feat(mir): Phase 25.1f完了 - Conservative PHI + ControlForm観測レイヤー

🎉 Conservative PHI Box理論による完全SSA構築

**Phase 7-B: Conservative PHI実装**
- 片方branchのみ定義変数に対応（emit_void使用）
- 全変数にPHI生成（Conservative Box理論）
- Stage-1 resolver全テスト緑化（3/3 PASS）

**Phase 25.1f: ControlForm観測レイヤー**
- LoopShape/IfShape/ControlForm構造定義
- Loop/If統一インターフェース実装
- debug_dump/debug_validate機能追加
- NYASH_CONTROL_FORM_TRACE環境変数対応

**主な変更**:
- src/mir/builder/phi.rs: Conservative PHI実装
- src/mir/control_form.rs: ControlForm構造（NEW）
- src/mir/loop_builder.rs: LoopForm v2デフォルト化

**テスト結果**:
✅ mir_stage1_using_resolver_min_fragment_verifies
✅ mir_stage1_using_resolver_full_collect_entries_verifies
✅ mir_parserbox_parse_program2_harness_parses_minimal_source

🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: ChatGPT <chatgpt@openai.com>

src/backend/mir_interpreter/exec.rs

@@ -36,9 +36,6 @@ impl MirInterpreter {
         let saved_fn = self.cur_fn.clone();
         self.cur_fn = Some(func.signature.name.clone());
 
-        // Check if this is a static box method call
-        let static_box_name = self.is_static_box_method(&func.signature.name);
-
         match arg_vals {
             Some(args) => {
                 // Regular parameter binding: params and args are 1:1

src/backend/mir_interpreter/handlers/boxes.rs

@@ -278,6 +278,7 @@ impl MirInterpreter {
     }
 
     // moved: try_handle_map_box → handlers/boxes_map.rs
+    #[allow(dead_code)]
     fn try_handle_map_box(
         &mut self,
         dst: Option<ValueId>,
@@ -289,6 +290,7 @@ impl MirInterpreter {
     }
 
     // moved: try_handle_string_box → handlers/boxes_string.rs
+    #[allow(dead_code)]
     fn try_handle_string_box(
         &mut self,
         dst: Option<ValueId>,
@@ -300,6 +302,7 @@ impl MirInterpreter {
     }
 
     // moved: try_handle_array_box → handlers/boxes_array.rs
+    #[allow(dead_code)]
     fn try_handle_array_box(
         &mut self,
         dst: Option<ValueId>,

src/backend/mir_interpreter/handlers/boxes_instance.rs

@@ -102,7 +102,7 @@ pub(super) fn try_handle_instance_box(
         } else {
             // Conservative fallback: search unique function by name tail ".method/arity"
             let tail = format!(".{}{}", method, format!("/{}", args.len()));
-            let mut cands: Vec<String> = this
+            let cands: Vec<String> = this
                 .functions
                 .keys()
                 .filter(|k| k.ends_with(&tail))

src/backend/mir_interpreter/handlers/boxes_object_fields.rs

@@ -1,5 +1,4 @@
 use super::*;
-use crate::box_trait::NyashBox;
 
 pub(super) fn try_handle_object_fields(
     this: &mut MirInterpreter,

src/backend/mir_interpreter/handlers/boxes_string.rs

@@ -1,5 +1,4 @@
 use super::*;
-use crate::box_trait::NyashBox;
 
 pub(super) fn try_handle_string_box(
     this: &mut MirInterpreter,

src/backend/mir_interpreter/handlers/externals.rs

@@ -3,6 +3,7 @@ use serde_json::Value as JsonValue;
 
 impl MirInterpreter {
     #[inline]
+    #[allow(dead_code)]
     fn ensure_mir_json_version_field(s: &str) -> String {
         match serde_json::from_str::<JsonValue>(s) {
             Ok(mut v) => {
@@ -28,6 +29,12 @@ impl MirInterpreter {
         let mbase = super::super::utils::normalize_arity_suffix(method);
         match (iface, mbase) {
             ("env", "get") => {
+                // Prefer provider-based resolution when available, fall back to process env.
+                if let Some(provider_res) = self.extern_provider_dispatch("env.get", args) {
+                    let result = provider_res?;
+                    self.write_result(dst, result);
+                    return Ok(());
+                }
                 if let Some(a0) = args.get(0) {
                     let key = self.reg_load(*a0)?.to_string();
                     let val = std::env::var(&key).ok();
@@ -135,14 +142,6 @@ impl MirInterpreter {
                 }
                 Ok(())
             }
-            ("env", "get") => {
-                // Delegate to provider
-                let ret = self
-                    .extern_provider_dispatch("env.get", args)
-                    .unwrap_or(Ok(VMValue::Void))?;
-                self.write_result(dst, ret);
-                Ok(())
-            }
             ("env", "set") => {
                 // Delegate to provider
                 let ret = self

src/backend/mir_interpreter/mod.rs

@@ -110,6 +110,7 @@ impl MirInterpreter {
 
     /// Check if a function name represents a static box method
     /// Format: "BoxName.method/Arity"
+    #[allow(dead_code)]
     fn is_static_box_method(&self, func_name: &str) -> Option<String> {
         if let Some((box_name, _rest)) = func_name.split_once('.') {
             if self.static_box_decls.contains_key(box_name) {

src/backend/mir_interpreter/utils/arg_validation.rs

@@ -44,6 +44,7 @@ impl MirInterpreter {
     /// # Returns
     /// 引数数が範囲内の場合はOk(())、そうでない場合はエラー
     #[inline]
+    #[allow(dead_code)]
     pub(crate) fn validate_args_range(
         &self,
         method: &str,
@@ -71,6 +72,7 @@ impl MirInterpreter {
     /// # Returns
     /// 引数数が最小値以上の場合はOk(())、そうでない場合はエラー
     #[inline]
+    #[allow(dead_code)]
     pub(crate) fn validate_args_min(
         &self,
         method: &str,

src/backend/mir_interpreter/utils/conversion_helpers.rs

@@ -42,6 +42,7 @@ impl MirInterpreter {
     /// # Errors
     /// * 値が整数でない場合はエラー
     #[inline]
+    #[allow(dead_code)]
     pub(crate) fn load_as_int(&mut self, vid: ValueId) -> Result<i64, VMError> {
         match self.reg_load(vid)? {
             VMValue::Integer(i) => Ok(i),
@@ -71,6 +72,7 @@ impl MirInterpreter {
     /// # Errors
     /// * 値がboolでない場合はエラー
     #[inline]
+    #[allow(dead_code)]
     pub(crate) fn load_as_bool(&mut self, vid: ValueId) -> Result<bool, VMError> {
         match self.reg_load(vid)? {
             VMValue::Bool(b) => Ok(b),
@@ -112,6 +114,7 @@ impl MirInterpreter {
     /// # Returns
     /// * `Result<Vec<VMValue>, VMError>` - 読み込んだVMValueのVec
     #[inline]
+    #[allow(dead_code)]
     pub(crate) fn load_args_as_values(
         &mut self,
         vids: &[ValueId],

src/backend/mir_interpreter/utils/destination_helpers.rs

@@ -13,6 +13,7 @@ impl MirInterpreter {
     /// * `dst` - 書き込み先のValueId (Noneの場合は何もしない)
     /// * `result` - 書き込むBox
     #[inline]
+    #[allow(dead_code)]
     pub(crate) fn write_box_result(
         &mut self,
         dst: Option<ValueId>,

src/backend/mir_interpreter/utils/error_helpers.rs

@@ -40,6 +40,7 @@ impl ErrorBuilder {
     /// // => "get expects Integer type, got String"
     /// ```
     #[inline]
+    #[allow(dead_code)]
     pub fn type_mismatch(method: &str, expected: &str, actual: &str) -> VMError {
         VMError::InvalidInstruction(format!("{} expects {} type, got {}", method, expected, actual))
     }
@@ -57,6 +58,7 @@ impl ErrorBuilder {
     /// // => "get index out of bounds: 5 >= 3"
     /// ```
     #[inline]
+    #[allow(dead_code)]
     pub fn out_of_bounds(method: &str, index: usize, len: usize) -> VMError {
         VMError::InvalidInstruction(format!("{} index out of bounds: {} >= {}", method, index, len))
     }
@@ -93,6 +95,7 @@ impl ErrorBuilder {
     /// // => "receiver must be ArrayBox"
     /// ```
     #[inline]
+    #[allow(dead_code)]
     pub fn receiver_type_error(expected: &str) -> VMError {
         VMError::InvalidInstruction(format!("receiver must be {}", expected))
     }
@@ -123,6 +126,7 @@ impl ErrorBuilder {
     /// // => "link_object expects at least 1 arg, got 0"
     /// ```
     #[inline]
+    #[allow(dead_code)]
     pub fn arg_count_min(method: &str, min: usize, actual: usize) -> VMError {
         VMError::InvalidInstruction(format!(
             "{} expects at least {} arg{}, got {}",
@@ -153,6 +157,7 @@ impl ErrorBuilder {
     /// // => "link_object: <error message>"
     /// ```
     #[inline]
+    #[allow(dead_code)]
     pub fn from_error(operation: &str, error: &dyn std::error::Error) -> VMError {
         VMError::InvalidInstruction(format!("{}: {}", operation, error))
     }
@@ -178,6 +183,7 @@ impl super::super::MirInterpreter {
     /// return Err(self.err_type_mismatch("get", "Integer", actual_type));
     /// ```
     #[inline]
+    #[allow(dead_code)]
     pub(crate) fn err_type_mismatch(&self, method: &str, expected: &str, actual: &str) -> VMError {
         ErrorBuilder::type_mismatch(method, expected, actual)
     }
@@ -189,6 +195,7 @@ impl super::super::MirInterpreter {
     /// return Err(self.err_out_of_bounds("get", idx, len));
     /// ```
     #[inline]
+    #[allow(dead_code)]
     pub(crate) fn err_out_of_bounds(&self, method: &str, index: usize, len: usize) -> VMError {
         ErrorBuilder::out_of_bounds(method, index, len)
     }

src/backend/mir_interpreter/utils/receiver_helpers.rs

@@ -15,6 +15,7 @@ impl MirInterpreter {
     /// # Returns
     /// 変換成功時はBox、失敗時はエラー
     #[inline]
+    #[allow(dead_code)]
     pub(crate) fn convert_to_box(
         &mut self,
         receiver: ValueId,