feat: 逐指令 trace 补 pc 并加 eval/run --trace 旗标

crates/oxide_cli/tests/cli_smoke.rs

@@ -47,3 +47,34 @@ fn bench_help() {
     let stdout = String::from_utf8_lossy(&output.stdout);
     assert!(stdout.contains("--iterations"), "bench --help should list --iterations flag");
 }
+
+#[test]
+fn eval_trace_flag_pc_lines() {
+    let output = Command::new(env!("CARGO_BIN_EXE_oxide"))
+        .args(["eval", "--trace", "1 + 2"])
+        .output()
+        .expect("failed to run oxide eval --trace");
+
+    assert!(output.status.success(), "eval --trace should exit 0");
+    // trace 行只走 stderr，stdout 保持纯结果。
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert_eq!(stdout.trim(), "3", "--trace 不应污染 stdout: {stdout}");
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(stderr.lines().all(|l| l.starts_with("pc=")), "trace 行应全部为 pc 行: {stderr}");
+    assert!(stderr.contains("LOAD_CONST"), "trace 应含 LOAD_CONST: {stderr}");
+    assert!(stderr.contains("ADD"), "trace 应含 ADD: {stderr}");
+    assert!(stderr.contains("HALT"), "trace 应含 HALT: {stderr}");
+}
+
+#[test]
+fn eval_no_trace_flag_no_pc_lines() {
+    let output = Command::new(env!("CARGO_BIN_EXE_oxide"))
+        .args(["eval", "1 + 2"])
+        .output()
+        .expect("failed to run oxide eval");
+
+    assert!(output.status.success(), "eval should exit 0");
+    // 默认路径零 trace 输出。
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(!stderr.contains("pc="), "默认路径不应有 trace 行: {stderr}");
+}