fix windows numpy import and add node timestamps

backend/frontend_build.py

@@ -0,0 +1,116 @@
+from __future__ import annotations
+
+import logging
+import os
+import subprocess
+import threading
+from pathlib import Path
+
+_BUILD_LOCK = threading.Lock()
+
+
+class FrontendBuildError(RuntimeError):
+    """Raised when the source frontend could not be rebuilt."""
+
+
+def _latest_mtime(root: Path) -> float:
+    if not root.exists():
+        return 0.0
+    return max(
+        (path.stat().st_mtime for path in root.rglob("*") if path.is_file()),
+        default=0.0,
+    )
+
+
+def source_frontend_mtime(frontend_dir: Path) -> float:
+    tracked_files = (
+        frontend_dir / "index.html",
+        frontend_dir / "package.json",
+        frontend_dir / "package-lock.json",
+        frontend_dir / "vite.config.js",
+    )
+    mtimes = [path.stat().st_mtime for path in tracked_files if path.exists()]
+    mtimes.append(_latest_mtime(frontend_dir / "src"))
+    mtimes.append(_latest_mtime(frontend_dir / "public"))
+    return max(mtimes, default=0.0)
+
+
+def dist_frontend_mtime(dist_dir: Path) -> float:
+    if not (dist_dir / "index.html").exists():
+        return 0.0
+    return _latest_mtime(dist_dir)
+
+
+def frontend_dist_is_stale(frontend_dir: Path, dist_dir: Path) -> bool:
+    return dist_frontend_mtime(dist_dir) < source_frontend_mtime(frontend_dir)
+
+
+def _npm_executable() -> str:
+    return "npm.cmd" if os.name == "nt" else "npm"
+
+
+def _format_build_output(stdout: str, stderr: str) -> str:
+    combined = "\n".join(part.strip() for part in (stdout, stderr) if part.strip())
+    if not combined:
+        return ""
+    lines = combined.splitlines()
+    if len(lines) > 40:
+        lines = lines[-40:]
+    return "\n".join(lines)
+
+
+def _build_failure_hint(detail: str) -> str:
+    if "spawn EPERM" not in detail:
+        return ""
+    return (
+        "Windows note: this build hit `spawn EPERM`, which usually means the current Node.js "
+        "install is not cooperating with esbuild. Node 20 LTS is the safest option here. "
+        "After switching, run `npm --prefix frontend install` and try again."
+    )
+
+
+def ensure_frontend_dist_ready(
+    project_root: Path,
+    frontend_dir: Path,
+    dist_dir: Path,
+    logger: logging.Logger | None = None,
+) -> bool:
+    if not frontend_dist_is_stale(frontend_dir, dist_dir):
+        return False
+
+    with _BUILD_LOCK:
+        if not frontend_dist_is_stale(frontend_dir, dist_dir):
+            return False
+
+        if logger is not None:
+            logger.info("Frontend sources changed; rebuilding frontend/dist before serving the web app.")
+
+        result = subprocess.run(
+            [_npm_executable(), "run", "build"],
+            cwd=str(project_root),
+            capture_output=True,
+            text=True,
+            check=False,
+        )
+        if result.returncode != 0:
+            detail = _format_build_output(result.stdout, result.stderr)
+            message = (
+                "Frontend build failed while refreshing frontend/dist. "
+                "Run `npm run build` from the repo root to inspect the full error."
+            )
+            hint = _build_failure_hint(detail)
+            if hint:
+                message = f"{message}\n\n{hint}"
+            if detail:
+                message = f"{message}\n\n{detail}"
+            raise FrontendBuildError(message)
+
+        if not (dist_dir / "index.html").exists():
+            raise FrontendBuildError(
+                "Frontend rebuild finished, but frontend/dist/index.html is still missing."
+            )
+
+        if logger is not None:
+            logger.info("Frontend rebuild complete.")
+
+        return True