feat(joinir): Phase 45 - JoinIR mode unification

Unified JoinIR routing logic through centralized JoinIrMode enum:

Key changes:
- Added JoinIrMode enum (StructuredOnly / NormalizedDev / NormalizedCanonical)
- Added current_joinir_mode() for centralized mode determination
- Refactored normalized_dev_enabled() as thin wrapper over mode enum
- Updated bridge.rs: mode-based routing with canonical P2-Core special handling
- Updated runner.rs: mode pattern matching for dev roundtrip path

Files modified:
- joinir_dev.rs: JoinIrMode enum + current_joinir_mode() (+49 lines)
- bridge.rs: Replaced boolean checks with mode pattern matching (+29 lines)
- runner.rs: Mode-based routing logic (+9 lines)
- CURRENT_TASK.md: Phase 45 implementation summary

Documentation:
- phase45-norm-mode-design.md: Complete design spec and implementation guide

Behavior preservation:
- Canonical P2-Core shapes: always Normalized→MIR(direct) (mode-independent)
- NormalizedDev mode: Structured→Normalized→MIR for supported shapes
- StructuredOnly mode: Structured→MIR direct (default)

Tests: 937/937 PASS (no regression, pure refactor)

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

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

src/config/env/joinir_dev.rs

@@ -1,8 +1,26 @@
 //! JoinIR development / experimental flags (SSOT).
 //! Phase 72-C: Consolidate all NYASH_JOINIR_* dev flags through centralized helpers.
+//! Phase 45: JoinIR mode unification (StructuredOnly / NormalizedDev / NormalizedCanonical)
 
 use crate::config::env::env_bool;
 
+/// Phase 45: JoinIR execution mode enum
+///
+/// Centralizes all JoinIR routing decisions (Structured vs Normalized paths).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum JoinIrMode {
+    /// Default mode: Structured→MIR direct (no Normalized layer)
+    StructuredOnly,
+
+    /// Development mode: Structured→Normalized→MIR(direct) for supported shapes
+    /// Requires `--features normalized_dev` + env var
+    NormalizedDev,
+
+    /// Future mode: All canonical shapes use Normalized→MIR(direct)
+    /// Currently unused, reserved for Phase 46+ canonical migration
+    NormalizedCanonical,
+}
+
 /// NYASH_JOINIR_LOWER_GENERIC=1 - Enable generic lowering path for JoinIR
 /// (CRITICAL: 15 occurrences in codebase)
 pub fn lower_generic_enabled() -> bool {
@@ -105,16 +123,37 @@ pub fn joinir_normalized_dev_run_enabled() -> bool {
     env_bool("NYASH_JOINIR_NORMALIZED_DEV_RUN")
 }
 
+/// Phase 45: Get current JoinIR execution mode
+///
+/// Determines routing based on feature flags and environment variables:
+/// - `--features normalized_dev` + `NYASH_JOINIR_NORMALIZED_DEV_RUN=1` → NormalizedDev
+/// - Otherwise → StructuredOnly
+///
+/// Note: NormalizedCanonical is reserved for future canonical migration (Phase 46+)
+pub fn current_joinir_mode() -> JoinIrMode {
+    #[cfg(feature = "normalized_dev")]
+    {
+        if joinir_normalized_dev_run_enabled() {
+            JoinIrMode::NormalizedDev
+        } else {
+            JoinIrMode::StructuredOnly
+        }
+    }
+
+    #[cfg(not(feature = "normalized_dev"))]
+    {
+        JoinIrMode::StructuredOnly
+    }
+}
+
 /// Unified switch for Normalized dev experiments (feature + env).
 ///
 /// - Requires `--features normalized_dev`
 /// - Requires `NYASH_JOINIR_NORMALIZED_DEV_RUN=1`
+///
+/// Phase 45: Now implemented as a thin wrapper over current_joinir_mode()
 pub fn normalized_dev_enabled() -> bool {
-    if cfg!(feature = "normalized_dev") {
-        joinir_normalized_dev_run_enabled()
-    } else {
-        false
-    }
+    matches!(current_joinir_mode(), JoinIrMode::NormalizedDev)
 }
 
 /// JOINIR_TEST_DEBUG=1 (or NYASH_JOINIR_TEST_DEBUG=1) - Verbose logging for normalized dev tests