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Deno Deploy: edge functions, CORS headers per isolate, and permission flags for outbound fetch
Each request runs in a fresh or warm isolate—cache CORS response fragments carefully to avoid leaking origins across tenants.
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denoedgecors
KV and queues
Background tasks triggered from HTTP handlers inherit the same CORS context only for the triggering request.
Cross-region replication may reorder responses—ensure `Vary: Origin` survives eventual consistency.
Local development
`deno task` dev servers differ from Deploy—mirror production CORS in integration tests.
Import maps from URLs need those hosts allowed in CORS when browsers load dynamic imports.