked only for `Tool.primitive_offers()`. Route arguments do
 not leak into that namespace, and tool options are not forwarded to
 `Tool.render()`. An offer that needs route-specific render behavior must capture
 the selected value in its `commit()` result (`RenderStep.data`). `AutoTool`
-does this automatically for generated straight and S-bend primitives: the flat
-mapping is snapshotted per selected primitive and passed to its generator as
-keyword arguments during rendering. AutoTool options must not change generated
+does this automatically for generated straight and S-bend primitives: the
+mapping is deep-copied per offer discovery and passed to its generator as
+keyword arguments during rendering. Consequently every AutoTool option value
+must be deep-copyable, and later mutation of nested caller-owned values does
+not affect a pending route. AutoTool options must not change generated
 ports or endpoint geometry. `PathTool` defines no tool options and rejects
 nonempty mappings.
 
@@ -360,9 +380,51 @@ Primitive offers are local planning objects:
 - `parameterized_bbox` may carry opaque future-router footprint metadata
 - `commit(parameter)` returns opaque render data consumed later by `render()`
 - `(min, max)` parameter domains are half-open; `(value, value)` is a fixed singleton
+- domains are validated when an offer is constructed, not when it is first evaluated
 - selected parameter values must be finite; domains may use infinite open bounds but not `NaN`
+- straight/bend domains require a finite nonnegative minimum; fixed singleton domains must be finite
 - `None` and `"unk"` ptypes are wildcards; concrete ptype mismatches reject an offer
 
+`AutoTool.add_straight(length_range=...)` and
+`AutoTool.add_sbend(jog_range=...)` now validate their ranges before metadata
+inference. `jog_range` is an absolute-magnitude range and must have a finite,
+nonnegative lower bound; AutoTool creates the corresponding positive and
+negative S offers itself. Invalid ranges now raise immediately instead of
+registering no offers.
+
+`ToolContractError` is exported from `masque` and `masque.builder`. It marks a
+broken Tool contract—such as an endpoint ptype that disagrees with its offer,
+an invalid evaluated cost, or rendered output that disagrees with the planned
+endpoint—and is fatal to route fallback. Ordinary `BuildError` raised by a
+planning callback remains a recoverable candidate rejection. Rendered output
+rotations are compared modulo one full turn; a port facing exactly backward is
+no longer accepted as equivalent. A `None` rotation remains an explicit
+wildcard.
+
+Custom Tool authors can exercise discovery, offer callbacks, committed data,
+and one-step rendering without depending on pytest:
+
+```python
+from masque.builder import ToolContractCase, validate_tool_contract
+
+validate_tool_contract(my_tool, (
+    ToolContractCase('straight', in_ptype='wire', probe_parameters=(10,)),
+    ToolContractCase('bend', in_ptype='wire', ccw=False),
+    ToolContractCase('bend', in_ptype='wire', ccw=True),
+    ToolContractCase('s', in_ptype='wire', require_offers=False),
+))
+```
+
+Cases derive representative parameters from each returned offer domain and
+may add explicit probes. Empty discovery is an error unless
+`require_offers=False`; bbox support is required only with `check_bbox=True`.
+Validation returns normally on success and otherwise raises an
+`ExceptionGroup` of contextual `ToolContractError`s.
+
+Positional routing bounds (`p`, `pos`, `position`, `x`, and `y`) now require a
+nearly Manhattan input-port direction. Arbitrarily angled ports remain valid
+for non-positional/extension routing.
+
 Heterogeneous `StraightOffer` and `SOffer` objects may be used as ptype
 adapters. Requested `out_ptype` constrains only the final route endpoint; any
 intermediate ptypes are chosen by the route solver.
@@ -717,8 +779,9 @@ These are additive, but available now from `masque` and `masque.builder`:
 - from `masque`: `RectCollection`, `boolean`, `OverlayLibrary`,
   `PortsLibraryView`, `IMaterializable`, `IBorrowing`, `LibraryBuilder`,
   `BuildReport`, `CellProvenance`, and `cell`
-- from `masque.builder`: `CostCallable`, the concrete primitive-offer classes,
-  and structured route error/status types
+- from `masque.builder`: `CostCallable`, `RenderStepKind`, the concrete
+  primitive-offer classes, structured route error/status types,
+  `ToolContractCase`, and `validate_tool_contract`
 
 ## Minimal migration checklist
 
diff --git a/examples/tutorial/pather.py b/examples/tutorial/pather.py
index 7813529..c536428 100644
--- a/examples/tutorial/pather.py
+++ b/examples/tutorial/pather.py
@@ -9,7 +9,9 @@ import numpy
 from numpy import pi
 from masque import Pather, Library, Pattern, Port, layer_t
 from masque.abstract import Abstract
-from masque.builder import BendOffer, RenderStep, StraightOffer, Tool
+from masque.builder import (
+    BendOffer, RenderStep, StraightOffer, Tool, ToolContractCase, validate_tool_contract,
+    )
 from masque.error import BuildError
 from masque.file.gdsii import writefile
 from masque.library import ILibrary, SINGLE_USE_PREFIX
@@ -419,6 +421,18 @@ def prepare_tools() -> tuple[Library, Tool, Tool]:
         bend = library.abstract('m2_bend'),
         transitions = via_transitions,
         )
+
+    # Custom tools can be checked independently of Pather or pytest. Automatic
+    # probes cover each offer domain; explicit probes can target useful process
+    # dimensions. Unsupported primitive families opt out with require_offers=False.
+    for tool in (M1_tool, M2_tool):
+        validate_tool_contract(tool, (
+            ToolContractCase('straight', in_ptype=tool.ptype, probe_parameters=(10_000,)),
+            ToolContractCase('bend', in_ptype=tool.ptype, ccw=False),
+            ToolContractCase('bend', in_ptype=tool.ptype, ccw=True),
+            ToolContractCase('s', in_ptype=tool.ptype, require_offers=False),
+            ToolContractCase('u', in_ptype=tool.ptype, require_offers=False),
+            ))
     return library, M1_tool, M2_tool
 
 
diff --git a/masque/__init__.py b/masque/__init__.py
index 89b45b0..bc0a466 100644
--- a/masque/__init__.py
+++ b/masque/__init__.py
@@ -84,6 +84,7 @@ from .ports import (
 from .abstract import Abstract as Abstract
 from .builder import (
     Tool as Tool,
+    ToolContractError as ToolContractError,
     Pather as Pather,
     RouteError as RouteError,
     RouteFailureDetails as RouteFailureDetails,
diff --git a/masque/builder/__init__.py b/masque/builder/__init__.py
index 4a92753..a4389f6 100644
--- a/masque/builder/__init__.py
+++ b/masque/builder/__init__.py
@@ -54,6 +54,7 @@ from .pather import (
     PortPather as PortPather,
 )
 from .error import (
+    ToolContractError as ToolContractError,
     RouteError as RouteError,
     RouteFailureDetails as RouteFailureDetails,
     RouteOperation as RouteOperation,
@@ -61,11 +62,16 @@ from .error import (
     MinimumStatus as MinimumStatus,
 )
 from .utils import ell as ell
+from .tool_testing import (
+    ToolContractCase as ToolContractCase,
+    validate_tool_contract as validate_tool_contract,
+)
 from .tools import (
     Tool as Tool,
     AutoTool as AutoTool,
     PathTool as PathTool,
     RenderStep as RenderStep,
+    RenderStepKind as RenderStepKind,
     PrimitiveKind as PrimitiveKind,
     CostCallable as CostCallable,
     GeneratedEndpointFn as GeneratedEndpointFn,
diff --git a/masque/builder/_tolerances.py b/masque/builder/_tolerances.py
new file mode 100644
index 0000000..5f179e3
--- /dev/null
+++ b/masque/builder/_tolerances.py
@@ -0,0 +1,48 @@
+"""Shared numeric tolerances for builder geometry and parameter comparisons."""
+from math import isclose, remainder, tau
+from typing import Any
+
+import numpy
+
+
+GEOMETRY_RTOL = 1e-5
+GEOMETRY_ATOL = 1e-8
+DOMAIN_RTOL = 1e-9
+DOMAIN_ATOL = 1e-12
+MANHATTAN_ANGLE_RTOL = 1e-9
+MANHATTAN_ANGLE_ATOL = 1e-9
+
+
+def scalar_close(a: float, b: float) -> bool:
+    """Match the solver's existing scalar-comparison behavior."""
+    return isclose(float(a), float(b), rel_tol=GEOMETRY_RTOL, abs_tol=GEOMETRY_ATOL)
+
+
+def array_close(a: Any, b: Any) -> bool:
+    """Match NumPy's historical builder geometry-comparison behavior."""
+    return bool(numpy.allclose(a, b, rtol=GEOMETRY_RTOL, atol=GEOMETRY_ATOL))
+
+
+def angles_equal(a: float, b: float) -> bool:
+    """Return true when two rotations are equal modulo one full turn."""
+    delta = remainder(float(a) - float(b), tau)
+    return isclose(delta, 0.0, rel_tol=GEOMETRY_RTOL, abs_tol=GEOMETRY_ATOL)
+
+
+def manhattan_axis(rotation: float) -> int | None:
+    """Return 0 for horizontal, 1 for vertical, or None for a non-cardinal angle."""
+    angle = float(rotation) % (numpy.pi / 2)
+    if isclose(
+            angle,
+            0.0,
+            rel_tol=MANHATTAN_ANGLE_RTOL,
+            abs_tol=MANHATTAN_ANGLE_ATOL,
+            ) or isclose(
+                angle,
+                numpy.pi / 2,
+                rel_tol=MANHATTAN_ANGLE_RTOL,
+                abs_tol=MANHATTAN_ANGLE_ATOL,
+                ):
+        quarter_turn = round(float(rotation) / (numpy.pi / 2))
+        return quarter_turn % 2
+    return None
diff --git a/masque/builder/error.py b/masque/builder/error.py
index 6a647ce..927c03c 100644
--- a/masque/builder/error.py
+++ b/masque/builder/error.py
@@ -12,6 +12,10 @@ from ..error import BuildError
 RouteOperation = Literal['trace', 'trace_to', 'jog', 'uturn']
 
 
+class ToolContractError(BuildError):
+    """A Tool returned data inconsistent with its routing contract."""
+
+
 class RouteFailurePolicy(Enum):
     """Whether route failure may be recovered through alternate/dead planning.
 
diff --git a/masque/builder/pather.py b/masque/builder/pather.py
index da1c0d9..15e0c59 100644
--- a/masque/builder/pather.py
+++ b/masque/builder/pather.py
@@ -76,13 +76,14 @@ from .planner.interface import (
     RoutePortContext,
     route_failure_policy,
     )
-from .error import RouteFailurePolicy
+from .error import RouteFailurePolicy, ToolContractError
 from .planner import (
     RouteTieBreakStrategy,
     RoutingPlanner,
     )
 from .planner.bounds import resolved_position_bound
 from .logging import PatherLogger
+from ._tolerances import angles_equal, array_close
 
 
 logger = logging.getLogger(__name__)
@@ -343,7 +344,7 @@ class Pather(PortList):
             if not steps:
                 continue
             port = self.ports.get(name, steps[-1].end_port)
-            prepared.append((name, RenderStep('P', None, port.copy(), port.copy(), None)))
+            prepared.append((name, RenderStep('plug', None, port.copy(), port.copy(), None)))
         return prepared
 
     def _commit_breaks(self, prepared: Iterable[tuple[str, RenderStep]]) -> None:
@@ -1130,7 +1131,7 @@ class Pather(PortList):
                     return
 
                 tool_name = type(batch[0].tool).__name__
-                raise BuildError(
+                raise ToolContractError(
                     f'Tool {tool_name}.render() returned missing single-use refs for {portspec}: {missing}'
                     )
 
@@ -1139,22 +1140,22 @@ class Pather(PortList):
                 actual = pat.ports.get(portspec)
                 tool_name = type(batch[0].tool).__name__
                 if actual is None:
-                    raise BuildError(
+                    raise ToolContractError(
                         f'Tool {tool_name}.render() did not produce output port {portspec!r}; '
                         f'expected {expected.describe()}'
                         )
 
-                offsets_match = bool(numpy.allclose(actual.offset, expected.offset))
+                offsets_match = array_close(actual.offset, expected.offset)
                 rotations_match = (
                     actual.rotation is None
                     or expected.rotation is None
-                    or bool(numpy.isclose(numpy.sin(actual.rotation - expected.rotation), 0))
+                    or angles_equal(actual.rotation, expected.rotation)
                     )
                 ptypes_match = ptypes_compatible(actual.ptype, expected.ptype)
                 if offsets_match and rotations_match and ptypes_match:
                     return
 
-                raise BuildError(
+                raise ToolContractError(
                     f'Tool {tool_name}.render() output port {portspec!r} does not match planned endpoint: '
                     f'expected {expected.describe()}, got {actual.describe()}'
                     )
@@ -1186,14 +1187,14 @@ class Pather(PortList):
                     continue
                 batch: list[RenderStep] = []
                 for step in steps:
-                    appendable = step.opcode in ('L', 'S', 'U')
+                    appendable = step.kind != 'plug'
                     same_tool = batch and step.tool is batch[0].tool
                     if batch and (not appendable or not same_tool or not batch[-1].is_continuous_with(step)):
                         render_batch(portspec, batch, append)
                         batch = []
                     if appendable:
                         batch.append(step)
-                    elif step.opcode == 'P' and portspec in pat.ports:
+                    elif step.kind == 'plug' and portspec in pat.ports:
                         del pat.ports[portspec]
                 if batch:
                     render_batch(portspec, batch, append)
@@ -1285,6 +1286,14 @@ class PortPather:
         self.pather = pather
         self.default_spacing = default_spacing
 
+    def _single_port(self, action: str) -> str:
+        """Return the selected port for an exact-one operation."""
+        if len(self.ports) != 1:
+            raise BuildError(
+                f'Unable to use implicit {action}() with {len(self.ports)} ports; expected exactly one.'
+                )
+        return self.ports[0]
+
     def retool(self, tool: Tool) -> Self:
         self.pather.retool(tool, self.ports)
         return self
@@ -1545,28 +1554,24 @@ class PortPather:
             strategy: RouteTieBreakStrategy | str | None = None,
             tool_options: Mapping[str, Any] | None = None,
             ) -> Self:
-        if len(self.ports) != 1:
-            raise BuildError(f'Unable to use implicit trace_into() with {len(self.ports)} ports; expected exactly one.')
+        port = self._single_port('trace_into')
         self.pather.trace_into(
-            self.ports[0], target_port, out_ptype=out_ptype, plug_destination=plug_destination,
+            port, target_port, out_ptype=out_ptype, plug_destination=plug_destination,
             thru=thru, strategy=strategy, tool_options=tool_options,
             )
         return self
 
     def plug(self, other: Abstract | str, other_port: str, **kwargs) -> Self:
-        if len(self.ports) > 1:
-            raise BuildError(f'Unable use implicit plug() with {len(self.ports)} ports.'
-                             'Use the pather or pattern directly to plug multiple ports.')
-        self.pather.plug(other, {self.ports[0]: other_port}, **kwargs)
+        port = self._single_port('plug')
+        self.pather.plug(other, {port: other_port}, **kwargs)
         return self
 
     def plugged(self, other_port: str | Mapping[str, str]) -> Self:
         if isinstance(other_port, Mapping):
             self.pather.plugged(dict(other_port))
-        elif len(self.ports) > 1:
-            raise BuildError(f'Unable use implicit plugged() with {len(self.ports)} (>1) ports.')
         else:
-            self.pather.plugged({self.ports[0]: other_port})
+            port = self._single_port('plugged')
+            self.pather.plugged({port: other_port})
         return self
 
     #
@@ -1604,9 +1609,7 @@ class PortPather:
         """ Rename active ports. """
         name_map: dict[str, str | None]
         if isinstance(name, str):
-            if len(self.ports) > 1:
-                raise BuildError('Use a mapping to rename >1 port')
-            name_map = {self.ports[0]: name}
+            name_map = {self._single_port('rename'): name}
         else:
             name_map = dict(name)
         self.pather.rename_ports(name_map)
@@ -1637,9 +1640,7 @@ class PortPather:
 
     def _normalize_copy_map(self, name: str | Mapping[str, str], action: str) -> dict[str, str]:
         if isinstance(name, str):
-            if len(self.ports) > 1:
-                raise BuildError(f'Use a mapping to {action} >1 port')
-            name_map = {self.ports[0]: name}
+            name_map = {self._single_port(action): name}
         else:
             name_map = dict(name)
 
diff --git a/masque/builder/planner/bounds.py b/masque/builder/planner/bounds.py
index 5b4404b..19a47d1 100644
--- a/masque/builder/planner/bounds.py
+++ b/masque/builder/planner/bounds.py
@@ -25,6 +25,7 @@ from numpy.typing import ArrayLike, NDArray
 from ...error import BuildError, PortError
 from ...ports import Port
 from ...utils import rotation_matrix_2d
+from .._tolerances import manhattan_axis
 from .interface import RoutePortContext
 
 
@@ -70,8 +71,13 @@ def resolved_position_bound(
     value = finite_scalar(raw_value, f'{key} positional bound')
     if port.rotation is None:
         raise BuildError('Ports must have rotation')
-    is_horiz = bool(numpy.isclose(port.rotation % pi, 0, rtol=1e-9, atol=1e-9))
-    if is_horiz:
+    axis = manhattan_axis(port.rotation)
+    if axis is None:
+        raise BuildError(
+            'Positional bounds require a nearly Manhattan port direction; '
+            f'got rotation {port.rotation:g}'
+            )
+    if axis == 0:
         if key == 'y':
             raise BuildError('Port is horizontal')
         target = Port((value, port.offset[1]), rotation=None)
diff --git a/masque/builder/planner/interface.py b/masque/builder/planner/interface.py
index 514779a..5be69c9 100644
--- a/masque/builder/planner/interface.py
+++ b/masque/builder/planner/interface.py
@@ -15,7 +15,7 @@ from dataclasses import dataclass
 from ...error import BuildError
 from ...ports import Port
 from ..tools import RenderStep, Tool
-from ..error import RouteError, RouteFailurePolicy
+from ..error import RouteError, RouteFailurePolicy, ToolContractError
 
 
 class RoutePlanningError(BuildError):
@@ -34,6 +34,8 @@ class RoutePlanningError(BuildError):
 
 def route_failure_policy(err: Exception) -> RouteFailurePolicy:
     """Return typed route recovery policy, defaulting generic errors to recoverable."""
+    if isinstance(err, ToolContractError):
+        return RouteFailurePolicy.FATAL
     if isinstance(err, RoutePlanningError):
         return err.policy
     if isinstance(err, RouteError):
diff --git a/masque/builder/planner/planner.py b/masque/builder/planner/planner.py
index 1d5837a..282a835 100644
--- a/masque/builder/planner/planner.py
+++ b/masque/builder/planner/planner.py
@@ -32,7 +32,7 @@ from __future__ import annotations
 from collections.abc import Iterable, Mapping, Sequence
 from dataclasses import dataclass, replace
 from itertools import combinations
-from math import cos, isclose as math_isclose, sin
+from math import cos, sin
 from typing import Any, Literal
 
 import numpy
@@ -50,6 +50,7 @@ from ..tools import (
     SOffer,
     StraightOffer,
     Tool,
+    UOffer,
     )
 from ..error import (
     MinimumStatus,
@@ -57,7 +58,9 @@ from ..error import (
     RouteFailureDetails,
     RouteFailurePolicy,
     RouteOperation,
+    ToolContractError,
     )
+from .._tolerances import scalar_close
 from ..utils import ell
 from . import bounds as planner_bounds
 from .interface import (
@@ -84,7 +87,7 @@ def validate_strategy(strategy: RouteTieBreakStrategy | str) -> RouteTieBreakStr
 
 def is_close(a: float, b: float) -> bool:
     """Compare route-solver scalars with the planner tolerance."""
-    return math_isclose(float(a), float(b), rel_tol=1e-5, abs_tol=1e-8)
+    return scalar_close(a, b)
 
 
 def clean_parameter(value: float) -> float:
@@ -225,8 +228,6 @@ class SelectedPrimitive:
     """Finite additive planning cost reported by the offer."""
     role: Literal['main', 'adapter'] = 'main'
     """Whether this step satisfies route geometry or adapts ptype."""
-    route_kind: PrimitiveKind | None = None
-    """Primitive kind used when querying the Tool for this step."""
 
 
 @dataclass(frozen=True, slots=True)
@@ -318,7 +319,7 @@ class Solver:
 
     def __init__(self, request: SolverRequest) -> None:
         self.request = request
-        self.eval_cache: dict[tuple[int, float, str | None, str | None, str, str, PrimitiveKind | None], SelectedPrimitive] = {}
+        self.eval_cache: dict[tuple[int, float, str | None, str | None, str, str], SelectedPrimitive] = {}
         self.offer_cache: dict[
             tuple[PrimitiveKind, str | None, str | None, tuple[tuple[str, Any], ...]],
             tuple[PrimitiveOffer, ...],
@@ -333,9 +334,9 @@ class Solver:
         for step in steps:
             if step.role == 'adapter':
                 continue
-            if step.route_kind == 'bend':
+            if step.offer.kind == 'bend':
                 count += 1
-            elif step.route_kind in ('s', 'u'):
+            elif step.offer.kind in ('s', 'u'):
                 count += 2
         return count
 
@@ -371,7 +372,6 @@ class Solver:
             tuple((
                 offer_key(step.offer),
                 step.role,
-                step.route_kind,
                 round(float(step.parameter), 9),
                 endpoint_key(step.out_port),
                 ) for step in candidate.steps),
@@ -448,16 +448,54 @@ class Solver:
         kwargs = dict(self.request.tool_options)
         if extra:
             kwargs.update(extra)
+
+        def query_tool() -> tuple[PrimitiveOffer, ...]:
+            expected_offer_type = {
+                'straight': StraightOffer,
+                'bend': BendOffer,
+                's': SOffer,
+                'u': UOffer,
+                }[kind]
+            offers = self.request.tool.primitive_offers(
+                kind,
+                in_ptype=in_ptype,
+                out_ptype=out_ptype,
+                **kwargs,
+                )
+            if not isinstance(offers, tuple):
+                raise ToolContractError(
+                    f'Tool.primitive_offers({kind!r}) must return a tuple, '
+                    f'got {type(offers).__name__}'
+                    )
+            for index, offer in enumerate(offers):
+                if not isinstance(offer, PrimitiveOffer):
+                    raise ToolContractError(
+                        f'Tool.primitive_offers({kind!r}) item {index} must be a PrimitiveOffer, '
+                        f'got {type(offer).__name__}'
+                        )
+                if offer.kind != kind:
+                    raise ToolContractError(
+                        f'Tool.primitive_offers({kind!r}) item {index} returned '
+                        f'{offer.kind!r} offer'
+                        )
+                if not isinstance(offer, expected_offer_type):
+                    raise ToolContractError(
+                        f'Tool.primitive_offers({kind!r}) item {index} must be '
+                        f'{expected_offer_type.__name__}, got {type(offer).__name__}'
+                        )
+            return offers
+
+        extra_items = tuple(sorted((extra or {}).items()))
         try:
-            cache_key = (kind, in_ptype, out_ptype, tuple(sorted(kwargs.items())))
+            cache_key = (kind, in_ptype, out_ptype, extra_items)
             hash(cache_key)
         except TypeError:
-            return self.request.tool.primitive_offers(kind, in_ptype=in_ptype, out_ptype=out_ptype, **kwargs)
+            return query_tool()
 
         cached = self.offer_cache.get(cache_key)
         if cached is not None:
             return cached
-        offers = self.request.tool.primitive_offers(kind, in_ptype=in_ptype, out_ptype=out_ptype, **kwargs)
+        offers = query_tool()
         self.offer_cache[cache_key] = offers
         return offers
 
@@ -469,7 +507,6 @@ class Solver:
             *,
             out_ptype: str | None,
             role: Literal['main', 'adapter'],
-            route_kind: PrimitiveKind | None,
             route_name: str | None = None,
             ) -> SelectedPrimitive:
         """
@@ -481,7 +518,7 @@ class Solver:
         """
         route_name = self.request.route_name if route_name is None else route_name
         selected = offer.canonicalize_parameter(clean_parameter(parameter))
-        key = (id(offer), round(float(selected), 12), in_ptype, out_ptype, role, route_name, route_kind)
+        key = (id(offer), round(float(selected), 12), in_ptype, out_ptype, role, route_name)
         cached = self.eval_cache.get(key)
         if cached is not None:
             return cached
@@ -491,28 +528,37 @@ class Solver:
         if isinstance(offer, SOffer) and is_close(selected, 0):
             raise BuildError('zero-jog S primitive candidates are not allowed')
         out_port = offer.endpoint_at(selected)
+        if not isinstance(out_port, Port):
+            raise ToolContractError(
+                f'{route_name} primitive endpoint_at() must return a Port, '
+                f'got {type(out_port).__name__}'
+                )
         if not ptypes_compatible(out_port.ptype, offer.out_ptype):
-            raise RoutePlanningError(
+            raise ToolContractError(
                 f'{route_name} primitive endpoint ptype does not match declared offer out_ptype',
-                policy=RouteFailurePolicy.FATAL,
                 )
         if out_ptype is not None and not ptypes_compatible(out_port.ptype, out_ptype):
             raise RoutePlanningError(
                 'Requested out_ptype does not match primitive endpoint ptype',
                 policy=RouteFailurePolicy.FATAL,
                 )
-        cost = float(offer.cost_at(selected))
+        try:
+            if type(offer).cost_at is PrimitiveOffer.cost_at:
+                cost = float(PrimitiveOffer._cost_for_endpoint(offer, selected, out_port))
+            else:
+                cost = float(offer.cost_at(selected))
+        except (TypeError, ValueError, OverflowError) as err:
+            raise ToolContractError(f'{route_name} primitive returned a non-numeric cost') from err
         if not numpy.isfinite(cost):
-            raise BuildError(f'{route_name} primitive returned non-finite cost')
+            raise ToolContractError(f'{route_name} primitive returned non-finite cost')
         if cost < 0:
-            raise BuildError(f'{route_name} primitive returned negative cost')
+            raise ToolContractError(f'{route_name} primitive returned negative cost')
         primitive = SelectedPrimitive(
             offer,
             selected,
             out_port,
             cost,
             role=role,
-            route_kind=route_kind,
             )
         self.eval_cache[key] = primitive
         return primitive
@@ -532,7 +578,7 @@ class Solver:
         for step in steps:
             out_port = step.out_port
             if out_port.rotation is None:
-                raise BuildError('Primitive endpoints must have rotation')
+                raise ToolContractError('Primitive endpoints must have rotation')
             angle_cos = cos(angle)
             angle_sin = sin(angle)
             x += angle_cos * float(out_port.x) - angle_sin * float(out_port.y)
@@ -573,7 +619,6 @@ class Solver:
                         current_ptype,
                         out_ptype=None,
                         role='adapter',
-                        route_kind=kind,
                         route_name=f'{kind} adapter',
                         )
                 except BuildError as err:
@@ -606,7 +651,6 @@ class Solver:
                     current_ptype,
                     out_ptype=None,
                     role='main',
-                    route_kind='straight',
                     route_name='trace',
                     )
             except BuildError as err:
@@ -642,7 +686,6 @@ class Solver:
                     current_ptype,
                     out_ptype=None,
                     role='main',
-                    route_kind='bend',
                     route_name='trace',
                     )
             except BuildError as err:
@@ -678,7 +721,6 @@ class Solver:
                         current_ptype,
                         out_ptype=None,
                         role='main',
-                        route_kind=kind,
                         route_name=route_name,
                         )
                 except BuildError as err:
@@ -814,7 +856,6 @@ class Solver:
                 current_ptype,
                 out_ptype=None,
                 role=step.role,
-                route_kind=step.route_kind,
                 )
             selected.append(selected_step)
             current_ptype = selected_step.out_port.ptype
@@ -1183,7 +1224,7 @@ class RoutingPlanner:
             out_port.rotate_around((0, 0), pi + port_rot)
             out_port.translate(current.offset)
             render_steps.append(RenderStep(
-                selected.offer.opcode,
+                selected.offer.kind,
                 leg.tool,
                 current.copy(),
                 out_port.copy(),
diff --git a/masque/builder/tool_testing.py b/masque/builder/tool_testing.py
new file mode 100644
index 0000000..44daf95
--- /dev/null
+++ b/masque/builder/tool_testing.py
@@ -0,0 +1,368 @@
+"""Pytest-independent contract checks for custom routing Tools."""
+from __future__ import annotations
+
+from copy import deepcopy
+from dataclasses import dataclass, field
+from math import isfinite
+from types import MappingProxyType
+from typing import TYPE_CHECKING, Any
+
+import numpy
+from numpy import pi
+
+from ..library import ILibrary, SINGLE_USE_PREFIX
+from ..ports import Port
+from ..utils import ptypes_compatible
+from ._tolerances import angles_equal, array_close, scalar_close
+from .error import ToolContractError
+from .tools import (
+    BendOffer, PrimitiveKind, PrimitiveOffer, RenderStep, SOffer, StraightOffer, Tool, UOffer,
+    )
+
+if TYPE_CHECKING:
+    from collections.abc import Mapping, Sequence
+
+
+_RESERVED_OPTION_KEYS = frozenset(('kind', 'in_ptype', 'out_ptype', 'ccw'))
+
+
+@dataclass(frozen=True, slots=True)
+class ToolContractCase:
+    """One primitive-discovery query to exercise against a custom Tool."""
+
+    kind: PrimitiveKind
+    in_ptype: str | None = None
+    out_ptype: str | None = None
+    ccw: bool | None = None
+    tool_options: Mapping[str, Any] = field(default_factory=lambda: MappingProxyType({}))
+    probe_parameters: tuple[float, ...] = ()
+    require_offers: bool = True
+    check_bbox: bool = False
+    label: str | None = None
+
+    def __post_init__(self) -> None:
+        if self.kind not in ('straight', 'bend', 's', 'u'):
+            raise ValueError(f'Unrecognized primitive kind {self.kind!r}')
+        if self.kind == 'bend':
+            if self.ccw is None:
+                raise ValueError('Bend ToolContractCase requires ccw')
+        elif self.ccw is not None:
+            raise ValueError('ccw is only valid for bend ToolContractCase')
+
+        try:
+            options = deepcopy(dict(self.tool_options))
+        except Exception as err:
+            raise ValueError('ToolContractCase.tool_options must be a deep-copyable mapping') from err
+        nonstring = [key for key in options if not isinstance(key, str)]
+        if nonstring:
+            raise ValueError(f'ToolContractCase.tool_options keys must be strings; got {nonstring!r}')
+        collisions = sorted(_RESERVED_OPTION_KEYS & options.keys())
+        if collisions:
+            raise ValueError(f'ToolContractCase.tool_options contains reserved keys: {", ".join(collisions)}')
+
+        try:
+            probes = tuple(float(value) for value in self.probe_parameters)
+        except (TypeError, ValueError, OverflowError) as err:
+            raise ValueError('ToolContractCase.probe_parameters must contain numeric scalars') from err
+        if not all(isfinite(value) for value in probes):
+            raise ValueError('ToolContractCase.probe_parameters must be finite')
+
+        object.__setattr__(self, 'ccw', None if self.ccw is None else bool(self.ccw))
+        object.__setattr__(self, 'tool_options', MappingProxyType(options))
+        object.__setattr__(self, 'probe_parameters', probes)
+
+
+def _automatic_probes(offer: PrimitiveOffer) -> tuple[float, ...]:
+    """Choose deterministic representative parameters inside one offer domain."""
+    lower, upper = (float(value) for value in offer.parameter_domain)
+    if lower == upper:
+        return (lower,)
+    if numpy.isfinite(lower) and numpy.isfinite(upper):
+        midpoint = lower / 2 + upper / 2
+        if midpoint == upper:
+            midpoint = float(numpy.nextafter(upper, lower))
+        return (lower, midpoint)
+    if numpy.isfinite(lower):
+        step = max(1.0, abs(lower) * 0.1)
+        return (lower, lower + step)
+    if numpy.isfinite(upper):
+        step = max(1.0, abs(upper) * 0.1)
+        return (upper - step, upper - 2 * step)
+    return (-1.0, 1.0)
+
+
+def _offer_probes(offer: PrimitiveOffer, extras: Sequence[float]) -> tuple[float, ...]:
+    """Combine automatic and applicable explicit probes without duplicates."""
+    probes: list[float] = []
+    for parameter in (*_automatic_probes(offer), *extras):
+        try:
+            selected = offer.canonicalize_parameter(parameter)
+        except Exception:
+            continue
+        if not any(scalar_close(selected, previous) for previous in probes):
+            probes.append(selected)
+    return tuple(probes)
+
+
+def _offer_metadata(offer: PrimitiveOffer) -> tuple[Any, ...]:
+    """Return discovery metadata that must remain stable across repeated queries."""
+    cost_policy: tuple[str, Any]
+    if callable(offer.cost):
+        cost_policy = ('callable', type(offer.cost).__qualname__)
+    else:
+        cost_policy = ('factor', float(offer.cost))
+    return (
+        type(offer),
+        offer.kind,
+        offer.in_ptype,
+        offer.out_ptype,
+        tuple(float(value) for value in offer.parameter_domain),
+        getattr(offer, 'ccw', None),
+        cost_policy,
+        )
+
+
+def _evaluated_cost(offer: PrimitiveOffer, parameter: float, endpoint: Port) -> float:
+    """Mirror the solver's one-endpoint base-cost path while honoring overrides."""
+    if type(offer).cost_at is PrimitiveOffer.cost_at:
+        return PrimitiveOffer._cost_for_endpoint(offer, parameter, endpoint)
+    return float(offer.cost_at(parameter))
+
+
+def validate_tool_contract(tool: Tool, cases: Sequence[ToolContractCase]) -> None:
+    """Validate Tool discovery, offer callbacks, and one-step rendering.
+
+    All independent violations are collected and raised as one
+    `ExceptionGroup` containing contextual `ToolContractError` instances.
+    """
+    cases = tuple(cases)
+    if not cases:
+        raise ValueError('validate_tool_contract() requires at least one case')
+
+    errors: list[ToolContractError] = []
+
+    def violation(context: str, message: str, cause: Exception | None = None) -> None:
+        err = ToolContractError(f'{context}: {message}')
+        if cause is not None:
+            err.__cause__ = cause
+        errors.append(err)
+
+    def discover(case: ToolContractCase, context: str, repetition: str) -> tuple[PrimitiveOffer, ...] | None:
+        expected_offer_type = {
+            'straight': StraightOffer,
+            'bend': BendOffer,
+            's': SOffer,
+            'u': UOffer,
+            }[case.kind]
+        try:
+            kwargs = deepcopy(dict(case.tool_options))
+            if case.kind == 'bend':
+                kwargs['ccw'] = case.ccw
+            offers = tool.primitive_offers(
+                case.kind,
+                in_ptype=case.in_ptype,
+                out_ptype=case.out_ptype,
+                **kwargs,
+                )
+        except Exception as err:
+            violation(context, f'{repetition} discovery raised {type(err).__name__}: {err}', err)
+            return None
+
+        if not isinstance(offers, tuple):
+            violation(context, f'{repetition} discovery returned {type(offers).__name__}, expected tuple')
+            return None
+        valid = True
+        for offer_index, offer in enumerate(offers):
+            if not isinstance(offer, PrimitiveOffer):
+                violation(
+                    context,
+                    f'{repetition} discovery item {offer_index} is {type(offer).__name__}, expected PrimitiveOffer',
+                    )
+                valid = False
+            elif offer.kind != case.kind:
+                violation(
+                    context,
+                    f'{repetition} discovery item {offer_index} has kind {offer.kind!r}, expected {case.kind!r}',
+                    )
+                valid = False
+            elif not isinstance(offer, expected_offer_type):
+                violation(
+                    context,
+                    f'{repetition} discovery item {offer_index} is {type(offer).__name__}, '
+                    f'expected {expected_offer_type.__name__}',
+                    )
+                valid = False
+        return offers if valid else None
+
+    for case_index, case in enumerate(cases):
+        context = case.label or f'case {case_index} ({case.kind})'
+        first = discover(case, context, 'first')
+        second = discover(case, context, 'repeated')
+        if first is None or second is None:
+            continue
+        if case.require_offers and not first:
+            violation(context, 'discovery returned no offers')
+        if len(first) != len(second):
+            violation(context, f'discovery count changed from {len(first)} to {len(second)}')
+
+        matched_explicit = [False] * len(case.probe_parameters)
+        for offer_index, offer in enumerate(first):
+            offer_context = f'{context}, offer {offer_index}'
+            repeated = second[offer_index] if offer_index < len(second) else None
+            if repeated is not None and _offer_metadata(offer) != _offer_metadata(repeated):
+                violation(offer_context, 'discovery metadata changed between repeated queries')
+
+            probes = _offer_probes(offer, case.probe_parameters)
+            for explicit_index, parameter in enumerate(case.probe_parameters):
+                try:
+                    offer.canonicalize_parameter(parameter)
+                except Exception:
+                    continue
+                matched_explicit[explicit_index] = True
+
+            stable_ptype: str | None = None
+            stable_rotation: float | None = None
+            has_stable_endpoint = False
+            for parameter in probes:
+                probe_context = f'{offer_context}, parameter {parameter:g}'
+                try:
+                    endpoint = offer.endpoint_at(parameter)
+                except Exception as err:
+                    violation(probe_context, f'endpoint_at() raised {type(err).__name__}: {err}', err)
+                    continue
+                if not isinstance(endpoint, Port):
+                    violation(probe_context, f'endpoint_at() returned {type(endpoint).__name__}, expected Port')
+                    continue
+                if not numpy.all(numpy.isfinite(endpoint.offset)):
+                    violation(probe_context, 'endpoint offset must be finite')
+                if endpoint.rotation is None or not numpy.isfinite(endpoint.rotation):
+                    violation(probe_context, 'endpoint rotation must be finite and specified')
+                if not ptypes_compatible(endpoint.ptype, offer.out_ptype):
+                    violation(probe_context, 'endpoint ptype does not match declared out_ptype')
+
+                if offer.kind in ('straight', 'bend') and not scalar_close(endpoint.x, parameter):
+                    violation(probe_context, 'straight/bend endpoint x must equal its parameter')
+                if offer.kind in ('s', 'u') and not scalar_close(endpoint.y, parameter):
+                    violation(probe_context, 'S/U endpoint y must equal its parameter')
+                expected_rotation = {
+                    'straight': pi,
+                    'bend': -pi / 2 if isinstance(offer, BendOffer) and offer.ccw else pi / 2,
+                    's': pi,
+                    'u': 0.0,
+                    }[offer.kind]
+                if endpoint.rotation is not None and not angles_equal(endpoint.rotation, expected_rotation):
+                    violation(
+                        probe_context,
+                        f'endpoint rotation does not match {offer.kind!r} geometry',
+                        )
+
+                if has_stable_endpoint:
+                    if endpoint.ptype != stable_ptype:
+                        violation(probe_context, 'endpoint ptype changes across the offer domain')
+                    if (
+                            endpoint.rotation is None
+                            or stable_rotation is None
+                            or not angles_equal(endpoint.rotation, stable_rotation)
+                            ):
+                        violation(probe_context, 'endpoint rotation changes across the offer domain')
+                else:
+                    stable_ptype = endpoint.ptype
+                    stable_rotation = endpoint.rotation
+                    has_stable_endpoint = True
+
+                try:
+                    cost = float(_evaluated_cost(offer, parameter, endpoint))
+                    if not numpy.isfinite(cost) or cost < 0:
+                        violation(probe_context, f'cost must be finite and nonnegative, got {cost!r}')
+                except Exception as err:
+                    violation(probe_context, f'cost_at() raised {type(err).__name__}: {err}', err)
+                    cost = None
+
+                if repeated is not None:
+                    try:
+                        repeated_endpoint = repeated.endpoint_at(parameter)
+                        repeated_cost = float(_evaluated_cost(repeated, parameter, repeated_endpoint))
+                        if (
+                                not isinstance(repeated_endpoint, Port)
+                                or not array_close(repeated_endpoint.offset, endpoint.offset)
+                                or repeated_endpoint.ptype != endpoint.ptype
+                                or repeated_endpoint.rotation is None
+                                or endpoint.rotation is None
+                                or not angles_equal(repeated_endpoint.rotation, endpoint.rotation)
+                                ):
+                            violation(probe_context, 'endpoint result changed after repeated discovery')
+                        if cost is not None and not scalar_close(repeated_cost, cost):
+                            violation(probe_context, 'cost result changed after repeated discovery')
+                    except Exception as err:
+                        violation(
+                            probe_context,
+                            f'repeated offer evaluation raised {type(err).__name__}: {err}',
+                            err,
+                            )
+
+                if case.check_bbox:
+                    try:
+                        offer.bbox_at(parameter)
+                    except Exception as err:
+                        violation(probe_context, f'bbox_at() raised {type(err).__name__}: {err}', err)
+
+                try:
+                    data = offer.commit(parameter)
+                except Exception as err:
+                    violation(probe_context, f'commit() raised {type(err).__name__}: {err}', err)
+                    continue
+
+                try:
+                    start = Port((0, 0), rotation=pi, ptype=offer.in_ptype or 'unk')
+                    tree = tool.render((RenderStep(offer.kind, tool, start, endpoint.copy(), data),))
+                except Exception as err:
+                    violation(probe_context, f'render() raised {type(err).__name__}: {err}', err)
+                    continue
+                if not isinstance(tree, ILibrary):
+                    violation(probe_context, f'render() returned {type(tree).__name__}, expected ILibrary')
+                    continue
+                try:
+                    top_name = tree.top()
+                    pattern = tree.top_pattern()
+                except Exception as err:
+                    violation(probe_context, f'rendered tree has no valid top cell: {err}', err)
+                    continue
+                missing = sorted(
+                    name
+                    for name in tree.dangling_refs(top_name)
+                    if isinstance(name, str) and name.startswith(SINGLE_USE_PREFIX)
+                    )
+                if missing:
+                    violation(probe_context, f'rendered tree has missing single-use refs: {missing}')
+                missing_ports = [name for name in ('A', 'B') if name not in pattern.ports]
+                if missing_ports:
+                    violation(probe_context, f'rendered top cell is missing ports: {missing_ports}')
+                    continue
+                input_port, output_port = pattern.ports['A'], pattern.ports['B']
+                if not ptypes_compatible(input_port.ptype, offer.in_ptype):
+                    violation(probe_context, 'rendered input ptype does not match offer in_ptype')
+                try:
+                    rendered_offset, rendered_rotation = input_port.measure_travel(output_port)
+                except Exception as err:
+                    violation(probe_context, f'unable to measure rendered endpoint: {err}', err)
+                    continue
+                if not array_close(rendered_offset, endpoint.offset):
+                    violation(probe_context, 'rendered output offset does not match planned endpoint')
+                if (
+                        rendered_rotation is None
+                        or endpoint.rotation is None
+                        or not angles_equal(rendered_rotation, endpoint.rotation)
+                        ):
+                    violation(probe_context, 'rendered output rotation does not match planned endpoint')
+                if not ptypes_compatible(output_port.ptype, endpoint.ptype):
+                    violation(probe_context, 'rendered output ptype does not match planned endpoint')
+
+        for parameter, matched in zip(case.probe_parameters, matched_explicit, strict=True):
+            if not matched:
+                violation(context, f'explicit probe {parameter:g} is outside every discovered offer domain')
+
+    if errors:
+        raise ExceptionGroup(
+            f'{type(tool).__name__} failed Tool contract validation with {len(errors)} violation(s)',
+            errors,
+            )
diff --git a/masque/builder/tools.py b/masque/builder/tools.py
index 588c8f0..125140e 100644
--- a/masque/builder/tools.py
+++ b/masque/builder/tools.py
@@ -45,10 +45,11 @@ search across Tools or infer `Pather.retool()` boundaries; transitions,
 cross-ptype routes, and adapter shapes must be exposed by the active Tool as
 primitive offers.
 """
-from typing import Literal, Any, Self
+from typing import Literal, Any, ClassVar, Self
 from collections import ChainMap
 from collections.abc import Sequence, Callable, Mapping
 from abc import ABC, abstractmethod
+from copy import deepcopy
 from dataclasses import dataclass, field, replace
 from math import isclose as scalar_isclose, isfinite as scalar_isfinite, isnan as scalar_isnan, sqrt
 from types import MappingProxyType
@@ -68,14 +69,16 @@ from ..abstract import Abstract
 from ..library import ILibrary, Library, SINGLE_USE_PREFIX
 from ..error import BuildError
 from ..shapes import Path
+from ._tolerances import DOMAIN_ATOL, DOMAIN_RTOL, array_close, angles_equal
+from .error import ToolContractError
 
 
 def _canonicalize_domain_value(
         value: float,
         domain: tuple[float, float],
         *,
-        rtol: float = 1e-9,
-        atol: float = 1e-12,
+        rtol: float = DOMAIN_RTOL,
+        atol: float = DOMAIN_ATOL,
         ) -> float:
     """
     Canonicalize a solved primitive parameter against a route domain.
@@ -107,6 +110,29 @@ def _canonicalize_domain_value(
     return vv
 
 
+def _validated_parameter_domain(
+        domain: tuple[float, float],
+        *,
+        name: str = 'Parameter domain',
+        nonnegative_minimum: bool = False,
+        ) -> tuple[float, float]:
+    """Validate and normalize a primitive parameter domain at construction time."""
+    try:
+        lower_raw, upper_raw = domain
+        lower, upper = float(lower_raw), float(upper_raw)
+    except (TypeError, ValueError, OverflowError) as err:
+        raise BuildError(f'{name} must be a pair of numeric bounds') from err
+    if scalar_isnan(lower) or scalar_isnan(upper):
+        raise BuildError(f'{name} must not contain NaN values: {domain}')
+    if lower > upper:
+        raise BuildError(f'{name} lower bound must not exceed upper bound: {domain}')
+    if lower == upper and not scalar_isfinite(lower):
+        raise BuildError(f'{name} singleton must be finite: {domain}')
+    if nonnegative_minimum and (not scalar_isfinite(lower) or lower < 0):
+        raise BuildError(f'{name} must have a finite, nonnegative minimum: {domain}')
+    return lower, upper
+
+
 EndpointCallable = Callable[[float], Port]
 CommitCallable = Callable[[float], Any]
 BBoxCallable = Callable[[float], NDArray[numpy.float64]]
@@ -114,6 +140,21 @@ DataCallable = Callable[[float], Any]
 BBoxForDataCallable = Callable[[Any], NDArray[numpy.float64]]
 CostCallable = Callable[[float, Port], float]
 PrimitiveKind = Literal['straight', 'bend', 's', 'u']
+RenderStepKind = PrimitiveKind | Literal['plug']
+RenderOpcode = Literal['L', 'S', 'U', 'P']
+
+
+def _opcode_for_kind(kind: RenderStepKind) -> RenderOpcode:
+    """Return the legacy render opcode derived from one canonical kind."""
+    if kind in ('straight', 'bend'):
+        return 'L'
+    if kind == 's':
+        return 'S'
+    if kind == 'u':
+        return 'U'
+    if kind == 'plug':
+        return 'P'
+    raise BuildError(f'Unrecognized render-step kind {kind!r}')
 
 
 def _validated_cost(cost: CostCallable | float) -> CostCallable | float:
@@ -130,13 +171,13 @@ def _validated_cost(cost: CostCallable | float) -> CostCallable | float:
 
 
 def _validated_cost_value(value: Any) -> float:
-    """Return a canonical evaluated cost or raise `BuildError`."""
+    """Return a canonical evaluated cost or raise `ToolContractError`."""
     try:
         cost = float(value)
     except (TypeError, ValueError, OverflowError) as err:
-        raise BuildError(f'Primitive cost must be a number, got {value!r}') from err
+        raise ToolContractError(f'Primitive cost must be a number, got {value!r}') from err
     if not scalar_isfinite(cost) or cost < 0:
-        raise BuildError(f'Primitive cost must be nonnegative and finite, got {cost:g}')
+        raise ToolContractError(f'Primitive cost must be nonnegative and finite, got {cost:g}')
     return cost
 
 
@@ -218,6 +259,7 @@ class PrimitiveOffer(ABC):
     """Reserved footprint metadata; the current solver does not inspect it."""
     endpoint_planner: EndpointCallable | None = None
     commit_planner: CommitCallable | None = None
+    kind: ClassVar[PrimitiveKind]
 
     def __post_init__(self) -> None:
         has_endpoint = self.endpoint_planner is not None
@@ -225,12 +267,18 @@ class PrimitiveOffer(ABC):
 
         if has_endpoint != has_commit:
             raise BuildError('PrimitiveOffer split callbacks require both endpoint_planner and commit_planner')
+        _validated_parameter_domain(
+            self.parameter_domain,
+            nonnegative_minimum=self.kind in ('straight', 'bend'),
+            )
         object.__setattr__(self, 'cost', _validated_cost(self.cost))
 
     @property
-    @abstractmethod
     def opcode(self) -> Literal['L', 'S', 'U']:
-        raise NotImplementedError
+        """Legacy render opcode derived from this offer's canonical kind."""
+        opcode = _opcode_for_kind(self.kind)
+        assert opcode != 'P'
+        return opcode
 
     @property
     @abstractmethod
@@ -266,8 +314,12 @@ class PrimitiveOffer(ABC):
             out_port = self.endpoint_planner(selected)
         else:
             out_port = self.endpoint_at(selected)
+        return self._cost_for_endpoint(selected, out_port)
+
+    def _cost_for_endpoint(self, parameter: float, out_port: Port) -> float:
+        """Evaluate the base cost policy using an endpoint already produced by planning."""
         if callable(self.cost):
-            value = self.cost(selected, out_port)
+            value = self.cost(parameter, out_port)
         else:
             default_cost = abs(float(out_port.x)) + (pi / 2) * abs(float(out_port.y))
             value = self.cost * default_cost
@@ -315,6 +367,7 @@ class PrimitiveOffer(ABC):
 @dataclass(frozen=True, slots=True)
 class StraightOffer(PrimitiveOffer):
     """Straight or straight-like primitive parameterized by public route length."""
+    kind: ClassVar[Literal['straight']] = 'straight'
     length_domain: tuple[float, float] = (0.0, numpy.inf)
 
     @classmethod
@@ -377,10 +430,6 @@ class StraightOffer(PrimitiveOffer):
             length_domain = (float(endpoint.x), float(endpoint.x)),
             )
 
-    @property
-    def opcode(self) -> Literal['L']:
-        return 'L'
-
     @property
     def parameter_domain(self) -> tuple[float, float]:
         return self.length_domain
@@ -389,6 +438,7 @@ class StraightOffer(PrimitiveOffer):
 @dataclass(frozen=True, slots=True)
 class BendOffer(PrimitiveOffer):
     """Single-turn L-route primitive parameterized by public route length."""
+    kind: ClassVar[Literal['bend']] = 'bend'
     ccw: bool = True
     length_domain: tuple[float, float] = (0.0, numpy.inf)
 
@@ -454,10 +504,6 @@ class BendOffer(PrimitiveOffer):
             length_domain = (float(endpoint.x), float(endpoint.x)),
             )
 
-    @property
-    def opcode(self) -> Literal['L']:
-        return 'L'
-
     @property
     def parameter_domain(self) -> tuple[float, float]:
         return self.length_domain
@@ -466,6 +512,7 @@ class BendOffer(PrimitiveOffer):
 @dataclass(frozen=True, slots=True)
 class SOffer(PrimitiveOffer):
     """Non-turning S-route primitive parameterized by jog for a fixed route length."""
+    kind: ClassVar[Literal['s']] = 's'
     jog_domain: tuple[float, float] = (-numpy.inf, numpy.inf)
 
     @classmethod
@@ -526,10 +573,6 @@ class SOffer(PrimitiveOffer):
             jog_domain = (float(endpoint.y), float(endpoint.y)),
             )
 
-    @property
-    def opcode(self) -> Literal['S']:
-        return 'S'
-
     @property
     def parameter_domain(self) -> tuple[float, float]:
         return self.jog_domain
@@ -538,6 +581,7 @@ class SOffer(PrimitiveOffer):
 @dataclass(frozen=True, slots=True)
 class UOffer(PrimitiveOffer):
     """U-turn-like primitive parameterized by jog for a fixed route length."""
+    kind: ClassVar[Literal['u']] = 'u'
     jog_domain: tuple[float, float] = (-numpy.inf, numpy.inf)
 
     @classmethod
@@ -598,10 +642,6 @@ class UOffer(PrimitiveOffer):
             jog_domain = (float(endpoint.y), float(endpoint.y)),
             )
 
-    @property
-    def opcode(self) -> Literal['U']:
-        return 'U'
-
     @property
     def parameter_domain(self) -> tuple[float, float]:
         return self.jog_domain
@@ -616,16 +656,11 @@ class RenderStep:
     passes batches of compatible steps to `Tool.render()` when `Pather.render()`
     is called.
     """
-    opcode: Literal['L', 'S', 'U', 'P']
-    """ What operation is being performed.
-        L: straight or single-bend primitive
-        S: S-like primitive
-        U: U-like primitive
-        P: plug
-    """
+    kind: RenderStepKind
+    """Canonical primitive kind, or `plug` for an assembly boundary."""
 
     tool: 'Tool | None'
-    """ Tool that produced this step, or `None` for `opcode='P'`. """
+    """Tool that produced this step, or `None` for `kind='plug'`."""
 
     start_port: Port
     """ Input-side port before this step is rendered. """
@@ -637,18 +672,28 @@ class RenderStep:
     """ Arbitrary tool-specific data"""
 
     def __post_init__(self) -> None:
-        if self.opcode != 'P' and self.tool is None:
-            raise BuildError('Got tool=None but the opcode is not "P"')
+        if self.kind not in ('straight', 'bend', 's', 'u', 'plug'):
+            raise BuildError(f'Unrecognized RenderStep kind {self.kind!r}')
+        if self.kind == 'plug':
+            if self.tool is not None:
+                raise BuildError('RenderStep kind="plug" requires tool=None')
+        elif self.tool is None:
+            raise BuildError('RenderStep requires a Tool unless kind="plug"')
+
+    @property
+    def opcode(self) -> RenderOpcode:
+        """Legacy opcode derived from the canonical render-step kind."""
+        return _opcode_for_kind(self.kind)
 
     def is_continuous_with(self, other: 'RenderStep') -> bool:
         """
         Check if another RenderStep can be appended to this one.
         """
         # Check continuity with tolerance
-        offsets_match = bool(numpy.allclose(other.start_port.offset, self.end_port.offset))
+        offsets_match = array_close(other.start_port.offset, self.end_port.offset)
         rotations_match = (other.start_port.rotation is None and self.end_port.rotation is None) or (
             other.start_port.rotation is not None and self.end_port.rotation is not None and
-            bool(numpy.isclose(other.start_port.rotation, self.end_port.rotation))
+            angles_equal(other.start_port.rotation, self.end_port.rotation)
         )
         return offsets_match and rotations_match
 
@@ -664,7 +709,7 @@ class RenderStep:
             pp.translate(translation)
 
         return RenderStep(
-            opcode = self.opcode,
+            kind = self.kind,
             tool = self.tool,
             start_port = new_start,
             end_port = new_end,
@@ -682,7 +727,7 @@ class RenderStep:
         new_end.flip_across(axis=axis)
 
         return RenderStep(
-            opcode = self.opcode,
+            kind = self.kind,
             tool = self.tool,
             start_port = new_start,
             end_port = new_end,
@@ -723,6 +768,10 @@ class Tool(ABC):
         - `'s'`: a non-turning `SOffer`
         - `'u'`: an `UOffer`
 
+        Every returned offer must have the requested canonical `kind` and use
+        its corresponding concrete offer class. Contract mismatches are fatal
+        rather than recoverable candidate rejection.
+
         Other `kwargs` come only from the Pather call's explicit
         `tool_options` mapping. Tools are responsible for validating the keys
         they support.
@@ -1013,6 +1062,11 @@ class AutoTool(Tool):
         two-port straight. Metadata inference does not receive route options.
         """
         cost = _validated_cost(cost)
+        length_range = _validated_parameter_domain(
+            length_range,
+            name='Straight length_range',
+            nonnegative_minimum=True,
+            )
         ptype, in_port_name = self._infer_straight_metadata(fn, length_range, ptype, in_port_name)
 
         def data_at(length: float) -> AutoTool.GeneratedData:
@@ -1055,25 +1109,37 @@ class AutoTool(Tool):
 
         in_port = abstract.ports[in_port_name]
         out_port = abstract.ports[out_port_name]
-        out_ptype = out_port.ptype
         source_clockwise = self._bend_clockwise(in_port, out_port)
         if clockwise is not None and bool(clockwise) != source_clockwise:
             raise BuildError('Bend clockwise argument does not match port orientations')
 
         for ccw in (False, True):
             target_clockwise = not bool(ccw)
-            bend_dxy, bend_angle = self._bend2dxy(in_port, out_port, source_clockwise, target_clockwise)
+            source_matches_target = source_clockwise == target_clockwise
+            if source_matches_target or mirror:
+                entry_port_name = in_port_name
+                entry_port, exit_port = in_port, out_port
+                geometry_clockwise = source_clockwise
+            else:
+                entry_port_name = out_port_name
+                entry_port, exit_port = out_port, in_port
+                geometry_clockwise = self._bend_clockwise(entry_port, exit_port)
+
+            bend_dxy, bend_angle = self._bend2dxy(
+                entry_port,
+                exit_port,
+                geometry_clockwise,
+                target_clockwise,
+                )
             bend_dx = float(bend_dxy[0])
             bend_dy = float(bend_dxy[1])
-            source_matches_target = source_clockwise == target_clockwise
             mirrored = mirror and not source_matches_target
-            port_name = in_port_name if (mirror or source_matches_target) else out_port_name
-            reusable_data = self.ReusableData(abstract, port_name, mirrored)
-            endpoint = Port((bend_dx, bend_dy), rotation=bend_angle, ptype=out_ptype)
+            reusable_data = self.ReusableData(abstract, entry_port_name, mirrored)
+            endpoint = Port((bend_dx, bend_dy), rotation=bend_angle, ptype=exit_port.ptype)
 
             self._bend_offers[int(ccw)].append(BendOffer.prebuilt(
-                in_ptype = in_port.ptype,
-                out_ptype = out_ptype,
+                in_ptype = entry_port.ptype,
+                out_ptype = exit_port.ptype,
                 endpoint = endpoint,
                 data = reusable_data,
                 ccw = ccw,
@@ -1105,6 +1171,11 @@ class AutoTool(Tool):
         Metadata inference and endpoint planning do not receive route options.
         """
         cost = _validated_cost(cost)
+        jog_range = _validated_parameter_domain(
+            jog_range,
+            name='S-bend jog_range',
+            nonnegative_minimum=True,
+            )
         ptype, in_port_name, out_port_name = self._infer_sbend_metadata(
             fn,
             jog_range,
@@ -1345,9 +1416,11 @@ class AutoTool(Tool):
 
     @staticmethod
     def _signed_jog_domains(magnitude_range: tuple[float, float]) -> tuple[tuple[float, float], ...]:
-        lower, upper = (float(magnitude_range[0]), float(magnitude_range[1]))
-        if lower < 0 or lower > upper:
-            return ()
+        lower, upper = _validated_parameter_domain(
+            magnitude_range,
+            name='S-bend jog_range',
+            nonnegative_minimum=True,
+            )
 
         if lower == upper:
             if lower == 0:
@@ -1374,7 +1447,10 @@ class AutoTool(Tool):
             ) -> tuple[PrimitiveOffer, ...]:
         _ = out_ptype
         ccw = kwargs.pop('ccw', None)
-        tool_options = MappingProxyType(dict(kwargs))
+        try:
+            tool_options = MappingProxyType(deepcopy(dict(kwargs)))
+        except Exception as err:
+            raise BuildError('AutoTool tool_options must be deep-copyable') from err
 
         def configured(offer: PrimitiveOffer) -> PrimitiveOffer:
             if not tool_options:
@@ -1652,12 +1728,12 @@ class PathTool(Tool):
             transform = rotation_matrix_2d(port_rot + pi)
             delta = step.end_port.offset - step.start_port.offset
             local_end = rotation_matrix_2d(-(port_rot + pi)) @ delta
-            if step.opcode == 'L':
+            if step.kind in ('straight', 'bend'):
                 local_vertices = self._plan_l_vertices(float(local_end[0]), float(local_end[1]))
-            elif step.opcode == 'S':
+            elif step.kind == 's':
                 local_vertices = self._plan_s_vertices(float(local_end[0]), float(local_end[1]))
             else:
-                raise BuildError(f'Unrecognized opcode "{step.opcode}"')
+                raise BuildError(f'Unsupported PathTool render kind {step.kind!r}')
 
             for vertex in local_vertices[1:]:
                 path_vertices.append(step.start_port.offset + transform @ vertex)
@@ -1666,6 +1742,6 @@ class PathTool(Tool):
         pat.path(layer=self.layer, width=self.width, vertices=path_vertices)
         pat.ports = {
             port_names[0]: local_batch[0].start_port.copy().rotate(pi),
-            port_names[1]: local_batch[-1].end_port.copy().rotate(pi),
+            port_names[1]: local_batch[-1].end_port.copy(),
             }
         return tree
diff --git a/masque/builder/utils.py b/masque/builder/utils.py
index e8f06a7..fab28fd 100644
--- a/masque/builder/utils.py
+++ b/masque/builder/utils.py
@@ -8,6 +8,7 @@ from numpy.typing import ArrayLike, NDArray
 
 from ..utils import rotation_matrix_2d, SupportsBool
 from ..error import BuildError
+from ._tolerances import manhattan_axis
 
 if TYPE_CHECKING:
     from ..ports import Port
@@ -135,7 +136,13 @@ def ell(
             raise BuildError('set_rotation must be finite')
         rotations = numpy.full_like(has_rotation, set_rotation, dtype=float)
 
-    is_horizontal = numpy.isclose(rotations[0] % pi, 0)
+    axis = manhattan_axis(float(rotations[0]))
+    if bound_type in _POSITION_BOUND_TYPES and axis is None:
+        raise BuildError(
+            'Positional bounds require a nearly Manhattan port direction; '
+            f'got rotation {rotations[0]:g}'
+            )
+    is_horizontal = axis == 0
     if bound_type in ('ymin', 'ymax') and is_horizontal:
         raise BuildError(f'Asked for {bound_type} position but ports are pointing along the x-axis!')
     if bound_type in ('xmin', 'xmax') and not is_horizontal:
diff --git a/masque/test/helpers.py b/masque/test/helpers.py
index 2ccea1a..9f69933 100644
--- a/masque/test/helpers.py
+++ b/masque/test/helpers.py
@@ -108,7 +108,7 @@ def assert_route_bend_budget(pather: Pather, portspec: str, max_bends: int) -> N
     """
     Assert a simple render-step bend budget for route signatures.
     """
-    bend_count = sum(1 for step in pather._paths[portspec] if step.opcode == 'L' and step.start_port.rotation != step.end_port.rotation)
+    bend_count = sum(1 for step in pather._paths[portspec] if step.kind == 'bend')
     assert bend_count <= max_bends
 
 
diff --git a/masque/test/test_autotool_planning.py b/masque/test/test_autotool_planning.py
index a311985..a0979ce 100644
--- a/masque/test/test_autotool_planning.py
+++ b/masque/test/test_autotool_planning.py
@@ -2,6 +2,7 @@ from contextlib import suppress
 from typing import Any
 
 import pytest
+import numpy
 from numpy import pi
 from numpy.testing import assert_allclose
 
@@ -58,7 +59,7 @@ def rendered_offer_tree(
         ) -> Library:
     start = Port((0, 0), rotation=0, ptype=source_ptype or offer.in_ptype or "unk")
     end, data = commit_offer(offer, parameter)
-    return tool.render((RenderStep(offer.opcode, tool, start, end, data),))
+    return tool.render((RenderStep(offer.kind, tool, start, end, data),))
 
 
 def _make_transition_straight(length: float, width: float = 2, ptype: str = "wire") -> Pattern:
@@ -375,7 +376,7 @@ def wildcard_transition_tool() -> tuple[AutoTool, Library]:
     tool = (
         AutoTool(bbox_library=lib)
         .add_straight(lambda length: make_straight(length, ptype="core"), "core", "A", length_range=(0, 1e8))
-        .add_sbend(make_core_sbend, "core", "A", "B", jog_range=(-1e8, 1e8))
+        .add_sbend(make_core_sbend, "core", "A", "B", jog_range=(0, 1e8))
         .add_transition(lib.abstract("wild_core"), "WILD", "CORE")
         )
     return tool, lib
@@ -684,6 +685,24 @@ def test_autotool_add_bend_inferred_names_allow_rotational_reuse_without_mirror(
     assert_rendered_offer_endpoint_matches_plan(tool, ccw_offer, 2, "wire")
 
 
+def test_autotool_add_bend_reverse_reuse_swaps_cross_ptypes() -> None:
+    lib = Library()
+    bend = make_bend(2, ptype="core", clockwise=True)
+    bend.ports["B"].ptype = "external"
+    lib["bend"] = bend
+
+    tool = AutoTool(bbox_library=lib).add_bend(lib.abstract("bend"), mirror=False)
+
+    cw_offer = tool.primitive_offers("bend", in_ptype="core", ccw=False)[0]
+    ccw_offer = tool.primitive_offers("bend", in_ptype="external", ccw=True)[0]
+    assert (cw_offer.in_ptype, cw_offer.out_ptype) == ("core", "external")
+    assert (ccw_offer.in_ptype, ccw_offer.out_ptype) == ("external", "core")
+    assert cw_offer.commit(2).port_name == "A"
+    assert ccw_offer.commit(2).port_name == "B"
+    assert_rendered_offer_endpoint_matches_plan(tool, cw_offer, 2, "core")
+    assert_rendered_offer_endpoint_matches_plan(tool, ccw_offer, 2, "external")
+
+
 def test_autotool_add_bend_rejects_clockwise_mismatch() -> None:
     lib = Library()
     lib["bend"] = make_bend(2, ptype="wire", clockwise=True)
@@ -966,6 +985,28 @@ def test_autotool_validates_cost_before_registering_any_offers() -> None:
         AutoTool().add_sbend(unused_sbend, jog_range=(-1, 1), cost=-1)
 
 
+@pytest.mark.parametrize('length_range', [(-1, 2), (2, 1), (numpy.nan, 2), (numpy.inf, numpy.inf)])
+def test_autotool_rejects_invalid_straight_range_before_sampling(
+        length_range: tuple[float, float],
+        ) -> None:
+    def unused_straight(_length: float) -> Pattern:
+        raise AssertionError('invalid range should be rejected before metadata inference')
+
+    with pytest.raises(BuildError, match='Straight length_range'):
+        AutoTool().add_straight(unused_straight, length_range=length_range)
+
+
+@pytest.mark.parametrize('jog_range', [(-1, 2), (2, 1), (numpy.nan, 2), (numpy.inf, numpy.inf)])
+def test_autotool_rejects_invalid_sbend_range_before_sampling(
+        jog_range: tuple[float, float],
+        ) -> None:
+    def unused_sbend(_jog: float) -> Pattern:
+        raise AssertionError('invalid range should be rejected before metadata inference')
+
+    with pytest.raises(BuildError, match='S-bend jog_range'):
+        AutoTool().add_sbend(unused_sbend, jog_range=jog_range)
+
+
 def test_autotool_s_offer_singleton_jog_range_includes_both_signs() -> None:
     tool = make_sbend_tool((4, 4))
     offers = tool.primitive_offers('s', in_ptype="core")
@@ -982,9 +1023,8 @@ def test_autotool_s_offer_singleton_jog_range_includes_both_signs() -> None:
 
 
 def test_autotool_s_offer_rejects_negative_minimum_jog_range() -> None:
-    tool = make_sbend_tool((-4, 4))
-
-    assert tool.primitive_offers('s', in_ptype="core") == ()
+    with pytest.raises(BuildError, match='finite, nonnegative minimum'):
+        make_sbend_tool((-4, 4))
 
 
 def test_autotool_uturn_offer_endpoint_matches_rendered_offer() -> None:
@@ -1107,7 +1147,12 @@ def test_pather_autotool_uses_l_offer_domains(multi_bend_tool: tuple[AutoTool, L
 def test_autotool_generated_primitives_snapshot_route_options() -> None:
     markers: list[str | None] = []
 
-    def make_marked_straight(length: float, marker: str | None = None) -> Pattern:
+    def make_marked_straight(
+            length: float,
+            marker: str | None = None,
+            nested: dict[str, list[int]] | None = None,
+            ) -> Pattern:
+        _ = nested
         markers.append(marker)
         return make_straight(length, ptype="wire")
 
@@ -1115,15 +1160,16 @@ def test_autotool_generated_primitives_snapshot_route_options() -> None:
     p = Pather(Library(), tools=tool, render='deferred')
     p.ports["A"] = Port((0, 0), 0, ptype="wire")
 
-    first_options = {'marker': 'first'}
+    first_options = {'marker': 'first', 'nested': {'values': [1]}}
     p.straight("A", 5, tool_options=first_options)
     first_options['marker'] = 'mutated'
+    first_options['nested']['values'].append(2)
     p.straight("A", 6, tool_options={'marker': 'second'})
 
     first_data, second_data = (step.data for step in p._paths['A'])
     assert isinstance(first_data, AutoTool.GeneratedData)
     assert isinstance(second_data, AutoTool.GeneratedData)
-    assert dict(first_data.tool_options) == {'marker': 'first'}
+    assert dict(first_data.tool_options) == {'marker': 'first', 'nested': {'values': [1]}}
     assert dict(second_data.tool_options) == {'marker': 'second'}
 
     p.render()
@@ -1131,6 +1177,17 @@ def test_autotool_generated_primitives_snapshot_route_options() -> None:
     assert markers == ['first', 'second']
 
 
+def test_autotool_route_options_must_be_deepcopyable() -> None:
+    class NotCopyable:
+        def __deepcopy__(self, memo: dict[int, Any]) -> None:
+            _ = memo
+            raise TypeError('no copy')
+
+    tool = AutoTool().add_straight(make_straight, 'wire', 'A')
+    with pytest.raises(BuildError, match='must be deep-copyable'):
+        tool.primitive_offers('straight', marker=NotCopyable())
+
+
 def test_autotool_route_options_do_not_attach_to_reusable_bends(
         multi_bend_tool: tuple[AutoTool, Library],
         ) -> None:
diff --git a/masque/test/test_pather_constraints.py b/masque/test/test_pather_constraints.py
index 56be6ff..30e3762 100644
--- a/masque/test/test_pather_constraints.py
+++ b/masque/test/test_pather_constraints.py
@@ -6,7 +6,9 @@ import pytest
 import numpy
 from numpy import pi
 
-from masque import MinimumStatus, Pather, PortPather, Library, Port, RouteError, RouteFailurePolicy
+from masque import (
+    MinimumStatus, Pather, PortPather, Library, Port, RouteError, RouteFailurePolicy,
+    )
 from masque.builder.planner import RoutePortContext, RoutingPlanner
 from masque.builder.planner.planner import NoLegalRouteError
 from masque.builder.tools import BendOffer, PathTool, RenderStep, StraightOffer, Tool, UOffer
@@ -510,6 +512,45 @@ def test_pather_positional_bound_requires_port_rotation() -> None:
         p.trace_to('A', None, x=-5)
 
 
+def test_pather_positional_bound_rejects_non_manhattan_rotation() -> None:
+    tool = PathTool(layer='M1', width=1, ptype='wire')
+    p = Pather(Library(), tools=tool, render='deferred')
+    p.pattern.ports['A'] = Port((0, 0), rotation=pi / 4, ptype='wire')
+
+    with pytest.raises(BuildError, match='nearly Manhattan'):
+        p.trace_to('A', None, p=-5)
+
+
+def test_pather_positional_bound_accepts_nearly_manhattan_rotation() -> None:
+    tool = PathTool(layer='M1', width=1, ptype='wire')
+    p = Pather(Library(), tools=tool, render='deferred')
+    p.pattern.ports['A'] = Port((0, 0), rotation=1e-10, ptype='wire')
+
+    p.trace_to('A', None, x=-5)
+    assert numpy.allclose(p.pattern.ports['A'].offset, (-5, -5e-10), atol=1e-8)
+
+
+def test_pather_bundle_position_bound_rejects_non_manhattan_rotation() -> None:
+    tool = PathTool(layer='M1', width=1, ptype='wire')
+    p = Pather(Library(), tools=tool, render='deferred')
+    p.pattern.ports['A'] = Port((0, 0), rotation=pi / 4, ptype='wire')
+    p.pattern.ports['B'] = Port((1, 1), rotation=pi / 4, ptype='wire')
+
+    with pytest.raises(BuildError, match='nearly Manhattan'):
+        p.trace(['A', 'B'], None, pmin=-5)
+
+
+def test_pather_bundle_extension_bound_allows_non_manhattan_rotation() -> None:
+    tool = PathTool(layer='M1', width=1, ptype='wire')
+    p = Pather(Library(), tools=tool, render='deferred')
+    p.pattern.ports['A'] = Port((0, 0), rotation=pi / 4, ptype='wire')
+    p.pattern.ports['B'] = Port((1, 1), rotation=pi / 4, ptype='wire')
+
+    p.trace(['A', 'B'], None, emin=5)
+    assert len(p._paths['A']) == 1
+    assert len(p._paths['B']) == 1
+
+
 def test_pather_jog_omitted_length_uses_minimum_length_route() -> None:
     lib = Library()
     tool = PathTool(layer='M1', width=1, ptype='wire')
diff --git a/masque/test/test_pather_core.py b/masque/test/test_pather_core.py
index fca27c8..93f874c 100644
--- a/masque/test/test_pather_core.py
+++ b/masque/test/test_pather_core.py
@@ -327,6 +327,22 @@ def test_selection_management() -> None:
     assert 'B' not in p.pattern.ports
     assert pp.ports == []
 
+
+@pytest.mark.parametrize('action', ['plug', 'plugged', 'rename', 'mark', 'fork'])
+def test_empty_selection_exact_one_operations_raise_build_error(action: str) -> None:
+    p = Pather(Library())
+    pp = p.at([])
+    operations = {
+        'plug': lambda: pp.plug('unused', 'A'),
+        'plugged': lambda: pp.plugged('A'),
+        'rename': lambda: pp.rename('new'),
+        'mark': lambda: pp.mark('new'),
+        'fork': lambda: pp.fork('new'),
+        }
+
+    with pytest.raises(BuildError, match='expected exactly one'):
+        operations[action]()
+
 def test_mark_fork() -> None:
     lib = Library()
     p = Pather(lib)
diff --git a/masque/test/test_pather_primitive_offers.py b/masque/test/test_pather_primitive_offers.py
index 0ab7ea4..b4ec414 100644
--- a/masque/test/test_pather_primitive_offers.py
+++ b/masque/test/test_pather_primitive_offers.py
@@ -6,8 +6,9 @@ import numpy
 import pytest
 from numpy import pi
 
-from masque import Library, Path, Port, Pather
+from masque import Library, Path, Port, Pather, ToolContractError
 from masque.builder.planner import RoutingPlanner
+from masque.builder.planner.planner import Solver, SolverRequest
 from masque.builder.tools import (
     BendOffer,
     PathTool,
@@ -46,6 +47,81 @@ class PlanningOnlyTool(Tool):
         return tree
 
 
+def test_tool_contract_error_is_fatal_even_when_an_alternate_offer_exists() -> None:
+    class BrokenTool(PlanningOnlyTool):
+        def primitive_offers(self, kind, *, in_ptype=None, out_ptype=None, **kwargs):  # noqa: ANN001,ANN202,ARG002
+            if kind != 'straight':
+                return ()
+            return (
+                StraightOffer(
+                    in_ptype='wire',
+                    out_ptype='wire',
+                    endpoint_planner=lambda length: Port((length, 0), pi, ptype='wrong'),
+                    commit_planner=lambda length: length,
+                    ),
+                StraightOffer.generated('wire', lambda length: length),
+                )
+
+    pather = Pather(
+        Library(),
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools=BrokenTool(),
+        render='deferred',
+        )
+    with pytest.raises(ToolContractError, match='declared offer out_ptype'):
+        pather.straight('A', 5)
+
+
+def test_callback_build_error_remains_recoverable_candidate_rejection() -> None:
+    class RecoverableTool(PlanningOnlyTool):
+        def primitive_offers(self, kind, *, in_ptype=None, out_ptype=None, **kwargs):  # noqa: ANN001,ANN202,ARG002
+            if kind != 'straight':
+                return ()
+
+            def rejected(length: float) -> Port:
+                raise BuildError(f'unsupported length {length}')
+
+            return (
+                StraightOffer(
+                    in_ptype='wire',
+                    out_ptype='wire',
+                    endpoint_planner=rejected,
+                    commit_planner=lambda length: length,
+                    ),
+                StraightOffer.generated('wire', lambda length: length),
+                )
+
+    pather = Pather(
+        Library(),
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools=RecoverableTool(),
+        render='deferred',
+        )
+    pather.straight('A', 5)
+    assert numpy.allclose(pather.ports['A'].offset, (-5, 0))
+
+
+def test_solver_offer_cache_accepts_unhashable_request_tool_options() -> None:
+    class CountingTool(PlanningOnlyTool):
+        calls = 0
+
+        def primitive_offers(self, kind, *, in_ptype=None, out_ptype=None, **kwargs):  # noqa: ANN001,ANN202,ARG002
+            self.calls += 1
+            assert kwargs == {'nested': []}
+            return ()
+
+    tool = CountingTool()
+    solver = Solver(SolverRequest(
+        family='straight',
+        tool=tool,
+        in_ptype='wire',
+        tool_options={'nested': []},
+        ))
+    solver.primitive_offers('straight', 'wire')
+    solver.primitive_offers('straight', 'wire')
+    assert tool.calls == 1
+
+
 def test_tool_requires_primitive_offers_override() -> None:
     class RenderOnlyTool(Tool):
         def render(self, batch, *, port_names=('A', 'B'), **kwargs) -> Library:      # noqa: ANN001,ANN202,ARG002
@@ -100,7 +176,19 @@ def test_offer_canonicalize_parameter_rejects_non_finite_parameter(value: float)
 
 def test_offer_canonicalize_parameter_rejects_reversed_domain() -> None:
     with pytest.raises(BuildError, match='lower bound must not exceed upper bound'):
-        canonicalize_offer_parameter(3, (10, 0))
+        StraightOffer(in_ptype='wire', out_ptype='wire', length_domain=(10, 0))
+
+
+@pytest.mark.parametrize('domain', [(numpy.nan, 1), (1, numpy.nan), (numpy.inf, numpy.inf)])
+def test_offer_rejects_invalid_domain_at_construction(domain: tuple[float, float]) -> None:
+    with pytest.raises(BuildError, match='domain'):
+        StraightOffer(in_ptype='wire', out_ptype='wire', length_domain=domain)
+
+
+@pytest.mark.parametrize('domain', [(-1, 2), (-numpy.inf, 2)])
+def test_length_offer_requires_finite_nonnegative_minimum(domain: tuple[float, float]) -> None:
+    with pytest.raises(BuildError, match='finite, nonnegative minimum'):
+        StraightOffer(in_ptype='wire', out_ptype='wire', length_domain=domain)
 
 
 def test_ptype_match_distinguishes_exact_wildcard_and_mismatch() -> None:
@@ -653,7 +741,7 @@ def test_solver_rejects_rotation_impossible_candidates_before_parameter_solving(
     p.straight('A', 7)
 
     assert p._paths['A'][0].data == {'kind': 'valid', 'length': 7}
-    assert invalid_parameters == [0.0, 0.0]
+    assert invalid_parameters == [0.0]
 
 
 def test_pather_commits_only_selected_offer() -> None:
diff --git a/masque/test/test_pather_rendering.py b/masque/test/test_pather_rendering.py
index 3c50e3b..70360ed 100644
--- a/masque/test/test_pather_rendering.py
+++ b/masque/test/test_pather_rendering.py
@@ -6,7 +6,7 @@ import numpy
 from numpy import pi
 from numpy.testing import assert_allclose
 
-from ..builder import Pather, RouteError
+from ..builder import Pather, RouteError, ToolContractError
 from ..builder.tools import PathTool, RenderStep, StraightOffer, Tool
 from ..error import BuildError
 from ..library import Library
@@ -307,7 +307,7 @@ def test_pathtool_bend_offer_render_geometry_matches_ports() -> None:
     offer = tool.primitive_offers("bend", in_ptype="wire", ccw=True)[0]
     start = Port((0, 0), rotation=pi, ptype="wire")
     end = offer.endpoint_at(1)
-    tree = tool.render((RenderStep(offer.opcode, tool, start, end, offer.commit(1)),))
+    tree = tool.render((RenderStep(offer.kind, tool, start, end, offer.commit(1)),))
     pat = tree.top_pattern()
     path_shape = cast("Path", pat.shapes[(1, 0)][0])
 
@@ -321,13 +321,13 @@ def test_pathtool_s_offer_render_geometry_matches_ports() -> None:
     offer = tool.primitive_offers("s", in_ptype="wire")[0]
     start = Port((0, 0), rotation=pi, ptype="wire")
     end = offer.endpoint_at(4)
-    tree = tool.render((RenderStep(offer.opcode, tool, start, end, offer.commit(4)),))
+    tree = tool.render((RenderStep(offer.kind, tool, start, end, offer.commit(4)),))
     pat = tree.top_pattern()
     path_shape = cast("Path", pat.shapes[(1, 0)][0])
 
     assert_allclose(path_shape.vertices, [[0, 0], [1, 0], [1, 4], [2, 4]], atol=1e-10)
     assert_allclose(pat.ports["B"].offset, [2, 4], atol=1e-10)
-    assert_allclose(pat.ports["B"].rotation, 0, atol=1e-10)
+    assert_allclose(pat.ports["B"].rotation, pi, atol=1e-10)
 
 def test_deferred_render_uturn_fallback() -> None:
     lib = Library()
@@ -362,7 +362,7 @@ def test_pather_render_auto_renames_single_use_tool_children() -> None:
             tree = Library()
             top = Pattern(ports={
                 port_names[0]: Port((0, 0), 0, ptype='wire'),
-                port_names[1]: Port((length, 0), 0, ptype='wire'),
+                port_names[1]: Port((length, 0), pi, ptype='wire'),
                 })
             child = Pattern(annotations={'batch': [len(batch)]})
             top.ref('_seg')
@@ -402,7 +402,7 @@ def test_custom_tool_render_preserves_segment_subtrees() -> None:
             tree = Library()
             top = Pattern(ports={
                 port_names[0]: Port((0, 0), 0, ptype='wire'),
-                port_names[1]: Port((length, 0), 0, ptype='wire'),
+                    port_names[1]: Port((length, 0), pi, ptype='wire'),
                 })
             child = Pattern(annotations={'length': [length]})
             top.ref('_seg')
@@ -479,7 +479,7 @@ def test_pather_render_allows_missing_non_single_use_tool_refs() -> None:
             tree = Library()
             top = Pattern(ports={
                 port_names[0]: Port((0, 0), 0, ptype='wire'),
-                port_names[1]: Port((length, 0), 0, ptype='wire'),
+                    port_names[1]: Port((length, 0), pi, ptype='wire'),
                 })
             top.ref('shared')
             tree['_top'] = top
@@ -530,6 +530,52 @@ def test_pather_render_rejects_output_port_that_misses_planned_endpoint(append:
     assert not p.pattern.refs
     assert not lib
 
+
+def test_pather_render_rejects_opposite_output_rotation() -> None:
+    class WrongRotationTool(Tool):
+        def primitive_offers(self, kind, *, in_ptype=None, out_ptype=None, **kwargs):  # noqa: ANN001,ANN202,ARG002
+            if kind != 'straight':
+                return ()
+            return (StraightOffer.generated('wire', lambda length: length),)
+
+        def render(self, batch, *, port_names=('A', 'B'), **kwargs) -> Library:  # noqa: ANN001,ANN202,ARG002
+            length = batch[0].data
+            tree = Library()
+            tree['_top'] = Pattern(ports={
+                port_names[0]: Port((0, 0), 0, ptype='wire'),
+                port_names[1]: Port((length, 0), 0, ptype='wire'),
+                })
+            return tree
+
+    p = Pather(Library(), tools=WrongRotationTool(), render='deferred')
+    p.pattern.ports['A'] = Port((0, 0), rotation=0, ptype='wire')
+    p.straight('A', 10)
+
+    with pytest.raises(ToolContractError, match='does not match planned endpoint'):
+        p.render()
+
+
+def test_pather_render_allows_unspecified_output_rotation() -> None:
+    class UnspecifiedRotationTool(Tool):
+        def primitive_offers(self, kind, *, in_ptype=None, out_ptype=None, **kwargs):  # noqa: ANN001,ANN202,ARG002
+            if kind != 'straight':
+                return ()
+            return (StraightOffer.generated('wire', lambda length: length),)
+
+        def render(self, batch, *, port_names=('A', 'B'), **kwargs) -> Library:  # noqa: ANN001,ANN202,ARG002
+            length = batch[0].data
+            tree = Library()
+            tree['_top'] = Pattern(ports={
+                port_names[0]: Port((0, 0), 0, ptype='wire'),
+                port_names[1]: Port((length, 0), None, ptype='wire'),
+                })
+            return tree
+
+    p = Pather(Library(), tools=UnspecifiedRotationTool(), render='deferred')
+    p.pattern.ports['A'] = Port((0, 0), rotation=0, ptype='wire')
+    p.straight('A', 10)
+    p.render()
+
 @pytest.mark.parametrize('append', [True, False])
 def test_pather_render_rejects_output_port_with_wrong_ptype(append: bool) -> None:
     class WrongPtypeTool(Tool):