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/validators/index.ts

@@ -344,6 +344,7 @@ export {
   pluginJobDeclarationSchema,
   pluginWebhookDeclarationSchema,
   pluginToolDeclarationSchema,
+  pluginEnvironmentDriverDeclarationSchema,
   pluginUiSlotDeclarationSchema,
   pluginLauncherActionDeclarationSchema,
   pluginLauncherRenderDeclarationSchema,
@@ -362,6 +363,7 @@ export {
   type PluginJobDeclarationInput,
   type PluginWebhookDeclarationInput,
   type PluginToolDeclarationInput,
+  type PluginEnvironmentDriverDeclarationInput,
   type PluginUiSlotDeclarationInput,
   type PluginLauncherActionDeclarationInput,
   type PluginLauncherRenderDeclarationInput,

packages/shared/src/validators/plugin.ts

@@ -107,6 +107,21 @@ export const pluginToolDeclarationSchema = z.object({
   parametersSchema: jsonSchemaSchema,
 });
 
+export const pluginEnvironmentDriverDeclarationSchema = z.object({
+  driverKey: z.string().min(1).regex(
+    /^[a-z0-9][a-z0-9._-]*$/,
+    "Environment driver key must start with a lowercase alphanumeric and contain only lowercase letters, digits, dots, hyphens, or underscores",
+  ),
+  kind: z.enum(["environment_driver", "sandbox_provider"]).optional(),
+  displayName: z.string().min(1).max(100),
+  description: z.string().max(500).optional(),
+  configSchema: jsonSchemaSchema,
+});
+
+export type PluginEnvironmentDriverDeclarationInput = z.infer<
+  typeof pluginEnvironmentDriverDeclarationSchema
+>;
+
 export type PluginToolDeclarationInput = z.infer<typeof pluginToolDeclarationSchema>;
 
 /**
@@ -410,11 +425,13 @@ export type PluginApiRouteDeclarationInput = z.infer<typeof pluginApiRouteDeclar
  * Cross-field rules enforced via `superRefine`:
  * - `entrypoints.ui` required when `ui.slots` declared
  * - `agent.tools.register` capability required when `tools` declared
+ * - `environment.drivers.register` capability required when `environmentDrivers` declared
  * - `jobs.schedule` capability required when `jobs` declared
  * - `webhooks.receive` capability required when `webhooks` declared
  * - duplicate `jobs[].jobKey` values are rejected
  * - duplicate `webhooks[].endpointKey` values are rejected
  * - duplicate `tools[].name` values are rejected
+ * - duplicate `environmentDrivers[].driverKey` values are rejected
  * - duplicate `ui.slots[].id` values are rejected
  *
  * @see PLUGIN_SPEC.md §10.1 — Manifest shape
@@ -453,6 +470,7 @@ export const pluginManifestV1Schema = z.object({
   tools: z.array(pluginToolDeclarationSchema).optional(),
   database: pluginDatabaseDeclarationSchema.optional(),
   apiRoutes: z.array(pluginApiRouteDeclarationSchema).optional(),
+  environmentDrivers: z.array(pluginEnvironmentDriverDeclarationSchema).optional(),
   launchers: z.array(pluginLauncherDeclarationSchema).optional(),
   ui: z.object({
     slots: z.array(pluginUiSlotDeclarationSchema).min(1).optional(),
@@ -500,6 +518,17 @@ export const pluginManifestV1Schema = z.object({
     }
   }
 
+  // environment drivers require environment.drivers.register
+  if (manifest.environmentDrivers && manifest.environmentDrivers.length > 0) {
+    if (!manifest.capabilities.includes("environment.drivers.register")) {
+      ctx.addIssue({
+        code: z.ZodIssueCode.custom,
+        message: "Capability 'environment.drivers.register' is required when environmentDrivers are declared",
+        path: ["capabilities"],
+      });
+    }
+  }
+
   // jobs require jobs.schedule (PLUGIN_SPEC.md §17)
   if (manifest.jobs && manifest.jobs.length > 0) {
     if (!manifest.capabilities.includes("jobs.schedule")) {
@@ -622,6 +651,19 @@ export const pluginManifestV1Schema = z.object({
     }
   }
 
+  // environment driver keys must be unique within the plugin
+  if (manifest.environmentDrivers) {
+    const driverKeys = manifest.environmentDrivers.map((d) => d.driverKey);
+    const duplicates = driverKeys.filter((key, i) => driverKeys.indexOf(key) !== i);
+    if (duplicates.length > 0) {
+      ctx.addIssue({
+        code: z.ZodIssueCode.custom,
+        message: `Duplicate environment driver keys: ${[...new Set(duplicates)].join(", ")}`,
+        path: ["environmentDrivers"],
+      });
+    }
+  }
+
   // UI slot ids must be unique within the plugin (namespaced at runtime)
   if (manifest.ui) {
     if (manifest.ui.slots) {