Nixpacks not restoring node_modules or custom Astro cache on rebuild

[idimilab]

Environment

• Dokploy Build Type: Nixpacks
• Node Version: 22
• Astro Version: 5.x

Configuration

Environment Variables (build-time)

NIXPACKS_NODE_VERSION=22
NIXPACKS_INSTALL_CACHE_DIRS=/app/node_modules
NIXPACKS_BUILD_CACHE_DIRS=/app/astro-cache

astro.config.mjs

export default defineConfig({
  cacheDir: 'astro-cache',
  // …other settings…
});

Steps to Reproduce
Push this configuration to a GitHub repo and trigger a Dokploy deploy.

Observe in the logs that pnpm install adds all 600+ packages and Astro re-optimizes 600+ images.

Trigger a second deploy without code changes.

Note that there are no “Restoring cache for…” log lines and both install & image optimization still run from scratch.

Expected Behavior
First build: Writes into /app/node_modules and /app/astro-cache.

Subsequent builds:

Restoring cache for: /app/node_modules
Restoring cache for: /app/astro-cache
making install and image optimization near-instant.

Actual Behavior
No cache restore steps appear.

Every build—first and subsequent—fully re-installs dependencies and re-optimizes all images.

Question
Is this a misconfiguration on my end or a bug in Nixpacks’ handling of custom cache directories?