feat(shm): ToolCall ring buffer(§13.3) — 栈帧模型 ring，push/pop 帧状态机

- ToolCallRing: 定长帧 ring buffer (64 frames × 112B)，状态机 FREE→CALLING→READING→READY→FREE
- Reserve: 环形扫描找 FREE 帧，全忙返回 ErrToolCallRingFull 背压
- SharedRef: pack/unpack 辅助函数
- unified.go: arena 分配器（arenaAlloc/arenaWrite/arenaRead）
- 5 个单测覆盖 init/reserve/背压/find/reuse

internal/plugin/proc/toollane_test.go

@@ -0,0 +1,166 @@
+package proc
+
+import (
+	"testing"
+	"unsafe"
+)
+
+func TestToolCallRing_InitAndReserve(t *testing.T) {
+	arenaSize := 256 * 1024
+	size := superBlockSize + int(shmDefaultSize) + int(evtTotalSize) + arenaSize + int(trlOffFrameBase+toolRingCap*toolFrameSize)
+	data := make([]byte, size)
+	putU32(data[0:], unifiedMagic)
+	putU32(data[4:], unifiedVersion)
+	putU32(data[16:], uint32(size))
+
+	ringData := data[size-int(trlOffFrameBase+toolRingCap*toolFrameSize) : size]
+	if err := InitToolRing(ringData); err != nil {
+		t.Fatalf("InitToolRing: %v", err)
+	}
+
+	ring, err := AttachToolRing(ringData)
+	if err != nil {
+		t.Fatalf("AttachToolRing: %v", err)
+	}
+	if ring.cap != toolRingCap {
+		t.Fatalf("cap: got %d, want %d", ring.cap, toolRingCap)
+	}
+
+	// Reserve 帧应成功
+	idx, err := ring.Reserve()
+	if err != nil {
+		t.Fatalf("Reserve: %v", err)
+	}
+	if idx != 0 {
+		t.Fatalf("首帧 index: got %d, want 0", idx)
+	}
+
+	// SetCalling -> GetCallingFrame -> SetReady -> GetReadyFrame -> ReleaseFrame
+	inputRef := SharedRef{Offset: 1024, Length: 100, Generation: 0, Flags: 1}
+	ring.SetCalling(idx, 42, "demo_upper", inputRef)
+
+	name, gotInput := ring.GetCallingFrame(idx)
+	if name != "demo_upper" {
+		t.Fatalf("GetCallingFrame name: got %q, want %q", name, "demo_upper")
+	}
+	if gotInput.Offset != 1024 || gotInput.Length != 100 {
+		t.Fatalf("GetCallingFrame input: got %+v", gotInput)
+	}
+
+	ring.SetReading(idx)
+
+	outputRef := SharedRef{Offset: 2048, Length: 50, Generation: 0, Flags: 0}
+	ring.SetReady(idx, outputRef)
+
+	reqID, gotOutput := ring.GetReadyFrame(idx)
+	if reqID != 42 {
+		t.Fatalf("GetReadyFrame reqID: got %d, want 42", reqID)
+	}
+	if gotOutput.Offset != 2048 || gotOutput.Length != 50 {
+		t.Fatalf("GetReadyFrame output: got %+v", gotOutput)
+	}
+
+	ring.ReleaseFrame(idx)
+
+	// 释放后应能重用
+	idx2, err := ring.Reserve()
+	if err != nil {
+		t.Fatalf("Reserve after release: %v", err)
+	}
+	if idx2 != 1 {
+		t.Fatalf("第二帧 index: got %d, want 1", idx2)
+	}
+}
+
+func TestToolCallRing_FullBackpressure(t *testing.T) {
+	size := int(toolRingCap)*int(toolFrameSize) + 64*1024
+	data := make([]byte, size)
+	if err := InitToolRing(data); err != nil {
+		t.Fatalf("InitToolRing: %v", err)
+	}
+	ring, err := AttachToolRing(data)
+	if err != nil {
+		t.Fatalf("AttachToolRing: %v", err)
+	}
+
+	// Reserve 所有帧
+	for i := uint32(0); i < toolRingCap; i++ {
+		idx, err := ring.Reserve()
+		if err != nil {
+			t.Fatalf("Reserve %d: %v", i, err)
+		}
+		ring.SetCalling(idx, uint64(i+1), "tool", SharedRef{})
+		ring.SetReading(idx)
+		// 不释放
+	}
+
+	// 再 Reserve 应失败（背压）
+	_, err = ring.Reserve()
+	if err != ErrToolCallRingFull {
+		t.Fatalf("满帧后 Reserve 应返回 ErrToolCallRingFull，实际: %v", err)
+	}
+
+	// 释放一帧后应恢复
+	ring.ReleaseFrame(0)
+	idx, err := ring.Reserve()
+	if err != nil {
+		t.Fatalf("释放后 Reserve: %v", err)
+	}
+	_ = idx
+}
+
+func TestToolCallRing_FindFrameByReqID(t *testing.T) {
+	size := int(toolRingCap)*int(toolFrameSize) + 64*1024
+	data := make([]byte, size)
+	if err := InitToolRing(data); err != nil {
+		t.Fatal(err)
+	}
+	ring, _ := AttachToolRing(data)
+
+	// 没有帧时应找不到
+	_, err := ring.FindFrameByReqID(999)
+	if err != ErrToolCallNotFound {
+		t.Fatalf("空 ring 应返回 ErrToolCallNotFound，实际: %v", err)
+	}
+
+	// Reserve + SetCalling 后应能找到
+	idx, _ := ring.Reserve()
+	ring.SetCalling(idx, 100, "tool_a", SharedRef{})
+	ring.SetReading(idx)
+
+	found, err := ring.FindFrameByReqID(100)
+	if err != nil {
+		t.Fatalf("FindFrameByReqID: %v", err)
+	}
+	if found != idx {
+		t.Fatalf("FindFrameByReqID: got %d, want %d", found, idx)
+	}
+
+	// Release 后应找不到
+	ring.ReleaseFrame(idx)
+	_, err = ring.FindFrameByReqID(100)
+	if err != ErrToolCallNotFound {
+		t.Fatalf("释放后应找不到，实际: %v", err)
+	}
+}
+
+func TestSharedRef_PackUnpack(t *testing.T) {
+	b := make([]byte, sharedRefSize)
+	ref := SharedRef{Offset: 1024, Length: 256, Generation: 7, Flags: 3}
+	packSharedRef(b, ref)
+	got := unpackSharedRef(b)
+	if got.Offset != ref.Offset || got.Length != ref.Length || got.Generation != ref.Generation || got.Flags != ref.Flags {
+		t.Fatalf("pack/unpack: got %+v, want %+v", got, ref)
+	}
+}
+
+func TestToolFrameLayoutAligned(t *testing.T) {
+	// 确保帧布局字段偏移与内存布局一致（安全断言）
+	var frame toolFrame
+	off := func(ptr *uint32) uint32 {
+		return uint32(uintptr(unsafe.Pointer(ptr)) - uintptr(unsafe.Pointer(&frame)))
+	}
+	if off(&frame.state) != toolFrameOffState {
+		t.Errorf("state offset: got %d, want %d", off(&frame.state), toolFrameOffState)
+	}
+}