[Fix, Test] (Espryt): deliver a death notice to every holder of a kind, retire the twin table's last sweep, and pin the bring-up call site under the armless knob pair

- BackendSlotTable links every instance into a per-type holder list; OnFrontendObjectDestroyed resolves the handle once, drops the twin in each holder by handle and frees the slot once, last - a notice delivered to one registry left the fixture's saved copy holding a dead twin, and its driver storage, for the life of the process (review v4 minor 2)
- ReclaimDeadSlots and CollectGarbageNow leave the slot table: nothing called them, so the header's "backstop" was a claim without a caller; the registry's pre-P2 CollectGarbageNow is a no-op on the handle arm (minor 1)
- HandleOf no longer memoises a null answer, which a second holder's acquire could never refresh (minor 8)
- EnsureProcessTeardownSentinel is armed by the slot table's first insertion, as D13 says; the registry arms it only on the legacy arm (minor 9)
- new SanityTest cases: OneDeathNoticeDropsTheTwinInEveryHolderOfTheKind, ASavedCopyOfARealRegistryDropsTheTwinOnTheSameNotice, ANegativeLookupIsNotCachedAcrossAnotherHoldersAcquire, and EglBringUpUnderTheArmlessKnobPairReturnsInsteadOfStopping, which runs InitPbufferSurface under the pair in a forked child and fails naming both knobs if InitDisplayAndContext ever stops there again (minor 4)
- AnArmlessKnobCombinationStopsInsteadOfSkippingTheLane writes a per-process, per-case log path and restores MOBILEGL_LOG_FILE_PATH and MG_Config::Features through RAII guards on every exit path (minor 5)

MobileGL/MG_Backend/DirectGLES/Managers.cpp

@@ -178,9 +178,16 @@ namespace MobileGL::MG_Backend::DirectGLES {
         // for all six - which is why the notice carries the kind rather than there being six
         // ops tables.
         //
+        // Each arm below names the registry GLOBAL of its kind, but DestroyByLifetimeId is
+        // static: it is answered by every table of that kind that exists at the moment - the
+        // global's own and any by-value copy a fixture or a context reset is holding - and
+        // the slot goes back once, after all of them have let go (SlotTables.h, the holder
+        // list). Naming one instance here is a spelling, not a choice of holder.
+        //
         // A notice that arrives after exit() has begun is dropped: past that point the twin's
         // destructor must not call into the driver (see InProcessTeardown()), and the process
-        // is about to hand every GPU object back anyway.
+        // is about to hand every GPU object back anyway. That twin is a deliberate leak, not
+        // garbage for a later collection - there is none on this arm.
         void OnFrontendStateObjectDestroyed(MG_Pipe::MGPipeKind kind, Uint64 lifetimeId) {
             if (InProcessTeardown()) return;
             switch (kind) {