refactor: 拆分 oxide_emit 为独立 emit pass crate（依赖倒置）

crates/oxide_emit/src/emit_ctx.rs

@@ -0,0 +1,47 @@
+//! Grouped `CompileCtx` sub-contexts.
+//!
+//! Splits the compiler's central `CompileCtx` so syntax-domain workers borrow
+//! only the slice they need: `LabelCtx` for jump-target resolution, `ScopeCtx`
+//! for identifier binding. `PatternCtx` is reserved for destructuring work.
+//! Execution-stream fields (insts, registers, pc, …) stay flat on
+//! `CompileCtx`.
+
+use crate::symbol_table::SymbolTable;
+use crate::LabelScope;
+use oxide_ir::operand::LabelId;
+
+/// Jump-target / labeled-statement resolution state.
+pub(crate) struct LabelCtx {
+    /// label id → 指令下标。id 连续递增，Vec 索引即 id；写入前须扩容。
+    pub(crate) label_pos: Vec<Option<usize>>,
+    pub(crate) loop_stack: Vec<(LabelId, LabelId)>,
+    pub(crate) switch_stack: Vec<LabelId>,
+    /// Active labeled-statement scopes (resolves `break label` / `continue label`).
+    pub(crate) label_scopes: Vec<LabelScope>,
+    /// Label names awaiting binding to the next emitted loop's continue target.
+    pub(crate) pending_loop_labels: Vec<String>,
+    pub(crate) label_counter: u32,
+}
+
+impl LabelCtx {
+    /// 按 id 扩容后写入 label 定义位置。
+    pub(crate) fn set_label_pos(&mut self, id: LabelId, pos: usize) {
+        if id as usize >= self.label_pos.len() {
+            self.label_pos.resize(id as usize + 1, None);
+        }
+        self.label_pos[id as usize] = Some(pos);
+    }
+}
+
+/// Identifier-binding state: symbols, builtin registers, private names.
+pub(crate) struct ScopeCtx {
+    pub(crate) symbols: SymbolTable,
+    pub(crate) builtin_reg_map: Vec<(String, u8)>,
+    pub(crate) private_name_map: Vec<(String, u32)>,
+    pub(crate) next_private_name_id: u32,
+}
+
+/// Reserved for destructuring-pattern state (Phase 15). Intentionally empty
+/// today; named so future pattern work has a home without touching `ScopeCtx`.
+#[allow(dead_code)]
+pub(crate) struct PatternCtx;