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/__tests__/issue-feedback-routes.test.ts

@@ -53,6 +53,23 @@ const mockIssueThreadInteractionService = vi.hoisted(() => ({
   expireRequestConfirmationsSupersededByComment: vi.fn(async () => []),
   expireStaleRequestConfirmationsForIssueDocument: vi.fn(async () => []),
 }));
+const mockEnvironmentService = vi.hoisted(() => ({
+  getById: vi.fn(async () => null),
+}));
+const mockExecutionWorkspaceService = vi.hoisted(() => ({}));
+const mockIssueReferenceService = vi.hoisted(() => ({
+  deleteDocumentSource: vi.fn(async () => undefined),
+  diffIssueReferenceSummary: vi.fn(() => ({
+    addedReferencedIssues: [],
+    removedReferencedIssues: [],
+    currentReferencedIssues: [],
+  })),
+  emptySummary: vi.fn(() => ({ outbound: [], inbound: [] })),
+  listIssueReferenceSummary: vi.fn(async () => ({ outbound: [], inbound: [] })),
+  syncComment: vi.fn(async () => undefined),
+  syncDocument: vi.fn(async () => undefined),
+  syncIssue: vi.fn(async () => undefined),
+}));
 
 function registerModuleMocks() {
   vi.doMock("@paperclipai/shared/telemetry", () => ({
@@ -68,25 +85,11 @@ function registerModuleMocks() {
     accessService: () => mockAccessService,
     agentService: () => mockAgentService,
     documentService: () => ({}),
-    executionWorkspaceService: () => ({}),
-    feedbackService: () => mockFeedbackService,
+    executionWorkspaceService: () => mockExecutionWorkspaceService,
     goalService: () => ({}),
     heartbeatService: () => mockHeartbeatService,
-    instanceSettingsService: () => mockInstanceSettingsService,
     issueApprovalService: () => ({}),
-    issueReferenceService: () => ({
-      deleteDocumentSource: async () => undefined,
-      diffIssueReferenceSummary: () => ({
-        addedReferencedIssues: [],
-        removedReferencedIssues: [],
-        currentReferencedIssues: [],
-      }),
-      emptySummary: () => ({ outbound: [], inbound: [] }),
-      listIssueReferenceSummary: async () => ({ outbound: [], inbound: [] }),
-      syncComment: async () => undefined,
-      syncDocument: async () => undefined,
-      syncIssue: async () => undefined,
-    }),
+    issueReferenceService: () => mockIssueReferenceService,
     issueService: () => mockIssueService,
     issueThreadInteractionService: () => mockIssueThreadInteractionService,
     logActivity: mockLogActivity,
@@ -94,6 +97,22 @@ function registerModuleMocks() {
     routineService: () => mockRoutineService,
     workProductService: () => ({}),
   }));
+
+  vi.doMock("../services/environments.js", () => ({
+    environmentService: () => mockEnvironmentService,
+  }));
+
+  vi.doMock("../services/execution-workspaces.js", () => ({
+    executionWorkspaceService: () => mockExecutionWorkspaceService,
+  }));
+
+  vi.doMock("../services/feedback.js", () => ({
+    feedbackService: () => mockFeedbackService,
+  }));
+
+  vi.doMock("../services/instance-settings.js", () => ({
+    instanceSettingsService: () => mockInstanceSettingsService,
+  }));
 }
 
 async function createApp(actor: Record<string, unknown>) {
@@ -118,6 +137,10 @@ describe("issue feedback trace routes", () => {
     vi.doUnmock("@paperclipai/shared/telemetry");
     vi.doUnmock("../telemetry.js");
     vi.doUnmock("../services/index.js");
+    vi.doUnmock("../services/environments.js");
+    vi.doUnmock("../services/execution-workspaces.js");
+    vi.doUnmock("../services/feedback.js");
+    vi.doUnmock("../services/instance-settings.js");
     vi.doUnmock("../routes/issues.js");
     vi.doUnmock("../middleware/index.js");
     registerModuleMocks();