Add auditing-agent-memory-with-as-of-system-time skill

[something1703]

Reconstructing exactly what an AI agent's memory contained at a past instant using AS OF SYSTEM TIME, for audit/deposition/compliance review: the historical-read pattern, the "silently reads current state instead of historical state" failure mode (and how to make it fail loudly instead), the garbage-collection window that bounds how far back a historical read can reach, extending gc.ttlseconds for retention obligations, and the access-control tension between historical reads and erasure requests.

Distilled from building a temporal-recall/deposition feature (explain(action_id) reconstructing exactly what an agent believed at decision time) on CockroachDB, generalized as a reusable skill.

What does this PR do?

Related Issue

Closes #

Type of Change

• New skill
• Skill update/improvement
• Documentation update
• Infrastructure/tooling change
• Bug fix

Skill Compliance Checklist

• SKILL.md includes required frontmatter fields (name, description)
• Skill name follows naming conventions (lowercase, hyphens, gerund form preferred)
• Skill name matches directory name exactly
• Description is specific and includes "when to use" trigger keywords
• Description is max 1024 characters
• Skill is under 500 lines (or uses references/ for detailed content)
• References official CockroachDB documentation (not duplicate content)
• Includes safety guardrails for risky operations (if applicable)
• Tested with at least one AI agent (manual validation)
• No time-sensitive information (version numbers, dates, "currently")
• Directory structure follows specification (only scripts/, references/, assets/ subdirs)
• No reserved words in skill name ("anthropic", "claude")
• Local validation passes: python scripts/validate-spec.py skills/

Documentation Updates

• README.md
• CONTRIBUTING.md
• Skill SKILL.md files
• Other (specify):

Testing

Manual testing:

• Tested with AI agent (specify which one):
• Verified skill is discoverable with appropriate prompts
• Validated technical accuracy against CockroachDB docs
• Tested any scripts or commands included in the skill

Automated testing:

• Local validation script passes: python scripts/validate-spec.py skills/
• CI validation will run automatically on this PR

Additional Context

Reviewer Notes

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By submitting this PR, I confirm:

• I have read the contributing guidelines
• I have followed the Agent Skills Specification
• I have tested my changes
• I am willing to address review feedback