refactor(mir): Remove CoreContext legacy fields (Phase 2-2/7)

完全移行→削除の安全順序（Option C）に従い、CoreContext の
deprecated フィールドと sync helpers を完全削除。

## Changes
- Migrated all access sites to core_ctx.* (SSOT allocators)
  - utils.rs: value_gen (3 sites), block_gen (1 site), temp_slot_counter (1 site)
  - loop_api.rs: block_gen (1 site)
  - phi_helpers.rs: value_gen (1 site)
  - builder.rs: sync helpers (2 methods), test assertions (2 sites)
- Removed 5 deprecated fields from builder.rs
  - value_gen: ValueIdGenerator
  - block_gen: BasicBlockIdGenerator
  - next_binding_id: u32
  - temp_slot_counter: u32
  - debug_join_counter: u32
- Removed sync helper calls (allocate_binding_id, debug_next_join_id)
- Removed field initializations from MirBuilder::new()
- Maintained Phase 136 P0 SSOT structure (next_value_id() remains as high-level API)

## Tests
- cargo build --release: PASS
- cargo test --release --lib: 1029 passed (4 pre-existing failures)
- Deprecation warnings: 435 → 456 (+21)
  Note: Warnings increased due to remaining deprecated field *uses* being exposed
  after removing the field *definitions*. This is expected during migration.

## Code metrics
- Net reduction: 40 lines (-56 removed, +16 modifications)
- Files changed: 4 (builder.rs, utils.rs, loop_api.rs, phi_helpers.rs)

Phase 2 Progress: 2/7 contexts complete (MetadataContext ✅, CoreContext ✅)

src/mir/builder.rs

@@ -91,15 +91,6 @@ pub struct MirBuilder {
     /// Direct field access for backward compatibility (migration in progress).
     pub(super) core_ctx: core_context::CoreContext,
 
-    /// [DEPRECATED] Value ID generator
-    /// Phase 136: Moved to core_ctx.value_gen (backward compat wrapper)
-    #[deprecated(note = "Use core_ctx.value_gen instead")]
-    pub(super) value_gen: ValueIdGenerator,
-
-    /// [DEPRECATED] Basic block ID generator
-    /// Phase 136: Moved to core_ctx.block_gen (backward compat wrapper)
-    #[deprecated(note = "Use core_ctx.block_gen instead")]
-    pub(super) block_gen: BasicBlockIdGenerator,
 
     /// [DEPRECATED] 箱理論: Static boxコンパイル時のコンテキスト分離
     /// Phase 136 Step 7/7: Moved to comp_ctx.compilation_context (backward compat wrapper)
@@ -259,11 +250,6 @@ pub struct MirBuilder {
     #[deprecated(note = "Use comp_ctx.reserved_value_ids instead")]
     pub(super) reserved_value_ids: HashSet<ValueId>,
 
-    /// [DEPRECATED] Phase 74: BindingId allocation counter (parallel to ValueId)
-    /// Phase 136: Moved to core_ctx.next_binding_id (backward compat wrapper)
-    #[deprecated(note = "Use core_ctx.next_binding_id instead")]
-    pub next_binding_id: u32,
-
     /// [DEPRECATED] Phase 74: BindingId mapping for lexical variable bindings
     /// Phase 136: Moved to binding_ctx.binding_map (backward compat wrapper)
     #[deprecated(note = "Use binding_ctx.binding_map instead")]
@@ -301,10 +287,6 @@ pub struct MirBuilder {
     pub(super) cleanup_allow_return: bool,
     pub(super) cleanup_allow_throw: bool,
 
-    /// [DEPRECATED] Internal counter for temporary pin slots (block-crossing ephemeral values)
-    /// Phase 136: Moved to core_ctx.temp_slot_counter (backward compat wrapper)
-    #[deprecated(note = "Use core_ctx.temp_slot_counter instead")]
-    temp_slot_counter: u32,
     /// If true, skip entry materialization of pinned slots on the next start_new_block call.
     suppress_pin_entry_copy_next: bool,
 
@@ -315,10 +297,6 @@ pub struct MirBuilder {
     /// Phase 136: Moved to scope_ctx.debug_scope_stack (backward compat wrapper)
     #[deprecated(note = "Use scope_ctx.debug_scope_stack instead")]
     debug_scope_stack: Vec<String>,
-    /// [DEPRECATED] Monotonic counter for region IDs (deterministic across a run).
-    /// Phase 136: Moved to core_ctx.debug_join_counter (backward compat wrapper)
-    #[deprecated(note = "Use core_ctx.debug_join_counter instead")]
-    debug_join_counter: u32,
 
     /// Local SSA cache: ensure per-block materialization for critical operands (e.g., recv)
     /// Key: (bb, original ValueId, kind) -> local ValueId
@@ -374,10 +352,6 @@ impl MirBuilder {
             // Phase 136 Step 2/7: Core context (new SSOT)
             core_ctx,
 
-            // Legacy fields (kept for backward compatibility, synced with core_ctx)
-            value_gen: ValueIdGenerator::new(),
-            block_gen: BasicBlockIdGenerator::new(),
-
             compilation_context: None, // 箱理論: デフォルトは従来モード
             type_ctx: type_context::TypeContext::new(), // Phase 136: Type context
             scope_ctx: scope_context::ScopeContext::new(), // Phase 136 Step 3/7: Scope context
@@ -408,7 +382,6 @@ impl MirBuilder {
             fn_body_ast: None,                  // Phase 200-C: Initialize to None
             reserved_value_ids: HashSet::new(), // Phase 201-A: Initialize to empty
 
-            next_binding_id: 0,           // Phase 74: Initialize BindingId counter (legacy)
             binding_map: BTreeMap::new(), // Phase 74: Initialize BindingId mapping
 
             loop_header_stack: Vec::new(),
@@ -422,12 +395,10 @@ impl MirBuilder {
             in_cleanup_block: false,
             cleanup_allow_return: false,
             cleanup_allow_throw: false,
-            temp_slot_counter: 0,         // Legacy (synced with core_ctx)
             suppress_pin_entry_copy_next: false,
 
             // Debug scope context
             debug_scope_stack: Vec::new(),
-            debug_join_counter: 0,        // Legacy (synced with core_ctx)
 
             local_ssa_map: HashMap::new(),
             schedule_mat_map: HashMap::new(),
@@ -549,12 +520,9 @@ impl MirBuilder {
     /// //                      next_value_id() -> ValueId(20)
     /// // }
     /// ```
-    #[allow(deprecated)]
     pub fn allocate_binding_id(&mut self) -> super::BindingId {
-        // Phase 136 Step 2/7: Use core_ctx as SSOT, sync legacy field
+        // Phase 136 Step 2/7 + Phase 2-2: Use core_ctx as SSOT (no sync needed)
-        let id = self.core_ctx.next_binding();
+        self.core_ctx.next_binding()
-        self.next_binding_id = self.core_ctx.next_binding_id;
-        id
     }
 
     // ---- Hint helpers (no-op by default) ----
@@ -576,12 +544,9 @@ impl MirBuilder {
     // Debug scope helpers (region_id for DebugHub events)
     // ----------------------
     #[inline]
-    #[allow(deprecated)]
     pub(crate) fn debug_next_join_id(&mut self) -> u32 {
-        // Phase 136 Step 2/7: Use core_ctx as SSOT, sync legacy field
+        // Phase 136 Step 2/7 + Phase 2-2: Use core_ctx as SSOT (no sync needed)
-        let id = self.core_ctx.next_debug_join();
+        self.core_ctx.next_debug_join()
-        self.debug_join_counter = self.core_ctx.debug_join_counter;
-        id
     }
 
     #[inline]
@@ -1317,7 +1282,7 @@ mod binding_id_tests {
     #[allow(deprecated)]
     fn test_binding_map_initialization() {
         let builder = MirBuilder::new();
-        assert_eq!(builder.next_binding_id, 0);
+        assert_eq!(builder.core_ctx.next_binding_id, 0);
         // Phase 136 Step 4/7: Check both binding_ctx (SSOT) and legacy field
         assert!(builder.binding_ctx.is_empty());
         assert!(builder.binding_map.is_empty());
@@ -1333,7 +1298,7 @@ mod binding_id_tests {
         assert_eq!(bid0.raw(), 0);
         assert_eq!(bid1.raw(), 1);
         assert_eq!(bid2.raw(), 2);
-        assert_eq!(builder.next_binding_id, 3);
+        assert_eq!(builder.core_ctx.next_binding_id, 3);
     }
 
     #[test]

src/mir/builder/utils.rs

@@ -41,10 +41,8 @@ impl super::MirBuilder {
             let candidate = if let Some(ref mut f) = self.current_function {
                 f.next_value_id() // Function context
             } else {
-                // Phase 136 Step 2/7: Use core_ctx as SSOT, sync legacy field
+                // Phase 136 Step 2/7 + Phase 2-2: Use core_ctx as SSOT (no sync needed)
-                let id = self.core_ctx.next_value();
+                self.core_ctx.next_value()
-                self.value_gen = self.core_ctx.value_gen.clone();
-                id
             };
 
             // Phase 201-A: Skip reserved PHI dst ValueIds
@@ -60,13 +58,10 @@ impl super::MirBuilder {
 
     /// Allocate a new BasicBlockId
     ///
-    /// Phase 136 Step 2/7: Uses core_ctx as SSOT, syncs legacy field.
+    /// Phase 136 Step 2/7 + Phase 2-2: Uses core_ctx as SSOT (no sync needed).
     #[inline]
-    #[allow(deprecated)]
     pub(crate) fn next_block_id(&mut self) -> super::BasicBlockId {
-        let id = self.core_ctx.next_block();
+        self.core_ctx.next_block()
-        self.block_gen = self.core_ctx.block_gen.clone();
-        id
     }
 
     // ---- LocalSSA convenience (readability helpers) ----
@@ -442,13 +437,13 @@ impl super::MirBuilder {
         v: super::ValueId,
         hint: &str,
     ) -> Result<super::ValueId, String> {
-        self.temp_slot_counter = self.temp_slot_counter.wrapping_add(1);
+        let slot_id = self.core_ctx.next_temp_slot();
-        let slot_name = format!("__pin${}${}", self.temp_slot_counter, hint);
+        let slot_name = format!("__pin${}${}", slot_id, hint);
         // Phase 25.1b: Use function-local ID allocator to avoid SSA verification failures
         let dst = if let Some(ref mut f) = self.current_function {
             f.next_value_id() // Function context: use local ID
         } else {
-            self.value_gen.next() // Module context: use global ID
+            self.core_ctx.next_value() // Module context: use core_ctx SSOT
         };
         self.emit_instruction(super::MirInstruction::Copy { dst, src: v })?;
         if super::utils::builder_debug_enabled()
@@ -479,7 +474,7 @@ impl super::MirBuilder {
         let dst = if let Some(ref mut f) = self.current_function {
             f.next_value_id() // Function context: use local ID
         } else {
-            self.value_gen.next() // Module context: use global ID
+            self.core_ctx.next_value() // Module context: use core_ctx SSOT
         };
         self.emit_instruction(super::MirInstruction::Copy { dst, src: v })?;
         // Propagate metadata (type/origin) from source to the new local copy

src/mir/loop_api.rs

@@ -83,7 +83,7 @@ pub fn build_simple_loop<L: LoopBuilderApi>(
 // === Legacy wiring: implement LoopBuilderApi for mir::builder::MirBuilder ===
 impl LoopBuilderApi for super::builder::MirBuilder {
     fn new_block(&mut self) -> BasicBlockId {
-        self.block_gen.next()
+        self.core_ctx.next_block()
     }
     fn current_block(&self) -> Result<BasicBlockId, String> {
         self.current_block

src/mir/utils/phi_helpers.rs

@@ -66,7 +66,7 @@ impl MirBuilder {
         let phi_val = if let Some(ref mut f) = self.current_function {
             f.next_value_id() // Function context: use local ID allocator
         } else {
-            self.value_gen.next() // Module context: use global ID allocator
+            self.core_ctx.next_value() // Module context: use core_ctx SSOT
         };
 
         // 統一された挿入ロジック（既存パターンと完全互換）