feat(control_tree): Phase 131 P1.5-P2 DirectValue exit reconnection

Implement DirectValue mode for Normalized shadow exit handling:

**P1.5 Changes**:
- Add ExitReconnectMode::DirectValue (skip exit PHI generation)
- Carry remapped_exit_values through merge result
- Update host variable_map directly with exit values
- Fix loop(true) { x = 1; break }; return x to return 1 correctly

**P2 Changes**:
- Normalize k_exit continuation entry/exit edges
- Rewrite TailCall(k_exit) → Jump(exit_block) for proper merge
- Add verify_all_terminator_targets_exist contract check
- Extend ExitLineReconnector to handle DirectValue mode

**Infrastructure**:
- tools/build_llvm.sh: Force TMPDIR under target/ (EXDEV mitigation)
- llvm_exe_runner.sh: Add exit_code verification support
- Phase 131 smokes: Update for dev-only + exit code validation

**Contracts**:
- PHI-free: Normalized path uses continuations only
- Exit values reconnect via remapped ValueIds
- Existing patterns unaffected (既定挙動不変)

Related: Phase 131 loop(true) break-once Normalized support

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

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

src/mir/join_ir/lowering/carrier_info.rs

@@ -91,6 +91,48 @@ pub enum CarrierInit {
     LoopLocalZero,
 }
 
+/// Phase 131 P1.5: Exit reconnection mode for JoinInlineBoundary
+///
+/// Controls whether exit values are reconnected via PHI generation or direct assignment.
+/// This separates Normalized shadow (DirectValue) from existing loop patterns (Phi).
+///
+/// # Design Principle (SSOT)
+///
+/// - **DirectValue**: Normalized loops prohibit PHI generation. Exit values are directly
+///   wired to variable_map using remapped_exit_values from MergeResult.
+/// - **Phi**: Existing loop patterns use PHI generation for exit value merging.
+///
+/// # Example
+///
+/// ```ignore
+/// // Normalized shadow: loop(true) { x = 1; break } → DirectValue
+/// JoinInlineBoundary { exit_reconnect_mode: ExitReconnectMode::DirectValue, .. }
+///
+/// // Traditional loop: loop(i < 3) { sum = sum + i } → Phi
+/// JoinInlineBoundary { exit_reconnect_mode: ExitReconnectMode::Phi, .. }
+/// ```
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ExitReconnectMode {
+    /// Existing loop patterns: PHI generation for exit value merging
+    ///
+    /// Used by Pattern 1-4 loops with multiple exit paths.
+    /// Exit values are collected into exit PHIs.
+    Phi,
+
+    /// Normalized shadow: Direct variable_map update, no PHI generation
+    ///
+    /// Used by loop(true) { <assign>*; break } pattern.
+    /// Exit values are directly wired using MergeResult.remapped_exit_values.
+    DirectValue,
+}
+
+impl Default for ExitReconnectMode {
+    /// Default to Phi mode for backward compatibility
+    fn default() -> Self {
+        Self::Phi
+    }
+}
+
 // Phase 229: ConditionAlias removed - redundant with promoted_loopbodylocals
 // The naming convention (old_name → "is_<old_name>" or "is_<old_name>_match")
 // is sufficient to resolve promoted variables dynamically.

src/mir/join_ir/lowering/inline_boundary.rs

@@ -43,7 +43,7 @@
 //!     ...
 //! ```
 
-use super::carrier_info::CarrierRole;
+use super::carrier_info::{CarrierRole, ExitReconnectMode};
 use crate::mir::ValueId;
 
 /// Explicit binding between JoinIR exit value and host variable
@@ -257,6 +257,15 @@ pub struct JoinInlineBoundary {
     /// - `Some(CarrierInfo)`: Full carrier metadata available
     /// - `None`: Legacy path (derive carriers from exit_bindings)
     pub carrier_info: Option<super::carrier_info::CarrierInfo>,
+
+    /// Phase 131 P1.5: Exit reconnection mode
+    ///
+    /// Controls whether exit values are reconnected via PHI generation (Phi)
+    /// or direct variable_map update (DirectValue).
+    ///
+    /// - `Phi` (default): Existing loop patterns use exit PHI generation
+    /// - `DirectValue`: Normalized shadow uses direct value wiring
+    pub exit_reconnect_mode: ExitReconnectMode,
 }
 
 impl JoinInlineBoundary {
@@ -284,6 +293,7 @@ impl JoinInlineBoundary {
             expr_result: None,          // Phase 33-14: Default to carrier-only pattern
             loop_var_name: None,        // Phase 33-16
             carrier_info: None,         // Phase 228: Default to None
+            exit_reconnect_mode: ExitReconnectMode::default(), // Phase 131 P1.5: Default to Phi
         }
     }
 
@@ -327,6 +337,7 @@ impl JoinInlineBoundary {
             expr_result: None,          // Phase 33-14
             loop_var_name: None,        // Phase 33-16
             carrier_info: None,         // Phase 228
+            exit_reconnect_mode: ExitReconnectMode::default(), // Phase 131 P1.5: Default to Phi
         }
     }
 
@@ -387,6 +398,7 @@ impl JoinInlineBoundary {
             expr_result: None,          // Phase 33-14
             loop_var_name: None,        // Phase 33-16
             carrier_info: None,         // Phase 228
+            exit_reconnect_mode: ExitReconnectMode::default(), // Phase 131 P1.5: Default to Phi
         }
     }
 
@@ -433,6 +445,7 @@ impl JoinInlineBoundary {
             expr_result: None,          // Phase 33-14
             loop_var_name: None,        // Phase 33-16
             carrier_info: None,         // Phase 228
+            exit_reconnect_mode: ExitReconnectMode::default(), // Phase 131 P1.5: Default to Phi
         }
     }
 
@@ -483,6 +496,7 @@ impl JoinInlineBoundary {
             expr_result: None,          // Phase 33-14
             loop_var_name: None,        // Phase 33-16
             carrier_info: None,         // Phase 228
+            exit_reconnect_mode: ExitReconnectMode::default(), // Phase 131 P1.5: Default to Phi
         }
     }
 
@@ -540,6 +554,7 @@ impl JoinInlineBoundary {
             expr_result: None,   // Phase 33-14
             loop_var_name: None, // Phase 33-16
             carrier_info: None,  // Phase 228
+            exit_reconnect_mode: ExitReconnectMode::default(), // Phase 131 P1.5: Default to Phi
         }
     }
 }

src/mir/join_ir/lowering/inline_boundary_builder.rs

@@ -82,6 +82,7 @@ pub struct JoinInlineBoundaryBuilder {
 impl JoinInlineBoundaryBuilder {
     /// Create a new builder with default empty boundary
     pub fn new() -> Self {
+        use crate::mir::join_ir::lowering::carrier_info::ExitReconnectMode;
         Self {
             boundary: JoinInlineBoundary {
                 join_inputs: vec![],
@@ -96,6 +97,7 @@ impl JoinInlineBoundaryBuilder {
                 expr_result: None,
                 loop_var_name: None,
                 carrier_info: None, // Phase 228: Initialize as None
+                exit_reconnect_mode: ExitReconnectMode::default(), // Phase 131 P1.5
             },
         }
     }