docs: assemblies are out of scope by design, and the priority order

CIVICVS ruled on 11 SEP that the absence of an assembly layer is chosen, not unfinished. Positioning is field work. Parts made and shipped by different manufacturers have no knowledge of each other assembly tolerances, and interchangeable manufacture works because of that separation rather than in spite of it. Fit up is resolved on site against conditions no designer had. PRECISION.md section 7 now says so, and closes with read this as a boundary that was chosen, not a gap to be filled.

Section 10 corrected. Its lock is on this document subject, not on the software roadmap, and it was misread that way once. Section 7 holds two kinds of entry: limits that may be lifted by work, and boundaries that were chosen and should not be. Without that distinction section 7 reads as a to do list.

Section 7 also separates geometry interchange from machine instructions. An STL or STEP describes a shape; a toolpath describes what a machine should do. The first is in scope and planned, the second is not. The two sat one line apart with nothing saying they differ in kind.

HANDOFF section 5 corrected: STL export needs no CAD kernel. A member here is prismatic by definition, so an STL is two triangulated caps and a quad strip. Verified in CT 100 that shapely constrained_delaunay_triangles handles a polygon with a hole correctly, area exact and no triangle inside the hole. That second check is the one that matters, because a triangulator that fills bores produces an STL which looks right in a slicer and prints solid where the conduit goes. STEP still needs the kernel.

Priority order recorded with its reasoning so a successor can disagree with the argument rather than only the sequence. STL export first because it is the only item producing physical feedback. Then an authorship field in the design record, one field and a one way door. Then per member stock for the conduit core. Then persistence, which nothing has ever written despite MECHCOMP_DATA_DIR being declared since staging. Then ACL, last, because access control over nothing is machinery without a subject.

A node is not an assembly. It is another artifact with declared interfaces and stays in scope. What is out of scope is positioning artifacts relative to one another. The project obligation is therefore to make each artifact interchangeable, which is what the stock descriptor and the design record already exist for.

docs/PRECISION.md

@@ -225,10 +225,22 @@ of a millimetre.
 
 This section is as important as section 6 and should be read with equal weight.
 
-**It has no assembly layer.** It describes the cross-section of *one* member.
-Nothing positions multiple members in a shared coordinate frame. For a bridge,
-each component would be modelled to the accuracy above — arranging them into a
-structure does not exist here and belongs in separate software.
+**It has no assembly layer — by design, not by omission.** It describes the
+cross-section of *one* member. Nothing positions multiple members in a shared
+coordinate frame, and nothing ever should.
+
+Positioning is field work. Parts made and shipped by different manufacturers
+have no knowledge of each other's assembly tolerances; interchangeable
+manufacture works *because* of that separation, not in spite of it. A bolt
+supplier holds a thread specification, not a tolerance stack for the bridge the
+bolt ends up in. Fit-up is resolved on site, against conditions no designer had.
+
+The compiler's obligation is therefore to make each member independently
+reproducible and to state its interfaces plainly. How members meet belongs to
+whoever is holding them.
+
+**Read this as a boundary that was chosen, not a gap to be filled.** A future
+contributor proposing an assembly layer is proposing a different product.
 
 **It models one shape family.** Prismatic members: a two-dimensional
 cross-section swept along a straight axis. Not tapers, not curved axes, not
@@ -258,7 +270,12 @@ criterion rather than 0.0001 mm.
 **It says nothing about surface finish, material properties, or joining.** Per
 section 0.
 
-**It does not generate machine instructions.** No toolpaths, no G-code, no slicing.
+**It does not generate machine instructions.** No toolpaths, no G-code, no
+slicing.
+
+Geometry interchange is a different thing and is *not* excluded here. An STL or
+a STEP file describes a shape; a toolpath describes what a machine should do.
+Exporting the former is in scope and planned; producing the latter is not.
 
 ---
 
@@ -276,6 +293,7 @@ section 0.
   with the square root of radius.
 - Accuracy does **not** degrade with object size.
 - **One member at a time. No assembly. No structural analysis. No toolpaths.**
+  The first three are chosen boundaries, not unfinished work — see section 7.
 
 ---
 
@@ -313,6 +331,17 @@ reproducible with `make test`.
 **This document is scoped by section 0. Additions that widen the scope should be
 refused, not accommodated.**
 
+**Section 0's lock is on this document's subject, not on the software's
+roadmap.** It exists to stop this becoming a general precision guide whose
+borrowed figures would look as authoritative as the measured ones. It is not a
+freeze on what the compiler may one day do, and it was misread that way once.
+
+**Section 7 holds two kinds of entry, and they are not the same.** Some are
+*limits* that may be lifted by work — untested ranges, absent export formats.
+Others are *boundaries* that were chosen and should not be — the absence of an
+assembly layer, of structural analysis, of toolpaths. Do not read section 7 as
+a to-do list. Each entry says which kind it is.
+
 If a reader needs casting tolerances, weld distortion, surface roughness or
 lithography, the answer is a different document — not another row in section 3's
 table. Every such row would look as authoritative as the measured ones while