🔧 refactor(llvm-py): Fix resolver PHI handling and add trace improvements

Changes to resolver.py:
- Improved PHI value tracking in _value_at_end_i64() (lines 268-285)
- Added trace logging for snap hits with PHI detection
- Fixed PHI placeholder reuse logic to preserve dominance
- PHI values now returned directly from snapshots when valid

Changes to llvm_builder.py:
- Fixed externcall instruction parsing (line 522: 'func' instead of 'name')
- Improved block snapshot tracing (line 439)
- Added PHI incoming metadata tracking (lines 316-376)
- Enhanced definition tracking for lifetime hints

This should help debug the string carry=0 issue in esc_dirname_smoke where
PHI values were being incorrectly coerced instead of preserved.

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

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

src/llvm_py/instructions/boxcall.py

@@ -213,11 +213,10 @@ def lower_boxcall(
             callee = _declare(module, "nyash.console.log", i64, [i8p])
             _ = builder.call(callee, [arg0_ptr], name="console_log_ptr")
         else:
-            # Fallback: resolve i64 and prefer pointer API via to_i8p_h bridge
-            if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
-                arg0 = resolver.resolve_i64(args[0], builder.block, preds, block_end_values, vmap, bb_map) if args else None
-            else:
-                arg0 = vmap.get(args[0]) if args else None
+            # Fallback: prefer raw vmap value; resolve only if missing (avoid synthesizing PHIs here)
+            arg0 = vmap.get(args[0]) if args else None
+            if arg0 is None and resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
+                arg0 = resolver.resolve_i64(args[0], builder.block, preds, block_end_values, vmap, bb_map)
             if arg0 is None:
                 arg0 = ir.Constant(i64, 0)
             # If we have a handle (i64), convert to i8* via bridge and log via pointer API