Add comprehensive SQL schema analysis documentation

[Copilot]

Analyzed the CASKFS PostgreSQL schema architecture and documented findings for development reference.

Analysis Scope

Examined 4 schema files implementing a three-layer architecture:

• Layer 0: Configuration and automation rules (config.sql)
• Layer 1: Content-addressed storage with SHA256 deduplication (layer1-cas.sql)
• Layer 2: Hierarchical file system with RBAC (layer2-fs.sql)
• Layer 3: RDF/Linked Data graph storage (layer3-ld.sql)

Documentation Added

docs/sql-schema-analysis.md - 700+ line technical analysis covering:

• 23 tables with field-level documentation and usage patterns
• 11 views including materialized view performance characteristics
• 7 stored functions with PL/pgSQL logic explanations
• Entity relationships and data flow across layers
• Performance considerations (40+ indexes, query patterns)
• Security model (permission inheritance, ACL lookup strategy)
• Actionable recommendations: materialized view refresh automation, validation constraints, garbage collection, schema versioning

Key Findings

Strengths:

• Content deduplication via hash-based storage
• Comprehensive RBAC with directory-level inheritance
• Efficient RDF querying through normalized URI storage and dual indexing
• Multi-cloud storage support

Optimization Opportunities:

• Automatic refresh for directory_user_permissions_lookup materialized view
• Hash format validation (CHECK (value ~ '^[a-f0-9]{64}$'))
• Unused hash garbage collection strategy
• Table partitioning for scale (millions of files/triples)

Original prompt

analyze the SQL schema and report back to me your findings

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