refactor(mir): Extract TypeContext from MirBuilder (Phase 136 follow-up 1/7)

## Summary
Extract type-related fields into dedicated TypeContext for better code
organization and maintainability. First step of 7-context refactoring plan.

## Changes
- **New**: src/mir/builder/type_context.rs
  - Consolidates value_types, value_kinds, value_origin_newbox
  - Provides clean API for type operations
  - BTreeMap/HashMap as appropriate for determinism

- **Modified**: src/mir/builder.rs
  - Add type_ctx field to MirBuilder
  - Deprecate old fields (backward compat)
  - Add sync helpers for gradual migration
  - Initialize type_ctx in new()

- **Doc**: phase-136-context-box-progress.md
  - Track refactoring progress (1/7 complete)
  - Document design principles
  - Plan next steps (CoreContext)

## Impact
- 16 files with 113 deprecated field usages
- No breaking changes (gradual migration)
- All tests pass (997/997)

## Test Results
✅ cargo build --release (warnings only)
✅ cargo test --release --lib (997 passed)
✅ phase135_trim_mir_verify.sh (PASS)
✅ phase132_exit_phi_parity.sh (3/3 PASS)

## Next Step
CoreContext extraction (ValueId/BlockId generators)

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/mir/builder.rs

@@ -52,6 +52,7 @@ mod router; // RouterPolicyBox（Unified vs BoxCall）
 mod schedule; // BlockScheduleBox（物理順序: PHI→materialize→body）
 mod ssa; // LocalSSA helpers (in-block materialization)
 mod stmts;
+mod type_context; // Phase 136 follow-up: TypeContext extraction
 mod type_facts; // Phase 136 follow-up: Type inference facts box
 pub(crate) mod type_registry;
 mod types; // types::annotation / inference（型注釈/推論の箱: 推論は後段）
@@ -88,6 +89,11 @@ pub struct MirBuilder {
     /// Noneの場合、従来のフィールドを使用（後方互換性）
     pub(super) compilation_context: Option<context::BoxCompilationContext>,
 
+    /// Phase 136 follow-up: Type information context
+    /// Consolidates value_types, value_kinds, value_origin_newbox for better organization.
+    /// Direct field access for backward compatibility (migration in progress).
+    pub(super) type_ctx: type_context::TypeContext,
+
     /// Variable name to ValueId mapping (for SSA conversion)
     /// 注意: compilation_contextがSomeの場合は使用されません
     /// Phase 25.1: HashMap → BTreeMap（PHI生成の決定性確保）
@@ -103,10 +109,12 @@ pub struct MirBuilder {
     #[allow(dead_code)]
     pub(super) pending_phis: Vec<(BasicBlockId, ValueId, String)>,
 
-    /// Origin tracking for simple optimizations (e.g., object.method after new)
+    /// [DEPRECATED] Origin tracking for simple optimizations (e.g., object.method after new)
     /// Maps a ValueId to the class name if it was produced by NewBox of that class
     /// 注意: compilation_contextがSomeの場合は使用されません
+    /// Phase 136: Moved to type_ctx.value_origin_newbox (backward compat wrapper)
     // Phase 25.1: HashMap → BTreeMap（決定性確保）
+    #[deprecated(note = "Use type_ctx.value_origin_newbox instead")]
     pub(super) value_origin_newbox: BTreeMap<ValueId, String>,
 
     /// Names of user-defined boxes declared in the current module
@@ -123,15 +131,19 @@ pub struct MirBuilder {
     /// Class-level field origin (cross-function heuristic): (BaseBoxName, field) -> FieldBoxName
     pub(super) field_origin_by_box: HashMap<(String, String), String>,
 
-    /// Optional per-value type annotations (MIR-level): ValueId -> MirType
+    /// [DEPRECATED] Optional per-value type annotations (MIR-level): ValueId -> MirType
     /// 注意: compilation_contextがSomeの場合は使用されません
+    /// Phase 136: Moved to type_ctx.value_types (backward compat wrapper)
     // Phase 25.1: HashMap → BTreeMap（決定性確保）
+    #[deprecated(note = "Use type_ctx.value_types instead")]
     pub(super) value_types: BTreeMap<ValueId, super::MirType>,
 
-    /// Phase 26-A: ValueId型情報マップ（型安全性強化）
+    /// [DEPRECATED] Phase 26-A: ValueId型情報マップ（型安全性強化）
     /// ValueId -> MirValueKind のマッピング
     /// - GUARDバグ予防: ValueId(0)がParameterかLocalか区別可能
     /// - デフォルト: 未登録のValueIdはTemporary扱い
+    /// Phase 136: Moved to type_ctx.value_kinds (backward compat wrapper)
+    #[deprecated(note = "Use type_ctx.value_kinds instead")]
     pub(super) value_kinds: HashMap<ValueId, super::MirValueKind>,
 
     /// 関数スコープの SlotRegistry（観測専用）
@@ -284,18 +296,19 @@ impl MirBuilder {
             current_block: None,
             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
+            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
             variable_map: BTreeMap::new(), // Phase 25.1: 決定性確保
             lexical_scope_stack: Vec::new(),
             pending_phis: Vec::new(),
-            value_origin_newbox: BTreeMap::new(), // Phase 25.1: 決定性確保
+            value_origin_newbox: BTreeMap::new(), // Phase 25.1: 決定性確保 (backward compat)
             user_defined_boxes: HashSet::new(),
             weak_fields_by_box: HashMap::new(),
             property_getters_by_box: HashMap::new(),
             field_origin_class: HashMap::new(),
             field_origin_by_box: HashMap::new(),
-            value_types: BTreeMap::new(), // Phase 25.1: 決定性確保
-            value_kinds: HashMap::new(),  // Phase 26-A: ValueId型安全化
+            value_types: BTreeMap::new(), // Phase 25.1: 決定性確保 (backward compat)
+            value_kinds: HashMap::new(),  // Phase 26-A: ValueId型安全化 (backward compat)
             current_slot_registry: None,
             type_registry: type_registry::TypeRegistry::new(),
             plugin_method_sigs,
@@ -344,6 +357,23 @@ impl MirBuilder {
         }
     }
 
+    // ---- Phase 136: TypeContext synchronization helpers ----
+    /// Sync type_ctx changes back to legacy fields (backward compatibility)
+    #[allow(deprecated)]
+    fn sync_type_ctx_to_legacy(&mut self) {
+        self.value_types = self.type_ctx.value_types.clone();
+        self.value_kinds = self.type_ctx.value_kinds.clone();
+        self.value_origin_newbox = self.type_ctx.value_origin_newbox.clone();
+    }
+
+    /// Sync legacy field changes to type_ctx (backward compatibility)
+    #[allow(deprecated)]
+    fn sync_legacy_to_type_ctx(&mut self) {
+        self.type_ctx.value_types = self.value_types.clone();
+        self.type_ctx.value_kinds = self.value_kinds.clone();
+        self.type_ctx.value_origin_newbox = self.value_origin_newbox.clone();
+    }
+
     /// Push/pop helpers for If merge context (best-effort; optional usage)
     pub(super) fn push_if_merge(&mut self, bb: BasicBlockId) {
         self.if_merge_stack.push(bb);