js-on-sx: baseline commit (278/280 unit, 148/148 slice, runner stub)

Initial commit of the lib/js/ tree and plans/ directory. A previous
session left template-string work in progress — 278/280 unit tests pass
(2 failing: tpl part-count off-by-one, escaped-backtick ident lookup).
test262-runner.py and scoreboard are placeholders (0/8 with 7 timeouts);
fixing the runner is the next queue item.

lib/js/conformance.sh

@@ -0,0 +1,130 @@
+#!/usr/bin/env bash
+# Cherry-picked test262 conformance runner for JS-on-SX.
+# Walks lib/js/test262-slice/**/*.js, evaluates each via js-eval,
+# and compares against the sibling .expected file (substring match).
+#
+# Usage:
+#   bash lib/js/conformance.sh          # summary only
+#   bash lib/js/conformance.sh -v       # per-test pass/fail
+
+set -uo pipefail
+cd "$(git rev-parse --show-toplevel)"
+
+SX_SERVER="hosts/ocaml/_build/default/bin/sx_server.exe"
+if [ ! -x "$SX_SERVER" ]; then
+  echo "ERROR: $SX_SERVER not found. Run: cd hosts/ocaml && dune build"
+  exit 1
+fi
+
+VERBOSE="${1:-}"
+SLICE_DIR="lib/js/test262-slice"
+PASS=0
+FAIL=0
+ERRORS=""
+
+# Find all .js fixtures (sorted for stable output).
+# Skip README.md and similar.
+mapfile -t FIXTURES < <(find "$SLICE_DIR" -type f -name '*.js' | sort)
+
+if [ ${#FIXTURES[@]} -eq 0 ]; then
+  echo "No fixtures found in $SLICE_DIR"
+  exit 1
+fi
+
+# Build one big batch script: load everything once, then one epoch per
+# fixture. Avoids the ~200ms boot cost of starting the server for each
+# test.
+
+TMPFILE=$(mktemp)
+trap "rm -f $TMPFILE" EXIT
+
+{
+  echo '(epoch 1)'
+  echo '(load "lib/r7rs.sx")'
+  echo '(epoch 2)'
+  echo '(load "lib/js/lexer.sx")'
+  echo '(epoch 3)'
+  echo '(load "lib/js/parser.sx")'
+  echo '(epoch 4)'
+  echo '(load "lib/js/transpile.sx")'
+  echo '(epoch 5)'
+  echo '(load "lib/js/runtime.sx")'
+
+  epoch=100
+  for f in "${FIXTURES[@]}"; do
+    # Read source, strip trailing newline, then escape for *two*
+    # nested SX string literals: the outer epoch `(eval "…")` and
+    # the inner `(js-eval "…")` that it wraps.
+    #
+    # Source char → final stream char
+    #   \  →  \\\\    (outer: becomes \\ ; inner: becomes \)
+    #   "  →  \\\"    (outer: becomes \" ; inner: becomes ")
+    #   nl →  \\n     (SX newline escape, survives both levels)
+    src=$(python3 -c '
+import sys
+s = open(sys.argv[1], "r", encoding="utf-8").read().rstrip("\n")
+# Two nested SX string literals: outer eval wraps inner js-eval.
+# Escape once for inner (JS source → SX inner string literal):
+inner = s.replace("\\", "\\\\").replace("\"", "\\\"").replace("\n", "\\n")
+# Escape the result again for the outer SX string literal:
+outer = inner.replace("\\", "\\\\").replace("\"", "\\\"")
+sys.stdout.write(outer)
+' "$f")
+    echo "(epoch $epoch)"
+    echo "(eval \"(js-eval \\\"$src\\\")\")"
+    epoch=$((epoch + 1))
+  done
+} > "$TMPFILE"
+
+OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
+
+# Iterate fixtures with the same epoch sequence and check each.
+epoch=100
+for f in "${FIXTURES[@]}"; do
+  expected=$(cat "${f%.js}.expected" | sed -e 's/[[:space:]]*$//' | head -n 1)
+  name="${f#${SLICE_DIR}/}"
+  name="${name%.js}"
+
+  # Actual output lives on the line after "(ok-len $epoch N)" or on
+  # "(ok $epoch VAL)" for short values. Errors surface as "(error …)".
+  actual=$(echo "$OUTPUT" | awk -v e="$epoch" '
+    $0 ~ ("^\\(ok-len "e" ") { getline; print; exit }
+    $0 ~ ("^\\(ok "e" ") { sub("^\\(ok "e" ", ""); sub(")$", ""); print; exit }
+    $0 ~ ("^\\(error "e" ") { print; exit }
+  ')
+  [ -z "$actual" ] && actual="<no output>"
+
+  if echo "$actual" | grep -qF -- "$expected"; then
+    PASS=$((PASS + 1))
+    [ "$VERBOSE" = "-v" ] && echo "  ✓ $name"
+  else
+    FAIL=$((FAIL + 1))
+    ERRORS+="  ✗ $name
+    expected: $expected
+    actual:   $actual
+"
+    [ "$VERBOSE" = "-v" ] && echo "  ✗ $name (expected: $expected, actual: $actual)"
+  fi
+
+  epoch=$((epoch + 1))
+done
+
+TOTAL=$((PASS + FAIL))
+PCT=$(awk "BEGIN{printf \"%.1f\", ($PASS/$TOTAL)*100}")
+
+echo
+if [ $FAIL -eq 0 ]; then
+  echo "✓ $PASS/$TOTAL test262-slice tests passed ($PCT%)"
+else
+  echo "✗ $PASS/$TOTAL passed, $FAIL failed ($PCT%):"
+  [ "$VERBOSE" != "-v" ] && echo "$ERRORS"
+fi
+
+# Phase 5 target: ≥50% pass.
+TARGET=50
+if (( $(echo "$PCT >= $TARGET" | bc -l 2>/dev/null || python3 -c "print($PCT >= $TARGET)") )); then
+  exit 0
+else
+  echo "(below target of ${TARGET}%)"
+  exit 1
+fi