fix: prevent duplicate post-compaction packing

[davidrobertson]

Summary

• Call lcm_pack_context once after compaction and consume structuredContent.markdown from that same result.
• Keep recovery pending for failed, malformed, inherited, or unrelated tool results.
• Make sanitized JSON keys inert and keep the recovery path platform-neutral.
• Align the hook, MCP instructions, recall skill, and README.

Validation

• Real Codex CLI 0.146.0 manual compaction: 1 PostCompact, 1 pack start, 1 pack completion, then normal continuation.
• Clean install and TypeScript check passed.
• 225 tests passed.
• Smoke test and package dry-run passed.
• Five exact-commit review lanes passed with no findings.