llvm(py): introduce BuildCtx + trace hub; refactor if-merge prepass + PHI wiring into module; unify logs; ctx-enable compare/ret/call/boxcall/externcall/typeop/newbox/safepoint; curated smoke option for if-merge; README updates; keep behavior stable

src/llvm_py/build_ctx.py

@@ -0,0 +1,34 @@
+"""
+Build context for instruction lowering and helpers.
+
+This structure aggregates frequently passed references so call sites can
+remain concise as we gradually refactor instruction signatures.
+"""
+
+from dataclasses import dataclass
+from typing import Any, Dict, List, Optional
+import llvmlite.ir as ir
+
+@dataclass
+class BuildCtx:
+    # Core IR handles
+    module: ir.Module
+    i64: ir.IntType
+    i32: ir.IntType
+    i8: ir.IntType
+    i1: ir.IntType
+    i8p: ir.PointerType
+
+    # SSA maps and CFG
+    vmap: Dict[int, ir.Value]
+    bb_map: Dict[int, ir.Block]
+    preds: Dict[int, List[int]]
+    block_end_values: Dict[int, Dict[int, ir.Value]]
+
+    # Resolver (value queries, casts, string-ish tags)
+    resolver: Any
+
+    # Optional diagnostics toggles (read from env by the builder)
+    trace_phi: bool = False
+    verbose: bool = False
+