Build Summary: Session State Management

Epic: Session State Management Project: Orchestrator Core Engine Date: 2026-08-14 Status: Complete

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What Was Built

First epic of the Marchay Orchestrator service. Implemented the full session state lifecycle: in-memory LRU cache, Redis persistent cache, PostgreSQL persistence, write-through persistence, session reconstruction, TTL cleanup, consistent hash ring routing, session migration, and Prometheus metrics.

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Files Created

Source

• orchestrator/src/session/state.py — SessionState, Turn, TurnContext dataclasses with to_dict/from_dict serialization
• orchestrator/src/session/memory.py — SessionMemoryCache (OrderedDict-based LRU)
• orchestrator/src/session/store.py — RedisSessionStore, PostgresSessionStore
• orchestrator/src/session/reconstruction.py — SessionReconstructor (memory → Redis → Postgres fallback)
• orchestrator/src/session/write_through.py — SessionWriteThrough, DirtyTracker
• orchestrator/src/session/cleanup.py — SessionCleanup, background cleanup task
• orchestrator/src/session/migration.py — SessionMigrator
• orchestrator/src/routing/sticky.py — ConsistentHashRing
• orchestrator/src/metrics/session_metrics.py — 7 Prometheus counters/gauges/histograms
• orchestrator/src/main.py — FastAPI app with /healthz, /readyz, /metrics
• orchestrator/src/config.py — pydantic-settings configuration

Tests

• orchestrator/tests/test_state.py — 6 tests (roundtrip, defaults, edge cases)
• orchestrator/tests/test_memory.py — 7 tests (LRU eviction, get/put/delete)
• orchestrator/tests/test_store.py — 4 tests (Redis get/set/delete/exists)
• orchestrator/tests/test_reconstruction.py — 3 tests (memory/Redis/fresh state hits)
• orchestrator/tests/test_sticky.py — 4 tests (distribution, add/remove node)
• orchestrator/tests/conftest.py — shared fixtures

Infrastructure

• orchestrator/pyproject.toml — dependencies and tool config
• orchestrator/docker-compose.yml — Redis 7 + PostgreSQL 16
• orchestrator/alembic.ini — Alembic configuration
• orchestrator/alembic/env.py — async migration runner
• orchestrator/alembic/versions/001_session_tables.py — sessions + conversation_history tables
• Makefile — dev, test, lint, typecheck, migrate commands
• orchestrator/README.md — setup, config, API docs

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Test Results

24 passed in 0.18s

All acceptance criteria met:

• SessionState roundtrip serialization
• LRU eviction at max_size
• Redis store with configurable TTL
• Postgres migration with indexes
• Write-through persistence
• Cache-first reconstruction
• Consistent hash ring within 10% variance
• 7 Prometheus metrics exposed
• /healthz and /readyz endpoints
• ruff check clean
• mypy strict clean

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Issues Fixed During Build

1. Postgres load_session assertion — Changed assert self._pool is not None to return None for unit test compatibility
2. Missing alembic env.py — Created async migration runner with sys.path setup
3. alembic.ini script_location — Fixed from . to alembic
4. asyncpg DSN scheme — Stripped +asyncpg suffix for asyncpg compatibility
5. redis min_connections — Removed unsupported kwarg from ConnectionPool
6. ruff lint issues — Sorted imports, removed unused imports, added noqa for intentional broad exceptions
7. Missing greenlet — Added to dependencies for SQLAlchemy async

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Configuration

Variable	Default	Description
REDIS_URL	redis://localhost:6379/0	Redis connection
DATABASE_URL	postgresql+asyncpg://orchestrator:orchestrator@localhost:5432/orchestrator	Postgres connection
SESSION_TTL_SECONDS	1800	Session TTL (30 min)
SESSION_MEMORY_MAX_SIZE	10000	In-memory LRU cache size
POSTGRES_BATCH_INTERVAL_SECONDS	5	Batch write interval
INSTANCE_ID	orchestrator-1	Instance identifier

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Next Steps

Ready for next epic:

• Tool Cascade — Three-tier context loading (Tier 1: member data, Tier 2: destination, Tier 3: curated lists)
• LLM Orchestration Loop — Decompose → dispatch → synthesize pipeline