[Feat] (Pipe): land the P1 contract - PipeInputsSwitch.h with MGB_CTX, the 63-field PipeInputs block with type-identical accessors, FillPoints.def and its G5b generator, the MOBILEGL_PIPE_PUSH/VERIFY options and the three verify knobs; pull build unchanged

- MG_Pipe/PipeInputsSwitch.h is the strangler switch (ARCHITECTURE.md 9.2): MGB_CTX is the
  live GLContext in the pull build and &gPipeInputs under MOBILEGL_PIPE_PUSH, so the pull
  arm's pGLContext spelling stays outside MG_Backend/ and purity gate C's grep.
- MG_Backend/MGPipe/PipeInputs.h holds one struct with every accessor a backend reads (63:
  the 61 Coverage.def rows plus GetBoundTransformFeedbackLifetimeId and
  HasOpenTransformFeedbackSpan), each keeping its GLContext name, parameters and return
  type so the site conversion is type-neutral; V fields are copied values, O fields are
  SharedPtr copies or pointers into the context, the seven F fields forward to the live
  context from MG_Impl/Pipe/PipeFill.cpp and are the only sticky ones (Coverage.def's
  MGP_COVERAGE_STICKY_LIST argues each: argument-keyed lookups and reverse-channel writes,
  never a version or generation counter).
- MG_Pipe/FillPoints.def is the verb table: one row per GLFunctionsTable function pointer in
  declaration order (69), nine classes and the may-read field rows; gen_pipe.py parses the
  struct and refuses a row set that is not exactly its member set, then emits
  generated/PipeFillPoints.inc (verb enum, class tables, per-class field masks with the
  sticky fields OR'ed in). MGP_FILL(Verb) in MG_Impl/Pipe/PipeFill.h is the fill point;
  MGPipeFillForVerb only bumps the serial, records the verb and stamps the sticky fields
  here - the per-class copies land in the next commit, the fill points in MG_Impl after.
- MOBILEGL_PIPE_POISON is derived once in PipeInputs.h from MOBILEGL_PIPE_PUSH and the DEBUG
  level, MOBILEGL_BUILD_DISAGGREGATED or MOBILEGL_PIPE_VERIFY (the tree has no
  MOBILEGL_DEBUG); under it every accessor is a read-side freshness check that aborts with
  Fatal{UnmigratedPipeInput, "Field@Verb"}.
- CMake: MOBILEGL_PIPE_PUSH and MOBILEGL_PIPE_VERIFY options (VERIFY forces PUSH on), the two
  new sources appended only under PUSH, the compile definitions; Config.h/ConfigLoader.cpp
  gain PipeVerifyFatal / PipeVerifyCorrupt / PipePoisonOmit under #if MOBILEGL_PIPE_PUSH so
  the pull build's FeaturesTable does not change size.
- Pull build proof: symbol_report.py against the 087685d1 baseline reports 0 added / 0
  removed / 0 resized / 0 renamed and a .text delta of 0; ctest -N names unchanged; gen_pipe
  --check clean; unit tests green in the pull, push and verify builds.

MobileGL/MG_Pipe/PipeInputsSwitch.h

@@ -0,0 +1,28 @@
+// MobileGL - MobileGL/MG_Pipe/PipeInputsSwitch.h
+// Copyright (c) 2025-2026 MobileGL-Dev
+// Licensed under the GNU Lesser General Public License v3.0:
+//   https://www.gnu.org/licenses/gpl-3.0.txt
+//   https://www.gnu.org/licenses/lgpl-3.0.txt
+// SPDX-License-Identifier: LGPL-3.0-only
+// End of Source File Header
+
+#pragma once
+#ifndef MOBILEGL_MG_PIPE_INPUTS_SWITCH_H   // belt and braces: reachable as <MG_Pipe/..> and <..> (CMakeLists.txt:531,535)
+#define MOBILEGL_MG_PIPE_INPUTS_SWITCH_H
+// The strangler switch (ARCHITECTURE.md 9.2). Every backend read of frontend state is spelled
+// MGB_CTX->Accessor(...). Pull arm: the live GLContext, so the pull build is the tree before P1
+// token for token. Push arm: the PipeInputs block the frontend fills at every verb boundary.
+// The pull arm is the ONLY place under MobileGL/ outside MG_State and MG_Impl that may spell
+// pGLContext; purity gate C greps MG_Backend/ for that token.
+#if MOBILEGL_PIPE_PUSH
+#include <MG_Backend/MGPipe/PipeInputs.h>
+#define MGB_CTX (&::MobileGL::MG_Pipe::gPipeInputs)
+#define MGB_CTX_LIVE (::MobileGL::MG_Pipe::gPipeInputs.IsLive())
+#define MGB_CTX_IDENTITY (::MobileGL::MG_Pipe::gPipeInputs.ContextIdentity())
+#else
+#include <MG_State/GLState/Core.h>
+#define MGB_CTX (::MobileGL::MG_State::pGLContext)
+#define MGB_CTX_LIVE (::MobileGL::MG_State::pGLContext != nullptr)
+#define MGB_CTX_IDENTITY (static_cast<const void*>(::MobileGL::MG_State::pGLContext.get()))
+#endif
+#endif