Improve backend test coverage and add coverage tooling

[patchmemory]

Summary

• Added coverage>=7.4 to dev dependencies for local coverage testing
• Added 18 new backend tests targeting low-coverage modules
• Improved overall backend coverage from 67% to 68%
• Added comprehensive coverage documentation to dev/prompts.md

Coverage Improvements

Module	Before	After	Change	Impact
api_interpreters.py	29%	60%	+31% ✅	Toggle/debug endpoints now tested
api_providers.py	20%	33%	+13% ✅	Provider roots & rclone validation tested
api_chat.py	34%	37%	+3%	GraphRAG endpoints & observability tested
registry.py	88%	94%	+6%	Improved via interpreter tests
Overall	67%	68%	+1%	197 tests passing (up from 179)

New Tests Added

test_chat_api.py (+7 tests)

• test_api_chat_missing_message - Validates error handling
• test_api_chat_history - Tests chat history endpoint
• test_api_chat_capabilities - Tests capabilities endpoint
• test_api_chat_graphrag_disabled_by_default - Tests GraphRAG disabled state
• test_api_chat_graphrag_missing_message - Tests GraphRAG error handling
• test_api_chat_context_refresh_disabled - Tests context refresh disabled
• test_api_chat_observability_graphrag - Tests observability endpoint

test_interpreters_registry_api.py (+4 tests)

• test_api_interpreters_effective_debug - Tests debug endpoint
• test_api_interpreters_toggle_enable - Tests enabling interpreters
• test_api_interpreters_toggle_disable - Tests disabling interpreters
• test_api_interpreters_toggle_default_enabled - Tests default toggle behavior

test_providers_api.py (+6 tests)

• test_provider_roots_default - Tests default provider roots
• test_provider_roots_specific_provider - Tests specific provider query
• test_provider_roots_invalid_provider - Tests error handling
• test_rclone_mounts_list - Tests mount listing
• test_rclone_mounts_create_missing_rclone - Tests rclone validation
• test_rclone_mounts_create_missing_remote - Tests remote validation
• test_rclone_mounts_create_missing_name - Tests name validation

Coverage Tooling

Added to dependencies:

• coverage>=7.4 in pyproject.toml and requirements.txt

Local usage:

# Install dependencies
pip install -r requirements.txt

# Run tests with coverage
python -m coverage run -m pytest tests/

# View terminal report
python -m coverage report

# Generate interactive HTML report
python -m coverage html
# Then open: htmlcov/index.html

Documentation:

• Added comprehensive "Backend (pytest) Coverage" section to dev/prompts.md
• Documents standard commands, usage patterns, and coverage targets
• Explains how to read HTML reports (green/red line highlighting)
• Sets target coverage levels: 90%+ for critical, 70%+ for core, 60%+ for API routes

Remaining Low Coverage Areas

Future work to reach 70%+ overall:

• api_files.py (37%) - Complex file operations
• link_service.py (40%) - Preview/execute workflows
• api_graph.py (42%) - Graph query endpoints
• label_service.py (50%) - Label CRUD operations

Test plan

• All 197 tests passing locally
• Coverage improved in targeted modules
• Documentation added to dev/prompts.md
• Dev submodule updated and pushed
• Dependencies added to pyproject.toml and requirements.txt

🤖 Generated with Claude Code