# Security

#### Read-Only Guarantee

Expressions cannot assign variables, mutate the context, or produce side effects:

* Assignment operators (=, +=, -=, ++, --) are rejected at the parser level
* Mutating methods (.push(), .pop(), .splice(), .sort(), .reverse(), .shift(),\
  .unshift()) are excluded from the method whitelist
* Block-body arrows (x => { ... }) are rejected — no variable declarations or multi-statement\
  logic
* Context serialization — variables are serialized into the Worker's separate V8 heap, so even\
  if an escape is found, mutations cannot propagate back to session state

#### Blocked Globals

Blocked Globals means that an expression or script cannot access global variables, global objects, or ambient system state. Only explicitly provided inputs are available.

* eval, Function — Code execution
* require, import — Module loading
* process, global, globalThis — Node.js internals
* setTimeout, setInterval — Async operations
* fetch, XMLHttpRequest — Network access
* console — Side effects
* Proxy, Reflect — Meta-programming

#### Protections

Protections are the enforced safeguards that ensure expressions remain safe, predictable, and non‑abusive, even when they come from untrusted sources. They define *what an expression is allowed to do*, *what it can never do*, and *how far it is allowed to go*.

* Think of protections as the **guardrails** around the expression engine.
* Worker Isolation: Each expression runs in a separate V8 isolate
* Hard Timeout: worker.terminate() kills hung expressions
* Memory Limits: Worker heap size capped at 64MB (configurable)
* Size Limits: Context, result, string, and array sizes enforced
* Prototype Blocking: No access to \_\_proto\_\_, constructor, prototype
* Auto-Recovery: Crashed workers are automatically replaced


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