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6/26/2026
Cache key bug cost $

Cache key bug cost $

Original: A one-line cache key bug cost me $187/month and leaked advertiser data across tenants

Short summary

A Cloudflare Worker SaaS leaked advertiser data across tenants for 6 weeks due to a cache-key bug missing tenant ID, costing $187/month of the $312 monthly Anthropic bill. The one-line fix reveals a deeper lesson: V8 isolates don't protect module-scope shared state across requests; each platform needs different isolation primitives (ExecutionContext on Workers, AsyncLocalStorage on Node). PostToolUse validation hooks prevent future leaks.

  • •Cache key missing tenant ID caused $187/month overspend and multi-tenant data leaks in production
  • •V8 isolates don't protect module-scope shared state; request isolation differs by platform
  • •Use ExecutionContext on Workers, AsyncLocalStorage on Node; add post-tool-use validation

Generated with AI, which can make mistakes.

#ai-tools
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