Hide the sandbox implementation from the harness's public API

[Tyler-R-Kendrick]

What

The harness package exported MxcSandbox and MxcSandboxSettings, baking the @microsoft/mxc-sdk dependency name into consumer code — and the exported signatures leaked the SDK's SandboxPolicy and SandboxSpawnOptions types directly. The sandbox is ours; which SDK enforces it is an implementation detail.

Changes

• Rename MxcSandbox / MxcSandboxSettings → HarnessSandbox / HarnessSandboxSettings, matching the package's existing naming (defineTrainingHarness, WriteAheadAgentBus).
• Fold the policy knobs into the sandbox settings. readonlyPaths, allowedHosts, and timeoutMs now live on HarnessSandboxSettings; the sandbox builds its SDK policy internally. createHarnessPolicy, HarnessPolicySettings, and sandboxPolicyVersion leave the public surface, which also stops consumers from repeating the workspace path in two places.
• Delete assertHarnessPolicy. With policy injection gone, every policy is built by createSandboxPolicy and satisfies the harness invariants (workspace-confined writes, no local network, allowlist-only outbound, no UI/clipboard/input) by construction.
• Drop the unused spawn passthrough, the last SDK type in the settings; nothing used it.
• README updated: MXC is still credited (and its preview warning kept) as prose, just not in the API.

The public index.d.ts no longer references @microsoft/mxc-sdk anywhere — the only remaining import is in the internal, unexported policy module.

Verification

npm run typecheck passes and all 81 tests pass (npm test), including the sandbox gating and symlink-escape suites, updated to the new constructor shape.

🤖 Generated with Claude Code

https://claude.ai/code/session_01TUJ2eCbU3JKNV4yZvvMJoE

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Generated by Claude Code

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: fa75be6a-fa6f-4a3f-900e-9bb382201a54

📥 Commits

Reviewing files that changed from the base of the PR and between b751276 and 487e0f6.

📒 Files selected for processing (5)

• packages/harness/README.md
• packages/harness/src/index.ts
• packages/harness/src/policy.ts
• packages/harness/src/sandbox.ts
• packages/harness/test/harness.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/simplify-harness-exports-wcdg6p

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