[Config, MG_Backend, MG_Test] (Disaggregated): P5e c0e - the two knobs and the caps arm

- IpcTable::RunAhead (MOBILEGL_IPC_RUN_AHEAD, default 1, forced 0 under PipeVerify beside
  BatchWaits) and IpcTable::PresentCredit (MOBILEGL_IPC_PRESENT_CREDIT, default 1, range
  1..8). Both parsed unconditionally like every other IPC knob and both in the IPC log
  line, because a knob that silently means nothing on one arm of an A/B is how an A/B
  stops being one.
- RUN_AHEAD=0 is an A/B CONTROL and not a negative one: identical server code, identical
  records, identical fill decision, and only the client's wait differs. VERB_BARRIER=0
  keeps its own meaning as the lockstep arm's negative control.
- MG_Backend/Init.cpp: kMGPipeP5eRunAheadReady = false, and the caps arm goes through
  MGPipeRunAheadCapBitsFor so the "DirectGLES only, and only once the integration commit
  flips the constant" decision has one spelling. A constant and not a knob: an operator
  must not be able to turn a half-migrated server into a run-ahead one, because the
  failure mode is a torn read that renders wrong rather than aborting.
- MagmaPipeIdentityTest pins both halves - no bit 10 for DirectVulkan whatever the
  integration constant says, bit 10 for DirectGLES only when it is true, and that one bit
  and nothing else.
- The push default becomes kMGPipeSubsystemsMigratedAtP5e (0x3fff). Inert: bit 13 is not
  in kMGPipeWiredSubsystems, so no emission gate opens on it; 0x1fff survives as P5e's
  "everything P4a had and nothing of mine" control.

MobileGL/ConfigLoader.cpp

@@ -8,7 +8,7 @@
 
 #include "Config.h"
 #if MOBILEGL_PIPE_PUSH
-// For kMGPipeSubsystemsMigratedAtP4a, the push build's PipePush default (the P2 and P3a
+// For kMGPipeSubsystemsMigratedAtP5e, the push build's PipePush default (the P2, P3a and P4a
 // constants beside it are the phase-by-phase controls, not the default). Push-only, so the
 // pull build's translation unit is unchanged.
 #include <MG_Pipe/MGPipe.h>
@@ -263,7 +263,7 @@ namespace MobileGL::MG_ConfigLoader {
         // environment is the all-subsystems-pull control that reproduces P1 exactly, and
         // kMGPipeSubsystemsMigratedAtP3a (0x1ff) is the phase-by-phase control - P4a's four
         // subsystems off, everything P3a landed still on.
-        features.PipePush = QueryEnvUint64("MOBILEGL_PIPE_PUSH", MG_Pipe::kMGPipeSubsystemsMigratedAtP4a);
+        features.PipePush = QueryEnvUint64("MOBILEGL_PIPE_PUSH", MG_Pipe::kMGPipeSubsystemsMigratedAtP5e);
 #else
         // Meaningless in a pull build: there is nothing to push. Config.h documents 0 as
         // "pull everything" and that stays literally true.
@@ -379,6 +379,17 @@ namespace MobileGL::MG_ConfigLoader {
         // point of use, which is where the "P11" in the message belongs.
         ipc.AdoptTier = QueryEnvUint32("MOBILEGL_IPC_ADOPT_TIER", 2, 0, 2);
         ipc.VerbBarrier = QueryEnvUint32("MOBILEGL_IPC_VERB_BARRIER", 1, 0, 1);
+        // P5e (MG_Remote/CONTRACT-P5E.md §1). The wait rule's A/B, parsed here like every
+        // other IPC knob and armed only where the server publishes kCapRunAheadApply.
+        ipc.RunAhead = QueryEnvUint32("MOBILEGL_IPC_RUN_AHEAD", 1, 0, 1);
+        // ... and forced OFF by the verify harness for BatchWaits' reason, one step further:
+        // run-ahead's whole point is that the client stops filling gPipeInputs for an
+        // unbarriered record, and the comparator has nothing left to compare when it does.
+        if (MG_Config::Features.PipeVerify) ipc.RunAhead = 0;
+        // The present credit (ruling 4). 1 is one frame of overlap; 8 is the ceiling because a
+        // deeper queue buys nothing on a CPU-bound client and pays for it in latency. 0 is NOT
+        // admitted: a credit of zero would mean "publish no present at all".
+        ipc.PresentCredit = QueryEnvUint32("MOBILEGL_IPC_PRESENT_CREDIT", 1, 1, 8);
         ipc.StrictErrors = QueryEnvFlag("MOBILEGL_IPC_STRICT_ERRORS");
         ipc.Audit = QueryEnvFlag("MOBILEGL_IPC_AUDIT");
         QueryEnvVariable("MOBILEGL_IPC_SERVER_AFFINITY", ipc.ServerAffinity, "auto");
@@ -387,9 +398,11 @@ namespace MobileGL::MG_ConfigLoader {
         // One line, on the arm where these numbers decide behaviour, because every one of
         // them is a number a bug report has to quote.
         MGLOG_I("Config: IPC ring=%uMiB stage=%uMiB spin=%uus persistent-block=%uKiB "
-                "adopt-tier=%u verb-barrier=%u strict=%d audit=%d affinity='%s'",
+                "adopt-tier=%u verb-barrier=%u run-ahead=%u present-credit=%u strict=%d "
+                "audit=%d affinity='%s'",
                 ipc.RingMb, ipc.StageMb, ipc.SpinUs, ipc.PersistentBlockKb, ipc.AdoptTier,
-                ipc.VerbBarrier, static_cast<int>(ipc.StrictErrors), static_cast<int>(ipc.Audit),
+                ipc.VerbBarrier, ipc.RunAhead, ipc.PresentCredit,
+                static_cast<int>(ipc.StrictErrors), static_cast<int>(ipc.Audit),
                 ipc.ServerAffinity.c_str());
         if (ipc.VerbBarrier == 0) {
             MGLOG_W("Config: MOBILEGL_IPC_VERB_BARRIER=0 is the R-1 NEGATIVE CONTROL and is "