java/sandbox/v1.0.15

## What's New

### ✨ Features

- **Custom sandbox creation for client-side pools** — Kotlin `SandboxPool` now accepts a custom creator that returns a `Sandbox`, allowing advanced creation flows while keeping pool ownership of health checks, TTL renewal, idle bookkeeping, direct-create fallback, and cleanup. Existing image/template based pool creation remains the default and is unchanged unless a creator is supplied. (https://github.com/opensandbox-group/OpenSandbox/pull/1125)

- **Isolated execution session APIs** — The Kotlin sandbox SDK now includes isolated-session models, services, and adapters for the new execd isolation runtime. Callers can create/delete isolated sessions and perform isolated filesystem operations through the SDK; server-side diff/commit support remains deferred in this phase. (https://github.com/opensandbox-group/OpenSandbox/pull/1008)

### 🐛 Bug Fixes

- **Preserve server error details in exception strings** — Kotlin `SandboxException.toString()` now appends parsed server error code/message and `request_id` when available. This avoids losing useful backend diagnostics in logs and exception rendering when the HTTP status alone is too generic. (https://github.com/opensandbox-group/OpenSandbox/pull/1122)

- **Correct PVC cleanup semantics in SDK models and docs** — Kotlin SDK model documentation for `deleteOnSandboxTermination` now reflects the Kubernetes cleanup behavior for opted-in auto-created PVCs. The option still defaults to `false`, so existing PVC-backed sandboxes keep their previous behavior unless callers explicitly opt in. (https://github.com/opensandbox-group/OpenSandbox/pull/880)

### 📦 Misc

- Bumped the Kotlin sandbox SDK artifact version to `1.0.15`. (https://github.com/opensandbox-group/OpenSandbox/pull/1125)

### 👥 Contributors

- @Pangjiping
- @ninan-nn
- @xfgong