feat(joinir): Phase 202-B Pattern 3 uses JoinValueSpace

Replace sequential value_counter (0u32) with JoinValueSpace allocator
in Pattern 3 (If-PHI) lowering for unified ValueId management.

Changes:
- loop_with_if_phi_minimal.rs: Replace value_counter with join_value_space.alloc_local()
- pattern3_with_if_phi.rs: Create JoinValueSpace and pass to lowerer
- loop_patterns/with_if_phi.rs: Update legacy wrapper to use JoinValueSpace

Benefits:
- Consistent with Pattern 2 implementation (Phase 201)
- Prevents ValueId collision in Local region (1000+)
- Clean separation: Param region (100-999) vs Local region (1000+)

Test status:
- All unit tests pass (5/5)
- E2E tests pass: loop_if_phi.hako, loop_if_phi_continue.hako

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

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

src/mir/builder/control_flow/joinir/patterns/pattern3_with_if_phi.rs

@@ -101,8 +101,12 @@ impl MirBuilder {
         // Phase 195: Use unified trace
         trace::trace().varmap("pattern3_start", &self.variable_map);
 
+        // Phase 202-B: Create JoinValueSpace for unified ValueId allocation
+        use crate::mir::join_ir::lowering::join_value_space::JoinValueSpace;
+        let mut join_value_space = JoinValueSpace::new();
+
         // Call Pattern 3 lowerer with preprocessed scope
-        let join_module = match lower_loop_with_if_phi_pattern(ctx.loop_scope) {
+        let join_module = match lower_loop_with_if_phi_pattern(ctx.loop_scope, &mut join_value_space) {
             Some(module) => module,
             None => {
                 // Phase 195: Use unified trace

src/mir/join_ir/lowering/loop_patterns/with_if_phi.rs

@@ -85,6 +85,7 @@ pub fn lower_loop_with_conditional_phi_to_joinir(
 ) -> Option<JoinInst> {
     // Phase 188-Impl-3: Delegate to minimal lowerer
     // TODO: Extract LoopScopeShape from loop_form for generic implementation
+    use crate::mir::join_ir::lowering::join_value_space::JoinValueSpace;
     use crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape;
     use crate::mir::join_ir::lowering::loop_with_if_phi_minimal::lower_loop_with_if_phi_pattern;
     use crate::mir::BasicBlockId;
@@ -105,8 +106,11 @@ pub fn lower_loop_with_conditional_phi_to_joinir(
         variable_definitions: BTreeMap::new(),
     };
 
+    // Phase 202-B: Create JoinValueSpace for unified ValueId allocation
+    let mut join_value_space = JoinValueSpace::new();
+
     // Generate JoinIR module
-    let _join_module = lower_loop_with_if_phi_pattern(placeholder_scope)?;
+    let _join_module = lower_loop_with_if_phi_pattern(placeholder_scope, &mut join_value_space)?;
 
     // Phase 188-Impl-3: Pattern 3 is now integrated via the router
     // This function delegates to loop_with_if_phi_minimal which generates JoinModule

src/mir/join_ir/lowering/loop_with_if_phi_minimal.rs

@@ -67,6 +67,7 @@
 //!
 //! Following the "80/20 rule" from CLAUDE.md - get it working first, generalize later.
 
+use crate::mir::join_ir::lowering::join_value_space::JoinValueSpace;
 use crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape;
 use crate::mir::join_ir::{
     BinOpKind, CompareOp, ConstValue, JoinFuncId, JoinFunction, JoinInst, JoinModule,
@@ -97,6 +98,7 @@ use crate::mir::ValueId;
 /// # Arguments
 ///
 /// * `_scope` - LoopScopeShape (reserved for future generic implementation)
+/// * `join_value_space` - Phase 202-B: Unified JoinIR ValueId allocator (Local region: 1000+)
 ///
 /// # Returns
 ///
@@ -109,15 +111,13 @@ use crate::mir::ValueId;
 /// - **Input slots**: ValueId(0), ValueId(1) in main function (i_init, sum_init)
 /// - **Output slot**: k_exit returns the final sum value
 /// - **Caller responsibility**: Create JoinInlineBoundary to map ValueIds
-pub(crate) fn lower_loop_with_if_phi_pattern(_scope: LoopScopeShape) -> Option<JoinModule> {
-    // Phase 188-Impl-3: Use local ValueId allocator (sequential from 0)
-    // JoinIR has NO knowledge of host ValueIds - boundary handled separately
-    let mut value_counter = 0u32;
-    let mut alloc_value = || {
-        let id = ValueId(value_counter);
-        value_counter += 1;
-        id
-    };
+pub(crate) fn lower_loop_with_if_phi_pattern(
+    _scope: LoopScopeShape,
+    join_value_space: &mut JoinValueSpace,
+) -> Option<JoinModule> {
+    // Phase 202-B: Use JoinValueSpace for unified ValueId allocation
+    // - Local region (1000+) ensures no collision with Param region (100-999)
+    let mut alloc_value = || join_value_space.alloc_local();
 
     let mut join_module = JoinModule::new();