ROADMAP: section 7 is binding. PRECISION: prismatic-only is a limit

ROADMAP opened by saying nothing in it is a promise. Section 7 holds eighteen standing principles cited by number as settled law from commit messages and from other documents - 4 governs what is hashed, 13 defines what a standard is, 17 governs what may write to a record, 18 governs how a contribution is admitted. A reader taking the header at its word would conclude Principle 17 is optional. The disclaimer now says what it always meant: it covers section 4 sequence and section 5 assumptions, not section 7.

Principle 5 gets the same qualification PROCESS section 8 got. A permanent deviation is the specification is right about facts on a host and would be licence to lower a REQ if read without limit.

PRECISION section 10 requires every section 7 entry to say whether it is a limit that work may lift or a boundary that was chosen. The prismatic-only entry said neither, which is the single most consequential ambiguity in the document. It is a limit, and the reason is now recorded: the oracle is a two-dimensional oracle with a scalar length multiplier - every recorded value is a property of the cross-section except LENGTH_MM, VOLUME_MM3 and MASS_G, and volume equals rounded section area times length to within 3.6e-12 across all 113 accepted cases. Lift it carelessly and that relation stops holding; nothing fails, it just stops meaning what it means. Anything keeping each station two-dimensional preserves it.

Also in PRECISION: STL export landed and is no longer planned. An absent export format is a limit; the refusal to emit toolpaths is a boundary.

ROADMAP section 4a corrected to match STAGING-STATE section 3a: nothing here is implemented on Kane Fabric, and SASE was used and never defined. The port is recorded done. The seed commit and test count are removed as derivable.

IDENTITY-CONTRACT: the rewrap owed from a76879f.

Applied by anchored patcher. Suite 643 passed, oracle intact. Documentation only.

docs/PRECISION.md

@@ -246,6 +246,24 @@ contributor proposing an assembly layer is proposing a different product.
 cross-section swept along a straight axis. Not tapers, not curved axes, not
 varying sections, not surfaces of revolution, not anything organic.
 
+**This is a limit, not a boundary** — §10's distinction, which this entry failed
+to state until 2026-09-13. It may be lifted by work, and the reason it exists is
+not that sweeping is the honest bound of what the compiler may claim.
+
+It exists because **the oracle is a two-dimensional oracle with a scalar length
+multiplier.** Of the values the 123 cases record, every one is a property of the
+cross-section except `LENGTH_MM`, `VOLUME_MM3` and `MASS_G` — and volume equals
+rounded section area times length to within 3.6e-12 across all 113 accepted
+cases. Lift the restriction carelessly and that relation stops holding. Nothing
+would fail; it would simply stop meaning what it means.
+
+Anything that keeps each station's section two-dimensional preserves it. A member
+modelled as an ordered set of prismatic segments, each carrying its own section,
+still verifies segment by segment through the existing machinery, and a
+one-segment member is byte-identical to today. Tapers and curved axes stay
+outside the family and should: they vary continuously rather than piecewise, and
+the volume relation would not survive them.
+
 **It performs no engineering analysis whatsoever.** No stress, no load, no
 deflection, no buckling, no fatigue, no thermal behaviour, no failure
 prediction. It reports geometry — area, wall thickness, mass — and nothing about
@@ -275,7 +293,12 @@ 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.
+Exporting the former is in scope; producing the latter is not.
+
+**STL export landed 2026-09-12** and needs no CAD kernel — a member is prismatic
+by definition, so the mesh is two triangulated caps and a quad strip down the
+boundary. STEP remains unbuilt. An absent export format is a *limit* in §10's
+sense; the refusal to emit toolpaths is a *boundary*.
 
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