## Thinking Path
> - Paperclip is an open-source AI-agent management platform; agents run
tasks inside sandboxed environments (Daytona, Kubernetes, E2B, etc.)
> - The control-plane ↔ sandbox file-transfer path flows through the
`environmentExecute` seam in `protocol.ts` — the only verb available to
plugins — which forces a base64-over-exec chunked loop for every file
move: workspace files, assets, Codex home sync
> - This transport is correct and safe, but it bypasses provider-native
bulk/streaming APIs (Daytona `uploadFiles`, K8s `FastUploadInterceptor`
/ volume mounts), leaving significant throughput on the table for large
workspaces
> - The right fix is an opt-in seam extension: providers with faster
native transfer declare two optional verbs; providers that do not opt in
stay on the existing fallback with zero code or behavior change required
> - This PR adds the first layer of that extension — two optional verbs
(`environmentSyncIn` / `environmentSyncOut`) in the plugin SDK, the
runtime plumbing to prefer the native path for the two clean
destroy-then-replace cases, and a doc for the contract
> - The core correctness invariant is byte-identical fallback: if no
provider opts in, execution is exactly what ships today;
`assertSyncOperationsConfined` enforces host-side path confinement for
providers that do opt in
> - No provider advertises the verbs yet → zero production behavior
change; future PRs wire up Daytona and K8s providers against this
contract
## Linked Issues or Issue Description
No public GitHub issue exists for this feature. Description follows the
`feature_request` issue template:
**Subsystem affected:**
packages/plugins — plugin system; packages/adapter-utils — adapter
runtime; server/ — EnvironmentRuntimeService
**Problem or motivation:**
Sandbox file transfers currently always use a base64-over-exec chunked
loop regardless of what the underlying provider supports. For workspaces
larger than a few MB this becomes the dominant wall-clock cost of every
sandbox run, and it bypasses bulk/stream APIs that providers like
Daytona already expose natively.
**Proposed solution:**
Add two optional, opt-in plugin hooks — `onEnvironmentSyncIn` /
`onEnvironmentSyncOut` — to the plugin SDK. When a provider defines both
hooks and both are advertised via the existing `supportedMethods`
negotiation, the runtime prefers the native path for the two clean
destroy-then-replace transfer cases; all other cases fall back to the
existing byte-identical base64 transport.
**Alternatives considered:**
An unconditional verb would require every provider to implement or stub
the verb. The opt-in / `METHOD_NOT_IMPLEMENTED` pattern (already used by
`environmentExecute`) preserves backward compatibility with zero
provider changes required.
**Roadmap alignment:**
Consistent with the ✅ "Cloud / Sandbox agents" and ✅ "Plugin system"
milestones; extends the plugin seam rather than adding
control-plane-level logic.
**Additional context:**
Searched open pull requests and issues for duplicate sandbox file-sync /
native-transfer work; none found.
## What Changed
- **`packages/plugins/sdk`**
- `protocol.ts`: two new optional `HostToWorkerMethods` —
`environmentSyncIn` / `environmentSyncOut` — plus generic
`SyncOperation`, `SyncFileMapping`, and `SyncOutcome` types
- `define-plugin.ts`: optional `onEnvironmentSyncIn` /
`onEnvironmentSyncOut` fields on `PluginDefinition`; worker advertises
each verb only when its hook is defined (else `METHOD_NOT_IMPLEMENTED`,
mirroring `environmentExecute`)
- `worker-rpc-host.ts`: route new verbs to plugin hooks
- `index.ts`: re-export new public types
- **`packages/adapter-utils`**
- `command-managed-runtime.ts`: expose optional `syncIn` / `syncOut` on
`CommandManagedRuntimeRunner` (available only when both verbs are
advertised); add `assertSyncOperationsConfined` host-side
path-confinement guard
- `sandbox-managed-runtime.ts`: `SandboxManagedRuntimeClient` gains
optional `syncIn` / `syncOut`; orchestrator prefers native path for
default-provision asset inbound and workspace-download-into-fresh-dir
outbound; all other paths keep the existing base64 fallback
- `sandbox-file-sync.test.ts` (new): 234-line characterization suite —
native-opt-in branch, fallback branch, `assertSyncOperationsConfined`
escape-path rejection, `followSymlinks` → tar `-h`
- `command-managed-runtime.test.ts`: negotiation + native-sync +
confinement tests
- **`server/src/services/environment-runtime.ts`**:
`EnvironmentRuntimeService` delegates to `syncIn` / `syncOut`, gated on
advertised support
- **`server/src/services/environment-execution-target.ts`**: minor
typing fix alongside the new verbs
- **`doc/plugins/SANDBOX_FILE_SYNC_HOOKS.md`** (new): documents the full
contract — opt-in / no-op guarantee, operation ordering,
provider-may-tar, atomicity, `followSymlinks`, secret modes (0600, no
window), path confinement, `operationId` opacity, resource bounds,
shell-quoting
## Verification
```bash
# SDK suite
pnpm --filter packages/plugins/sdk test
# Adapter-utils suite (includes new sandbox-file-sync characterization tests)
pnpm --filter packages/adapter-utils test
# Expected: 255 pass / 4 skip
# Type-check across affected packages
pnpm --filter packages/plugins/sdk typecheck
pnpm --filter packages/adapter-utils typecheck
# Server changed-file spot check:
cd server && npx tsc --noEmit --skipLibCheck 2>&1 | grep -E "environment-(runtime|execution-target)" | head -20
```
Key behavioral invariant to spot-check: with no provider opting in (the
current state), run any sandbox task and confirm file-transfer behavior
is byte-for-byte identical to what the pre-PR code produces. The
characterization tests assert this at the unit level.
## Risks
- **Zero production risk today**: no provider advertises
`environmentSyncIn` / `environmentSyncOut`, so the new code paths are
unreachable in production; all real traffic stays on the existing base64
fallback
- **Path confinement**: `assertSyncOperationsConfined` rejects any
`targetPath` that escapes the declared root — this is the primary
security boundary for future providers. The test suite covers
escape-path rejection
- **Atomicity**: the contract delegates atomicity to providers; the doc
explicitly calls out that directory-level ops are not guaranteed atomic
- **Secret transport**: credential assets (e.g., Codex `auth.json`,
directory mappings) continue to use the existing tar path — they do not
go through the new verbs in any current provider
> 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
Provider: Anthropic
Model: `claude-sonnet-4-6` (Claude Sonnet 4.6)
Context window: 200 K tokens
Capabilities: extended tool use, multi-file code generation, agentic
reasoning via the Paperclip agent framework
## 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 searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` /
`Closes: #` / `Refs: #` OR (b) described the issue in-PR following the
relevant issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge
---------
Co-authored-by: Harold Kim <harold@paperclip.ing>
Co-authored-by: Paperclip <noreply@paperclip.ing>
Nicky Leach