Add sandbox environment support (#4415)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies.
> - The environment/runtime layer decides where agent work executes and
how the control plane reaches those runtimes.
> - Today Paperclip can run locally and over SSH, but sandboxed
execution needs a first-class environment model instead of one-off
adapter behavior.
> - We also want sandbox providers to be pluggable so the core does not
hardcode every provider implementation.
> - This branch adds the Sandbox environment path, the provider
contract, and a deterministic fake provider plugin.
> - That required synchronized changes across shared contracts, plugin
SDK surfaces, server runtime orchestration, and the UI
environment/workspace flows.
> - The result is that sandbox execution becomes a core control-plane
capability while keeping provider implementations extensible and
testable.

## What Changed

- Added sandbox runtime support to the environment execution path,
including runtime URL discovery, sandbox execution targeting,
orchestration, and heartbeat integration.
- Added plugin-provider support for sandbox environments so providers
can be supplied via plugins instead of hardcoded server logic.
- Added the fake sandbox provider plugin with deterministic behavior
suitable for local and automated testing.
- Updated shared types, validators, plugin protocol definitions, and SDK
helpers to carry sandbox provider and workspace-runtime contracts across
package boundaries.
- Updated server routes and services so companies can create sandbox
environments, select them for work, and execute work through the sandbox
runtime path.
- Updated the UI environment and workspace surfaces to expose sandbox
environment configuration and selection.
- Added test coverage for sandbox runtime behavior, provider seams,
environment route guards, orchestration, and the fake provider plugin.

## Verification

- Ran locally before the final fixture-only scrub:
  - `pnpm -r typecheck`
  - `pnpm test:run`
  - `pnpm build`
- Ran locally after the final scrub amend:
  - `pnpm vitest run server/src/__tests__/runtime-api.test.ts`
- Reviewer spot checks:
  - create a sandbox environment backed by the fake provider plugin
  - run work through that environment
- confirm sandbox provider execution does not inherit host secrets
implicitly

## Risks

- This touches shared contracts, plugin SDK plumbing, server runtime
orchestration, and UI environment/workspace flows, so regressions would
likely show up as cross-layer mismatches rather than isolated type
errors.
- Runtime URL discovery and sandbox callback selection are sensitive to
host/bind configuration; if that logic is wrong, sandbox-backed
callbacks may fail even when execution succeeds.
- The fake provider plugin is intentionally deterministic and
test-oriented; future providers may expose capability gaps that this
branch does not yet cover.

## Model Used

- OpenAI Codex coding agent on a GPT-5-class backend in the
Paperclip/Codex harness. Exact backend model ID is not exposed
in-session. Tool-assisted workflow with shell execution, file editing,
git history inspection, and local test execution.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [ ] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

packages/shared/src/environment-support.ts

@@ -1,15 +1,31 @@
 import type { AgentAdapterType, EnvironmentDriver } from "./constants.js";
+import type { SandboxEnvironmentProvider } from "./types/environment.js";
 
 export type EnvironmentSupportStatus = "supported" | "unsupported";
 
 export interface AdapterEnvironmentSupport {
   adapterType: AgentAdapterType;
   drivers: Record<EnvironmentDriver, EnvironmentSupportStatus>;
+  sandboxProviders: Record<SandboxEnvironmentProvider, EnvironmentSupportStatus>;
+}
+
+export interface EnvironmentProviderCapability {
+  status: EnvironmentSupportStatus;
+  supportsSavedProbe: boolean;
+  supportsUnsavedProbe: boolean;
+  supportsRunExecution: boolean;
+  supportsReusableLeases: boolean;
+  displayName?: string;
+  description?: string;
+  source?: "builtin" | "plugin";
+  pluginKey?: string;
+  pluginId?: string;
 }
 
 export interface EnvironmentCapabilities {
   adapters: AdapterEnvironmentSupport[];
   drivers: Record<EnvironmentDriver, EnvironmentSupportStatus>;
+  sandboxProviders: Record<SandboxEnvironmentProvider, EnvironmentProviderCapability>;
 }
 
 const REMOTE_MANAGED_ADAPTERS = new Set<AgentAdapterType>([
@@ -27,10 +43,19 @@ export function adapterSupportsRemoteManagedEnvironments(adapterType: string): b
 
 export function supportedEnvironmentDriversForAdapter(adapterType: string): EnvironmentDriver[] {
   return adapterSupportsRemoteManagedEnvironments(adapterType)
-    ? ["local", "ssh"]
+    ? ["local", "ssh", "sandbox"]
     : ["local"];
 }
 
+export function supportedSandboxProvidersForAdapter(
+  adapterType: string,
+  additionalProviders: readonly string[] = [],
+): SandboxEnvironmentProvider[] {
+  return adapterSupportsRemoteManagedEnvironments(adapterType)
+    ? Array.from(new Set(additionalProviders)) as SandboxEnvironmentProvider[]
+    : [];
+}
+
 export function isEnvironmentDriverSupportedForAdapter(
   adapterType: string,
   driver: string,
@@ -38,27 +63,83 @@ export function isEnvironmentDriverSupportedForAdapter(
   return supportedEnvironmentDriversForAdapter(adapterType).includes(driver as EnvironmentDriver);
 }
 
+export function isSandboxProviderSupportedForAdapter(
+  adapterType: string,
+  provider: string | null | undefined,
+  additionalProviders: readonly string[] = [],
+): boolean {
+  if (!provider) return false;
+  return supportedSandboxProvidersForAdapter(adapterType, additionalProviders).includes(
+    provider as SandboxEnvironmentProvider,
+  );
+}
+
 export function getAdapterEnvironmentSupport(
   adapterType: AgentAdapterType,
+  additionalSandboxProviders: readonly string[] = [],
 ): AdapterEnvironmentSupport {
   const supportedDrivers = new Set(supportedEnvironmentDriversForAdapter(adapterType));
+  const supportedProviders = new Set(supportedSandboxProvidersForAdapter(adapterType, additionalSandboxProviders));
+  const sandboxProviders: Record<SandboxEnvironmentProvider, EnvironmentSupportStatus> = {
+    fake: supportedProviders.has("fake") ? "supported" : "unsupported",
+  };
+  for (const provider of additionalSandboxProviders) {
+    sandboxProviders[provider as SandboxEnvironmentProvider] = supportedProviders.has(provider as SandboxEnvironmentProvider)
+      ? "supported"
+      : "unsupported";
+  }
   return {
     adapterType,
     drivers: {
       local: supportedDrivers.has("local") ? "supported" : "unsupported",
       ssh: supportedDrivers.has("ssh") ? "supported" : "unsupported",
+      sandbox: supportedDrivers.has("sandbox") ? "supported" : "unsupported",
+      plugin: supportedDrivers.has("plugin") ? "supported" : "unsupported",
     },
+    sandboxProviders,
   };
 }
 
 export function getEnvironmentCapabilities(
   adapterTypes: readonly AgentAdapterType[],
+  options: {
+    sandboxProviders?: Record<string, Partial<EnvironmentProviderCapability>>;
+  } = {},
 ): EnvironmentCapabilities {
+  const pluginProviderKeys = Object.keys(options.sandboxProviders ?? {});
+  const sandboxProviders: Record<SandboxEnvironmentProvider, EnvironmentProviderCapability> = {
+    fake: {
+      status: "unsupported",
+      supportsSavedProbe: true,
+      supportsUnsavedProbe: true,
+      supportsRunExecution: false,
+      supportsReusableLeases: true,
+      displayName: "Fake",
+      source: "builtin",
+    },
+  };
+  for (const [provider, capability] of Object.entries(options.sandboxProviders ?? {})) {
+    sandboxProviders[provider as SandboxEnvironmentProvider] = {
+      status: capability.status ?? "supported",
+      supportsSavedProbe: capability.supportsSavedProbe ?? true,
+      supportsUnsavedProbe: capability.supportsUnsavedProbe ?? true,
+      supportsRunExecution: capability.supportsRunExecution ?? true,
+      supportsReusableLeases: capability.supportsReusableLeases ?? true,
+      displayName: capability.displayName,
+      description: capability.description,
+      source: capability.source ?? "plugin",
+      pluginKey: capability.pluginKey,
+      pluginId: capability.pluginId,
+    };
+  }
   return {
-    adapters: adapterTypes.map((adapterType) => getAdapterEnvironmentSupport(adapterType)),
+    adapters: adapterTypes.map((adapterType) => getAdapterEnvironmentSupport(adapterType, pluginProviderKeys)),
     drivers: {
       local: "supported",
       ssh: "supported",
+      sandbox: "supported",
+      plugin: "unsupported",
     },
+    sandboxProviders,
   };
 }