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/reference/language/match-guards.md

@@ -0,0 +1,41 @@
+# Match Guards — Syntax and Lowering (MVP + Design Notes)
+
+Status: reference + design additions during freeze (no implementation changes)
+
+Scope
+- Guarded branches as a readable form of first-match selection.
+- Canonical lowering target: if/else chain + PHI merges.
+
+Syntax (MVP)
+- Guard chain (first-match wins):
+  ```nyash
+  guard <cond> -> { /* then */ }
+  guard <cond> -> { /* then */ }
+  else         -> { /* else */ }
+  ```
+- Conditions may combine comparisons, `is/as` type checks, and literals with `&&` / `||`.
+
+Lowering
+- Always lowers to a linear if/else chain with early exit on first true guard.
+- Merge points use normal PHI formation invariants (see `reference/mir/phi_invariants.md`).
+
+Design additions (frozen; docs only)
+- Range Pattern (sugar):
+  - `guard x in '0'..'9' -> { ... }`
+  - Lowers to: `('0' <= x && x <= '9')`.
+  - Multiple ranges: `in A..B || C..D` → OR of each bound check.
+- CharClass (predefined sets):
+  - `Digit ≡ '0'..'9'`, `AZ ≡ 'A'..'Z'`, `az ≡ 'a'..'z'`, `Alnum ≡ Digit || AZ || az`, `Space ≡ ' '\t\r\n` (MVP set; expandable later).
+  - `guard ch in Digit -> { ... }` expands to range checks.
+
+Errors & Rules (MVP)
+- Default `_` branch does not accept guards.
+- Type guard succeeds inside the then-branch; bindings (e.g., `StringBox(s)`) are introduced at branch head.
+- Short-circuit semantics follow standard branch evaluation (right side is evaluated only if needed).
+
+Observability (design)
+- `NYASH_FLOW_TRACE=1` may trace how guard chains desugar into if/else.
+
+Notes
+- This page describes existing guard semantics and adds range/charclass as documentation-only sugar during freeze.
+