docs(runner): clarify phase 6 port ownership

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/paperclip-runner/docs/architecture.md

@@ -206,6 +206,7 @@ buildable, testable, and runnable against the mock adapter.
 The proposed Phase 6 seam is recorded in
 [Phase 6 Thin Paperclip Adapter Boundary](design/phase-6-thin-paperclip-adapter.md).
 It keeps one dependency direction, branches only after Paperclip workspace and
-environment realization, uses a server-bound implementation of the public
-ports, and returns to the existing Paperclip finalization path. The proposal is
+environment realization, composes a package-owned `NativeSessionBackend` with
+a server-bound `ControlPlanePort`, and returns to the existing Paperclip
+finalization path. The core seam contains no runner behavior. The proposal is
 design-only until the CTO gate accepts it.

packages/paperclip-runner/docs/design/phase-6-thin-paperclip-adapter.md

@@ -13,6 +13,13 @@ Paperclip will integrate the native runner through two public package ports:
 - `ControlPlanePort` accepts validated PRP events and terminal results from the
   package and exposes durable acknowledgement and replay cursors.
 
+The two ports are complementary, not two core implementations. The runner
+package supplies the `NativeSessionBackend` implementation; Paperclip supplies
+the server-bound `ControlPlanePort` implementation. The core adapter only
+composes those public contracts and translates the final result into existing
+Paperclip types. It does not implement a native backend or contain runner
+behavior.
+
 The dependency direction is one way:
 
 ```text

packages/paperclip-runner/spec/paperclip-native-runner-implementation-plan.md

@@ -425,7 +425,8 @@ No Phase 6 implementation code starts until the CTO gate accepts that record.
 
 **Deliverables:**
 
-- Paperclip implementation of `ControlPlanePort`/`NativeSessionBackend` in a narrow integration package or service boundary;
+- a package-owned `NativeSessionBackend`, a server-bound Paperclip
+  `ControlPlanePort`, and a narrow core seam that only composes them;
 - feature-flagged runtime selection;
 - mapping to existing workspace preparation/finalization, cancellation, budgets, approvals, audit, and issue status authority;
 - native event persistence/replay adapter using the proven schema;