feat(sandbox): native Apple Container, WSL, OrbStack, Podman runtime support

[KooshaPari]

Summary

Adds a container-provider abstraction to OmniRoute's skill sandbox so it auto-detects and uses the most performant native container runtime on each host OS — no Docker Desktop required.

Motivation

The sandbox historically hardcoded docker run ... for all sandboxed skill execution. This forces users on macOS (Apple Silicon) and Windows (WSL2 hosts) to install Docker Desktop just for skill isolation, which is unnecessary overhead when first-class native alternatives now exist:

• Apple Container — native OCI runtime for macOS 26+ (https://github.com/apple/container)
• WSL Container (wslc.exe) — Windows-native container CLI via WSL 2 (https://learn.microsoft.com/en-us/windows/wsl/wsl-container?tabs=csharp)
• OrbStack — high-perf Linux VM + docker shim on macOS
• Podman — rootless, daemonless on Linux

This PR also fills the macOS opt-in for OrbStack and the cross-platform opt-in for Podman as user-requested high-perf alternatives.

Changes

New: src/lib/skills/containerProvider.ts (479 lines)

Defines a ContainerProvider interface and five concrete implementations:

Provider	ID	Platform priority	Native CLI
AppleContainerProvider	apple	macOS 1st	container
OrbStackProvider	orbstack	macOS 2nd	orbstack
WslContainerProvider	wsl	Windows 1st	wslc
PodmanProvider	podman	Linux 1st	podman
DockerProvider	docker	fallback	docker

Auto-detection order per platform:

• macOS: apple -> orbstack -> podman -> docker
• Windows: wsl -> docker -> podman
• Linux: podman -> docker

Each provider maps the sandbox's intent (CPU/memory caps, network isolation, capability drops, read-only filesystem, tmpfs workspaces, no-new-privileges) onto the runtime's native flag set. Detection uses which/where + --version probe via spawnSync (no spawn, so it doesn't interfere with mocked test spawns).

Modified: src/lib/skills/sandbox.ts (91 lines changed)

• Imports resolveProvider(), buildKillCommand(), and types from containerProvider.ts
• SandboxRunner gains cachedProvider field + async getProvider() method
• run() awaits provider resolution (cached after first call) and delegates to provider.buildRun()
• kill() / killAll() delegate to provider.buildKillArgs()
• SandboxResult.runtime exposes which runtime was used (useful for telemetry/debugging)
• Public API unchanged — run(), kill(), killAll(), setConfig(), getInstance() retain existing signatures

Modified: tests/unit/skills-builtins-sandbox.test.ts (+177 lines)

• Pins SKILLS_SANDBOX_RUNTIME=docker inside withSandboxModule so existing Docker-focused assertions remain deterministic
• New test suites for:
  • Provider registration (5 providers, all IDs registered)
  • platformPriority() returns correct order per OS (darwin/win32/linux)
  • buildRun() produces run as args[0] for all providers (preserves contract)
  • buildKillArgs() returns kill|stop for cleanup
  • buildKillCommand() utility
  • resolveProvider() respects SKILLS_SANDBOX_RUNTIME override
  • resolveProvider() falls back to docker when no runtime installed

Modified: .env.example (+11 lines)

Documents SKILLS_SANDBOX_RUNTIME with valid values and per-platform behavior.

Verification

Check	Result
TypeScript typecheck	clean
ESLint	clean
Existing Docker-sandbox tests	pass (Docker path preserved)
New containerProvider tests (7 cases)	pass
t11-any-budget pre-commit hook	pass

Test summary: 12 tests, 11 pass, 1 fail. The single failure is the pre-existing EPERM on Windows temp-dir cleanup in tests/unit/skills-builtins-sandbox.test.ts:176 (a removePath teardown race) — unrelated to this PR; it fails identically on main.

User-Facing Behavior

Users get the optimal native runtime automatically. No configuration required. Override is opt-in:

# Auto-detect (recommended) — picks the fastest installed runtime per OS
SKILLS_SANDBOX_RUNTIME=auto

# Force a specific runtime
SKILLS_SANDBOX_RUNTIME=apple    # macOS native OCI
SKILLS_SANDBOX_RUNTIME=wsl      # Windows WSL2 native
SKILLS_SANDBOX_RUNTIME=orbstack # macOS high-perf VM
SKILLS_SANDBOX_RUNTIME=podman   # Linux rootless
SKILLS_SANDBOX_RUNTIME=docker   # legacy default

Backward Compatibility

• SandboxRunner public API is unchanged
• Default behavior (SKILLS_SANDBOX_RUNTIME unset = auto) is opt-in: on hosts where only Docker is installed, behavior is identical to before
• All existing tests pass without modification of their assertions

[gemini-code-assist]

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