fix(windows): real toolchain probing, HOME/TEMP env, and gate portability

code_run.py: shutil.which() finding a compiler executable on PATH doesn't
mean it's a usable toolchain on Windows -- rustc's MSVC target also needs
Microsoft's linker, and an MSYS2 gcc/clang driver can remain resolvable after
one of its runtime DLLs has broken. Both cases silently turned every C/C++/
Rust snippet into a compile error while the capability check said "ready".
_compiled_tool() now actually compiles+links a trivial known-good program
per candidate (Windows only; POSIX keeps the cheap which(1) check since
release hosts install compiler packages atomically) and caches the result.

Also fixes the run/compile child environment: HOME/TMPDIR don't control
Windows' real temp/profile resolution (expanduser() reaches the actual user
profile, GetTempPath() falls back to the Windows directory), letting a
snippet escape the scratch directory or fail outright. _child_env() now also
sets TEMP/TMP/USERPROFILE on Windows.

tests/conftest.py (new): isolates curry_store's SQLite singleton into a
per-run temp directory via NEXUS_CURRY_DB before any test module imports
synapse, and cleans it up at session end -- the release gate no longer
writes test constants into the checkout's live data/curry.db. .gitignore
picks up /data/curry.db for whatever still lands there locally.

bin/check.sh: falls back to Promethean/Scripts/python.exe when
Promethean/bin/python doesn't exist, so the gate actually runs on a Windows
venv instead of immediately exiting "no Promethean venv".

Verified independently: 254 passed, 0 failed, 8 skipped (tests + management)
-- the 12 C/C++/Rust toolchain failures present all session are gone. Full
bin/check.sh run end-to-end on this Windows checkout: pytest, eslint,
frontend node:test (57/57), PowerShell/shell parse, and the wheel/sdist
packaging + twine + content checks all report OK.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -13,6 +13,7 @@ synapse/memory/memory.db
 synapse/memory/memory.db-wal
 synapse/memory/memory.db-shm
 assets/gitnexus-logo.svg
+/data/curry.db
 *.db-wal
 *.db-shm
 .DS_Store

bin/check.sh

@@ -9,14 +9,18 @@ cd "$(dirname "$0")/.."
 
 fail=0
 
-if [ ! -x Promethean/bin/python ]; then
+if [ -x Promethean/bin/python ]; then
+    NEXUS_CHECK_PY=Promethean/bin/python
+elif [ -x Promethean/Scripts/python.exe ]; then
+    NEXUS_CHECK_PY=Promethean/Scripts/python.exe
+else
     echo "!! no Promethean venv - run ./install.sh first" >&2
     exit 1
 fi
 
 echo "== pytest =="
 # Explicit dirs: a bare `pytest` would walk Promethean/ and node_modules too.
-Promethean/bin/python -m pytest -q tests management || fail=1
+"$NEXUS_CHECK_PY" -m pytest -q tests management || fail=1
 
 echo "== eslint =="
 if [ -d interface/web/node_modules ]; then
@@ -57,13 +61,13 @@ done
 echo "== packaging =="
 # The wheel is the other shippable artifact, so it belongs in the same gate:
 # a broken pyproject or a missing web build only shows up at build time.
-if Promethean/bin/python -c "import build, twine" 2>/dev/null; then
+if "$NEXUS_CHECK_PY" -c "import build, twine" 2>/dev/null; then
     rm -rf .build-check
-    if Promethean/bin/python -m build --outdir .build-check >/dev/null 2>&1; then
-        Promethean/bin/python -m twine check .build-check/* || fail=1
+    if "$NEXUS_CHECK_PY" -m build --outdir .build-check >/dev/null 2>&1; then
+        "$NEXUS_CHECK_PY" -m twine check .build-check/* || fail=1
         # The compiled UI has to actually be inside the wheel - a wheel that
         # builds but ships no dist/ serves a blank page.
-        Promethean/bin/python - <<'PY' || fail=1
+        "$NEXUS_CHECK_PY" - <<'PY' || fail=1
 import glob, sys, zipfile
 wheels = glob.glob(".build-check/*.whl")
 if not wheels:

synapse/code_run.py

@@ -17,9 +17,9 @@ module actually provides is *containment by limits*, layered:
                   every call waits for the user's Approve/Deny in chat.
   2. Screening    `critique` rejects the obvious-abuse shapes (sockets, process
                   spawning, absolute paths) before anything is written to disk.
-  3. Isolation    cwd is a fresh temp dir that is deleted afterwards; HOME and
-                  TMPDIR point at it; the environment is scrubbed to a small
-                  allowlist.
+  3. Isolation    cwd is a fresh temp dir that is deleted afterwards; home and
+                  temp environment variables point at it; the environment is
+                  scrubbed to a small allowlist.
   4. Limits       wall-clock timeout, RLIMIT_CPU/AS/FSIZE/NPROC on POSIX,
                   truncated output.
   5. Network      on Linux, `unshare -rn` when unprivileged user namespaces are
@@ -40,6 +40,7 @@ import shutil
 import subprocess
 import sys
 import tempfile
+from functools import lru_cache
 from pathlib import Path
 
 # Wall clock. Compilation gets its own, larger budget: rustc on a cold cache
@@ -186,6 +187,52 @@ def _erlang_write_source(source: str) -> str:
     return source
 
 
+@lru_cache(maxsize=None)
+def _compiled_tool(lang: str, candidates: tuple[str, ...]) -> str | None:
+    """Resolve a compiler, verifying the complete Windows toolchain once.
+
+    A compiler executable alone is not a usable toolchain on Windows: rustc's
+    MSVC target also needs Microsoft's linker, and an MSYS2 driver can remain on
+    PATH after one of its runtime DLLs has broken. Both cases otherwise make the
+    capability monitor say "ready" and turn every snippet into a compile error.
+    POSIX keeps the cheap historical which(1) check; the release hosts there
+    install compiler packages atomically.
+    """
+    found = [tool for name in candidates if (tool := shutil.which(name))]
+    if sys.platform != "win32":
+        return found[0] if found else None
+    for tool in found:
+        if _probe_compiled_tool(lang, tool):
+            return tool
+    return None
+
+
+def _probe_compiled_tool(lang: str, tool: str) -> bool:
+    """Compile a minimal known-good program with the runner's real child env."""
+    source = {
+        "c": "int main(void){return 0;}",
+        "cpp": "int main(){return 0;}",
+        "rust": "fn main() {}",
+    }[lang]
+    try:
+        with tempfile.TemporaryDirectory(prefix="nexus-toolchain-") as tmp:
+            workdir = Path(tmp)
+            entry = RUN_LANGS[lang]
+            src = workdir / entry["source_name"](source)
+            src.write_text(source, encoding="utf-8")
+            exe = str(workdir / "probe.exe")
+            built = _spawn(
+                entry["compile"](tool, str(src), exe),
+                workdir,
+                _child_env(lang, workdir),
+                COMPILE_TIMEOUT,
+                constrain_memory=False,
+            )
+            return built.returncode == 0 and Path(exe).is_file()
+    except (OSError, subprocess.SubprocessError):
+        return False
+
+
 # The one place that says which languages can be executed. Each entry owns that
 # language's screening, toolchain probe and argv. The tool schema's `lang` enum,
 # the capability line in the system prompt and the dispatch below are all derived
@@ -211,7 +258,7 @@ RUN_LANGS: dict[str, dict] = {
     },
     "c": {
         "summary": "single-file C program (C11, libm linked)",
-        "tool": lambda: shutil.which("cc") or shutil.which("gcc") or shutil.which("clang"),
+        "tool": lambda: _compiled_tool("c", ("cc", "gcc", "clang")),
         "install": "install a C compiler (clang or gcc)",
         "source_name": _source_name("main.c"),
         "compile": lambda cc, src, exe: [cc, "-std=c11", "-O0", "-Wall", "-o", exe, src, "-lm"],
@@ -221,7 +268,7 @@ RUN_LANGS: dict[str, dict] = {
     },
     "cpp": {
         "summary": "single-file C++ program (C++17)",
-        "tool": lambda: shutil.which("c++") or shutil.which("g++") or shutil.which("clang++"),
+        "tool": lambda: _compiled_tool("cpp", ("c++", "g++", "clang++")),
         "install": "install a C++ compiler (clang++ or g++)",
         "source_name": _source_name("main.cpp"),
         "compile": lambda cc, src, exe: [cc, "-std=c++17", "-O0", "-Wall", "-o", exe, src],
@@ -231,7 +278,7 @@ RUN_LANGS: dict[str, dict] = {
     },
     "rust": {
         "summary": "single-file Rust program (2021 edition, std only)",
-        "tool": lambda: shutil.which("rustc"),
+        "tool": lambda: _compiled_tool("rust", ("rustc",)),
         "install": "install Rust (https://rustup.rs)",
         "source_name": _source_name("main.rs"),
         # Debug build: -O roughly triples compile time for snippets that run for
@@ -301,8 +348,17 @@ def _child_env(lang: str, workdir: Path) -> dict:
         if default.is_dir():
             env["RUSTUP_HOME"] = str(default)
             env.setdefault("CARGO_HOME", str(Path.home() / ".cargo"))
-    env["HOME"] = str(workdir)
-    env["TMPDIR"] = str(workdir)
+    scratch = str(workdir)
+    env["HOME"] = scratch
+    env["TMPDIR"] = scratch
+    # Windows ignores HOME/TMPDIR in its standard path helpers. Without these,
+    # expanduser() reaches the real profile and GetTempPath() falls back to the
+    # Windows directory; GCC and rustc then either escape the scratch directory
+    # or fail because a normal user cannot write there.
+    env["TEMP"] = scratch
+    env["TMP"] = scratch
+    if os.name == "nt":
+        env["USERPROFILE"] = scratch
     env.setdefault("LC_ALL", "C.UTF-8")
     return env
 

tests/conftest.py

@@ -0,0 +1,23 @@
+"""Test-process isolation for persistent runtime state."""
+from __future__ import annotations
+
+import os
+import shutil
+import sys
+import tempfile
+from pathlib import Path
+
+
+# curry_store constructs its SQLite singleton during test collection. Point it
+# at a per-run directory before any test module imports synapse, so the release
+# gate is repeatable and never writes test constants into the checkout's live
+# data/curry.db.
+_TEST_STATE = Path(tempfile.mkdtemp(prefix="nexus-pytest-"))
+os.environ["NEXUS_CURRY_DB"] = str(_TEST_STATE / "curry.db")
+
+
+def pytest_sessionfinish(session, exitstatus):
+    module = sys.modules.get("synapse.curry_store")
+    if module is not None:
+        module.curry_db.close()
+    shutil.rmtree(_TEST_STATE, ignore_errors=True)

tests/test_code_run.py

@@ -232,10 +232,40 @@ def test_home_points_at_the_scratch_dir():
     assert "nexus-run-" in out["stdout"]
 
 
+def test_temp_points_at_the_scratch_dir():
+    """Compilers and snippets must not fall back to a host temp directory."""
+    out = code_run.run("python", "import tempfile\nprint(tempfile.gettempdir())")
+    assert "nexus-run-" in out["stdout"]
+
+
 # ---------------------------------------------------------------------------
 # Toolchains
 # ---------------------------------------------------------------------------
 
+def test_windows_compiler_resolver_skips_broken_candidates(monkeypatch):
+    """An executable on PATH is not enough when its linker/runtime is broken."""
+    code_run._compiled_tool.cache_clear()
+    monkeypatch.setattr(code_run.sys, "platform", "win32")
+    monkeypatch.setattr(
+        code_run.shutil, "which", lambda name: f"C:\\tools\\{name}.exe"
+    )
+    probes = []
+
+    def probe(lang, tool):
+        probes.append((lang, tool))
+        return tool.endswith("clang.exe")
+
+    monkeypatch.setattr(code_run, "_probe_compiled_tool", probe)
+    try:
+        assert code_run._compiled_tool("c", ("gcc", "clang")) == "C:\\tools\\clang.exe"
+        assert probes == [
+            ("c", "C:\\tools\\gcc.exe"),
+            ("c", "C:\\tools\\clang.exe"),
+        ]
+    finally:
+        code_run._compiled_tool.cache_clear()
+
+
 def test_a_missing_toolchain_explains_itself(monkeypatch):
     """The model has to be able to tell 'you cannot run this here' from 'your
     code is wrong' — otherwise it rewrites a correct program repeatedly."""