fix(mir/builder): use function-local ValueId throughout MIR builder

Phase 25.1b: Complete SSA fix - eliminate all global ValueId usage in function contexts.

Root cause: ~75 locations throughout MIR builder were using global value
generator (self.value_gen.next()) instead of function-local allocator
(f.next_value_id()), causing SSA verification failures and runtime
"use of undefined value" errors.

Solution:
- Added next_value_id() helper that automatically chooses correct allocator
- Fixed 19 files with ~75 occurrences of ValueId allocation
- All function-context allocations now use function-local IDs

Files modified:
- src/mir/builder/utils.rs: Added next_value_id() helper, fixed 8 locations
- src/mir/builder/builder_calls.rs: 17 fixes
- src/mir/builder/ops.rs: 8 fixes
- src/mir/builder/stmts.rs: 7 fixes
- src/mir/builder/emission/constant.rs: 6 fixes
- src/mir/builder/rewrite/*.rs: 10 fixes
- + 13 other files

Verification:
- cargo build --release: SUCCESS
- Simple tests with NYASH_VM_VERIFY_MIR=1: Zero undefined errors
- Multi-parameter static methods: All working

Known remaining: ValueId(22) in Stage-B (separate issue to investigate)

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

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

lang/src/vm/hakorune-vm/extern_provider.hako

@@ -3,6 +3,7 @@
 // Scope (20.38準備): env.get / console.log のみ（C‑ABI導線は後段で接続）。
 
 using selfhost.vm.hakorune-vm.str_cast as StrCast
+using selfhost.shared.host_bridge.codegen_bridge as CodegenBridgeBox
 
 static box HakoruneExternProviderBox {
   get(name, args) {
@@ -31,11 +32,11 @@ static box HakoruneExternProviderBox {
     }
     if name == "env.mirbuilder.emit" {
       // Optional C‑ABI bridge（既定OFF）: タグを出力しつつ、Rust 側 extern_provider に最小接続
-      if env.get("HAKO_V1_EXTERN_PROVIDER_C_ABI") == "1" {
-        print("[extern/c-abi:mirbuilder.emit]")
-        // Call through to Core extern dispatcher and return the produced JSON (v1)
-        local out = hostbridge.extern_invoke("env.mirbuilder", "emit", args)
-        return "" + out
+        if env.get("HAKO_V1_EXTERN_PROVIDER_C_ABI") == "1" {
+          print("[extern/c-abi:mirbuilder.emit]")
+          // Call through to Core extern dispatcher and return the produced JSON (v1)
+          local out = hostbridge.extern_invoke("env.mirbuilder", "emit", args)
+          return "" + out
       }
       // Default: return empty string (verify/dev stub keeps rc=0)
       return ""
@@ -48,12 +49,20 @@ static box HakoruneExternProviderBox {
         // Call through to Core extern dispatcher and return produced object path
         // 現段階では Core 側で C-API/llvmlite の切替を行う。
         // 互換のため *_ny も最終的に emit_object へ委譲する。
-        local out = hostbridge.extern_invoke("env.codegen", "emit_object", args)
+        local out = CodegenBridgeBox.emit_object_args(args)
         return "" + out
       }
       // Default: return empty string (verify/dev stub keeps rc=0)
       return ""
     }
+    if name == "env.box_introspect.kind" {
+      if env.get("HAKO_V1_EXTERN_PROVIDER_C_ABI") == "1" {
+        if env.get("HAKO_CABI_TRACE") == "1" { print("[extern/c-abi:box_introspect.kind]") }
+        local out = hostbridge.extern_invoke("env.box_introspect", "kind", args)
+        return "" + out
+      }
+      return ""
+    }
     // Unknown: return null for now (caller decides Fail‑Fast)
     return null
   }