Added Phase 4 (TDD) client integration verification tests for snapshots. ## Tests Added (5 total) All tests verify that clients work correctly with snapshots without any code changes: 1. **test_client_unaware_of_snapshot_source** - Verifies clients receive standard sync response format regardless of snapshot vs live query - Confirms data integrity when snapshot is used - File: tests/test_snapshot_e2e.py:1132-1167 2. **test_client_version_tracking_with_snapshot** - Tests client correctly tracks server version when bootstrapped from snapshot - Verifies incremental sync works after snapshot bootstrap - File: tests/test_snapshot_e2e.py:1169-1259 3. **test_client_incremental_sync_after_snapshot_bootstrap** - Tests client can perform incremental sync after bootstrapping from snapshot - Confirms only new changes are received in subsequent syncs - File: tests/test_snapshot_e2e.py:1261-1322 4. **test_snapshot_large_dataset** - Tests snapshot creation and usage with large dataset (100 issues, 50 milestones) - Verifies snapshot compression is working - File: tests/test_snapshot_e2e.py:1324-1381 5. **test_snapshot_during_concurrent_sync** - Tests snapshot creation doesn't interfere with concurrent client syncs - Verifies snapshot+delta merge works correctly - File: tests/test_snapshot_e2e.py:1383-1449 ## Test Results All 29 snapshot tests pass (24 existing + 5 new): - TestSnapshotCreation: 6 tests - TestSnapshotUsage: 7 tests - TestSnapshotEdgeCases: 11 tests - TestClientIntegration: 5 tests (NEW) Test coverage increased for server/routes/sync.py from 49% to 56%. ## Implementation Notes Tests verify that: - Clients receive identical response format from snapshot vs live query - Server version tracking works correctly across snapshot bootstrap - Incremental sync after snapshot bootstrap only returns new changes - Large datasets are handled efficiently with compression - Concurrent syncs work correctly with snapshot merging All tests use the existing snapshot infrastructure (TRCKR-177) without requiring client code changes.