# Sandbox provider capability contract

A sandbox provider plugin declares an environment driver with
`kind: "sandbox_provider"`. Each driver can declare a set of optional sandbox
capabilities. This document is the contract for a third-party provider author.
It states what to declare, which worker methods each capability needs, what an
omitted key means, and when the host narrows or denies a capability.

Read [Sandbox file-sync lifecycle hooks](./SANDBOX_FILE_SYNC_HOOKS.md) for the
native file-transfer hooks. Read the driver declaration shape in
[the plugin specification](./PLUGIN_SPEC.md).

## Fresh lease acquisition timeout

A driver can declare `defaultAcquireTimeoutMs` as a positive integer of at most
86,400,000 milliseconds. The host uses it for `environmentAcquireLease` when the
resolved config has no positive finite numeric `timeoutMs`. A positive numeric
`bridgeRequestTimeoutMs` can extend that budget. The host adds 30 seconds for RPC
overhead. This applies to both sandbox providers and generic plugin drivers.

Daytona declares 300,000 milliseconds for the entire fresh acquisition. Creation,
workspace setup, shell detection, expiry setup, and inline failure cleanup share
that budget. Its host RPC can therefore wait 330 seconds instead of the worker's
normal 30 seconds. On timeout the provider returns the attempt's scoped cleanup
record for durable host reconciliation. Late SDK results cannot admit the lease
or start the next setup phase.
Drivers that omit the declaration keep the existing fallback. The host does not
infer this budget from config-schema defaults: a field named `timeoutMs` can
describe sandbox lifetime instead of the time needed to acquire it.

This declaration does not change provider config, lease expiry, the resume
deadline, or other lifecycle calls. Providers must still enforce their operation
timeouts and report uncertain allocations for cleanup. A bundled plugin must bump
its manifest version when adding the field so existing installations receive it.

## How the host resolves an effective capability

The host never trusts a declaration alone. For every run it resolves each
capability as the intersection of three inputs:

```
effective = verified ∩ declared ∩ narrowing
```

- **verified** — the methods the live worker advertised in
  `InitializeResult.supportedMethods`. The host maps each capability to the
  worker methods it needs (see the table below). A capability is verified only
  when the worker advertises every required method. An empty or missing method
  list verifies nothing, so every capability resolves `false`.
- **declared** — the values in the driver declaration. A declared key is
  optional (see the next section).
- **narrowing** — a per-run restriction from the lease policy or the resolved
  provider config. A narrowing can only remove a capability, never add one.

A capability is effective only when all three allow it. A declaration therefore
never grants a capability that the worker did not verify.

## The declaration is optional and partial

Declare capabilities through the nested `sandboxCapabilities` object on the
driver declaration:

```ts
environmentDrivers: [
  {
    driverKey: "my-provider",
    kind: "sandbox_provider",
    displayName: "My Provider",
    configSchema: { type: "object", properties: {} },
    sandboxCapabilities: {
      reusableLeases: true,
      nativeSyncIn: true,
      nativeSyncOut: true,
      persistentProcessSessions: false,
      independentControlCommands: false,
      incrementalSessionOutput: false,
    },
  },
]
```

Every key is optional. For a valid, identified provider each key has one of three
states:

- **Omitted** — the host defers to verified worker discovery. The capability is
  effective when the worker advertises the required methods and no narrowing
  removes it. Omission is the correct default for a provider that follows the
  standard method contract. `reusableLeases` and `incrementalSessionOutput` are
  the two exceptions: an omitted key never grants either capability. Both are
  opt-in (see the next two sections).
- **`false`** — the host narrows the capability to off. The capability is never
  effective, even when the worker advertises the required methods.
- **`true`** — the host still requires the verified prerequisites. A `true`
  value never grants a capability without them. It documents intent and lets the
  host present the capability, but the worker must still advertise the required
  methods.

## Reusable leases need an explicit opt-in

Reusable leases are the exception to the omission rule above. The host grants
reusable-lease acquisition only when the declaration sets `reusableLeases` to
`true`. The provider opts in through one of two fields:

- the nested `sandboxCapabilities.reusableLeases: true`, or
- the legacy `supportsReusableLeases: true`.

An omitted key leaves `reusableLeases` unset. An unset key does not make the
provider eligible for reusable-lease acquisition, and it does not advertise
provider-level reusable support. The host then always creates an ephemeral lease.

The opt-in never removes the other prerequisites. The worker must still verify
all three lifecycle methods, `environmentResumeLease`, `environmentReleaseLease`,
and `environmentDestroyLease`, and per-run narrowing still applies.

The two opt-in fields have a fixed precedence. The host keeps the legacy
`supportsReusableLeases` field for backward compatibility, and it folds the field
into `sandboxCapabilities.reusableLeases`.

- When only `supportsReusableLeases` is present, the host reads it as
  `reusableLeases`.
- When both `supportsReusableLeases` and `sandboxCapabilities.reusableLeases` are
  present, the nested value wins.

A manifest with legacy `true` and nested `false` therefore resolves to `false`.
Prefer the nested `sandboxCapabilities.reusableLeases` in a new manifest.

## Incremental session output needs an explicit opt-in

Incremental session output is the second exception to the omission rule. The host
selects the session-output streaming path only when the declaration sets
`incrementalSessionOutput` to `true`. An omitted key resolves the capability to
`false`, so the host keeps the output-file poll path.

The reason is that this key is a behavioral guarantee, not a worker-method
property. A generic one-shot provider can keep persistent process sessions and run
independent control commands, yet it never emits incremental stdout and stderr
from a live session. The two broad capabilities do not imply incremental output,
so the host requires the provider to declare the behavior. A provider that streams
incremental session output declares `sandboxCapabilities.incrementalSessionOutput:
true`; every other provider omits the key and keeps the poll path.

The opt-in never removes the prerequisites. The worker must still verify
`environmentExecute`, and per-run narrowing still applies. A config-resolution
failure narrows the capability to off (see [Failure behavior](#failure-behavior)).

## The capabilities and their worker-method prerequisites

| Capability | Required worker methods | Meaning |
| --- | --- | --- |
| `reusableLeases` | `environmentResumeLease`, `environmentReleaseLease`, **and** `environmentDestroyLease` | The host retains a provider lease and resumes it across runs. |
| `nativeSyncIn` | `environmentSyncIn` | The host transfers files into the sandbox through the native inbound hook. |
| `nativeSyncOut` | `environmentSyncOut` | The host transfers files out of the sandbox through the native outbound hook. |
| `persistentProcessSessions` | `environmentExecute` | The provider keeps a persistent process session open across commands. |
| `independentControlCommands` | `environmentExecute` | The provider runs a one-shot control command beside a long-lived command. |
| `incrementalSessionOutput` | `environmentExecute` | The provider streams incremental stdout and stderr from a live session. Opt-in: an omitted key resolves `false`. |

Reusable leases need all three lifecycle methods. The host resumes a lease with
`environmentResumeLease`, ends it with `environmentReleaseLease`, and tears down a
stale lease with `environmentDestroyLease`. The reuse path destroys a stale lease
when a resume fails, so a provider that cannot destroy a lease would strand it. A
worker that omits any of the three methods never gets reusable leases, even with a
positive declaration. The host then always creates an ephemeral lease.

The host advertises and consumes the two native sync methods as a pair. Define
both or neither. See [Sandbox file-sync lifecycle hooks](./SANDBOX_FILE_SYNC_HOOKS.md).

## Target and config narrowing

A narrowing removes a capability that the provider verified and declared but that
this run cannot use.

- **Ephemeral lease policy.** A lease that the host does not retain never reuses.
  The host narrows `reusableLeases` to off for an ephemeral lease and keeps it on
  only for a reuse-by-environment lease.
- **Kubernetes Job backend.** A Job-backed lease, or a lease the host marked as
  unable to run native file sync, disables native sync. The host narrows
  `nativeSyncIn` and `nativeSyncOut` to off and keeps the base64-over-exec
  fallback.

## Failure behavior

The host fails closed on two failure states. It never grants a capability from an
unknown state.

- **Config-resolution failure.** A provider whose config the host cannot resolve
  is untrusted. The host narrows `persistentProcessSessions` and
  `incrementalSessionOutput` to off instead of allowing either through an empty
  config.
- **Exact-plugin identity failure.** A retained lease pins the exact plugin that
  acquired it. When that plugin is absent, or when it no longer declares this
  provider key with the `sandbox_provider` kind, the host cannot establish the
  declaration. It resolves every effective capability to `false`, no matter what
  methods a stale worker still advertises. An omitted `sandboxCapabilities`
  object on a valid, identified plugin is a different state; the host defers to
  verified discovery for that case.

## Concurrency capabilities are not part of the contract

Earlier drafts listed two concurrency keys, `concurrentSyncAndExec` and
`concurrentSyncOperations`. The runtime never exposed a scheduling choice that
read either key, so a declaration had no effect. The host removed both keys. The
strict capability validator now rejects them as unknown keys. The host can
reintroduce a concurrency capability when a runtime path enforces it.

### Preserving an unexported workspace

Native export recovery requires the separately discovered `environmentStopLease` RPC (`onEnvironmentStopLease`). It stops the exact allocation and preserves files regardless of its normal release policy. A failed or unconfirmed stop must throw and must never fall back to deletion. The host uses the recorded plugin ID and defers when that worker does not advertise the hook; a generic release method is insufficient evidence of stop-only support. Normal successful ephemeral release remains destructive after verified copyback.

Daytona stop-only preservation disables provider auto-delete and refreshes the provider record to confirm the disabled policy before stopping. An unavailable or unconfirmed policy leaves cleanup pending; it never falls back to stop or delete. The original ephemeral destroy policy applies only after exact accepted-result copyback and commitment.