[Fix] (Espryt): tell the backend when a frontend object dies instead of discovering it in a garbage sweep

- P2 step e2, as far as the file-ownership table lets one package take it. New frontend
  header MG_State/GLState/StateObjectDeathNotice.h carries BufferBackendOps' shape for the
  other six kinds: an ops table the backend fills in, and one entry point that takes
  {kind, lifetimeId} rather than the object, because by the time the last SharedPtr has
  dropped there is no object left to pass and the lifetime id is exactly what the client
  slot allocator resolves a handle from. Declared only under MOBILEGL_PIPE_PUSH, so the
  pull build's symbol set is untouched.
- BackendSlotTable::DestroyByLifetimeId drops the twin and returns the slot at the moment
  the object goes, instead of at the next sweep - which for a renderbuffer or a texture
  atlas is the difference between freeing the driver allocation now and freeing it 64
  creations from now. It returns the slot only when THIS table holds it: two holders of one
  kind already exist (the ScopedDirectGLESTextureBindings fixture; Magma's subsystem-4
  table shares the VertexElementsCso kind), and a table that never twinned the object must
  not free a slot the other one still names. The legacy arm keys on the frontend heap
  address, cannot answer a notice at all, and keeps the sweep - which is the announced-
  versus-discovered half of the A/B the compile-time arm exists for.
- Managers.cpp registers one dispatcher for all six kinds from ResolveEsprytSlotTablesArm(),
  i.e. exactly when the arm that can answer a notice is the arm that runs, and drops a
  notice that arrives after exit() has begun.
- FIRING it needs a destructor per class, and the P2 ownership table gives
  {Texture,Framebuffer,Sampler,VertexArray}State/* to other packages, so only ProgramObject
  and RenderbufferObject raise it here. The other four still rely on the sweep; their four
  one-line calls retire it entirely.
- Three cases pin the three halves: the slot comes back with no sweep and the notice is
  idempotent and does not free another holder's slot; a program and a renderbuffer announce
  their own death when the last SharedPtr drops and not before; and the handle arm actually
  installs a consumer, rather than the two halves each being fine on their own.

MobileGL/MG_Backend/DirectGLES/Managers.cpp

@@ -12,6 +12,7 @@
 #include "DirectGLES.h"
 #include "BackendObject_DirectGLES.h"
 #include <Config.h>
+#include <MG_State/GLState/StateObjectDeathNotice.h>
 #include <MG_Util/ShaderTranspiler/ShaderCompiler.h>
 #include <MG_Util/ShaderTranspiler/TranslationCache.h>
 
@@ -171,6 +172,48 @@ namespace MobileGL::MG_Backend::DirectGLES {
     }
 
 #if MOBILEGL_PIPE_PUSH
+    namespace {
+        // P2 step e2's dispatcher: the frontend told us an object died, so free its slot and
+        // drop its twin NOW. One entry point for all six kinds, because the answer is the same
+        // for all six - which is why the notice carries the kind rather than there being six
+        // ops tables.
+        //
+        // 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.
+        void OnFrontendStateObjectDestroyed(MG_Pipe::MGPipeKind kind, Uint64 lifetimeId) {
+            if (InProcessTeardown()) return;
+            switch (kind) {
+            case MG_Pipe::MGPipeKind::Texture:
+                TextureImpl::g_backendTextureObjects.DestroyByLifetimeId(lifetimeId);
+                break;
+            case MG_Pipe::MGPipeKind::Framebuffer:
+                FramebufferImpl::g_backendFramebufferObjects.DestroyByLifetimeId(lifetimeId);
+                break;
+            case MG_Pipe::MGPipeKind::Renderbuffer:
+                RenderbufferImpl::g_backendRenderbufferObjects.DestroyByLifetimeId(lifetimeId);
+                break;
+            case MG_Pipe::MGPipeKind::SamplerCso:
+                SamplerImpl::g_backendSamplerObjects.DestroyByLifetimeId(lifetimeId);
+                break;
+            case MG_Pipe::MGPipeKind::ShaderCso:
+                PrgramImpl::g_backendProgramObjects.DestroyByLifetimeId(lifetimeId);
+                break;
+            case MG_Pipe::MGPipeKind::VertexElementsCso:
+                VertexArrayImpl::g_backendVertexArrayObjects.DestroyByLifetimeId(lifetimeId);
+                break;
+            default:
+                // Buffer already has its own death signal (BufferBackendOps::OnDestroy) and
+                // every other kind has no backend twin table here.
+                break;
+            }
+        }
+
+        const MG_State::GLState::StateObjectDeathOps g_glesStateObjectDeathOps = {
+            .OnDestroyed = OnFrontendStateObjectDestroyed,
+        };
+    } // namespace
+
     Bool ResolveEsprytSlotTablesArm() {
         // Resolved once and latched by the inline EsprytSlotTablesEnabled() in SlotTables.h:
         // the two arms of StateBackendObjectRegistry keep their twins in different containers,
@@ -196,6 +239,12 @@ namespace MobileGL::MG_Backend::DirectGLES {
                         "is clear but MOBILEGL_PIPE_LEGACY_MEMOS=0\"}");
                 std::abort();
             }
+            if (bitSet) {
+                // The notice is only consumable on the handle arm (the legacy registry keys on
+                // the frontend ADDRESS, which is gone by the time a destructor speaks), so it is
+                // installed exactly where it can be answered. Once per process, cold.
+                MG_State::GLState::SetStateObjectDeathOps(&g_glesStateObjectDeathOps);
+            }
             return bitSet;
 #else
             // The legacy arm is not compiled, so the handle arm is the only arm. The bit still
@@ -204,6 +253,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
                 MGLOG_D("MGPipe: kMGPipeSubsystemEsprytSlots is clear but this build has no "
                         "legacy twin registry; running the handle arm anyway");
             }
+            MG_State::GLState::SetStateObjectDeathOps(&g_glesStateObjectDeathOps);
             return true;
 #endif
         }

MobileGL/MG_Backend/DirectGLES/Managers.h

@@ -417,6 +417,19 @@ namespace MobileGL::MG_Backend::DirectGLES {
             return nullptr;
         }
 
+        // P2 step e2. The legacy arm cannot answer this at all - its key is the frontend heap
+        // ADDRESS and the object is already gone by the time the notice arrives - so there it
+        // is a no-op and the garbage sweep stays its only death signal. That asymmetry is not
+        // an oversight: it is the A/B the compile-time arm exists to make measurable
+        // (ARCHITECTURE.md 9.6), and announced-versus-discovered death is one of the things
+        // being measured.
+        Bool DestroyByLifetimeId(Uint64 lifetimeId) {
+            if (EsprytSlotTablesEnabled()) {
+                return m_slotTable.DestroyByLifetimeId(lifetimeId);
+            }
+            return false;
+        }
+
         // fn(const StatePtr& state, const BackendPtr& twin) over every live entry. The legacy
         // begin()/end() handed out the map key, i.e. the raw frontend address - exactly the
         // identity the backend must stop reading - and handed it out for entries whose state

MobileGL/MG_Backend/DirectGLES/SlotTables.h

@@ -33,17 +33,19 @@
 //  * Slots are dense per kind, which is what lets the server side (ARCHITECTURE.md 10.1,
 //    MG_Remote/Server/PipeObjectTables) be an array rather than an object graph.
 //
-// What has NOT changed, deliberately, and is this file's one departure from the P2 brief
-// (recorded in the package result file): a frontend object's death is still discovered rather
-// than announced. The brief's step e2 - a BufferBackendOps-shaped OnDestroy for the other six
-// kinds - has to be installed in MG_State/GLState/{Texture,Framebuffer,Renderbuffer,Sampler,
-// Program,VertexArray}State/*, and the P2 file-ownership table gives every one of those files
-// to another package. So the table keeps ONE weak_ptr per entry and uses it for exactly one
-// thing: ReclaimDeadSlots() frees the slot - and the twin, and the driver storage it owns -
-// once the frontend object is gone. That is a liveness sweep, not an identity test, and it is
-// what bumps Gen, which is precisely the ABA defence: a slot is only ever handed out again
-// after it was freed. When e2 lands, ReclaimDeadSlots() becomes the fallback path of an
-// explicit Destroy(handle) and the sweep call sites go away.
+// Death: announced where the package may announce it, discovered everywhere else.
+// DestroyByLifetimeId() below is step e2's backend half and it is complete - it drops the twin
+// and returns the slot the moment the frontend object's last SharedPtr goes - and the notice
+// that drives it (MG_State/GLState/StateObjectDeathNotice.h, BufferBackendOps' shape) is
+// registered for all six kinds. What is only PARTLY wired is the firing side: a destructor has
+// to raise the notice, and of the six object classes the P2 file-ownership table gives
+// {Texture,Framebuffer,Sampler,VertexArray}State/* to other packages, so only ProgramObject
+// and RenderbufferObject fire it here. The four that do not still rely on the sweep, which is
+// why the table keeps ONE weak_ptr per entry and uses it for exactly one thing:
+// ReclaimDeadSlots() frees the slot - and the twin, and the driver storage it owns - once the
+// frontend object is gone. That is a liveness sweep, not an identity test, and it is what
+// bumps Gen, which is precisely the ABA defence: a slot is only ever handed out again after it
+// was freed. The four remaining one-line destructor calls retire the sweep entirely.
 //
 // Because the sweep is still the only death signal, this table carries BOTH of the drivers
 // the registry it replaces carries, and for the same reasons:
@@ -221,6 +223,40 @@ namespace MobileGL::MG_Backend::DirectGLES {
             m_isCollecting = false;
         }
 
+        // P2 step e2's backend half: the frontend object with this lifetime id has just been
+        // DESTROYED, so drop its twin and return its slot now rather than waiting for a sweep
+        // to notice the weak_ptr expired. Announced death is what the sweep is a stand-in for;
+        // it frees the driver storage the twin owns at the moment the application let go of
+        // the object, which is what Managers.h's "dead gigabytes" note is about.
+        //
+        // Returns whether this table held the slot. The slot goes back to the allocator ONLY
+        // then, and this is not defensive: two holders of one kind already exist (the
+        // ScopedDirectGLESTextureBindings fixture's saved copy is a second live table of kind
+        // Texture; Magma's subsystem-4 table shares the VertexElementsCso kind), and a table
+        // that never twinned the object must not free a slot the other one still names.
+        Bool DestroyByLifetimeId(Uint64 lifetimeId) {
+            const MG_Pipe::MGPipeHandle handle =
+                MG_Pipe::MGPipeSlots().FindByLifetimeId(kKind, lifetimeId);
+            if (MG_Pipe::MGPipeHandleIsNull(handle)) return false;
+            if (handle.Slot >= m_slots.size()) return false;
+            // Same ordering rule as ReclaimDeadSlots(): the twin's destructor is a driver call
+            // and could re-enter GetOrCreate and resize m_slots, so nothing that outlives it
+            // may be a reference into the vector.
+            BackendPtr dead;
+            {
+                Entry& entry = m_slots[handle.Slot];
+                if (!entry.Live || entry.Gen != handle.Gen) return false;
+                dead = std::move(entry.backend);
+                entry.backend.reset();
+                entry.stateRef.reset();
+                entry.Live = false;
+            }
+            if (m_memoHandle.Slot == handle.Slot) ForgetHandle();
+            MG_Pipe::MGPipeSlots().Free(kKind, handle);
+            dead.reset();
+            return true;
+        }
+
         void CollectGarbageIfNeeded() {
             ++m_gcTick;
             if (m_gcTick < kGCInterval) return;