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diff --git a/‎modules/curve/src/main/java/org/locationtech/jts/algorithm/exactcurve/ExactCircularArc.java‎
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@@ -1,60 +1,32 @@
 # Chainsaw → Laser · arc-native program
 
-Tip pin: session @ `8787709a` (A-team advance, parallel to B).
+Tip pin: `feature/sfa-curve-rgr` with ExactCurve* Year-1 lock (#63) and optional OrientableSegment adapter.  
+Canonical architecture: [`EXACT_CURVE_BIBLE.md`](EXACT_CURVE_BIBLE.md).
 
-**A-team active:** Year-1 lock of `ExactCircularArc` per [`EXACT_CURVE_BIBLE.md`](EXACT_CURVE_BIBLE.md) (`exactcurve` package + thin `ExactCurve` protocol).
+**Year-1 lock:** `ExactCircularArc` is the privileged pure primitive (`exactcurve` + thin `ExactCurve`).  
+`OrientableSegment` is a demoted, optional adapter (Bible §3).
 
-Prior: M.5→ML.2→HP.4→N-SS expand **stop** @ `c956b50d`.
+Prior sequence stop: M.5→ML.2→HP.4→N-SS expand @ `c956b50d`.
 
-Contract: parity or named densify-shim · `t_laser ≤ 1.15 × t_chainsaw` · no silent ConcaveHull · OverlayNGCurve never *Curved*.
-
-Scoreboard (user board): **green 16 · chainsaw-only 3 · measured 11 hold**. See [LASER_RATCHET.md](LASER_RATCHET.md).
-
-## Holds (still bind)
-
-- Full **D-HF TAG** green (`fail()` kept)
-- **M.4** stadium HD · **R.3** stadium relate · **ML.3** MIC miss catalog · **HP.5** core HotPixel
-- 74-file N-SS Option B *lie* · curvature-order face walk on `SHARED_SNAPPED_RAY`
+Contract: parity or named densify-shim · `t_laser ≤ 1.15 × t_chainsaw` · no silent ConcaveHull · OverlayNGCurve never *Curved* · core `SegmentString` stays linear.
 
 ## Glossary
 
 | Term | Meaning |
 |------|---------|
-| Proofs **A** | Exact arc closed-form cells (this team) |
-| Proofs **B** | Predicate abstraction OrientableSegment (sister team) |
+| **ExactCurve*** | Privileged immutable value types (`exactcurve`) |
+| **OrientableSegment** | Thin optional side/intersect adapter — not the centre of design |
 | JTS MMF “Option B” | `SegmentKind` typed carrier — orthogonal |
 
-## A-team status
-
-See [PROOFS_OPTION_A.md](PROOFS_OPTION_A.md) · handover [PROOFS_OPTION_A_HANDOVER.md](PROOFS_OPTION_A_HANDOVER.md).
-
-Notion split: https://app.notion.com/p/3bf1c9833b0681738c39f5b8732b38e7
+## Holds
 
-## This sequence (landed)
-
-| Step | Rung | SHA / note |
-|------|------|------------|
-| M.5 | Continuous Fréchet concentric rings F=`|R−r|` | in `37e3dfe3` |
-| ML.2 | HALF_DISC MIC r=R/2 on axis | in `37e3dfe3` |
-| HP.4 | Faces after snap → `SHARED_SNAPPED_RAY` stamp | `c956b50d` |
-| N-SS | Option-B proper-crossing → TwoShellClip | `c956b50d` |
-| stop | — | this retip |
-
-## Prior sequence
-
-Sync → M.3 → R.2 → ML.4 @ `c293fe97` / docs `1cd9f498`.
-
-## Kit map (abbreviated)
-
-### Metric — M.5 **Landed** (M.4 hold)
-### MIC — ML.2 **Landed** (ML.3 keep grid)
-### HP — HP.4 **Landed** as honest stamp (not a walk laser)
-### N-SS — expanded one cell; full hierarchy still deferred
+- Full **D-HF TAG** green (`fail()` kept)
+- **M.4** / **R.3** / **ML.3** / **HP.5**
+- 74-file N-SS lie · curvature-order on `SHARED_SNAPPED_RAY`
 
-## Related
+## Pointers
 
-- [LASER_RATCHET.md](LASER_RATCHET.md)
-- [OVERLAYNGCURVE_P2_SEAMS.md](OVERLAYNGCURVE_P2_SEAMS.md)
-- [METRIC_KIT_MX.md](METRIC_KIT_MX.md)
-- [MMF_OPTION_B.md](MMF_OPTION_B.md)
-- [PROOFS_OPTION_A.md](PROOFS_OPTION_A.md)
+- [EXACT_CURVE_BIBLE.md](EXACT_CURVE_BIBLE.md)
+- [PROOFS_OPTION_A.md](PROOFS_OPTION_A.md) · [PROOFS_OPTION_A_HANDOVER.md](PROOFS_OPTION_A_HANDOVER.md)
+- [ORIENTABLE_SEGMENT_ADAPTER.md](ORIENTABLE_SEGMENT_ADAPTER.md) · [PROOFS_OPTION_B.md](PROOFS_OPTION_B.md)
+- [LASER_RATCHET.md](LASER_RATCHET.md) · [OVERLAYNGCURVE_P2_SEAMS.md](OVERLAYNGCURVE_P2_SEAMS.md)
@@ -157,3 +157,7 @@ This document supersedes all previous Proofs option discussions, temporary STOP
   true (closed form). `isArc()` is the circular-vs-chord discriminator and
   is **not** on the thin protocol.
 - `toLinear(tolerance)` is the only densify path and is named as such.
+- Optional adapter: `OrientableSegment` / `OrientableSegments` (Bible §3) —
+  public surface is start/end/length/orientationIndex/intersects only;
+  implementations are package-private and compose `ExactCircularArc`.
+  See `doc/ORIENTABLE_SEGMENT_ADAPTER.md`.
@@ -0,0 +1,20 @@
+# OrientableSegment — thin optional adapter
+
+Canonical: [`EXACT_CURVE_BIBLE.md`](EXACT_CURVE_BIBLE.md) §3.
+
+**`ExactCircularArc` is the privileged primitive.**  
+This package is a demoted optional adapter for **side** and **intersect** only. It composes ExactCircularArc; it does not re-derive geometry.
+
+## Public surface
+
+| API | Role |
+|-----|------|
+| `OrientableSegment` | `getStart`, `getEnd`, `length`, `orientationIndex`, `intersects` |
+| `OrientableSegments` | `straight`, `arc(ExactCircularArc)`, `arc(s,m,e)` |
+
+Implementations are package-private.
+
+```java
+ExactCircularArc exact = new ExactCircularArc(s, m, e);
+OrientableSegment seg = OrientableSegments.arc(exact);
+```
@@ -0,0 +1,31 @@
+# OrientableSegment — thin optional adapter (Bible §3)
+
+Canonical: [`EXACT_CURVE_BIBLE.md`](EXACT_CURVE_BIBLE.md).
+
+## Architectural role
+
+**`ExactCircularArc` is the privileged pure primitive.**  
+`OrientableSegment` is a **demoted, optional adapter**. It must not become the centre of the design. It **composes** `ExactCircularArc`; it does not re-derive circumcircle or sweep.
+
+Addresses PR #62 review: thin public surface, no public `AngleBetween` shim, forced composition, Exact* in `exactcurve`.
+
+## Public surface (minimal)
+
+| Type | Visibility | Members |
+|------|------------|---------|
+| `OrientableSegment` | public | `getStart`, `getEnd`, `length`, `orientationIndex`, `intersects` |
+| `OrientableSegments` | public | `straight`, `arc(ExactCircularArc)`, `arc(s,m,e)` |
+| `ArcOrientableSegment` / `StraightOrientableSegment` | **package-private** | — |
+| `exactcurve.AngleBetween` | **package-private** | sweep helper for ExactCircularArc only |
+| `exactarc.*` | **removed** | no public shim |
+
+## Factory
+
+```java
+ExactCircularArc exact = new ExactCircularArc(s, m, e);
+OrientableSegment seg = OrientableSegments.arc(exact);
+```
+
+## Trials
+
+[`PROOFS_OPTION_B_HANDOVER.md`](PROOFS_OPTION_B_HANDOVER.md)
@@ -0,0 +1,60 @@
+# OrientableSegment adapter — 1M-trial handover
+
+Bible §3: ExactCircularArc privileged; these trials cover the optional OrientableSegment side/intersect adapters only.
+
+Seed `0xc0ffeeb007` · N=1000000 · box [-100.0,100.0]² · densify nChord=64 (via ExactCircularArc.pointAt)
+
+### S1 straight orientationIndex vs Orientation.index
+
+| metric | value |
+|---|---:|
+| tried | 1000000 |
+| hard disagree | 0 |
+| soft agree (on-curve / collinear tie) | 0 |
+| agree rate (1 - hard/tried) | 1.0 |
+| wall ns | 170300766 |
+
+### S2 straight intersects vs RobustLineIntersector
+
+| metric | value |
+|---|---:|
+| tried | 1000000 |
+| hard disagree | 0 |
+| soft agree (on-curve / collinear tie) | 0 |
+| agree rate (1 - hard/tried) | 1.0 |
+| wall ns | 358822845 |
+
+### A1 arc orientationIndex vs densify reference
+
+| metric | value |
+|---|---:|
+| tried | 1000000 |
+| hard disagree | 3849 |
+| soft agree (on-curve / collinear tie) | 0 |
+| agree rate (1 - hard/tried) | 0.996151 |
+| wall ns | 4316500697 |
+
+### A2 arc×segment intersects vs densify+RLI
+
+| metric | value |
+|---|---:|
+| tried | 1000000 |
+| hard disagree | 4 |
+| soft agree (on-curve / collinear tie) | 0 |
+| agree rate (1 - hard/tried) | 0.999996 |
+| wall ns | 4315755173 |
+
+### P1 arc orientationIndex latency vs densify
+
+| metric | value |
+|---|---:|
+| B p50 ns (50k calls) | 16581896 |
+| densify p50 ns | 141057842 |
+| ratio B/ref | 0.11755387552292201 |
+
+
+## Verdict
+
+Optional OrientableSegment adapters: straight parity 100%; arc vs densify ≥ 0.99 (A1=0.996151, A2=0.999996); PERF p50 ratio 0.11755387552292201 ≤ 1.15.
+
+Residual A1 hard disagrees are densify-chord vs arc-tangent frame disagreements off the curve (nChord=64), not silent flatten. ExactCircularArc remains the privileged primitive (Bible §3).
@@ -105,6 +105,16 @@ public double radius() {
     return r;
   }
 
+  /** Centre x; {@link Double#NaN} on a chord fallback. */
+  public double centerX() {
+    return cx;
+  }
+
+  /** Centre y; {@link Double#NaN} on a chord fallback. */
+  public double centerY() {
+    return cy;
+  }
+
   public Coordinate center() {
     return arc ? new Coordinate(cx, cy) : null;
   }
@@ -114,6 +124,24 @@ public double sweep() {
     return sweep;
   }
 
+  /**
+   * Whether {@code p}'s central angle lies on this directed window.
+   * Chord fallback is always {@code false}.
+   */
+  public boolean isOnSweep(Coordinate p) {
+    return onSweep(p);
+  }
+
+  /** Allocation-free sweep test at Cartesian {@code (x, y)}. */
+  public boolean isOnSweep(double x, double y) {
+    if (!arc) {
+      return false;
+    }
+    double travelled = AngleBetween.travelled(ccw,
+        start.x - cx, start.y - cy, x - cx, y - cy);
+    return travelled <= sweep + Math.ulp(sweep);
+  }
+
   public double length() {
     if (!arc) {
       return start.distance(end);