feat: Implement Phase 3.4 - Subscription System (CFOS-27)

[jayscambler]

Summary

• Implement polling-based subscription system for monitoring dataset changes
• Add 4 new subscription tools to the MCP server
• Enable clients to watch for changes without constant polling

Implementation Details

New Components:

• SubscriptionManager: Core class for tracking dataset changes using Lance versioning
• 4 subscription tools: subscribe_changes, poll_changes, unsubscribe, get_subscriptions
• Comprehensive test suite with 11 tests (all passing)

Key Features:

• Version-based change detection: Efficiently compares Lance dataset versions
• Long polling support: Clients can wait up to 300s for changes
• Resource filtering: Monitor documents, collections, or all resources
• Transport-agnostic: Works with stdio, ready for HTTP/SSE

Architecture:

contextframe/mcp/subscriptions/
├── __init__.py
├── manager.py          # SubscriptionManager with change detection
└── tools.py           # 4 subscription tools

Test Plan

• Run subscription tests: uv run pytest contextframe/tests/test_mcp/test_subscription_tools.py -v
• Verify all 11 tests pass
• Check test coverage (100% for subscription tools)
• Manual testing with MCP client
• Performance testing with large datasets

Progress Update

Phase 3.4 Complete!

• Total tools implemented: 35/43
• Next: Phase 3.5 (HTTP Transport) or Phase 3.6 (Analytics & Performance)

Related to #27

[linear]

CFOS-27 MCP Server Components