Phase 3: Move host files to hosts/python/ and hosts/javascript/

Python: bootstrap.py, platform.py, transpiler.sx, boundary_parser.py, tests/
JavaScript: bootstrap.py, cli.py, platform.py, transpiler.sx
Both bootstrappers verified — build from new locations, output to shared/.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/python/tests/run_continuation_tests.py

@@ -0,0 +1,106 @@
+#!/usr/bin/env python3
+"""Run test-continuations.sx using the bootstrapped evaluator with continuations enabled."""
+from __future__ import annotations
+import os, sys, subprocess, tempfile
+
+_HERE = os.path.dirname(os.path.abspath(__file__))
+_PROJECT = os.path.abspath(os.path.join(_HERE, "..", "..", ".."))
+sys.path.insert(0, _PROJECT)
+
+# Bootstrap a fresh sx_ref with continuations enabled
+print("Bootstrapping with --extensions continuations ...")
+result = subprocess.run(
+    [sys.executable, os.path.join(_HERE, "bootstrap_py.py"),
+     "--extensions", "continuations"],
+    capture_output=True, text=True, cwd=_PROJECT,
+)
+if result.returncode != 0:
+    print("Bootstrap FAILED:")
+    print(result.stderr)
+    sys.exit(1)
+
+# Write to temp file and import
+tmp = tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False, dir=_HERE)
+tmp.write(result.stdout)
+tmp.close()
+
+try:
+    import importlib.util
+    spec = importlib.util.spec_from_file_location("sx_ref_cont", tmp.name)
+    mod = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(mod)
+finally:
+    os.unlink(tmp.name)
+
+from shared.sx.types import NIL
+parse_all = mod.sx_parse
+
+# Use tree-walk evaluator for interpreting .sx test files.
+# CEK is now the default, but test runners need tree-walk so that
+# transpiled HO forms (ho_map, etc.) don't re-enter CEK mid-evaluation.
+eval_expr = mod._tree_walk_eval_expr
+trampoline = mod._tree_walk_trampoline
+mod.eval_expr = eval_expr
+mod.trampoline = trampoline
+env = mod.make_env()
+
+# Platform test functions
+_suite_stack: list[str] = []
+_pass_count = 0
+_fail_count = 0
+
+def _try_call(thunk):
+    try:
+        trampoline(eval_expr([thunk], env))
+        return {"ok": True}
+    except Exception as e:
+        return {"ok": False, "error": str(e)}
+
+def _report_pass(name):
+    global _pass_count
+    _pass_count += 1
+    ctx = " > ".join(_suite_stack)
+    print(f"  PASS: {ctx} > {name}")
+    return NIL
+
+def _report_fail(name, error):
+    global _fail_count
+    _fail_count += 1
+    ctx = " > ".join(_suite_stack)
+    print(f"  FAIL: {ctx} > {name}: {error}")
+    return NIL
+
+def _push_suite(name):
+    _suite_stack.append(name)
+    print(f"{'  ' * (len(_suite_stack)-1)}Suite: {name}")
+    return NIL
+
+def _pop_suite():
+    if _suite_stack:
+        _suite_stack.pop()
+    return NIL
+
+env["try-call"] = _try_call
+env["report-pass"] = _report_pass
+env["report-fail"] = _report_fail
+env["push-suite"] = _push_suite
+env["pop-suite"] = _pop_suite
+
+# Load test framework
+with open(os.path.join(_HERE, "test-framework.sx")) as f:
+    for expr in parse_all(f.read()):
+        trampoline(eval_expr(expr, env))
+
+# Run tests
+print("=" * 60)
+print("Running test-continuations.sx")
+print("=" * 60)
+
+with open(os.path.join(_HERE, "test-continuations.sx")) as f:
+    for expr in parse_all(f.read()):
+        trampoline(eval_expr(expr, env))
+
+print("=" * 60)
+print(f"Results: {_pass_count} passed, {_fail_count} failed")
+print("=" * 60)
+sys.exit(1 if _fail_count > 0 else 0)