Add E2B sandbox provider plugin (#4452)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - Sandbox environments are part of that execution layer, and the
recent core refactor moved provider-specific behavior to a generic
plugin seam
> - This pull request adds a dedicated `@paperclipai/plugin-e2b` package
so E2B can live entirely outside core host code
> - Because the feature is still unreleased, the plugin should model
third-party packaging directly instead of carrying extra
backward-compatibility complexity in core or the workspace lockfile
> - This branch therefore makes the E2B provider a standalone
publishable package, documents the package-local dev flow, and keeps the
publish manifest/runtime dependency story correct
> - The benefit is that E2B becomes a true plugin reference
implementation that can be installed by package name without reopening
core Paperclip code

## What Changed

- Added `packages/plugins/paperclip-plugin-e2b` as the E2B sandbox
provider plugin package
- Implemented config validation, lease acquire/resume/release/destroy
handlers, workspace realization, and command execution for E2B sandboxes
- Excluded the E2B plugin package from the root workspace so the repo no
longer needs `pnpm-lock.yaml` churn for its third-party dependency graph
- Added package-local development/install support plus a prepack
manifest generator so the published tarball still declares
`@paperclipai/plugin-sdk` and `e2b` runtime dependencies
- Addressed review feedback by fixing sandbox cleanup on acquire
failures, rejecting blank templates, normalizing fractional `timeoutMs`,
and always passing the configured template name to the E2B SDK
- Updated focused Vitest coverage for config normalization, validation,
acquire cleanup, command execution, and lease release behavior
- Updated the Dockerfile deps stage to copy the E2B package manifest so
the policy check stays in sync

## Verification

- `cd packages/plugins/paperclip-plugin-e2b && pnpm install
--ignore-workspace --no-lockfile`
- `cd packages/plugins/paperclip-plugin-e2b && pnpm build`
- `cd packages/plugins/paperclip-plugin-e2b && pnpm --ignore-workspace
test`
- `cd packages/plugins/paperclip-plugin-e2b && pnpm --ignore-workspace
typecheck`
- `cd packages/plugins/paperclip-plugin-e2b && npm pack --dry-run`

## Risks

- The package now relies on a prepack manifest rewrite so the
publish-time dependency list stays correct while the repo-local dev
manifest stays workspace-light
- The current repo snapshot is still unreleased, so the generated
publish manifest points at the repo SDK version until the normal release
flow rewrites versions before publish
- Real-world E2B environments may still expose edge cases around
lifecycle timing or sandbox metadata beyond the mocked unit coverage

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- OpenAI Codex via `codex_local`
- Model ID: `gpt-5.4`
- Reasoning effort: `high`
- Context window observed in runtime session metadata: `258400` tokens
- Capabilities used: terminal tool execution, git, GitHub CLI, and local
build/test inspection

## 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/sandbox-providers/e2b/package.json

@@ -0,0 +1,61 @@
+{
+  "name": "@paperclipai/plugin-e2b",
+  "version": "0.1.0",
+  "description": "E2B sandbox provider plugin for Paperclip environments",
+  "license": "MIT",
+  "homepage": "https://github.com/paperclipai/paperclip",
+  "bugs": {
+    "url": "https://github.com/paperclipai/paperclip/issues"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/paperclipai/paperclip",
+    "directory": "packages/plugins/sandbox-providers/e2b"
+  },
+  "type": "module",
+  "exports": {
+    ".": "./src/index.ts"
+  },
+  "publishConfig": {
+    "access": "public",
+    "exports": {
+      ".": {
+        "types": "./dist/index.d.ts",
+        "import": "./dist/index.js"
+      }
+    },
+    "main": "./dist/index.js",
+    "types": "./dist/index.d.ts"
+  },
+  "files": [
+    "dist"
+  ],
+  "paperclipPlugin": {
+    "manifest": "./dist/manifest.js",
+    "worker": "./dist/worker.js"
+  },
+  "keywords": [
+    "paperclip",
+    "plugin",
+    "sandbox",
+    "e2b"
+  ],
+  "scripts": {
+    "postinstall": "node ../../../../scripts/link-plugin-dev-sdk.mjs",
+    "prebuild": "pnpm -C ../../../.. --filter @paperclipai/plugin-sdk build",
+    "build": "rm -rf dist && tsc",
+    "clean": "rm -rf dist",
+    "typecheck": "pnpm -C ../../../.. --filter @paperclipai/plugin-sdk build && tsc --noEmit",
+    "test": "vitest run --config vitest.config.ts",
+    "prepack": "rm -f package.dev.json && cp package.json package.dev.json && node ../../../../scripts/generate-plugin-package-json.mjs",
+    "postpack": "if [ -f package.dev.json ]; then mv package.dev.json package.json; fi"
+  },
+  "dependencies": {
+    "e2b": "^2.19.0"
+  },
+  "devDependencies": {
+    "@types/node": "^24.6.0",
+    "typescript": "^5.7.3",
+    "vitest": "^3.2.4"
+  }
+}