[drew]

Summary

Add suspend/resume to the V8 isolation-backend example and demonstrate retained JavaScript state through the OpenShell CLI. This PR is stacked on #4765; its diff contains only the example implementation and documentation.

Related Issue

Closes #4857

Depends on #4765 (shared sandbox lifecycle APIs, gateway, supervisor, and SDK support).

The author has verified repository ADMIN access; the linked issue does not yet have an acceptance label.

Changes

• Retain the running V8 isolate in backend memory during suspension and continue it under a fresh supervisor generation on resume.
• Keep restore-reference handoff private to the example driver and backend.
• Preserve retained state after failed restores and readiness timeouts, and clean up failed supervisor launches.
• Demonstrate a counter continuing through suspension in guest.js; document basic CLI commands in the example README.
• Add focused tests for freezing, retained-state ownership, retry, and supervisor timeout cleanup.

Testing

• Parent branch's existing V8 example builds with only unsupported-operation compatibility stubs.
• Seven V8 example tests pass on the combined stack.
• Fifteen gateway suspend/resume tests pass with the parent review fixes.
• Repository commit checks pass, including workspace/example Clippy, formatting, protobuf lint, and Markdown lint.
• Extraction preserves the previously tested example files byte for byte. The preceding CLI E2E held suspension for 14 seconds, resumed counts 1 through 12 without replaying initialization, and completed with exit code 0.

Limitations

State lives in backend process memory. Restarting the backend loses the retained isolate; use an explicit sandbox start for a clean boot. The example does not provide durable heap snapshots.

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Relevant example implementation documentation updated