[MG_Pipe, MG_Backend, MG_Remote, MG_Test] (Disaggregated): P5e wave 1 integration - one body per seam, and the stamp waits for ra

- c0e and id were implemented in parallel and each declared the two shared seams,
  so the merge produced five duplicate definitions the text could not collide:
  MGPipeBarriered, MGPipeApplierCurrentRecordIsBarriered and the three by-handle
  twin resolvers. Resolved per ID-99 and ID-103.
- MGPipeBarriered keeps c0e's real body (the static wait-class column, the XFB
  escalation and the client-array escalation); id's constant-true placeholder goes.
- The current-record flag keeps c0e's thread_local storage and setter and loses
  id's MGPipeApplierState member: it describes which record THIS THREAD is inside,
  not per-context state the applier owns, and the allocator guard that reads it
  would otherwise have to find the right context's applier first. id's test hook
  posts through the setter.
- The three resolvers keep id's real bodies beside each registry; c0e's asserting
  stubs for them go. The seam stubs no package has bodied yet stay.
- ApplyOne stamps `true` while kMGPipeP5eClientWaitRuleLanded is false. The
  predicate says what the client WILL do; until ra changes EmitAndWaitTails the
  client still blocks after every record, so a `false` stamp would withdraw the
  §4.4 exemption from a probe the client's own wait still makes safe. The
  predicate is computed on every record regardless, so it is exercised for the
  whole phase instead of first running on the day it starts deciding.
- Gates on the merged tree: unit 2206/2206, integration-split 111/111, both
  generators --check/--self-test green, include closure 0 problems, dirty surface
  rc 0, doc citations one pre-existing CONTRACT-P5.md line (c0e retired another).

MobileGL/MG_Test/Wire/RemoteClientTest.cpp

@@ -1915,8 +1915,10 @@ TEST(RemoteGuards, AnAllocatorProbeInsideAnExemptionScopeFromTheApplyThreadIsFat
         Srv::ServerLoopInstance().RunOnApplyThread(
             +[](void* self) -> MobileGLResult {
                 auto& probe = *static_cast<Probe*>(self);
-                // The record being applied is one the client did NOT park behind.
-                MG_Pipe::MGPipeApplier().CurrentRecordBarriered = false;
+                // The record being applied is one the client did NOT park behind. The stamp is
+                // the thread_local the sink writes (ID-103), so setting it here puts this
+                // thread in exactly the state an unbarriered apply is in.
+                MG_Pipe::MGPipeApplierSetCurrentRecordBarriered(false);
                 const MG_Pipe::MGPipeFrontendKeyedRegistryScope frontendKeyedRegistry;
                 probe.table->HandleOf(probe.texture);
                 return MOBILEGL_OK;