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/protocol.ts

@@ -325,6 +325,99 @@ export interface ExecuteToolParams {
   runContext: ToolRunContext;
 }
 
+export interface PluginEnvironmentDiagnostic {
+  severity: "info" | "warning" | "error";
+  message: string;
+  code?: string;
+  details?: Record<string, unknown>;
+}
+
+export interface PluginEnvironmentDriverBaseParams {
+  driverKey: string;
+  companyId: string;
+  environmentId: string;
+  config: Record<string, unknown>;
+}
+
+export interface PluginEnvironmentValidateConfigParams {
+  driverKey: string;
+  config: Record<string, unknown>;
+}
+
+export interface PluginEnvironmentValidationResult {
+  ok: boolean;
+  warnings?: string[];
+  errors?: string[];
+  normalizedConfig?: Record<string, unknown>;
+}
+
+export interface PluginEnvironmentProbeParams extends PluginEnvironmentDriverBaseParams {}
+
+export interface PluginEnvironmentProbeResult {
+  ok: boolean;
+  summary?: string;
+  diagnostics?: PluginEnvironmentDiagnostic[];
+  metadata?: Record<string, unknown>;
+}
+
+export interface PluginEnvironmentLease {
+  providerLeaseId: string | null;
+  metadata?: Record<string, unknown>;
+  expiresAt?: string | null;
+}
+
+export interface PluginEnvironmentAcquireLeaseParams extends PluginEnvironmentDriverBaseParams {
+  runId: string;
+  workspaceMode?: string;
+  requestedCwd?: string;
+}
+
+export interface PluginEnvironmentResumeLeaseParams extends PluginEnvironmentDriverBaseParams {
+  providerLeaseId: string;
+  leaseMetadata?: Record<string, unknown>;
+}
+
+export interface PluginEnvironmentReleaseLeaseParams extends PluginEnvironmentDriverBaseParams {
+  providerLeaseId: string | null;
+  leaseMetadata?: Record<string, unknown>;
+}
+
+export interface PluginEnvironmentDestroyLeaseParams extends PluginEnvironmentReleaseLeaseParams {}
+
+export interface PluginEnvironmentRealizeWorkspaceParams extends PluginEnvironmentDriverBaseParams {
+  lease: PluginEnvironmentLease;
+  workspace: {
+    localPath?: string;
+    remotePath?: string;
+    mode?: string;
+    metadata?: Record<string, unknown>;
+  };
+}
+
+export interface PluginEnvironmentRealizeWorkspaceResult {
+  cwd: string;
+  metadata?: Record<string, unknown>;
+}
+
+export interface PluginEnvironmentExecuteParams extends PluginEnvironmentDriverBaseParams {
+  lease: PluginEnvironmentLease;
+  command: string;
+  args?: string[];
+  cwd?: string;
+  env?: Record<string, string>;
+  stdin?: string;
+  timeoutMs?: number;
+}
+
+export interface PluginEnvironmentExecuteResult {
+  exitCode: number | null;
+  signal?: string | null;
+  timedOut: boolean;
+  stdout: string;
+  stderr: string;
+  metadata?: Record<string, unknown>;
+}
+
 // ---------------------------------------------------------------------------
 // UI launcher / modal host interaction payloads
 // ---------------------------------------------------------------------------
@@ -394,6 +487,38 @@ export interface HostToWorkerMethods {
   performAction: [params: PerformActionParams, result: unknown];
   /** @see PLUGIN_SPEC.md §13.10 */
   executeTool: [params: ExecuteToolParams, result: ToolResult];
+  environmentValidateConfig: [
+    params: PluginEnvironmentValidateConfigParams,
+    result: PluginEnvironmentValidationResult,
+  ];
+  environmentProbe: [
+    params: PluginEnvironmentProbeParams,
+    result: PluginEnvironmentProbeResult,
+  ];
+  environmentAcquireLease: [
+    params: PluginEnvironmentAcquireLeaseParams,
+    result: PluginEnvironmentLease,
+  ];
+  environmentResumeLease: [
+    params: PluginEnvironmentResumeLeaseParams,
+    result: PluginEnvironmentLease,
+  ];
+  environmentReleaseLease: [
+    params: PluginEnvironmentReleaseLeaseParams,
+    result: void,
+  ];
+  environmentDestroyLease: [
+    params: PluginEnvironmentDestroyLeaseParams,
+    result: void,
+  ];
+  environmentRealizeWorkspace: [
+    params: PluginEnvironmentRealizeWorkspaceParams,
+    result: PluginEnvironmentRealizeWorkspaceResult,
+  ];
+  environmentExecute: [
+    params: PluginEnvironmentExecuteParams,
+    result: PluginEnvironmentExecuteResult,
+  ];
 }
 
 /** Union of all host→worker method names. */
@@ -417,6 +542,14 @@ export const HOST_TO_WORKER_OPTIONAL_METHODS: readonly HostToWorkerMethodName[]
   "getData",
   "performAction",
   "executeTool",
+  "environmentValidateConfig",
+  "environmentProbe",
+  "environmentAcquireLease",
+  "environmentResumeLease",
+  "environmentReleaseLease",
+  "environmentDestroyLease",
+  "environmentRealizeWorkspace",
+  "environmentExecute",
 ] as const;
 
 // ---------------------------------------------------------------------------