From 306f0b4c83573813c6aa5068ae62ce2fdb00d5b1 Mon Sep 17 00:00:00 2001
From: Jan Petykiewicz <jan@mpxd.net>
Date: Sun, 12 Jul 2026 15:18:00 -0700
Subject: [PATCH 1/4] [Pather] handle empty or duplicate port lists

---
 masque/builder/pather.py | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/masque/builder/pather.py b/masque/builder/pather.py
index cbf87f4..877cd6d 100644
--- a/masque/builder/pather.py
+++ b/masque/builder/pather.py
@@ -159,6 +159,16 @@ class Pather(PortList):
 
     def _route_contexts(self, portspecs: Sequence[str]) -> tuple[RoutePortContext, ...]:
         """Snapshot several ports in request order for bundle planning."""
+        if not portspecs:
+            raise BuildError('Routing requires at least one port')
+        seen: set[str] = set()
+        duplicates: set[str] = set()
+        for portspec in portspecs:
+            if portspec in seen:
+                duplicates.add(portspec)
+            seen.add(portspec)
+        if duplicates:
+            raise BuildError(f'Routing port names must be unique; got duplicates: {sorted(duplicates)}')
         return tuple(self._route_context(portspec) for portspec in portspecs)
 
     @property

From 09b131026fd58522bc1b0e0dffa7daefdbc6f206 Mon Sep 17 00:00:00 2001
From: Jan Petykiewicz <jan@mpxd.net>
Date: Sun, 12 Jul 2026 15:26:24 -0700
Subject: [PATCH 2/4] [Tool] tighten constraints on tool parameters

---
 masque/builder/tools.py | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/masque/builder/tools.py b/masque/builder/tools.py
index 40097a0..702fe7c 100644
--- a/masque/builder/tools.py
+++ b/masque/builder/tools.py
@@ -15,6 +15,15 @@ jog is left of travel; returned endpoint ports describe the primitive output in
 that same local frame. The planner transforms selected endpoints into layout
 coordinates only after a complete route has been chosen.
 
+Primitive parameters are also the basis for route-failure diagnostics. Tools
+must keep endpoint topology stable across each offer domain: length-like
+Straight/Bend offers use a finite, attained, nonnegative minimum and advance
+their local x coordinate by the selected length; S/U offers move their local y
+coordinate by the selected jog. Endpoint rotation and output ptype must not
+vary with the parameter and must agree with the concrete offer kind and its
+declared `out_ptype`. These are Tool contract requirements rather than
+exhaustively runtime-checked properties.
+
 Tool authors should treat offer planning callbacks as pure descriptions. The
 solver may call `endpoint_at()`, `cost_at()`, and `bbox_at()` many times while
 enumerating candidate compositions, ptype adapters, and parameter solutions.
@@ -166,6 +175,13 @@ class PrimitiveOffer(ABC):
     Parameter domains are half-open `[min, max)` ranges, except `(value, value)`
     is a closed singleton for fixed-size primitives. `None` and `"unk"` ptypes
     are wildcards; incompatible concrete ptypes are rejected by `Pather`.
+
+    Custom offers must have stable endpoint ptype and rotation throughout their
+    domain. Straight/Bend length domains must have a finite, attained,
+    nonnegative minimum and produce local `x == parameter`; S/U offers produce
+    local `y == parameter`. The planner relies on these invariants when it
+    diagnoses whether a failed constrained route has a preferred minimum-length
+    alternative or is unsupported at every legal length.
     """
     in_ptype: str | None
     out_ptype: str | None

From 3a3cd854a5a136d01bd9215daa6dfd4bedad4172 Mon Sep 17 00:00:00 2001
From: Jan Petykiewicz <jan@mpxd.net>
Date: Sun, 12 Jul 2026 15:27:14 -0700
Subject: [PATCH 3/4] [Pather/Planner] Improve error reporting

---
 masque/__init__.py                     |   2 +
 masque/builder/__init__.py             |   5 +
 masque/builder/error.py                |  65 +++++
 masque/builder/planner/planner.py      | 330 +++++++++++++++++++++++--
 masque/builder/utils.py                |  67 +++--
 masque/test/test_builder.py            |  44 ++++
 masque/test/test_pather_constraints.py | 302 +++++++++++++++++++++-
 masque/test/test_pather_core.py        |  13 +-
 masque/test/test_pather_rendering.py   |   7 +-
 9 files changed, 777 insertions(+), 58 deletions(-)
 create mode 100644 masque/builder/error.py

diff --git a/masque/__init__.py b/masque/__init__.py
index b5dddde..6598e2f 100644
--- a/masque/__init__.py
+++ b/masque/__init__.py
@@ -82,6 +82,8 @@ from .abstract import Abstract as Abstract
 from .builder import (
     Tool as Tool,
     Pather as Pather,
+    RouteError as RouteError,
+    RouteFailureDetails as RouteFailureDetails,
     RenderStep as RenderStep,
     AutoTool as AutoTool,
     PathTool as PathTool,
diff --git a/masque/builder/__init__.py b/masque/builder/__init__.py
index 5bd3914..76fd1f8 100644
--- a/masque/builder/__init__.py
+++ b/masque/builder/__init__.py
@@ -41,6 +41,11 @@ from .pather import (
     Pather as Pather,
     PortPather as PortPather,
 )
+from .error import (
+    RouteError as RouteError,
+    RouteFailureDetails as RouteFailureDetails,
+    RouteOperation as RouteOperation,
+)
 from .utils import ell as ell
 from .tools import (
     Tool as Tool,
diff --git a/masque/builder/error.py b/masque/builder/error.py
new file mode 100644
index 0000000..e8f00fd
--- /dev/null
+++ b/masque/builder/error.py
@@ -0,0 +1,65 @@
+"""Public routing failure diagnostics."""
+from typing import Any, Literal
+from collections.abc import Mapping
+from dataclasses import dataclass
+from pprint import pformat
+from types import MappingProxyType
+
+from ..error import BuildError
+
+
+RouteOperation = Literal['trace', 'trace_to', 'jog', 'uturn']
+
+
+@dataclass(frozen=True, slots=True)
+class RouteFailureDetails:
+    """Structured context for a failed Pather routing request."""
+
+    operation: RouteOperation
+    portspec: str
+    in_ptype: str | None
+    out_ptype: str | None
+    request: Mapping[str, Any]
+    resolved_length: float | None
+    resolved_jog: float | None
+    minimum_length: float | None
+    minimum_attempted: bool
+    minimum_exhausted: bool
+    cause: str
+    minimum_cause: str | None = None
+
+    def __post_init__(self) -> None:
+        object.__setattr__(self, 'request', MappingProxyType(dict(self.request)))
+
+
+class RouteError(BuildError):
+    """A route-selection failure with structured request diagnostics."""
+
+    details: RouteFailureDetails
+    fatal: bool
+
+    def __init__(self, details: RouteFailureDetails, *, fatal: bool = False) -> None:
+        self.details = details
+        self.fatal = fatal
+        if not details.minimum_attempted:
+            minimum = 'not evaluated'
+        elif details.minimum_length is not None:
+            minimum = f'{details.minimum_length:g}'
+        elif details.minimum_exhausted:
+            minimum = 'unavailable (no legal route exists at any length)'
+        else:
+            minimum = 'unavailable (minimum-length calculation failed)'
+
+        lines = [
+            f'Unable to plan {details.operation} route for port {details.portspec!r}:',
+            f'  in_ptype: {details.in_ptype!r}',
+            f'  out_ptype: {details.out_ptype!r}',
+            f'  request: {pformat(dict(details.request), compact=True)}',
+            f'  resolved_length: {details.resolved_length!r}',
+            f'  resolved_jog: {details.resolved_jog!r}',
+            f'  preferred_minimum_length: {minimum}',
+            f'  cause: {details.cause}',
+            ]
+        if details.minimum_cause is not None:
+            lines.append(f'  minimum_failure: {details.minimum_cause}')
+        super().__init__('\n'.join(lines))
diff --git a/masque/builder/planner/planner.py b/masque/builder/planner/planner.py
index 913758e..548d429 100644
--- a/masque/builder/planner/planner.py
+++ b/masque/builder/planner/planner.py
@@ -22,7 +22,7 @@ from __future__ import annotations
 # ruff: noqa: ANN401,PLR0912,PLR0913,PLR0915,TC001,TC002,TC003
 
 from collections.abc import Iterable, Mapping, Sequence
-from dataclasses import dataclass
+from dataclasses import dataclass, replace
 from itertools import combinations
 from math import cos, isclose as math_isclose, sin
 from typing import Any, Literal
@@ -43,6 +43,7 @@ from ..tools import (
     StraightOffer,
     Tool,
     )
+from ..error import RouteError, RouteFailureDetails, RouteOperation
 from ..utils import ell
 from . import bounds as planner_bounds
 from .interface import (
@@ -56,6 +57,10 @@ from .interface import (
 RouteTieBreakStrategy = Literal['straight_first', 'turn_first']
 
 
+class NoLegalRouteError(BuildError):
+    """Internal marker for exhaustive candidate-selection failure."""
+
+
 def validate_strategy(strategy: RouteTieBreakStrategy | str) -> RouteTieBreakStrategy:
     """Return a supported route tie-break strategy or raise a routing error."""
     if strategy in ('straight_first', 'turn_first'):
@@ -396,9 +401,11 @@ class Solver:
             if errors:
                 last_error = errors[-1]
                 if self.request.route_name in str(last_error):
-                    raise last_error
-                raise BuildError(f'{self.request.route_name} route is unsupported: {last_error}') from last_error
-            raise BuildError(f'No legal primitive offer for {self.request.route_name}')
+                    raise NoLegalRouteError(str(last_error)) from last_error
+                raise NoLegalRouteError(
+                    f'{self.request.route_name} route is unsupported: {last_error}'
+                    ) from last_error
+            raise NoLegalRouteError(f'No legal primitive offer for {self.request.route_name}')
 
         return min(
             candidates,
@@ -1038,6 +1045,9 @@ class RoutingPlanner:
             self,
             family: PrimitiveKind,
             context: RoutePortContext,
+            operation: RouteOperation | None = None,
+            diagnostic_request: Mapping[str, Any] | None = None,
+            /,
             *,
             length: float | None = None,
             jog: float | None = None,
@@ -1049,6 +1059,32 @@ class RoutingPlanner:
             **kwargs: Any,
             ) -> RouteLeg:
         """Solve one route leg and attach it to its source Pather context."""
+        if operation is None:
+            if family in ('straight', 'bend'):
+                operation = 'trace'
+            elif family == 's':
+                operation = 'jog'
+            else:
+                operation = 'uturn'
+        if diagnostic_request is None:
+            diagnostic_request = {}
+
+        if length is not None and (not numpy.isfinite(length) or length < 0):
+            details = RouteFailureDetails(
+                operation=operation,
+                portspec=context.portspec,
+                in_ptype=context.port.ptype,
+                out_ptype=kwargs.get('out_ptype'),
+                request=diagnostic_request,
+                resolved_length=float(length),
+                resolved_jog=None if jog is None else float(jog),
+                minimum_length=None,
+                minimum_attempted=False,
+                minimum_exhausted=False,
+                cause='Resolved route length must be finite and nonnegative',
+                )
+            raise RouteError(details, fatal=True)
+
         request = self.route_request(
             family=family,
             context=context,
@@ -1062,10 +1098,47 @@ class RoutingPlanner:
             )
         try:
             candidate = self.solver_for_request(request).solve()
-        except BuildError as err:
-            if family == 'u' and length is None and not getattr(err, 'fatal', False):
-                raise BuildError('No legal primitive offer for omitted-length U-turn') from err
-            raise
+        except NoLegalRouteError as err:
+            cause = (
+                'No legal primitive offer for omitted-length U-turn'
+                if family == 'u' and length is None
+                else str(err)
+                )
+
+            minimum_length: float | None = None
+            minimum_cause: str | None = None
+            minimum_exhausted = False
+            if length is None:
+                minimum_cause = cause
+                minimum_exhausted = True
+            else:
+                minimum_request = replace(request, length=None)
+                try:
+                    minimum_candidate = self.solver_for_request(minimum_request).solve()
+                    minimum_length = minimum_candidate.public_length
+                except NoLegalRouteError as minimum_err:
+                    minimum_cause = str(minimum_err)
+                    minimum_exhausted = True
+                except Exception as minimum_err:
+                    if route_error_is_fatal(minimum_err):
+                        raise
+                    minimum_cause = str(minimum_err)
+
+            details = RouteFailureDetails(
+                operation=operation,
+                portspec=context.portspec,
+                in_ptype=context.port.ptype,
+                out_ptype=request.out_ptype,
+                request=diagnostic_request,
+                resolved_length=None if length is None else float(length),
+                resolved_jog=None if jog is None else float(jog),
+                minimum_length=minimum_length,
+                minimum_attempted=True,
+                minimum_exhausted=minimum_exhausted,
+                cause=cause,
+                minimum_cause=minimum_cause,
+                )
+            raise RouteError(details) from err
         return self.route_leg_from_candidate(context, candidate, plug_into=plug_into)
 
     def prepared_route_action_from_leg(
@@ -1129,25 +1202,87 @@ class RoutingPlanner:
             ) -> PreparedRouteResult:
         """Plan straight or single-bend traces, including `each` and bundle-bound modes."""
         route_bounds = dict(bounds)
+        request_details = {'ccw': ccw, **{
+            key: value for key, value in route_bounds.items() if value is not None
+            }}
+        if length is not None:
+            request_details['length'] = length
+        if spacing is not None:
+            request_details['spacing'] = spacing
+        if strategy is not None:
+            request_details['strategy'] = strategy
+        operation: RouteOperation = 'trace'
+        diagnostic_request = request_details
+        return self._plan_trace_route(
+            contexts,
+            ccw,
+            length,
+            operation,
+            diagnostic_request,
+            spacing=spacing,
+            strategy=strategy,
+            **route_bounds,
+            )
+
+    def _plan_trace_route(
+            self,
+            contexts: Sequence[RoutePortContext],
+            ccw: SupportsBool | None,
+            length: float | None,
+            operation: RouteOperation,
+            diagnostic_request: Mapping[str, Any],
+            /,
+            *,
+            spacing: float | ArrayLike | None,
+            strategy: RouteTieBreakStrategy | str | None,
+            **route_bounds: Any,
+            ) -> PreparedRouteResult:
         portspec = tuple(context.portspec for context in contexts)
         planner_bounds.validate_trace_args(portspec, length=length, spacing=spacing, bounds=route_bounds)
         family: Literal['straight', 'bend'] = 'straight' if ccw is None else 'bend'
         if length is not None:
-            leg = self.plan_leg(family, contexts[0], length=length, ccw=ccw, strategy=strategy, **route_bounds)
+            leg = self.plan_leg(
+                family,
+                contexts[0],
+                operation,
+                diagnostic_request,
+                length=length,
+                ccw=ccw,
+                strategy=strategy,
+                **route_bounds,
+                )
             return self.prepared_result_from_legs((leg,))
 
         if route_bounds.get('each') is not None:
             each = route_bounds.pop('each')
             return PreparedRouteResult(tuple(
                 self.prepared_route_action_from_leg(
-                    self.plan_leg(family, context, length=each, ccw=ccw, strategy=strategy, **route_bounds),
+                    self.plan_leg(
+                        family,
+                        context,
+                        operation,
+                        diagnostic_request,
+                        length=each,
+                        ccw=ccw,
+                        strategy=strategy,
+                        **route_bounds,
+                        ),
                     )
                 for context in contexts
                 ))
 
         bundle_bounds = planner_bounds.present_bundle_bounds(route_bounds)
         if not bundle_bounds:
-            leg = self.plan_leg(family, contexts[0], length=None, ccw=ccw, strategy=strategy, **route_bounds)
+            leg = self.plan_leg(
+                family,
+                contexts[0],
+                operation,
+                diagnostic_request,
+                length=None,
+                ccw=ccw,
+                strategy=strategy,
+                **route_bounds,
+                )
             return self.prepared_result_from_legs((leg,))
 
         bound_type = bundle_bounds[0]
@@ -1164,7 +1299,16 @@ class RoutingPlanner:
         actions = []
         for port_name, route_length in extensions.items():
             context = next(context for context in contexts if context.portspec == port_name)
-            leg = self.plan_leg(family, context, length=route_length, ccw=ccw, strategy=strategy, **route_bounds)
+            leg = self.plan_leg(
+                family,
+                context,
+                operation,
+                diagnostic_request,
+                length=route_length,
+                ccw=ccw,
+                strategy=strategy,
+                **route_bounds,
+                )
             actions.append(self.prepared_route_action_from_leg(leg))
         return PreparedRouteResult(tuple(actions))
 
@@ -1179,6 +1323,37 @@ class RoutingPlanner:
             ) -> PreparedRouteResult:
         """Plan `trace_to()` by resolving positional targets or delegating to `trace()` modes."""
         route_bounds = dict(bounds)
+        request_details = {'ccw': ccw, **{
+            key: value for key, value in route_bounds.items() if value is not None
+            }}
+        if spacing is not None:
+            request_details['spacing'] = spacing
+        if strategy is not None:
+            request_details['strategy'] = strategy
+        operation: RouteOperation = 'trace_to'
+        diagnostic_request = request_details
+        return self._plan_trace_to_route(
+            contexts,
+            ccw,
+            operation,
+            diagnostic_request,
+            spacing=spacing,
+            strategy=strategy,
+            **route_bounds,
+            )
+
+    def _plan_trace_to_route(
+            self,
+            contexts: Sequence[RoutePortContext],
+            ccw: SupportsBool | None,
+            operation: RouteOperation,
+            diagnostic_request: Mapping[str, Any],
+            /,
+            *,
+            spacing: float | ArrayLike | None,
+            strategy: RouteTieBreakStrategy | str | None,
+            **route_bounds: Any,
+            ) -> PreparedRouteResult:
         if len(contexts) == 1:
             resolved = planner_bounds.resolved_position_bound(contexts[0].port, route_bounds, allow_length=False)
         else:
@@ -1186,7 +1361,16 @@ class RoutingPlanner:
             if any(route_bounds.get(key) is not None for key in planner_bounds.POSITION_KEYS):
                 raise BuildError('Position bounds only allowed with a single port')
         if resolved is None:
-            return self.plan_trace_route(contexts, ccw, spacing=spacing, strategy=strategy, **route_bounds)
+            return self._plan_trace_route(
+                contexts,
+                ccw,
+                route_bounds.pop('length', None),
+                operation,
+                diagnostic_request,
+                spacing=spacing,
+                strategy=strategy,
+                **route_bounds,
+                )
 
         planner_bounds.validate_trace_to_positional_args(spacing=spacing, bounds=route_bounds)
         _key, _value, length = resolved
@@ -1196,7 +1380,16 @@ class RoutingPlanner:
             if key not in planner_bounds.POSITION_KEYS and key != 'length'
         }
         family: Literal['straight', 'bend'] = 'straight' if ccw is None else 'bend'
-        leg = self.plan_leg(family, contexts[0], length=length, ccw=ccw, strategy=strategy, **other_bounds)
+        leg = self.plan_leg(
+            family,
+            contexts[0],
+            operation,
+            diagnostic_request,
+            length=length,
+            ccw=ccw,
+            strategy=strategy,
+            **other_bounds,
+            )
         return self.prepared_result_from_legs((leg,))
 
     def plan_jog_route(
@@ -1210,8 +1403,28 @@ class RoutingPlanner:
             **bounds: Any,
             ) -> PreparedRouteResult:
         """Plan S-bend routes for single ports or spaced bundles."""
+        request_details = {'offset': offset, **{
+            key: value for key, value in bounds.items() if value is not None
+            }}
+        if length is not None:
+            request_details['length'] = length
+        if spacing is not None:
+            request_details['spacing'] = spacing
+        if strategy is not None:
+            request_details['strategy'] = strategy
+        operation: RouteOperation = 'jog'
+        diagnostic_request = request_details
         if numpy.isclose(offset, 0):
-            return self.plan_trace_to_route(contexts, None, length=length, spacing=spacing, strategy=strategy, **bounds)
+            return self._plan_trace_to_route(
+                contexts,
+                None,
+                operation,
+                diagnostic_request,
+                length=length,
+                spacing=spacing,
+                strategy=strategy,
+                **bounds,
+                )
         route_bounds = dict(bounds)
         portspec = tuple(context.portspec for context in contexts)
         planner_bounds.validate_jog_args(portspec, length=length, spacing=spacing, bounds=route_bounds)
@@ -1224,9 +1437,28 @@ class RoutingPlanner:
         if len(contexts) > 1:
             return PreparedRouteResult(tuple(
                 self.prepared_route_action_from_leg(leg)
-                for leg in self.plan_su_bundle_routes('s', contexts, offset, length, spacing, strategy=strategy, **other_bounds)
+                for leg in self.plan_su_bundle_routes(
+                    's',
+                    contexts,
+                    offset,
+                    length,
+                    spacing,
+                    operation,
+                    diagnostic_request,
+                    strategy=strategy,
+                    **other_bounds,
+                    )
                 ))
-        leg = self.plan_leg('s', contexts[0], length=length, jog=offset, strategy=strategy, **other_bounds)
+        leg = self.plan_leg(
+            's',
+            contexts[0],
+            operation,
+            diagnostic_request,
+            length=length,
+            jog=offset,
+            strategy=strategy,
+            **other_bounds,
+            )
         return self.prepared_result_from_legs((leg,))
 
     def plan_uturn_route(
@@ -1241,14 +1473,44 @@ class RoutingPlanner:
             ) -> PreparedRouteResult:
         """Plan U-turn routes for single ports or spaced bundles."""
         route_bounds = dict(bounds)
+        request_details = {'offset': offset, **{
+            key: value for key, value in route_bounds.items() if value is not None
+            }}
+        if length is not None:
+            request_details['length'] = length
+        if spacing is not None:
+            request_details['spacing'] = spacing
+        if strategy is not None:
+            request_details['strategy'] = strategy
+        operation: RouteOperation = 'uturn'
+        diagnostic_request = request_details
         portspec = tuple(context.portspec for context in contexts)
         planner_bounds.validate_uturn_args(portspec, spacing=spacing, bounds=route_bounds)
         if len(contexts) > 1:
             return PreparedRouteResult(tuple(
                 self.prepared_route_action_from_leg(leg)
-                for leg in self.plan_su_bundle_routes('u', contexts, offset, length, spacing, strategy=strategy, **route_bounds)
+                for leg in self.plan_su_bundle_routes(
+                    'u',
+                    contexts,
+                    offset,
+                    length,
+                    spacing,
+                    operation,
+                    diagnostic_request,
+                    strategy=strategy,
+                    **route_bounds,
+                    )
                 ))
-        leg = self.plan_leg('u', contexts[0], length=length, jog=offset, strategy=strategy, **route_bounds)
+        leg = self.plan_leg(
+            'u',
+            contexts[0],
+            operation,
+            diagnostic_request,
+            length=length,
+            jog=offset,
+            strategy=strategy,
+            **route_bounds,
+            )
         return self.prepared_result_from_legs((leg,))
 
     def plan_su_bundle_routes(
@@ -1258,6 +1520,9 @@ class RoutingPlanner:
             offset: float,
             length: float | None,
             spacing: float | ArrayLike | None,
+            operation: RouteOperation,
+            diagnostic_request: Mapping[str, Any],
+            /,
             *,
             strategy: RouteTieBreakStrategy | str | None = None,
             **kwargs: Any,
@@ -1270,14 +1535,32 @@ class RoutingPlanner:
         and offset so all legs can be planned independently.
         """
         if len(contexts) == 1:
-            return (self.plan_leg(kind, contexts[0], length=length, jog=offset, strategy=strategy, **kwargs),)
+            return (self.plan_leg(
+                kind,
+                contexts[0],
+                operation,
+                diagnostic_request,
+                length=length,
+                jog=offset,
+                strategy=strategy,
+                **kwargs,
+                ),)
         route_name = 'jog' if kind == 's' else 'uturn'
         if kind == 'u' and is_close(offset, 0):
             raise BuildError('multi-port uturn() requires nonzero offset to determine bundle ordering')
         contexts_by_name = {context.portspec: context for context in contexts}
         initial_specs = planner_bounds.su_bundle_specs(contexts, offset, 0, spacing, route_name=route_name)
         anchor_portspec, _anchor_length, _anchor_offset = initial_specs[0]
-        anchor = self.plan_leg(kind, contexts_by_name[anchor_portspec], length=length, jog=offset, strategy=strategy, **kwargs)
+        anchor = self.plan_leg(
+            kind,
+            contexts_by_name[anchor_portspec],
+            operation,
+            diagnostic_request,
+            length=length,
+            jog=offset,
+            strategy=strategy,
+            **kwargs,
+            )
         base_length = anchor.candidate.public_length
         specs = planner_bounds.su_bundle_specs(contexts, offset, base_length, spacing, route_name=route_name)
         first_portspec, _first_length, _first_offset = specs[0]
@@ -1287,7 +1570,10 @@ class RoutingPlanner:
                 routes_by_name[spec_portspec] = self.plan_leg(
                     'straight',
                     contexts_by_name[spec_portspec],
+                    operation,
+                    diagnostic_request,
                     length=spec_length,
+                    jog=spec_offset,
                     strategy=strategy,
                     **kwargs,
                     )
@@ -1295,6 +1581,8 @@ class RoutingPlanner:
                 routes_by_name[spec_portspec] = self.plan_leg(
                     kind,
                     contexts_by_name[spec_portspec],
+                    operation,
+                    diagnostic_request,
                     length=spec_length,
                     jog=spec_offset,
                     strategy=strategy,
diff --git a/masque/builder/utils.py b/masque/builder/utils.py
index ca36fff..ceea550 100644
--- a/masque/builder/utils.py
+++ b/masque/builder/utils.py
@@ -1,5 +1,5 @@
-from typing import SupportsFloat, cast, TYPE_CHECKING
-from collections.abc import Mapping, Sequence
+from typing import TYPE_CHECKING
+from collections.abc import Mapping
 from pprint import pformat
 
 import numpy
@@ -13,6 +13,17 @@ if TYPE_CHECKING:
     from ..ports import Port
 
 
+_EXTENSION_BOUND_TYPES = (
+    'emin', 'min_extension',
+    'emax', 'max_extension',
+    'min_past_furthest',
+    )
+_POSITION_MIN_BOUND_TYPES = ('pmin', 'min_position', 'xmin', 'ymin')
+_POSITION_MAX_BOUND_TYPES = ('pmax', 'max_position', 'xmax', 'ymax')
+_POSITION_BOUND_TYPES = _POSITION_MIN_BOUND_TYPES + _POSITION_MAX_BOUND_TYPES
+_BOUND_TYPES = _EXTENSION_BOUND_TYPES + _POSITION_BOUND_TYPES
+
+
 def ell(
         ports: Mapping[str, 'Port'],
         ccw: SupportsBool | None,
@@ -82,6 +93,18 @@ def ell(
     """
     if not ports:
         raise BuildError('Empty port list passed to `ell()`')
+    if bound_type not in _BOUND_TYPES:
+        raise BuildError(f'Invalid bound type {bound_type!r}; expected one of {_BOUND_TYPES}')
+
+    try:
+        bound_arr = numpy.asarray(bound, dtype=float)
+    except (TypeError, ValueError) as err:
+        raise BuildError('bound must be a numeric scalar or length-2 vector') from err
+    if bound_arr.size not in (1, 2):
+        raise BuildError(f'bound must be scalar or have length 2; got {bound_arr.size} values')
+    if not numpy.all(numpy.isfinite(bound_arr)):
+        raise BuildError('bound must contain only finite values')
+    bound_values = bound_arr.reshape(-1)
 
     if ccw is None:
         if spacing is not None and not numpy.allclose(spacing, 0):
@@ -173,38 +196,34 @@ def ell(
         travel = d_to_align - (ch_offsets.max() - ch_offsets)
         offsets = travel - travel.min().clip(max=0)
 
-    rot_bound: SupportsFloat
-    if bound_type in ('emin', 'min_extension',
-                      'emax', 'max_extension',
-                      'min_past_furthest',):
-        if numpy.size(bound) == 2:
-            bound = cast('Sequence[float]', bound)
-            rot_bound = (rot_matrix @ ((bound[0], 0),
-                                       (0, bound[1])))[0, :]
-        else:
-            bound = cast('float', bound)
-            rot_bound = numpy.array(bound)
+    if bound_type in _EXTENSION_BOUND_TYPES:
+        if numpy.any(bound_values < 0):
+            raise BuildError(f'Got negative bound for extension: {bound_values}')
 
-        if rot_bound < 0:
-            raise BuildError(f'Got negative bound for extension: {rot_bound}')
+        if bound_values.size == 2:
+            horizontal_weight = abs(float(numpy.cos(direction)))
+            vertical_weight = abs(float(numpy.sin(direction)))
+            use_x = horizontal_weight > vertical_weight or numpy.isclose(horizontal_weight, vertical_weight)
+            rot_bound = float(bound_values[0 if use_x else 1])
+        else:
+            rot_bound = float(bound_values[0])
 
         if bound_type in ('emin', 'min_extension', 'min_past_furthest'):
-            offsets += rot_bound.max()
+            offsets += rot_bound
         elif bound_type in ('emax', 'max_extension'):
-            offsets += rot_bound.min() - offsets.max()
+            offsets += rot_bound - offsets.max()
     else:
-        if numpy.size(bound) == 2:
-            bound = cast('Sequence[float]', bound)
-            rot_bound = (rot_matrix @ bound)[0]
+        if bound_values.size == 2:
+            rot_bound = float((rot_matrix @ bound_values)[0])
         else:
-            bound = cast('float', bound)
             neg = (direction + pi / 4) % (2 * pi) > pi
-            rot_bound = -bound if neg else bound
+            bound_scalar = float(bound_values[0])
+            rot_bound = -bound_scalar if neg else bound_scalar
 
         min_possible = x_start + offsets
-        if bound_type in ('pmax', 'max_position', 'xmax', 'ymax'):
+        if bound_type in _POSITION_MAX_BOUND_TYPES:
             extension = rot_bound - min_possible.max()
-        elif bound_type in ('pmin', 'min_position', 'xmin', 'ymin'):
+        else:
             extension = rot_bound - min_possible.min()
 
         offsets += extension
diff --git a/masque/test/test_builder.py b/masque/test/test_builder.py
index 53c0a8c..5251622 100644
--- a/masque/test/test_builder.py
+++ b/masque/test/test_builder.py
@@ -14,11 +14,17 @@ from ..ports import Port
 def test_builder_public_imports() -> None:
     from masque import PortPather as TopPortPather
     from masque import RenderStep as TopRenderStep
+    from masque import RouteError as TopRouteError
+    from masque import RouteFailureDetails as TopRouteFailureDetails
     from masque.builder import PortPather as BuilderPortPather
     from masque.builder import RenderStep as BuilderRenderStep
+    from masque.builder import RouteError as BuilderRouteError
+    from masque.builder import RouteFailureDetails as BuilderRouteFailureDetails
 
     assert TopPortPather is BuilderPortPather
     assert TopRenderStep is BuilderRenderStep
+    assert TopRouteError is BuilderRouteError
+    assert TopRouteFailureDetails is BuilderRouteFailureDetails
 
 
 def test_builder_init() -> None:
@@ -171,3 +177,41 @@ def test_ell_handles_array_spacing_when_ccw_none() -> None:
 
     with pytest.raises(BuildError, match='Spacing must be 0 or None'):
         ell(ports, None, 'min_extension', 5, spacing=numpy.array([1, 0]))
+
+
+@pytest.mark.parametrize('bound_type', ['emin', 'emax', 'min_past_furthest'])
+@pytest.mark.parametrize(
+    ('rotation', 'expected'),
+    [
+        (0, 5),
+        (pi / 2, 7),
+        (pi / 6, 5),
+        (pi / 3, 7),
+        (pi / 4, 5),
+    ],
+    )
+def test_ell_extension_vector_selects_dominant_route_axis(
+        bound_type: str,
+        rotation: float,
+        expected: float,
+        ) -> None:
+    result = ell({'A': Port((0, 0), rotation)}, None, bound_type, (5, 7), spacing=0)
+
+    assert_allclose(result['A'], expected)
+
+
+@pytest.mark.parametrize('bound', [(-1, 2), (1, -2), (numpy.nan, 2), (1, numpy.inf), (1, 2, 3)])
+def test_ell_rejects_invalid_extension_vector(bound: tuple[float, ...]) -> None:
+    with pytest.raises(BuildError, match='bound|negative'):
+        ell({'A': Port((0, 0), 0)}, None, 'emin', bound, spacing=0)
+
+
+def test_ell_position_vector_still_projects_onto_route_direction() -> None:
+    result = ell({'A': Port((0, 0), pi)}, None, 'pmax', (5, 7), spacing=0)
+
+    assert_allclose(result['A'], 5)
+
+
+def test_ell_rejects_invalid_bound_type() -> None:
+    with pytest.raises(BuildError, match='Invalid bound type'):
+        ell({'A': Port((0, 0), 0)}, None, 'nearest', 5, spacing=0)
diff --git a/masque/test/test_pather_constraints.py b/masque/test/test_pather_constraints.py
index fab1c68..f695acd 100644
--- a/masque/test/test_pather_constraints.py
+++ b/masque/test/test_pather_constraints.py
@@ -5,9 +5,9 @@ import pytest
 import numpy
 from numpy import pi
 
-from masque import Pather, Library, Port
+from masque import Pather, Library, Port, RouteError
 from masque.builder.planner import RoutePortContext, RoutingPlanner
-from masque.builder.tools import BendOffer, PathTool, RenderStep, StraightOffer, Tool
+from masque.builder.tools import BendOffer, PathTool, RenderStep, StraightOffer, Tool, UOffer
 from masque.error import BuildError
 from masque.library import ILibrary
 
@@ -114,15 +114,306 @@ class CountingPathTool(PathTool):
         return super().render(batch, port_names=port_names, **kwargs)
 
 
+class RequestCountingTool(PlanningOnlyTool):
+    def __init__(self) -> None:
+        self.offer_calls = 0
+
+    def primitive_offers(
+            self,
+            kind: Literal['straight', 'bend', 's', 'u'],
+            *,
+            in_ptype: str | None = None,
+            out_ptype: str | None = None,
+            **kwargs: Any,
+            ) -> tuple[Any, ...]:
+        self.offer_calls += 1
+        return super().primitive_offers(
+            kind,
+            in_ptype=in_ptype,
+            out_ptype=out_ptype,
+            **kwargs,
+            )
+
+
+class PreferredMinimumTool(PlanningOnlyTool):
+    def __init__(self) -> None:
+        self.commit_calls = 0
+        self.diagnostic_context_kwargs: list[Any] = []
+
+    def _commit(self, parameter: float) -> dict[str, float]:
+        self.commit_calls += 1
+        return {'parameter': parameter}
+
+    def primitive_offers(
+            self,
+            kind: Literal['straight', 'bend', 's', 'u'],
+            *,
+            in_ptype: str | None = None,
+            out_ptype: str | None = None,
+            **kwargs: Any,
+            ) -> tuple[Any, ...]:
+        _ = out_ptype
+        self.diagnostic_context_kwargs.append(kwargs.get('diagnostic_context'))
+        if kind == 'bend':
+            ccw = bool(kwargs['ccw'])
+            rotation = -pi / 2 if ccw else pi / 2
+            jog = 1 if ccw else -1
+            return (
+                BendOffer(
+                    in_ptype=in_ptype,
+                    out_ptype='wide',
+                    priority_bias=100,
+                    ccw=ccw,
+                    length_domain=(2, 2),
+                    endpoint_planner=lambda _length: Port((2, jog), rotation, ptype='wide'),
+                    commit_planner=self._commit,
+                    ),
+                BendOffer(
+                    in_ptype=in_ptype,
+                    out_ptype='wide',
+                    ccw=ccw,
+                    length_domain=(5, 5),
+                    endpoint_planner=lambda _length: Port((5, jog), rotation, ptype='wide'),
+                    commit_planner=self._commit,
+                    ),
+                )
+        if kind == 'u':
+            return (UOffer(
+                in_ptype=in_ptype,
+                out_ptype='wide',
+                jog_domain=(4, 4),
+                endpoint_planner=lambda _jog: Port((5, 4), 0, ptype='wide'),
+                commit_planner=self._commit,
+                ),)
+        return ()
+
+
+def test_route_error_reports_preferred_minimum_and_request_details() -> None:
+    tool = PreferredMinimumTool()
+    p = Pather(
+        Library(),
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools=tool,
+        render='deferred',
+        )
+
+    with pytest.raises(RouteError) as exc_info:
+        p.ccw('A', 1, out_ptype='wide', diagnostic_context='tool-value')
+
+    details = exc_info.value.details
+    assert isinstance(exc_info.value, BuildError)
+    assert details.operation == 'trace_to'
+    assert details.portspec == 'A'
+    assert details.in_ptype == 'wire'
+    assert details.out_ptype == 'wide'
+    assert details.request == {
+        'ccw': True,
+        'length': 1,
+        'out_ptype': 'wide',
+        'diagnostic_context': 'tool-value',
+        }
+    assert details.resolved_length == 1
+    assert details.resolved_jog is None
+    # The length-2 route exists, but normal cost ranking prefers length 5.
+    assert details.minimum_length == 5
+    assert details.minimum_attempted
+    assert not details.minimum_exhausted
+    assert details.minimum_cause is None
+    assert 'preferred_minimum_length: 5' in str(exc_info.value)
+    assert tool.commit_calls == 0
+    assert tool.diagnostic_context_kwargs
+    assert set(tool.diagnostic_context_kwargs) == {'tool-value'}
+    assert not p._paths
+    with pytest.raises(TypeError):
+        details.request['new'] = 'value'  # type: ignore[index]
+
+
+def test_route_error_reports_uturn_preferred_minimum() -> None:
+    tool = PreferredMinimumTool()
+    p = Pather(
+        Library(),
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools=tool,
+        render='deferred',
+        )
+
+    with pytest.raises(RouteError) as exc_info:
+        p.uturn('A', 4, length=1, out_ptype='wide')
+
+    details = exc_info.value.details
+    assert details.operation == 'uturn'
+    assert details.resolved_length == 1
+    assert details.resolved_jog == 4
+    assert details.minimum_length == 5
+    assert tool.commit_calls == 0
+
+
+def test_route_error_reports_no_route_at_any_length() -> None:
+    p = Pather(
+        Library(),
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools=PathTool(layer='M1', width=2, ptype='wire'),
+        render='deferred',
+        )
+
+    with pytest.raises(RouteError) as exc_info:
+        p.ccw('A', 10, out_ptype='optical')
+
+    details = exc_info.value.details
+    assert details.minimum_attempted
+    assert details.minimum_length is None
+    assert details.minimum_exhausted
+    assert details.minimum_cause is not None
+    assert 'no legal route exists at any length' in str(exc_info.value)
+
+
+@pytest.mark.parametrize('length', [-1, numpy.nan, numpy.inf])
+def test_invalid_route_length_fails_before_offer_query_or_dead_fallback(length: float) -> None:
+    tool = RequestCountingTool()
+    p = Pather(
+        Library(),
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools=tool,
+        render='deferred',
+        ).set_dead()
+
+    with pytest.raises(RouteError) as exc_info:
+        p.ccw('A', length)
+
+    details = exc_info.value.details
+    assert not details.minimum_attempted
+    assert details.minimum_length is None
+    assert tool.offer_calls == 0
+    assert numpy.allclose(p.ports['A'].offset, (0, 0))
+
+
+def test_negative_position_length_reports_bound_without_offer_query() -> None:
+    tool = RequestCountingTool()
+    p = Pather(
+        Library(),
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools=tool,
+        render='deferred',
+        )
+
+    with pytest.raises(RouteError) as exc_info:
+        p.ccw('A', x=1)
+
+    details = exc_info.value.details
+    assert details.request == {'ccw': True, 'x': 1}
+    assert details.resolved_length == -1
+    assert not details.minimum_attempted
+    assert tool.offer_calls == 0
+
+
+def test_negative_bundle_length_reports_failing_port_and_bound() -> None:
+    tool = RequestCountingTool()
+    p = Pather(
+        Library(),
+        ports={
+            'A': Port((0, 0), rotation=0, ptype='wire'),
+            'B': Port((0, 4), rotation=0, ptype='wire'),
+            },
+        tools=tool,
+        render='deferred',
+        )
+
+    with pytest.raises(RouteError) as exc_info:
+        p.trace(['A', 'B'], True, emax=0, spacing=2)
+
+    details = exc_info.value.details
+    assert details.portspec == 'A'
+    assert details.request == {'ccw': True, 'emax': 0, 'spacing': 2}
+    assert details.resolved_length == -2
+    assert not details.minimum_attempted
+    assert tool.offer_calls == 0
+
+
+def test_negative_each_length_reports_failing_port_without_offer_query() -> None:
+    tool = RequestCountingTool()
+    p = Pather(
+        Library(),
+        ports={
+            'A': Port((0, 0), rotation=0, ptype='wire'),
+            'B': Port((0, 4), rotation=0, ptype='wire'),
+            },
+        tools=tool,
+        render='deferred',
+        )
+
+    with pytest.raises(RouteError) as exc_info:
+        p.trace(['A', 'B'], None, each=-2)
+
+    details = exc_info.value.details
+    assert details.portspec == 'A'
+    assert details.request == {'ccw': None, 'each': -2}
+    assert details.resolved_length == -2
+    assert not details.minimum_attempted
+    assert tool.offer_calls == 0
+
+
+@pytest.mark.parametrize(
+    'operation',
+    [
+        lambda p: p.trace([], None, length=1),
+        lambda p: p.trace_to([], None, length=1),
+        lambda p: p.jog([], 2, length=3),
+        lambda p: p.uturn([], 2, length=3),
+    ],
+    ids=['trace', 'trace_to', 'jog', 'uturn'],
+    )
+def test_pather_rejects_empty_route_selection_before_planning(operation: Any) -> None:
+    tool = RequestCountingTool()
+    p = Pather(Library(), tools=tool, render='deferred')
+
+    with pytest.raises(BuildError, match='at least one port'):
+        operation(p)
+
+    assert tool.offer_calls == 0
+    assert not p.ports
+    assert not p._paths
+
+
+@pytest.mark.parametrize(
+    'operation',
+    [
+        lambda p: p.trace(['A', 'A'], None, each=1),
+        lambda p: p.trace_to(['A', 'A'], None, xmin=-10),
+        lambda p: p.jog(['A', 'A'], 2, length=3, spacing=1),
+        lambda p: p.uturn(['A', 'A'], 2, length=3, spacing=1),
+        lambda p: p.at(['A', 'A']).straight(1),
+    ],
+    ids=['trace', 'trace_to', 'jog', 'uturn', 'port_pather'],
+    )
+def test_pather_rejects_duplicate_route_selection_before_planning(operation: Any) -> None:
+    tool = RequestCountingTool()
+    p = Pather(
+        Library(),
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools=tool,
+        render='deferred',
+        )
+
+    with pytest.raises(BuildError, match=r"duplicates: \['A'\]"):
+        operation(p)
+
+    assert tool.offer_calls == 0
+    assert numpy.allclose(p.ports['A'].offset, (0, 0))
+    assert not p._paths
+
+
 def test_pather_jog_failed_two_bend_route_is_atomic() -> None:
     lib = Library()
     tool = PathTool(layer='M1', width=2, ptype='wire')
     p = Pather(lib, tools=tool, render='immediate')
     p.pattern.ports['A'] = Port((0, 0), rotation=0, ptype='wire')
 
-    with pytest.raises(BuildError, match='S-bend'):
+    with pytest.raises(RouteError, match='S-bend') as exc_info:
         p.jog('A', 1.5, length=1.5)
 
+    assert exc_info.value.details.minimum_length == 2
+    assert exc_info.value.details.resolved_jog == 1.5
+
     assert numpy.allclose(p.pattern.ports['A'].offset, (0, 0))
     assert p.pattern.ports['A'].rotation == 0
     assert len(p._paths['A']) == 0
@@ -593,9 +884,12 @@ def test_pather_uturn_failed_two_bend_route_is_atomic() -> None:
     p = Pather(lib, tools=tool)
     p.pattern.ports['A'] = Port((0, 0), rotation=0, ptype='wire')
 
-    with pytest.raises(BuildError, match='U-turn'):
+    with pytest.raises(RouteError, match='U-turn') as exc_info:
         p.uturn('A', 1.5, length=0)
 
+    assert exc_info.value.details.minimum_attempted
+    assert exc_info.value.details.minimum_length is None
+
     assert numpy.allclose(p.pattern.ports['A'].offset, (0, 0))
     assert p.pattern.ports['A'].rotation == 0
     assert len(p._paths['A']) == 0
diff --git a/masque/test/test_pather_core.py b/masque/test/test_pather_core.py
index ddf869b..cfc426b 100644
--- a/masque/test/test_pather_core.py
+++ b/masque/test/test_pather_core.py
@@ -5,7 +5,7 @@ import numpy
 from numpy import pi
 from numpy.testing import assert_allclose, assert_equal
 
-from masque import Pather, Library, Pattern, Port
+from masque import Pather, Library, Pattern, Port, RouteError
 from masque.builder import PathTool, PrimitiveOffer, StraightOffer
 from masque.builder.planner import RoutingPlanner
 from masque.error import BuildError, PortError
@@ -136,12 +136,13 @@ def test_pather_dead_ports() -> None:
     p = Pather(lib, ports={"in": Port((0, 0), 0)}, tools=tool)
     p.set_dead()
 
-    p.straight("in", -10)
+    with pytest.raises(RouteError, match='finite and nonnegative'):
+        p.straight("in", -10)
 
-    assert_allclose(p.ports["in"].offset, [10, 0], atol=1e-10)
+    assert_allclose(p.ports["in"].offset, [0, 0], atol=1e-10)
 
     p.straight("in", 20)
-    assert_allclose(p.ports["in"].offset, [-10, 0], atol=1e-10)
+    assert_allclose(p.ports["in"].offset, [-20, 0], atol=1e-10)
 
     assert not p.pattern.has_shapes()
 
@@ -394,9 +395,9 @@ def test_pather_dead_fallback_preserves_out_ptype() -> None:
     p.pattern.ports['A'] = Port((0, 0), rotation=0, ptype='wire')
     p.set_dead()
 
-    p.straight('A', -1000, out_ptype='other')
+    p.straight('A', 1000, out_ptype='other')
 
-    assert numpy.allclose(p.pattern.ports['A'].offset, (1000, 0))
+    assert numpy.allclose(p.pattern.ports['A'].offset, (-1000, 0))
     assert p.pattern.ports['A'].ptype == 'other'
     assert len(p._paths['A']) == 0
 
diff --git a/masque/test/test_pather_rendering.py b/masque/test/test_pather_rendering.py
index 186faf4..677fa12 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
+from ..builder import Pather, RouteError
 from ..builder.tools import PathTool, RenderStep, StraightOffer, Tool
 from ..error import BuildError
 from ..library import Library
@@ -122,9 +122,10 @@ def test_deferred_render_dead_ports() -> None:
     rp = Pather(lib, ports={"in": Port((0, 0), 0)}, tools=tool, render='deferred')
     rp.set_dead()
 
-    rp.straight("in", -10)
+    with pytest.raises(RouteError, match='finite and nonnegative'):
+        rp.straight("in", -10)
 
-    assert_allclose(rp.ports["in"].offset, [10, 0], atol=1e-10)
+    assert_allclose(rp.ports["in"].offset, [0, 0], atol=1e-10)
 
     assert len(rp._paths["in"]) == 0
 

From 49713896c3af7d06279b1bb1556dae88f6ad0024 Mon Sep 17 00:00:00 2001
From: Jan Petykiewicz <jan@mpxd.net>
Date: Sun, 12 Jul 2026 17:25:13 -0700
Subject: [PATCH 4/4] [Pather/Planner] Doc cleanup and more informative error
 enums

---
 masque/__init__.py                     |  2 +
 masque/builder/__init__.py             | 32 +++++++----
 masque/builder/error.py                | 53 +++++++++++++++---
 masque/builder/pather.py               | 60 +++++++++++++++++----
 masque/builder/planner/__init__.py     |  2 +-
 masque/builder/planner/interface.py    | 35 +++++++-----
 masque/builder/planner/planner.py      | 74 +++++++++++++++-----------
 masque/builder/tools.py                | 24 +++++----
 masque/test/test_builder.py            | 35 +++++++++++-
 masque/test/test_pather_constraints.py | 62 +++++++++++++++++----
 masque/test/test_pather_core.py        | 24 +++++++++
 masque/test/test_pather_rendering.py   | 54 +++++++++++++++++++
 masque/test/test_pather_trace_into.py  |  8 +--
 13 files changed, 370 insertions(+), 95 deletions(-)

diff --git a/masque/__init__.py b/masque/__init__.py
index 6598e2f..defd1ef 100644
--- a/masque/__init__.py
+++ b/masque/__init__.py
@@ -84,6 +84,8 @@ from .builder import (
     Pather as Pather,
     RouteError as RouteError,
     RouteFailureDetails as RouteFailureDetails,
+    RouteFailurePolicy as RouteFailurePolicy,
+    MinimumStatus as MinimumStatus,
     RenderStep as RenderStep,
     AutoTool as AutoTool,
     PathTool as PathTool,
diff --git a/masque/builder/__init__.py b/masque/builder/__init__.py
index 76fd1f8..eba23ba 100644
--- a/masque/builder/__init__.py
+++ b/masque/builder/__init__.py
@@ -8,16 +8,23 @@ optional footprint metadata, and a commit hook for producing tool-specific
 render data after a concrete parameter has been selected.
 
 `Pather` owns user-facing route operations such as `trace()`, `jog()`,
-`uturn()`, and `trace_into()`. For each operation, it asks the active `Tool` for
-offers and passes those offers plus route constraints to the internal router.
-The router selects a sequence of internal selected primitives, each pairing an
-offer with a concrete parameter, endpoint, and cost.
+`uturn()`, and `trace_into()`. The internal planner resolves each operation into
+one or more `SolverRequest`s. This normalization is why the public routing API
+can remain a convenient keyword-based interface without making the solver
+stringly typed internally. A pure solver search selects a `Candidate`, and a
+`RouteLeg` attaches that candidate to its copied source port and Tool. Only
+after selection succeeds are the chosen offers materialized through
+`offer.commit(parameter)` into a `PreparedRouteResult` containing
+`RenderStep.data`. `Pather` then applies that prepared result to its live ports
+and pending render queue.
 
-Route commit is separate from route selection. Once a route is selected,
-`Pather` calls `offer.commit(parameter)` only for the selected primitives and
-stores the returned opaque tool payload in `RenderStep.data`. Later,
-`Pather.render()` batches compatible `RenderStep`s and calls `Tool.render()` to
-turn those committed payloads into geometry.
+Selection is pure with respect to caller-owned Pattern, Library, and Pather
+state. Tool offer discovery and endpoint/cost/bbox callbacks must likewise be
+deterministic and must not mutate that state. `commit()` is the first
+selected-offer materialization hook, but it still must not mutate the live
+layout. `Tool.render()` is the geometry mutation boundary: later,
+`Pather.render()` batches compatible `RenderStep`s and inserts the resulting
+geometry into the Pattern and Library.
 
 `PrimitiveOffer` and `RenderStep.data` are the tool-facing contract.
 `RenderStep` is `Pather`'s deferred-render record, and
@@ -31,6 +38,11 @@ The practical layering is:
 - Pather applies the prepared result to ports, deferred render queues, and the
   target pattern/library.
 
+`Pather` intentionally remains a Pattern-oriented facade rather than exposing
+separate assembly and routing objects: its user model is a working Pattern with
+routing tools attached. The ownership phases above are internal boundaries,
+not additional objects callers must coordinate.
+
 Code outside the builder package should prefer the exports here over importing
 from `masque.builder.planner`. The planner package is intentionally available
 for tests and internal maintenance, but it is not the compatibility boundary
@@ -45,6 +57,8 @@ from .error import (
     RouteError as RouteError,
     RouteFailureDetails as RouteFailureDetails,
     RouteOperation as RouteOperation,
+    RouteFailurePolicy as RouteFailurePolicy,
+    MinimumStatus as MinimumStatus,
 )
 from .utils import ell as ell
 from .tools import (
diff --git a/masque/builder/error.py b/masque/builder/error.py
index e8f00fd..6a647ce 100644
--- a/masque/builder/error.py
+++ b/masque/builder/error.py
@@ -2,6 +2,7 @@
 from typing import Any, Literal
 from collections.abc import Mapping
 from dataclasses import dataclass
+from enum import Enum, auto
 from pprint import pformat
 from types import MappingProxyType
 
@@ -11,6 +12,33 @@ from ..error import BuildError
 RouteOperation = Literal['trace', 'trace_to', 'jog', 'uturn']
 
 
+class RouteFailurePolicy(Enum):
+    """Whether route failure may be recovered through alternate/dead planning.
+
+    `RECOVERABLE` means a caller-controlled fallback may try another planning
+    branch. `FATAL` marks an invalid request or broken planning contract that
+    must be reported directly.
+    """
+
+    RECOVERABLE = auto()
+    FATAL = auto()
+
+
+class MinimumStatus(Enum):
+    """Outcome of preferred-minimum-length diagnosis.
+
+    `NOT_EVALUATED` is used when diagnosis is inapplicable, notably for an
+    invalid resolved length. `FOUND` carries `minimum_length`; `NO_ROUTE` means
+    exhaustive planning found no legal unconstrained route; `FAILED` means the
+    secondary diagnostic calculation itself raised a recoverable error.
+    """
+
+    NOT_EVALUATED = auto()
+    FOUND = auto()
+    NO_ROUTE = auto()
+    FAILED = auto()
+
+
 @dataclass(frozen=True, slots=True)
 class RouteFailureDetails:
     """Structured context for a failed Pather routing request."""
@@ -23,12 +51,15 @@ class RouteFailureDetails:
     resolved_length: float | None
     resolved_jog: float | None
     minimum_length: float | None
-    minimum_attempted: bool
-    minimum_exhausted: bool
+    minimum_status: MinimumStatus
     cause: str
     minimum_cause: str | None = None
 
     def __post_init__(self) -> None:
+        if self.minimum_status is MinimumStatus.FOUND and self.minimum_length is None:
+            raise BuildError('MinimumStatus.FOUND requires minimum_length')
+        if self.minimum_status is not MinimumStatus.FOUND and self.minimum_length is not None:
+            raise BuildError(f'{self.minimum_status} requires minimum_length=None')
         object.__setattr__(self, 'request', MappingProxyType(dict(self.request)))
 
 
@@ -36,16 +67,22 @@ class RouteError(BuildError):
     """A route-selection failure with structured request diagnostics."""
 
     details: RouteFailureDetails
-    fatal: bool
+    policy: RouteFailurePolicy
 
-    def __init__(self, details: RouteFailureDetails, *, fatal: bool = False) -> None:
+    def __init__(
+            self,
+            details: RouteFailureDetails,
+            *,
+            policy: RouteFailurePolicy = RouteFailurePolicy.RECOVERABLE,
+            ) -> None:
         self.details = details
-        self.fatal = fatal
-        if not details.minimum_attempted:
+        self.policy = policy
+        if details.minimum_status is MinimumStatus.NOT_EVALUATED:
             minimum = 'not evaluated'
-        elif details.minimum_length is not None:
+        elif details.minimum_status is MinimumStatus.FOUND:
+            assert details.minimum_length is not None
             minimum = f'{details.minimum_length:g}'
-        elif details.minimum_exhausted:
+        elif details.minimum_status is MinimumStatus.NO_ROUTE:
             minimum = 'unavailable (no legal route exists at any length)'
         else:
             minimum = 'unavailable (minimum-length calculation failed)'
diff --git a/masque/builder/pather.py b/masque/builder/pather.py
index 877cd6d..9d6b46b 100644
--- a/masque/builder/pather.py
+++ b/masque/builder/pather.py
@@ -22,10 +22,25 @@ Routing is split into four ownership phases:
 
 This split keeps selection failures largely transactional for live Pather
 state: unsupported primitive combinations can fail before the Pattern, pending
-step queue, or Library are touched. Once selected offers are committed and
-prepared actions are applied, later commit, plug, rename, render, or insertion
-failures may leave partial output; that mutation boundary belongs to Pather,
-not to Tool implementations or the route solver.
+step queue, or Library are touched. Once prepared actions are applied, plug,
+rename, render, or insertion failures may leave partial output; that mutation
+boundary belongs to Pather, not to Tool implementations or the route solver.
+
+Routing policy follows port names. Port-specific Tool assignments and
+`PortPather` selections remain attached to their names rather than following a
+physical port through arbitrary renames. Pending `RenderStep`s are different:
+they snapshot their geometric endpoints when planned. The `_paths` keys are
+rendering buckets used for ordering and batching those historical steps, not
+identities that can retarget their saved geometry when a name is deleted or
+reused.
+
+While pending steps exist, mutate ports through Pather's methods. Directly
+editing `pather.pattern.ports` bypasses the bookkeeping that maintains render
+buckets and is unsupported.
+
+Rendering is not transactional across Pattern and Library mutations. A render
+exception is terminal for that Pather: callers may catch it for reporting or
+cleanup, but must not retry rendering or continue routing with the same object.
 """
 from typing import Self, Any, Literal, overload
 from collections.abc import Iterator, Iterable, Mapping, MutableMapping, Sequence
@@ -55,8 +70,9 @@ from .tools import (
 from .planner.interface import (
     PreparedRouteResult,
     RoutePortContext,
-    route_error_is_fatal,
+    route_failure_policy,
     )
+from .error import RouteFailurePolicy
 from .planner import (
     RouteTieBreakStrategy,
     RoutingPlanner,
@@ -116,6 +132,9 @@ class Pather(PortList):
     """
     Tool objects used to dynamically generate new routing segments.
     A key of `None` indicates the default `Tool`.
+
+    Non-`None` keys are policies attached to port names. Renaming a port does
+    not transfer its Tool assignment to the new name.
     """
 
     planner: RoutingPlanner
@@ -555,7 +574,7 @@ class Pather(PortList):
             try:
                 result = self.planner.plan_trace_route(contexts, ccw, length, spacing=spacing, strategy=strategy, **bounds)
             except (BuildError, NotImplementedError) as err:
-                if not self._dead or route_error_is_fatal(err):
+                if not self._dead or route_failure_policy(err) is RouteFailurePolicy.FATAL:
                     raise
                 if length is not None and len(contexts) == 1:
                     context = contexts[0]
@@ -612,7 +631,11 @@ class Pather(PortList):
             try:
                 result = self.planner.plan_trace_to_route(contexts, ccw, spacing=spacing, strategy=strategy, **bounds)
             except (BuildError, NotImplementedError) as err:
-                if not self._dead or len(contexts) != 1 or route_error_is_fatal(err):
+                if (
+                        not self._dead
+                        or len(contexts) != 1
+                        or route_failure_policy(err) is RouteFailurePolicy.FATAL
+                        ):
                     raise
                 if bounds.get('length') is not None:
                     length = bounds['length']
@@ -684,7 +707,11 @@ class Pather(PortList):
             try:
                 result = self.planner.plan_jog_route(contexts, offset, length, spacing=spacing, strategy=strategy, **bounds)
             except (BuildError, NotImplementedError) as err:
-                if not self._dead or len(contexts) != 1 or route_error_is_fatal(err):
+                if (
+                        not self._dead
+                        or len(contexts) != 1
+                        or route_failure_policy(err) is RouteFailurePolicy.FATAL
+                        ):
                     raise
                 if numpy.isclose(offset, 0):
                     if length is None:
@@ -750,7 +777,7 @@ class Pather(PortList):
                         not self._dead
                         or len(contexts) != 1
                         or length is None
-                        or route_error_is_fatal(err)
+                        or route_failure_policy(err) is RouteFailurePolicy.FATAL
                         ):
                     raise
                 context = contexts[0]
@@ -830,6 +857,11 @@ class Pather(PortList):
         Consecutive compatible `RenderStep`s are batched by port and Tool, then
         passed to `Tool.render()`. After insertion, the rendered output port is
         checked against the endpoint that planning selected.
+
+        Rendering may modify the Library before every batch has completed and
+        does not provide rollback. If this method raises, the Pather must be
+        treated as unusable; retrying or continuing to route with it is
+        unsupported.
         """
         with self._logger.log_operation(self, 'render', None, append=append):
             tool_port_names = ('A', 'B')
@@ -902,7 +934,7 @@ class Pather(PortList):
                 batch: list[RenderStep] = []
                 for step in steps:
                     appendable = step.opcode in ('L', 'S', 'U')
-                    same_tool = batch and step.tool == batch[0].tool
+                    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 = []
@@ -982,7 +1014,13 @@ class Pather(PortList):
 
 
 class PortPather:
-    """ Port state manager for fluent pathing. """
+    """
+    Port-name selection for fluent pathing.
+
+    The selection stores names, not stable physical port identities. Its own
+    rename/delete helpers update the selection, but unrelated changes made
+    through the parent Pather do not retarget it.
+    """
     def __init__(
             self,
             ports: str | Iterable[str],
diff --git a/masque/builder/planner/__init__.py b/masque/builder/planner/__init__.py
index f2df9e6..41c53d6 100644
--- a/masque/builder/planner/__init__.py
+++ b/masque/builder/planner/__init__.py
@@ -10,7 +10,7 @@ from .interface import (
     PreparedRouteResult as PreparedRouteResult,
     RoutePlanningError as RoutePlanningError,
     RoutePortContext as RoutePortContext,
-    route_error_is_fatal as route_error_is_fatal,
+    route_failure_policy as route_failure_policy,
     )
 from .planner import RouteTieBreakStrategy as RouteTieBreakStrategy
 from .planner import RoutingPlanner as RoutingPlanner
diff --git a/masque/builder/planner/interface.py b/masque/builder/planner/interface.py
index 58028df..514779a 100644
--- a/masque/builder/planner/interface.py
+++ b/masque/builder/planner/interface.py
@@ -15,21 +15,30 @@ from dataclasses import dataclass
 from ...error import BuildError
 from ...ports import Port
 from ..tools import RenderStep, Tool
+from ..error import RouteError, RouteFailurePolicy
 
 
 class RoutePlanningError(BuildError):
     """Route-planning error with fallback policy metadata."""
 
-    fatal: bool
+    policy: RouteFailurePolicy
 
-    def __init__(self, *args: object, fatal: bool = False) -> None:
+    def __init__(
+            self,
+            *args: object,
+            policy: RouteFailurePolicy = RouteFailurePolicy.RECOVERABLE,
+            ) -> None:
         super().__init__(*args)
-        self.fatal = fatal
+        self.policy = policy
 
 
-def route_error_is_fatal(err: Exception) -> bool:
-    """Return true when a planning error should bypass dead-Pather fallback."""
-    return bool(getattr(err, 'fatal', False))
+def route_failure_policy(err: Exception) -> RouteFailurePolicy:
+    """Return typed route recovery policy, defaulting generic errors to recoverable."""
+    if isinstance(err, RoutePlanningError):
+        return err.policy
+    if isinstance(err, RouteError):
+        return err.policy
+    return RouteFailurePolicy.RECOVERABLE
 
 
 @dataclass(frozen=True, slots=True)
@@ -54,9 +63,10 @@ class PreparedRouteAction:
     """
     Prepared mutation for one routed Pather port.
 
-    The planner has already committed selected primitive offers into
-    `render_steps` and computed the final live port. `plug_into`, when set,
-    names the destination port to consume after the route endpoint is applied.
+    Pure selection has already completed, and the planner has materialized the
+    selected primitive offers into `render_steps` and computed the final live
+    port. `plug_into`, when set, names the destination port to consume after the
+    route endpoint is applied.
     """
     portspec: str
     """Live Pather port name to update."""
@@ -73,9 +83,10 @@ class PreparedRouteResult:
     """
     Complete prepared result for one Pather routing operation.
 
-    `actions` are applied first. `renames` are deferred until after all route
-    actions so trace-into/thru behavior can be represented without exposing the
-    solver's selected primitive sequence to Pather.
+    `actions` contain materialized, committed render data and are applied first.
+    `renames` are deferred until after all route actions so trace-into/thru
+    behavior can be represented without exposing the solver's selected
+    primitive sequence to Pather.
     """
     actions: tuple[PreparedRouteAction, ...]
     """Prepared per-port route mutations."""
diff --git a/masque/builder/planner/planner.py b/masque/builder/planner/planner.py
index 548d429..6e6a3c0 100644
--- a/masque/builder/planner/planner.py
+++ b/masque/builder/planner/planner.py
@@ -6,11 +6,19 @@ Tool primitive offers. `Pather` passes copied `RoutePortContext` snapshots here;
 the planner returns `PreparedRouteResult` records that describe pending
 mutations without applying them to the live Pattern.
 
-Public routing modes and bounds are normalized by `bounds.py` before the solver
-sees them. This module plans one route intent at a time: it queries Tool offers,
-enumerates bounded primitive compositions, inserts ptype adapters, solves
-primitive parameters, ranks candidates, and commits only the selected offers
-into `RenderStep` payloads.
+Public routing modes and bounds are normalized by `bounds.py` into per-leg
+`SolverRequest` values. `Solver` performs the pure search: it queries Tool
+offers, enumerates bounded primitive compositions, inserts ptype adapters,
+solves primitive parameters, and returns the ranked `Candidate`. A `RouteLeg`
+then attaches the candidate to its copied source port and Tool. Preparation is
+the layer above selection: only chosen offers are committed into `RenderStep`
+payloads and returned in a `PreparedRouteResult` for Pather to apply.
+
+These named stages are architectural boundaries even though most of their
+implementation is currently co-located in this module. File layout is an
+internal organization choice; the distinction between normalized request,
+pure selection, prepared result, and live application is the meaningful
+mutation boundary.
 
 All search is performed in Tool-local route coordinates. The active input port
 is at the origin, travel is along +x, and positive jog is to the left. After a
@@ -43,7 +51,13 @@ from ..tools import (
     StraightOffer,
     Tool,
     )
-from ..error import RouteError, RouteFailureDetails, RouteOperation
+from ..error import (
+    MinimumStatus,
+    RouteError,
+    RouteFailureDetails,
+    RouteFailurePolicy,
+    RouteOperation,
+    )
 from ..utils import ell
 from . import bounds as planner_bounds
 from .interface import (
@@ -51,7 +65,7 @@ from .interface import (
     PreparedRouteResult,
     RoutePlanningError,
     RoutePortContext,
-    route_error_is_fatal,
+    route_failure_policy,
     )
 
 RouteTieBreakStrategy = Literal['straight_first', 'turn_first']
@@ -149,7 +163,7 @@ def is_adapter_offer(offer: PrimitiveOffer) -> bool:
 
 def raise_if_fatal(err: Exception) -> None:
     """Propagate fatal planning errors while allowing normal candidate rejection."""
-    if getattr(err, 'fatal', False):
+    if route_failure_policy(err) is RouteFailurePolicy.FATAL:
         raise err
 
 
@@ -231,9 +245,9 @@ class Candidate:
 
 
 @dataclass(frozen=True, slots=True)
-class RouteRequest:
+class SolverRequest:
     """
-    Normalized solver input for one route leg.
+    Normalized input for one `Solver` invocation and one route leg.
 
     Public Pather calls are converted into this smaller shape before grammar
     enumeration. `length`, `jog`, and `out_ptype` become endpoint constraints;
@@ -302,7 +316,7 @@ class Solver:
     enumerated so fixed and adjustable offers share the same path.
     """
 
-    def __init__(self, request: RouteRequest) -> None:
+    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.offer_cache: dict[
@@ -396,7 +410,7 @@ class Solver:
 
         if not candidates:
             for err in errors:
-                if getattr(err, 'fatal', False):
+                if route_failure_policy(err) is RouteFailurePolicy.FATAL:
                     raise err
             if errors:
                 last_error = errors[-1]
@@ -476,12 +490,12 @@ class Solver:
         if not ptypes_compatible(out_port.ptype, offer.out_ptype):
             raise RoutePlanningError(
                 f'{route_name} primitive endpoint ptype does not match declared offer out_ptype',
-                fatal=True,
+                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',
-                fatal=True,
+                policy=RouteFailurePolicy.FATAL,
                 )
         cost = float(offer.cost_at(selected))
         if not numpy.isfinite(cost):
@@ -993,7 +1007,7 @@ class RoutingPlanner:
             bands.append((4, 4))
         return tuple(bands)
 
-    def route_request(
+    def solver_request(
             self,
             family: PrimitiveKind,
             context: RoutePortContext,
@@ -1005,9 +1019,9 @@ class RoutingPlanner:
             max_bends: int | None = None,
             strategy: RouteTieBreakStrategy | str | None = None,
             **kwargs: Any,
-            ) -> RouteRequest:
+            ) -> SolverRequest:
         """Build normalized solver input for one route leg."""
-        return RouteRequest(
+        return SolverRequest(
             family=family,
             tool=context.tool,
             in_ptype=context.port.ptype,
@@ -1021,7 +1035,7 @@ class RoutingPlanner:
             strategy=self.resolve_strategy(strategy),
             )
 
-    def solver_for_request(self, request: RouteRequest) -> Solver:
+    def solver_for_request(self, request: SolverRequest) -> Solver:
         """Construct the solver for a route request."""
         return Solver(request)
 
@@ -1079,13 +1093,12 @@ class RoutingPlanner:
                 resolved_length=float(length),
                 resolved_jog=None if jog is None else float(jog),
                 minimum_length=None,
-                minimum_attempted=False,
-                minimum_exhausted=False,
+                minimum_status=MinimumStatus.NOT_EVALUATED,
                 cause='Resolved route length must be finite and nonnegative',
                 )
-            raise RouteError(details, fatal=True)
+            raise RouteError(details, policy=RouteFailurePolicy.FATAL)
 
-        request = self.route_request(
+        request = self.solver_request(
             family=family,
             context=context,
             length=length,
@@ -1107,22 +1120,24 @@ class RoutingPlanner:
 
             minimum_length: float | None = None
             minimum_cause: str | None = None
-            minimum_exhausted = False
+            minimum_status: MinimumStatus
             if length is None:
                 minimum_cause = cause
-                minimum_exhausted = True
+                minimum_status = MinimumStatus.NO_ROUTE
             else:
                 minimum_request = replace(request, length=None)
                 try:
                     minimum_candidate = self.solver_for_request(minimum_request).solve()
                     minimum_length = minimum_candidate.public_length
+                    minimum_status = MinimumStatus.FOUND
                 except NoLegalRouteError as minimum_err:
                     minimum_cause = str(minimum_err)
-                    minimum_exhausted = True
+                    minimum_status = MinimumStatus.NO_ROUTE
                 except Exception as minimum_err:
-                    if route_error_is_fatal(minimum_err):
+                    if route_failure_policy(minimum_err) is RouteFailurePolicy.FATAL:
                         raise
                     minimum_cause = str(minimum_err)
+                    minimum_status = MinimumStatus.FAILED
 
             details = RouteFailureDetails(
                 operation=operation,
@@ -1133,8 +1148,7 @@ class RoutingPlanner:
                 resolved_length=None if length is None else float(length),
                 resolved_jog=None if jog is None else float(jog),
                 minimum_length=minimum_length,
-                minimum_attempted=True,
-                minimum_exhausted=minimum_exhausted,
+                minimum_status=minimum_status,
                 cause=cause,
                 minimum_cause=minimum_cause,
                 )
@@ -1619,7 +1633,7 @@ class RoutingPlanner:
         desired.rotation = port_dst.rotation - pi
         desired.ptype = out_ptype
         family, length, jog, ccw = self.trace_into_spec(context_src.port, desired)
-        request = self.route_request(
+        request = self.solver_request(
             family,
             context_src,
             length=length,
@@ -1638,7 +1652,7 @@ class RoutingPlanner:
                 candidate = solver.solve(min_bends=min_bends, max_bends=max_bends)
                 break
             except (BuildError, NotImplementedError) as err:
-                if route_error_is_fatal(err):
+                if route_failure_policy(err) is RouteFailurePolicy.FATAL:
                     raise
                 last_error = err
         if candidate is None:
diff --git a/masque/builder/tools.py b/masque/builder/tools.py
index 702fe7c..9db7645 100644
--- a/masque/builder/tools.py
+++ b/masque/builder/tools.py
@@ -25,11 +25,13 @@ declared `out_ptype`. These are Tool contract requirements rather than
 exhaustively runtime-checked properties.
 
 Tool authors should treat offer planning callbacks as pure descriptions. The
-solver may call `endpoint_at()`, `cost_at()`, and `bbox_at()` many times while
-enumerating candidate compositions, ptype adapters, and parameter solutions.
-Those callbacks should be deterministic and should not mutate a Library,
-Pattern, or live Pather. `commit()` is the first selected-offer hook: it runs
-only for primitives in the chosen route and returns the opaque value stored in
+solver may call `endpoint_at()` and `cost_at()` many times while enumerating
+candidate compositions, ptype adapters, and parameter solutions. Those
+callbacks should be deterministic and should not mutate a Library, Pattern, or
+live Pather. `bbox_at()` follows the same purity contract, but footprint data is
+currently reserved for future footprint-aware planning and is not consumed by
+the solver. `commit()` is the first selected-offer hook: it runs only for
+primitives in the chosen route and returns the opaque value stored in
 `RenderStep.data`.
 
 `render()` is the geometry-construction hook. Pather calls it later with a
@@ -188,6 +190,7 @@ class PrimitiveOffer(ABC):
     priority_bias: float = 0.0
     bbox_planner: BBoxCallable | None = None
     parameterized_bbox: Any | None = None
+    """Reserved footprint metadata; the current solver does not inspect it."""
     endpoint_planner: EndpointCallable | None = None
     commit_planner: CommitCallable | None = None
 
@@ -242,10 +245,11 @@ class PrimitiveOffer(ABC):
 
     def bbox_at(self, parameter: float) -> NDArray[numpy.float64]:
         """
-        Return local primitive bounds for footprint-aware planning.
+        Return local primitive bounds for future footprint-aware planning.
 
         Tools may omit this hook by raising `NotImplementedError`; when present
         it must return a finite `(2, 2)` min/max array in local coordinates.
+        The current route solver does not call this method.
         """
         if self.bbox_planner is None:
             raise NotImplementedError
@@ -266,9 +270,11 @@ class PrimitiveOffer(ABC):
         """
         Produce opaque render data for a selected primitive.
 
-        `Pather` calls this only for selected primitives while preparing
-        `RenderStep.data`. Unselected candidates are evaluated by endpoint/cost
-        only and should not need commit-side work.
+        Routing preparation calls this only for selected primitives while
+        building `RenderStep.data`. Unselected candidates are evaluated by
+        endpoint/cost only and should not need commit-side work. This is a
+        materialization hook, not the live-layout mutation boundary: it must not
+        mutate the caller's Pather, Pattern, or Library.
         """
         selected = self.canonicalize_parameter(parameter)
         if self.commit_planner is not None:
diff --git a/masque/test/test_builder.py b/masque/test/test_builder.py
index 5251622..4bf5c53 100644
--- a/masque/test/test_builder.py
+++ b/masque/test/test_builder.py
@@ -3,7 +3,7 @@ import pytest
 from numpy.testing import assert_equal, assert_allclose
 from numpy import pi
 
-from ..builder import Pather
+from ..builder import MinimumStatus, Pather, RouteFailureDetails
 from ..builder.utils import ell
 from ..error import BuildError
 from ..library import Library
@@ -16,15 +16,48 @@ def test_builder_public_imports() -> None:
     from masque import RenderStep as TopRenderStep
     from masque import RouteError as TopRouteError
     from masque import RouteFailureDetails as TopRouteFailureDetails
+    from masque import RouteFailurePolicy as TopRouteFailurePolicy
+    from masque import MinimumStatus as TopMinimumStatus
     from masque.builder import PortPather as BuilderPortPather
     from masque.builder import RenderStep as BuilderRenderStep
     from masque.builder import RouteError as BuilderRouteError
     from masque.builder import RouteFailureDetails as BuilderRouteFailureDetails
+    from masque.builder import RouteFailurePolicy as BuilderRouteFailurePolicy
+    from masque.builder import MinimumStatus as BuilderMinimumStatus
 
     assert TopPortPather is BuilderPortPather
     assert TopRenderStep is BuilderRenderStep
     assert TopRouteError is BuilderRouteError
     assert TopRouteFailureDetails is BuilderRouteFailureDetails
+    assert TopRouteFailurePolicy is BuilderRouteFailurePolicy
+    assert TopMinimumStatus is BuilderMinimumStatus
+
+
+def test_route_failure_details_enforces_minimum_status_invariants() -> None:
+    common = {
+        'operation': 'trace',
+        'portspec': 'A',
+        'in_ptype': 'wire',
+        'out_ptype': 'wide',
+        'request': {},
+        'resolved_length': 1,
+        'resolved_jog': None,
+        'cause': 'no route',
+        }
+
+    with pytest.raises(BuildError, match='FOUND requires minimum_length'):
+        RouteFailureDetails(
+            **common,
+            minimum_length=None,
+            minimum_status=MinimumStatus.FOUND,
+            )
+
+    with pytest.raises(BuildError, match='requires minimum_length=None'):
+        RouteFailureDetails(
+            **common,
+            minimum_length=2,
+            minimum_status=MinimumStatus.NO_ROUTE,
+            )
 
 
 def test_builder_init() -> None:
diff --git a/masque/test/test_pather_constraints.py b/masque/test/test_pather_constraints.py
index f695acd..e1c0744 100644
--- a/masque/test/test_pather_constraints.py
+++ b/masque/test/test_pather_constraints.py
@@ -5,8 +5,9 @@ import pytest
 import numpy
 from numpy import pi
 
-from masque import Pather, Library, Port, RouteError
+from masque import MinimumStatus, Pather, 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
 from masque.error import BuildError
 from masque.library import ILibrary
@@ -216,8 +217,8 @@ def test_route_error_reports_preferred_minimum_and_request_details() -> None:
     assert details.resolved_jog is None
     # The length-2 route exists, but normal cost ranking prefers length 5.
     assert details.minimum_length == 5
-    assert details.minimum_attempted
-    assert not details.minimum_exhausted
+    assert details.minimum_status is MinimumStatus.FOUND
+    assert exc_info.value.policy is RouteFailurePolicy.RECOVERABLE
     assert details.minimum_cause is None
     assert 'preferred_minimum_length: 5' in str(exc_info.value)
     assert tool.commit_calls == 0
@@ -260,13 +261,53 @@ def test_route_error_reports_no_route_at_any_length() -> None:
         p.ccw('A', 10, out_ptype='optical')
 
     details = exc_info.value.details
-    assert details.minimum_attempted
+    assert details.minimum_status is MinimumStatus.NO_ROUTE
     assert details.minimum_length is None
-    assert details.minimum_exhausted
     assert details.minimum_cause is not None
     assert 'no legal route exists at any length' in str(exc_info.value)
 
 
+def test_route_error_reports_failed_minimum_diagnosis(monkeypatch: pytest.MonkeyPatch) -> None:
+    planner = RoutingPlanner()
+    context = RoutePortContext(
+        'A',
+        Port((0, 0), rotation=0, ptype='wire'),
+        PlanningOnlyTool(),
+        )
+    solve_count = 0
+
+    def solver_for_request(_request: Any) -> Any:
+        nonlocal solve_count
+        solve_count += 1
+        current_solve = solve_count
+
+        class FailingSolver:
+            def solve(self) -> Never:
+                if current_solve == 1:
+                    raise NoLegalRouteError('requested length has no route')
+                raise RuntimeError('minimum diagnosis failed')
+
+        return FailingSolver()
+
+    monkeypatch.setattr(planner, 'solver_for_request', solver_for_request)
+
+    with pytest.raises(RouteError) as exc_info:
+        planner.plan_leg(
+            'bend',
+            context,
+            'trace_to',
+            {'ccw': True, 'length': 1},
+            length=1,
+            ccw=True,
+            )
+
+    details = exc_info.value.details
+    assert details.minimum_status is MinimumStatus.FAILED
+    assert details.minimum_length is None
+    assert details.minimum_cause == 'minimum diagnosis failed'
+    assert 'minimum-length calculation failed' in str(exc_info.value)
+
+
 @pytest.mark.parametrize('length', [-1, numpy.nan, numpy.inf])
 def test_invalid_route_length_fails_before_offer_query_or_dead_fallback(length: float) -> None:
     tool = RequestCountingTool()
@@ -281,7 +322,8 @@ def test_invalid_route_length_fails_before_offer_query_or_dead_fallback(length:
         p.ccw('A', length)
 
     details = exc_info.value.details
-    assert not details.minimum_attempted
+    assert details.minimum_status is MinimumStatus.NOT_EVALUATED
+    assert exc_info.value.policy is RouteFailurePolicy.FATAL
     assert details.minimum_length is None
     assert tool.offer_calls == 0
     assert numpy.allclose(p.ports['A'].offset, (0, 0))
@@ -302,7 +344,7 @@ def test_negative_position_length_reports_bound_without_offer_query() -> None:
     details = exc_info.value.details
     assert details.request == {'ccw': True, 'x': 1}
     assert details.resolved_length == -1
-    assert not details.minimum_attempted
+    assert details.minimum_status is MinimumStatus.NOT_EVALUATED
     assert tool.offer_calls == 0
 
 
@@ -325,7 +367,7 @@ def test_negative_bundle_length_reports_failing_port_and_bound() -> None:
     assert details.portspec == 'A'
     assert details.request == {'ccw': True, 'emax': 0, 'spacing': 2}
     assert details.resolved_length == -2
-    assert not details.minimum_attempted
+    assert details.minimum_status is MinimumStatus.NOT_EVALUATED
     assert tool.offer_calls == 0
 
 
@@ -348,7 +390,7 @@ def test_negative_each_length_reports_failing_port_without_offer_query() -> None
     assert details.portspec == 'A'
     assert details.request == {'ccw': None, 'each': -2}
     assert details.resolved_length == -2
-    assert not details.minimum_attempted
+    assert details.minimum_status is MinimumStatus.NOT_EVALUATED
     assert tool.offer_calls == 0
 
 
@@ -887,7 +929,7 @@ def test_pather_uturn_failed_two_bend_route_is_atomic() -> None:
     with pytest.raises(RouteError, match='U-turn') as exc_info:
         p.uturn('A', 1.5, length=0)
 
-    assert exc_info.value.details.minimum_attempted
+    assert exc_info.value.details.minimum_status is MinimumStatus.NO_ROUTE
     assert exc_info.value.details.minimum_length is None
 
     assert numpy.allclose(p.pattern.ports['A'].offset, (0, 0))
diff --git a/masque/test/test_pather_core.py b/masque/test/test_pather_core.py
index cfc426b..fca27c8 100644
--- a/masque/test/test_pather_core.py
+++ b/masque/test/test_pather_core.py
@@ -93,6 +93,30 @@ def test_pather_accepts_and_reuses_planner_instance() -> None:
     assert planner.trace_to_calls == 2
 
 
+def test_port_tool_policy_and_portpather_selection_follow_names() -> None:
+    default_tool = PathTool(layer=(1, 0), width=1, ptype='wire')
+    named_tool = PathTool(layer=(2, 0), width=1, ptype='wire')
+    p = Pather(
+        Library(),
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools={None: default_tool, 'A': named_tool},
+        render='deferred',
+        )
+    selected = p.at('A')
+
+    p.rename_ports({'A': 'B'})
+
+    assert selected.ports == ['A']
+    assert p.tools['A'] is named_tool
+    assert 'B' not in p.tools
+    p.straight('B', 1)
+    assert p._paths['B'][0].tool is default_tool
+
+    p.mkport('A', Port((10, 0), rotation=0, ptype='wire'))
+    p.straight('A', 1)
+    assert p._paths['A'][0].tool is named_tool
+
+
 def test_pather_straight(pather_setup: tuple[Pather, PathTool, Library]) -> None:
     p, tool, lib = pather_setup
     p.straight("start", 10)
diff --git a/masque/test/test_pather_rendering.py b/masque/test/test_pather_rendering.py
index 677fa12..3c50e3b 100644
--- a/masque/test/test_pather_rendering.py
+++ b/masque/test/test_pather_rendering.py
@@ -101,6 +101,60 @@ def test_deferred_render_retool(deferred_render_setup: tuple[Pather, PathTool, L
     assert len(rp.pattern.shapes[(1, 0)]) == 1
     assert len(rp.pattern.shapes[(2, 0)]) == 1
 
+
+def test_deferred_render_batches_tools_by_identity() -> None:
+    class CountingTool(PathTool):
+        def __init__(self, *args, **kwargs) -> None:  # noqa: ANN002,ANN003
+            super().__init__(*args, **kwargs)
+            self.render_calls = 0
+
+        def render(self, *args, **kwargs):  # noqa: ANN002,ANN003,ANN202
+            self.render_calls += 1
+            return super().render(*args, **kwargs)
+
+    lib = Library()
+    tool1 = CountingTool(layer=(1, 0), width=2, ptype='wire')
+    tool2 = CountingTool(layer=(1, 0), width=2, ptype='wire')
+    assert tool1 == tool2
+    assert tool1 is not tool2
+    p = Pather(
+        lib,
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools=tool1,
+        render='deferred',
+        )
+
+    p.straight('A', 5)
+    p.retool(tool2, 'A')
+    p.straight('A', 5)
+    p.render()
+
+    assert tool1.render_calls == 1
+    assert tool2.render_calls == 1
+    assert len(p.pattern.shapes[(1, 0)]) == 2
+
+
+def test_deleted_name_reuse_does_not_retarget_pending_render_steps() -> None:
+    lib = Library()
+    tool = PathTool(layer=(1, 0), width=2, ptype='wire')
+    p = Pather(
+        lib,
+        ports={'A': Port((0, 0), rotation=0, ptype='wire')},
+        tools=tool,
+        render='deferred',
+        )
+
+    p.straight('A', 5)
+    original_step = p._paths['A'][0]
+    p.rename_ports({'A': None})
+    p.mkport('A', Port((100, 0), rotation=0, ptype='wire'))
+    p.straight('A', 5)
+
+    assert len(p._paths['A']) == 2
+    assert_allclose(original_step.start_port.offset, (0, 0))
+    assert_allclose(original_step.end_port.offset, (-5, 0))
+    assert_allclose(p._paths['A'][1].start_port.offset, (100, 0))
+
 def test_portpather_translate_only_affects_future_steps(deferred_render_setup: tuple[Pather, PathTool, Library]) -> None:
     rp, tool, lib = deferred_render_setup
     pp = rp.at("start")
diff --git a/masque/test/test_pather_trace_into.py b/masque/test/test_pather_trace_into.py
index ed967dd..f79ecc1 100644
--- a/masque/test/test_pather_trace_into.py
+++ b/masque/test/test_pather_trace_into.py
@@ -5,9 +5,9 @@ import pytest
 from numpy import pi
 from numpy.testing import assert_equal
 
-from masque import Library, PathTool, Port, Pather
+from masque import Library, PathTool, Port, Pather, RouteFailurePolicy
 from masque.builder.planner import PreparedRouteResult, RoutePlanningError, RoutePortContext, RoutingPlanner
-from masque.builder.planner.planner import Candidate, RouteRequest
+from masque.builder.planner.planner import Candidate, SolverRequest
 from masque.builder.tools import BendOffer, PrimitiveOffer, StraightOffer, Tool
 from masque.error import BuildError, PortError
 
@@ -280,7 +280,7 @@ class TraceIntoBudgetSolver:
         band = (min_bends, max_bends)
         self.attempts.append(band)
         if band in self.fatal_at:
-            raise RoutePlanningError('fatal', fatal=True)
+            raise RoutePlanningError('fatal', policy=RouteFailurePolicy.FATAL)
         if band not in self.successes:
             raise BuildError('try next budget')
         return Candidate((), Port((0, 0), rotation=0, ptype='wire'), 0.0, 0, 0.0)
@@ -291,7 +291,7 @@ class TraceIntoBudgetPlanner(RoutingPlanner):
         self.solver = TraceIntoBudgetSolver(successes, fatal_at=fatal_at)
         self.solver_requests = 0
 
-    def solver_for_request(self, request: RouteRequest) -> Any:
+    def solver_for_request(self, request: SolverRequest) -> Any:
         _ = request
         self.solver_requests += 1
         return self.solver