[FEAT] agentic-core conversation and responses database CRUD.

[maralbahari]

Summary

This will be part of agentic-core after #29 merged will open for review

Integrated complete SQLx-based storage layer for persistent conversation and response management. Implements trait-based CRUD operations with connection pooling supporting SQLite, PostgreSQL, and MySQL. Two main stores (ConversationStore and ResponseStore) handle persisting input/output items with metadata and rehydrating full conversation/response history from database.

Features:

• Database connection pooling with optional URL configuration (defaults to SQLite)
• ConversationStore: persist turns with items and responses, rehydrate full conversation history
• ResponseStore: persist responses with items and metadata, rehydrate by response ID
• Schema migrations and initialization via SchemaManager
• Type-safe database models with sqlx FromRow derive

Test Plan

Unit tests (39 passing):

• Model CRUD operations, schema initialization, type conversions, error handling
• IO conversion from data types resulted from database models to Rust data types.

Integration tests (18 passing):

• Store-level CRUD, error handling for disabled/missing resources
• Multi-turn conversations with response chaining
• Concurrent operations, foreign key constraints, edge cases

Benchmarks:

• conversation_persist: measure insertion of items and response records
• response_persist: measure response creation with item tracking
• conversation_rehydrate: measure full conversation retrieval from database
• response_rehydrate: measure response history lookup by ID

All tests pass. No clippy warnings.

Running Benchmarks

To run the storage CRUD benchmarks:

cargo bench -p agentic-core --bench storage_crud 

Or run with specific sample count and target time:

cargo bench -p agentic-core --bench storage_crud -- --sample-size 100 --warm-up-time 3.000 s

Benchmark Results

Benchmarking conversation_persist
conversation_persist    time:   [1.4119 ms 1.4390 ms 1.4663 ms]

Benchmarking response_persist
response_persist        time:   [893.67 µs 908.53 µs 923.55 µs]

Benchmarking conversation_rehydrate
conversation_rehydrate  time:   [1.4377 ms 1.4701 ms 1.5037 ms]

Benchmarking response_rehydrate
response_rehydrate      time:   [1.0061 ms 1.0270 ms 1.0488 ms]

Performance Notes

Response persist is ~1.5x faster than conversation persist because:

• ResponseStore.persist() stores history_item_ids directly in the responses table (single lookup)
• ConversationStore.persist() must query the items table to determine the next sequence number for conversation items (additional query)