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A Session selects an Environment: reusable configuration for packages, networking, resources and execution requirements. Admission freezes those requirements for the Run. An Environment is separate from a physical allocation or a persistent Computer.

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Where execution runs

Checkfu’s execution direction is Checkfu-managed Cloudflare or a customer-owned Cloudflare installation. Each route must satisfy the selected Environment and the Harness’s requirements. Bring-your-own sandbox services, including Daytona, are being retired as product routes. Customer-owned Cloudflare is separate from BYOH (bring your own Harness) and BYOK (bring your own model-provider key). A custom Harness does not select a sandbox provider, and a model-provider key does not grant machine control. The exact deployment must make the required runtime available. A configured adapter, protocol connection or checked-in fixture does not establish that a Workspace can execute the workload. See capability status for current support and availability.

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Request the capabilities your work needs

Code execution, browser access, desktop viewing and input are separate capabilities. A Computer can be headless and has an owner independent of the Session. A Session borrowing a Computer detaches when it finishes; destroying the Computer requires its owner’s authority. Execution must satisfy the frozen Environment requirements or refuse the work. It must not silently substitute a different runtime, weaker network boundary or empty retained machine. Do not infer a base image, operating system, mount capacity or recovery grade from an Environment name.

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Retained state and recovery

Retained conversation history, restored files, native checkpoints and running process recovery are distinct promises. Files restored into a new allocation do not prove that the prior native process resumed. A checkpoint is usable only where the selected Harness, runtime and retention policy support it. Standard retention and ZDR have different requirements. Selecting ZDR must not silently fall back to execution that retains prohibited content. Neither a checkpoint nor retained history proves that an external effect completed.