ci: add GitHub Actions workflow; runner: prefer PyVM in selfhost paths; stage3: add LLVM + bridge acceptance smokes; docs: update env flags

tools/smokes/curated_llvm_stage3.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Curated LLVM Stage-3 acceptance smoke (llvmlite harness)
+# Usage: tools/smokes/curated_llvm_stage3.sh [--phi-off]
+
+ROOT_DIR=$(cd "$(dirname "$0")/../.." && pwd)
+BIN="$ROOT_DIR/target/release/nyash"
+
+if ! [ -x "$BIN" ]; then
+  echo "[curated-llvm-stage3] building nyash (release, features=llvm)" >&2
+  cargo build --release --features llvm >/dev/null
+fi
+
+export NYASH_LLVM_USE_HARNESS=1
+
+if [[ "${1:-}" == "--phi-off" ]]; then
+  export NYASH_MIR_NO_PHI=1
+  export NYASH_VERIFY_ALLOW_NO_PHI=1
+  echo "[curated-llvm-stage3] PHI-off (edge-copy) enabled" >&2
+fi
+
+run_ok() {
+  local path="$1"
+  echo "[curated-llvm-stage3] RUN --backend llvm: ${path}"
+  timeout 10s "$BIN" --backend llvm "$path" >/dev/null
+}
+
+# A) try/catch/finally without actual throw
+run_ok "$ROOT_DIR/apps/tests/stage3_try_finally_basic.nyash"
+
+# B) throw in dead branch (acceptance only)
+run_ok "$ROOT_DIR/apps/tests/stage3_throw_dead_branch.nyash"
+
+# C) repeat with trap disabled (robustness; should be no-op here)
+NYASH_LLVM_TRAP_ON_THROW=0 run_ok "$ROOT_DIR/apps/tests/stage3_try_finally_basic.nyash"
+NYASH_LLVM_TRAP_ON_THROW=0 run_ok "$ROOT_DIR/apps/tests/stage3_throw_dead_branch.nyash"
+
+echo "[curated-llvm-stage3] OK"
+