feat: Temporal.PlainTime.from 三分支解析（字符串/实例/bag）

crates/oxide_builtins/src/temporal.rs

@@ -4529,6 +4529,27 @@ pub fn plain_time_value_of<H: VmHost>(vm: &mut H, _args: &[u8]) -> NativeResult
     NativeResult::Err(crate::error::create_type_error(vm, "Temporal.PlainTime has no valueOf"))
 }
 
+/// `Temporal.PlainTime.from(item, options)`：从字符串、PlainTime/ZDT/PlainDateTime 实例或 property bag 构造。
+pub fn plain_time_from<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    let value = if args.len() > 1 { vm.reg(args[1]) } else { JsValue::undefined() };
+    if value.is_string() {
+        // 规范顺序：先 ParseTemporalTimeString，再 ToTemporalOverflow(options)。
+        let total_ns = match parse_plain_time_string(&to_string(value)) {
+            Some(ns) => ns,
+            None => {
+                return NativeResult::Err(crate::error::create_range_error(vm, "invalid ISO 8601 time"));
+            }
+        };
+        native_try!(temporal_overflow(vm, args));
+        make_plain_time(vm, total_ns)
+    } else {
+        // 对象分支：实例复制 / property bag 统一走 plain_time_like_ns（含缺省 0 与约束钳制）。
+        native_try!(temporal_overflow(vm, args));
+        let total_ns = native_try!(plain_time_like_ns(vm, value));
+        make_plain_time(vm, total_ns)
+    }
+}
+
 // ───────────────────── PlainDateTime 基础方法 ─────────────────────
 
 /// `Temporal.PlainDateTime` 构造器：保存 ISO 日期与午夜后纳秒。

crates/oxide_vm/src/bindings/bind_temporal.rs

@@ -620,6 +620,12 @@ pub fn bind_temporal(core: &Arc<KernelCore>, session: &KernelSession, global: &m
         .map_or(0, |props| props.len() as u32)
         .saturating_sub(1);
     plain_time_ctor.set_data_meta(length_pos, PropAttributes::new(false, false, true));
+    apply_binding_table(
+        world,
+        plain_time_ctor,
+        core,
+        &[("from", oxide_builtins::temporal::plain_time_from::<crate::vm::Vm> as *const (), 1)],
+    );
 
     let plain_time_proto_ptr = world.plain_time_proto.as_ptr() as *mut JsObject;
     let plain_time_proto = unsafe { &mut *plain_time_proto_ptr };