selfhost(pyvm): MiniVmPrints – prefer JSON route early-return (ok==1) to avoid fallback loops; keep default behavior unchanged elsewhere

docs/guides/dev-local-alias.md

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+# Dev Sugar: @name = expr as local declaration
+
+Status: dev-only, pre-expand sugar (no spec change)
+
+Goal
+- Speed up local declarations during development without impacting readability in shared code.
+
+Syntax (dev sugar)
+- Line-head only:
+  - `@name = expr` → `local name = expr`
+  - `@name: Type = expr` → `local name: Type = expr`
+
+Rules
+- Valid only at line start (leading spaces allowed). Inside expressions it is ignored.
+- Declaration-only: not allowed for reassignments; use `name = expr` for assignments.
+- Semantics are identical to `local` (scope/cleanup unchanged). Zero runtime cost.
+
+Enablement
+- Use the provided pre-expander script for dev: `tools/dev/at_local_preexpand.sh`.
+- Example:
+  - `tools/dev/at_local_preexpand.sh apps/tests/dev_sugar/at_local_basic.nyash > /tmp/out.nyash`
+  - `NYASH_VM_USE_PY=1 ./target/release/nyash --backend vm /tmp/out.nyash`
+
+Style
+- Shared/committed code: prefer explicit `local` (nyfmt may normalize @ to `local`).
+- Dev/repl/prototype: `@` is acceptable to reduce noise.
+
+Notes
+- This is a text pre-expansion; it does not change the parser or MIR.
+- The pattern is conservative to avoid collisions with comments and inline usages.
+