pyvm: split op handlers into ops_core/ops_box/ops_ctrl; add ops_flow + intrinsic; delegate vm.py without behavior change

net-plugin: modularize constants (consts.rs) and sockets (sockets.rs); remove legacy commented socket code; fix unused imports
mir: move instruction unit tests to tests/mir_instruction_unit.rs (file lean-up); no semantic changes
runner/pyvm: ensure using pre-strip; misc docs updates

Build: cargo build ok; legacy cfg warnings remain as before

docs/architecture/phi-and-ssa.md

@@ -0,0 +1,23 @@
+# PHI and SSA in Nyash
+
+Overview
+- Nyash lowers high-level control flow (If/Loop/Match) to MIR and backends that rely on SSA form.
+- We prioritize IR hygiene and observability while keeping runtime cost at zero.
+
+Design points
+- PHI hygiene: no empty PHIs; PHIs at block head only.
+- JoinResult hint: when both branches assign the same variable, we emit a MIR hint for diagnostics.
+- Loop carriers: loops may expose a carrier observation (≤ N variables, where N is unconstrained by design; smokes emphasize common cases).
+
+Normalization
+- If: may optionally wrap into LoopForm under a conservative gate (dev only). Semantics remain unchanged.
+- Match: scrutinee evaluated once, guard fused; normalized to nested If‑chain in macro/core pass.
+
+Testing
+- LLVM smokes: fixed small cases ensure no empty PHIs and head placement.
+- MIR smokes: trace `scope|join|loop` to validate shaping without peeking into IR details.
+
+Roadmap
+- Remove text-level sanitization once finalize‑PHI is trustworthy across Loop/If/Match.
+- Expand goldens to cover nested joins and multi‑carrier loops while keeping CI light.
+