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/plugins/sdk/src/worker-rpc-host.ts

@@ -76,6 +76,14 @@ import type {
   GetDataParams,
   PerformActionParams,
   ExecuteToolParams,
+  PluginEnvironmentAcquireLeaseParams,
+  PluginEnvironmentDestroyLeaseParams,
+  PluginEnvironmentExecuteParams,
+  PluginEnvironmentRealizeWorkspaceParams,
+  PluginEnvironmentReleaseLeaseParams,
+  PluginEnvironmentResumeLeaseParams,
+  PluginEnvironmentValidateConfigParams,
+  PluginEnvironmentProbeParams,
   WorkerToHostMethodName,
   WorkerToHostMethods,
 } from "./protocol.js";
@@ -1079,6 +1087,30 @@ export function startWorkerRpcHost(options: WorkerRpcHostOptions): WorkerRpcHost
       case "executeTool":
         return handleExecuteTool(params as ExecuteToolParams);
 
+      case "environmentValidateConfig":
+        return handleEnvironmentValidateConfig(params as PluginEnvironmentValidateConfigParams);
+
+      case "environmentProbe":
+        return handleEnvironmentProbe(params as PluginEnvironmentProbeParams);
+
+      case "environmentAcquireLease":
+        return handleEnvironmentAcquireLease(params as PluginEnvironmentAcquireLeaseParams);
+
+      case "environmentResumeLease":
+        return handleEnvironmentResumeLease(params as PluginEnvironmentResumeLeaseParams);
+
+      case "environmentReleaseLease":
+        return handleEnvironmentReleaseLease(params as PluginEnvironmentReleaseLeaseParams);
+
+      case "environmentDestroyLease":
+        return handleEnvironmentDestroyLease(params as PluginEnvironmentDestroyLeaseParams);
+
+      case "environmentRealizeWorkspace":
+        return handleEnvironmentRealizeWorkspace(params as PluginEnvironmentRealizeWorkspaceParams);
+
+      case "environmentExecute":
+        return handleEnvironmentExecute(params as PluginEnvironmentExecuteParams);
+
       default:
         throw Object.assign(
           new Error(`Unknown method: ${method}`),
@@ -1112,6 +1144,14 @@ export function startWorkerRpcHost(options: WorkerRpcHostOptions): WorkerRpcHost
     if (plugin.definition.onHealth) supportedMethods.push("health");
     if (plugin.definition.onShutdown) supportedMethods.push("shutdown");
     if (plugin.definition.onApiRequest) supportedMethods.push("handleApiRequest");
+    if (plugin.definition.onEnvironmentValidateConfig) supportedMethods.push("environmentValidateConfig");
+    if (plugin.definition.onEnvironmentProbe) supportedMethods.push("environmentProbe");
+    if (plugin.definition.onEnvironmentAcquireLease) supportedMethods.push("environmentAcquireLease");
+    if (plugin.definition.onEnvironmentResumeLease) supportedMethods.push("environmentResumeLease");
+    if (plugin.definition.onEnvironmentReleaseLease) supportedMethods.push("environmentReleaseLease");
+    if (plugin.definition.onEnvironmentDestroyLease) supportedMethods.push("environmentDestroyLease");
+    if (plugin.definition.onEnvironmentRealizeWorkspace) supportedMethods.push("environmentRealizeWorkspace");
+    if (plugin.definition.onEnvironmentExecute) supportedMethods.push("environmentExecute");
 
     return { ok: true, supportedMethods };
   }
@@ -1255,6 +1295,71 @@ export function startWorkerRpcHost(options: WorkerRpcHostOptions): WorkerRpcHost
     return entry.fn(params.parameters, params.runContext);
   }
 
+  function methodNotImplemented(method: string): Error & { code: number } {
+    return Object.assign(
+      new Error(`${method} is not implemented by this plugin`),
+      { code: PLUGIN_RPC_ERROR_CODES.METHOD_NOT_IMPLEMENTED },
+    );
+  }
+
+  async function handleEnvironmentValidateConfig(
+    params: PluginEnvironmentValidateConfigParams,
+  ) {
+    if (!plugin.definition.onEnvironmentValidateConfig) {
+      throw methodNotImplemented("environmentValidateConfig");
+    }
+    return plugin.definition.onEnvironmentValidateConfig(params);
+  }
+
+  async function handleEnvironmentProbe(params: PluginEnvironmentProbeParams) {
+    if (!plugin.definition.onEnvironmentProbe) {
+      throw methodNotImplemented("environmentProbe");
+    }
+    return plugin.definition.onEnvironmentProbe(params);
+  }
+
+  async function handleEnvironmentAcquireLease(params: PluginEnvironmentAcquireLeaseParams) {
+    if (!plugin.definition.onEnvironmentAcquireLease) {
+      throw methodNotImplemented("environmentAcquireLease");
+    }
+    return plugin.definition.onEnvironmentAcquireLease(params);
+  }
+
+  async function handleEnvironmentResumeLease(params: PluginEnvironmentResumeLeaseParams) {
+    if (!plugin.definition.onEnvironmentResumeLease) {
+      throw methodNotImplemented("environmentResumeLease");
+    }
+    return plugin.definition.onEnvironmentResumeLease(params);
+  }
+
+  async function handleEnvironmentReleaseLease(params: PluginEnvironmentReleaseLeaseParams) {
+    if (!plugin.definition.onEnvironmentReleaseLease) {
+      throw methodNotImplemented("environmentReleaseLease");
+    }
+    return plugin.definition.onEnvironmentReleaseLease(params);
+  }
+
+  async function handleEnvironmentDestroyLease(params: PluginEnvironmentDestroyLeaseParams) {
+    if (!plugin.definition.onEnvironmentDestroyLease) {
+      throw methodNotImplemented("environmentDestroyLease");
+    }
+    return plugin.definition.onEnvironmentDestroyLease(params);
+  }
+
+  async function handleEnvironmentRealizeWorkspace(params: PluginEnvironmentRealizeWorkspaceParams) {
+    if (!plugin.definition.onEnvironmentRealizeWorkspace) {
+      throw methodNotImplemented("environmentRealizeWorkspace");
+    }
+    return plugin.definition.onEnvironmentRealizeWorkspace(params);
+  }
+
+  async function handleEnvironmentExecute(params: PluginEnvironmentExecuteParams) {
+    if (!plugin.definition.onEnvironmentExecute) {
+      throw methodNotImplemented("environmentExecute");
+    }
+    return plugin.definition.onEnvironmentExecute(params);
+  }
+
   // -----------------------------------------------------------------------
   // Event filter helper
   // -----------------------------------------------------------------------