Add designing-agent-memory-schemas skill (query-and-schema-design)

[Vector897]

What does this PR do?

Adds a new skill, designing-agent-memory-schemas, to the query-and-schema-design domain. It guides developers through designing CockroachDB schemas for AI agent memory: an episodic/semantic memory table with a VECTOR column, a prefix-filtered vector index for per-agent cosine ANN, a two-stage retrieval query shape, history-preserving reconciliation via a supersedes self-reference, set-based forgetting-curve decay, crash-safe checkpoint and audit companion tables, and optional row-level TTL.

Every SQL statement in the skill was executed and verified live against a CockroachDB Cloud Basic cluster (v26.x) while building an agent memory layer for the CockroachDB × AWS hackathon.

Related Issue

Closes #16

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 (507)
• Skill is under 500 lines (208)
• References official CockroachDB documentation (not duplicate content)
• Includes safety guardrails for risky operations (if applicable)
• Tested with at least one AI agent (manual validation — the schema patterns were driven end-to-end by an agent against a live Cloud Basic cluster)
• No time-sensitive information (version bounds live in the compatibility field, matching existing skills)
• Directory structure follows specification (single SKILL.md)
• No reserved words in skill name ("anthropic", "claude")
• Local validation passes: python scripts/validate-spec.py skills/

Note on validation: validate-spec.py emits one gerund-form warning for this name; the check's prefix whitelist doesn't include "designing", so already-merged skills like designing-application-transactions trigger the same warning. Happy to rename if maintainers prefer.

Documentation Updates

None required.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.