misc doc updates

MIGRATION.md

@@ -421,6 +421,10 @@ may add explicit probes. Empty discovery is an error unless
 Validation returns normally on success and otherwise raises an
 `ExceptionGroup` of contextual `ToolContractError`s.
 
+Run this validation during Tool development, testing, or application startup.
+It is the comprehensive semantic preflight for custom Tools; those checks are
+intentionally not repeated for every offer evaluation in the routing hot path.
+
 Positional routing bounds (`p`, `pos`, `position`, `x`, and `y`) now require a
 nearly Manhattan input-port direction. Arbitrarily angled ports remain valid
 for non-positional/extension routing.
@@ -449,9 +453,12 @@ import it from user code.
 `trace_into()` uses the same primitive-offer route selection and now searches
 bounded route topologies with up to four bend roles. This preserves the common
 straight, bend, S-like, U-like, and dogleg cases while allowing routes that
-need an additional bounded bend pair. Among legal bounded candidates,
-`trace_into()` selects the lowest total primitive-offer cost; bend count and
-step count are used only to break exact cost ties.
+need an additional bounded bend pair. Bend-family requests search one-bend
+routes before three-bend routes; other families search zero-to-two-bend routes
+before four-bend routes. The first band with a legal route wins. Within that
+band, candidates are ordered by total primitive-offer cost, adapter count, step
+count, and deterministic discovery order. The route `strategy` affects only
+that final discovery-order tie-break.
 
 Explicit-length `jog()` routes may also be satisfied by composing a straight
 primitive before or after an omitted-length native S primitive. `uturn()` routes

README.md

@@ -275,8 +275,6 @@ my_pattern.ref(_make_my_subpattern(), offset=..., ...)
 ```
 
 
-## TODO
+## Development
 
-* PolyCollection & arrow-based read/write
-* Bus-to-bus connections?
-* tuple / string layer auto-translation
+Project-level planned work is tracked in [TODO.md](TODO.md).

masque/builder/__init__.py

@@ -31,6 +31,11 @@ geometry into the Pattern and Library.
 `masque.builder.planner` is an internal planner implementation rather than a
 stable public API.
 
+Custom Tool authors should run `validate_tool_contract()` as a development or
+application-startup preflight. It performs the comprehensive semantic checks
+that are intentionally not repeated during route selection, keeping the normal
+routing path focused on search rather than contract verification.
+
 The practical layering is:
 - user code drives `Pather` and chooses Tools per port or by default,
 - Tools describe local legal motion primitives without touching Pather state,

masque/builder/pather.py

@@ -1064,11 +1064,14 @@ class Pather(PortList):
 
         The current baseline searches bounded primitive-offer routes with up to
         four bend roles, including straight, single-bend, S-like, U-like, and
-        dogleg topologies. The lowest-cost legal bounded candidate is selected;
-        bend count, step count, and search order are tie-breakers only. `strategy`
-        controls straight-first vs turn-first search order within those ties.
-        Custom planning options may be supplied through `tool_options`; they are
-        forwarded only to primitive offer generation.
+        dogleg topologies. Bend-family requests try one-bend routes before
+        three-bend routes; other families try zero-to-two-bend routes before
+        four-bend routes. The first band with a legal candidate wins. Within a
+        band, candidates are ordered by total cost, adapter count, step count,
+        and deterministic discovery order. `strategy` controls straight-first
+        vs turn-first discovery order and therefore only the final tie-break.
+        Custom planning options may be supplied through `tool_options`; they
+        are forwarded only to primitive offer generation.
 
         If `plug_destination` is `True`, the destination port is consumed by the final step.
         If `thru` is provided, that port is renamed to the source name after the route is complete.