步骤4：用例 21_var_temp（VAR_TEMP 每周期重置语义）+ 文档更新 + 修复 store_target STORE 缺 func 隐藏 bug

tests/src/cases_test.cpp

@@ -65,6 +65,7 @@ namespace {
         {"18_tof_ctu", Outcome::Ok, ""},
         {"19_recursive_call", Outcome::CompileError, "recursive call"},
         {"20_line1", Outcome::Ok, ""},
+        {"21_var_temp", Outcome::Ok, ""},
     };
 
     bool run_case(const char* dir, Outcome want, const char* keyword) {

tests/src/compiler_test.cpp

@@ -202,7 +202,7 @@ static bool test_all_cases() {
         }
         ++n;
     }
-    CHECK(n == 20);
+    CHECK(n == 21);
     return true;
 }
 

tests/src/vm_test.cpp

@@ -37,11 +37,19 @@ static int g_checks = 0;
 
 // ---- 数据区槽访问 ----
 
-/// 槽宽 = 与下一槽 addr 的差（紧凑布局下按实际宽读写，避免覆盖相邻槽）。
+/// 槽宽 = 与下一槽 addr 的差（紧凑布局下按实际宽读写，避免覆盖相邻槽）；
+/// 最后一槽（下一槽越界返回 0）按值区剩余字节兜底。
 static uint32_t slot_width(const vm::Machine& m, int s) {
     const uint32_t a = m.slot_addr(static_cast<uint32_t>(s));
     const uint32_t b = m.slot_addr(static_cast<uint32_t>(s + 1));
-    return (b > a && b - a < 8) ? (b - a) : 8;
+    if (b > a && b - a < 8) {
+        return b - a;
+    }
+    if (b == 0) {
+        const uint32_t rem = static_cast<uint32_t>(m.data_len()) - a;
+        return rem < 8 ? rem : 8;
+    }
+    return 8;
 }
 
 static int64_t slot(const vm::Machine& m, int s) {
@@ -357,6 +365,15 @@ static bool test_cases_positive() {
     CHECK(make_machine("tests/cases/18_tof_ctu", &m, &err));
     CHECK(m.run_cycle() == vm::Fault::None);
 
+    // 21 VAR_TEMP：tmp/t 每周期重置，persist 累积 → a = 10107/10108/10109
+    CHECK(make_machine("tests/cases/21_var_temp", &m, &err));
+    m.run_cycle();
+    CHECK(slot(m, 0) == 10107);
+    m.run_cycle();
+    CHECK(slot(m, 0) == 10108);
+    CHECK(m.run_cycle() == vm::Fault::None);
+    CHECK(slot(m, 0) == 10109);
+
     // 20 line1：I 组合 → Q0_0 真值表（槽 0=急停 1=I0_0 2=I0_1 3=Q0_0）
     CHECK(make_machine("tests/cases/20_line1", &m, &err));
     struct {