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

server/src/routes/environments.ts

@@ -12,8 +12,6 @@ import { validate } from "../middleware/validate.js";
 import {
   accessService,
   agentService,
-  environmentService,
-  executionWorkspaceService,
   issueService,
   logActivity,
   projectService,
@@ -27,9 +25,16 @@ import {
 } from "../services/environment-config.js";
 import { probeEnvironment } from "../services/environment-probe.js";
 import { secretService } from "../services/secrets.js";
+import { listReadyPluginEnvironmentDrivers } from "../services/plugin-environment-driver.js";
 import { assertCompanyAccess, getActorInfo } from "./authz.js";
+import type { PluginWorkerManager } from "../services/plugin-worker-manager.js";
+import { environmentService } from "../services/environments.js";
+import { executionWorkspaceService } from "../services/execution-workspaces.js";
 
-export function environmentRoutes(db: Db) {
+export function environmentRoutes(
+  db: Db,
+  options: { pluginWorkerManager?: PluginWorkerManager } = {},
+) {
   const router = Router();
   const agents = agentService(db);
   const access = accessService(db);
@@ -159,7 +164,30 @@ export function environmentRoutes(db: Db) {
   router.get("/companies/:companyId/environments/capabilities", async (req, res) => {
     const companyId = req.params.companyId as string;
     assertCompanyAccess(req, companyId);
-    res.json(getEnvironmentCapabilities(AGENT_ADAPTER_TYPES));
+    const pluginDrivers = await listReadyPluginEnvironmentDrivers({
+      db,
+      workerManager: options.pluginWorkerManager,
+    });
+    res.json(getEnvironmentCapabilities(
+      AGENT_ADAPTER_TYPES,
+      {
+        sandboxProviders: Object.fromEntries(pluginDrivers.map((driver) => [
+          driver.driverKey,
+          {
+            status: "supported" as const,
+            supportsSavedProbe: true,
+            supportsUnsavedProbe: true,
+            supportsRunExecution: true,
+            supportsReusableLeases: true,
+            displayName: driver.displayName,
+            description: driver.description,
+            source: "plugin" as const,
+            pluginKey: driver.pluginKey,
+            pluginId: driver.pluginId,
+          },
+        ])),
+      },
+    ));
   });
 
   router.post("/companies/:companyId/environments", validate(createEnvironmentSchema), async (req, res) => {
@@ -178,6 +206,7 @@ export function environmentRoutes(db: Db) {
           agentId: actor.agentId,
           userId: actor.actorType === "user" ? actor.actorId : null,
         },
+        pluginWorkerManager: options.pluginWorkerManager,
       }),
     };
     const environment = await svc.create(companyId, input);
@@ -280,6 +309,7 @@ export function environmentRoutes(db: Db) {
                 agentId: actor.agentId,
                 userId: actor.actorType === "user" ? actor.actorId : null,
               },
+              pluginWorkerManager: options.pluginWorkerManager,
             }),
           }
         : {}),
@@ -351,7 +381,9 @@ export function environmentRoutes(db: Db) {
     }
     await assertCanMutateEnvironments(req, environment.companyId);
     const actor = getActorInfo(req);
-    const probe = await probeEnvironment(db, environment);
+    const probe = await probeEnvironment(db, environment, {
+      pluginWorkerManager: options.pluginWorkerManager,
+    });
     await logActivity(db, {
       companyId: environment.companyId,
       actorType: actor.actorType,
@@ -394,6 +426,7 @@ export function environmentRoutes(db: Db) {
         updatedAt: new Date(),
       };
       const probe = await probeEnvironment(db, environment, {
+        pluginWorkerManager: options.pluginWorkerManager,
         resolvedConfig: {
           driver: req.body.driver,
           config: normalizedConfig,