feat(sandbox): implement sandbox archive upload/download endpoints and security enhancements

- Added sandbox archive upload and download proxy endpoints with signed URL verification.
- Introduced security helpers for generating and verifying signed URLs.
- Updated file-related API routes to include sandbox archive functionality.
- Refactored app asset storage methods to streamline download/upload URL generation.

api/agent-notes/controllers/files/__init__.py.md

@@ -1,6 +1,6 @@
 Summary:
 - Registers file-related API namespaces and routes for files service.
-- Includes app-assets download/upload proxy controllers.
+- Includes app-assets and sandbox archive proxy controllers.
 
 Invariants:
 - files_ns must include all file controller modules to register routes.

api/agent-notes/controllers/files/sandbox_archive.py.md

@@ -0,0 +1,14 @@
+Summary:
+- Sandbox archive upload/download proxy endpoints (signed URL verification, stream to storage).
+
+Invariants:
+- Validates tenant_id and sandbox_id UUIDs.
+- Verifies tenant-scoped signature and expiration before storage access.
+- URL uses expires_at/nonce/sign query params.
+
+Edge Cases:
+- Missing archive returns NotFound.
+- Invalid signature or expired link returns Forbidden.
+
+Tests:
+- Add unit tests for signature validation if needed.

api/agent-notes/core/sandbox/sandbox.py.md

@@ -0,0 +1,9 @@
+Summary:
+- Sandbox lifecycle wrapper (ready/cancel/fail signals, mount/unmount, release).
+
+Invariants:
+- wait_ready raises with the original initialization error as the cause.
+- release always attempts unmount and environment release, logging failures.
+
+Tests:
+- Covered by sandbox lifecycle/unit tests and workflow execution error handling.

api/agent-notes/core/sandbox/security/__init__.py.md

@@ -0,0 +1,2 @@
+Summary:
+- Sandbox security helper modules.

api/agent-notes/core/sandbox/security/archive_signer.py.md

@@ -0,0 +1,13 @@
+Summary:
+- Generates and verifies signed URLs for sandbox archive upload/download.
+
+Invariants:
+- tenant_id and sandbox_id must be UUIDs.
+- Signatures are tenant-scoped and include operation, expiry, and nonce.
+
+Edge Cases:
+- Missing tenant private key raises ValueError.
+- Expired or tampered signatures are rejected.
+
+Tests:
+- Add unit tests if sandbox archive signature behavior expands.

api/agent-notes/core/sandbox/storage/archive_storage.py.md

@@ -0,0 +1,12 @@
+Summary:
+- Manages sandbox archive uploads/downloads for workspace persistence.
+
+Invariants:
+- Archive storage key is sandbox/<tenant_id>/<sandbox_id>.tar.gz.
+- Signed URLs are tenant-scoped and use external files URL.
+
+Edge Cases:
+- Missing archive skips mount.
+
+Tests:
+- Covered indirectly via sandbox integration tests.