docs: update CURRENT_TASK with Box Theory PHI plan (defer/finalize) and MIR v0.5 type meta; add parity tooling and PyVM scaffolding

impl(pyvm/llvmlite):
- add tools/parity.sh; tools/pyvm_runner.py; src/llvm_py/pyvm/*
- emit string const as handle type in MIR JSON; add dst_type hints
- unify '+' to concat_hh with from_i64/from_i8_string bridges; console print via to_i8p_h
- add runtime bridges: nyash.box.from_i64, nyash.string.to_i8p_h

tests:
- add apps/tests/min_str_cat_loop (minimal repro for string cat loop)

tools/pyvm_runner.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+"""
+Nyash PyVM runner (scaffold)
+
+Usage:
+  - python3 tools/pyvm_runner.py --in mir.json [--entry Main.main]
+
+Executes MIR(JSON) using a tiny Python interpreter for a minimal opcode set:
+  - const/binop/compare/branch/jump/ret
+  - newbox (ConsoleBox, StringBox minimal)
+  - boxcall (String: length/substring/lastIndexOf; Console: print/println/log)
+  - externcall (nyash.console.println)
+
+On success, exits with the integer return value if it is an Integer; otherwise 0.
+Outputs produced by println/log are written to stdout.
+"""
+
+import argparse
+import json
+import sys
+import os
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+PYVM_DIR = ROOT / "src" / "llvm_py" / "pyvm"
+
+# Ensure imports can find the package root (src)
+SRC_DIR = ROOT / "src"
+if str(SRC_DIR) not in sys.path:
+    sys.path.insert(0, str(SRC_DIR))
+
+from llvm_py.pyvm.vm import PyVM  # type: ignore
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("--in", dest="infile", required=True, help="MIR JSON input")
+    ap.add_argument("--entry", dest="entry", default="Main.main", help="Entry function (default Main.main)")
+    args = ap.parse_args()
+
+    with open(args.infile, "r") as f:
+        program = json.load(f)
+
+    vm = PyVM(program)
+    # Fallbacks for entry name
+    entry = args.entry
+    fun_names = {f.get("name", "") for f in program.get("functions", [])}
+    if entry not in fun_names:
+        if "main" in fun_names:
+            entry = "main"
+        elif "Main.main" in fun_names:
+            entry = "Main.main"
+
+    result = vm.run(entry)
+    # Exit code convention: integers propagate; bool -> 0/1; else 0
+    code = 0
+    if isinstance(result, bool):
+        code = 1 if result else 0
+    elif isinstance(result, int):
+        # Clamp to 32-bit exit code domain
+        code = int(result) & 0xFFFFFFFF
+        if code & 0x80000000:
+            code = -((~code + 1) & 0xFFFFFFFF)
+    # For parity comparisons, avoid emitting extra lines here.
+    sys.exit(code)
+
+
+if __name__ == "__main__":
+    try:
+        main()
+    except Exception as e:
+        import traceback
+        print(f"[pyvm] error: {e}", file=sys.stderr)
+        if sys.stderr and (os.environ.get('NYASH_CLI_VERBOSE') == '1' or True):
+            traceback.print_exc()
+        sys.exit(1)