feat: Schema Extension System for Modular ProjectBundle Extensions (arch-07)

[djm81]

Description

Schema extension system (arch-07) for modular ProjectBundle extensions: modules can extend Feature and ProjectBundle with namespaced custom fields without modifying core models. Adds extensions dict, get_extension/set_extension accessors, optional schema_extensions in module-package.yaml, and ExtensionRegistry with collision detection. Includes docs, quality gate fixes (format, type-check), and version 0.33.0.

Fixes #213

New Features #213

Contract References: @icontract and @beartype on Feature.get_extension/set_extension, ProjectBundle.get_extension/set_extension, SchemaExtension validation, ExtensionRegistry.register/get_extensions/list_all.

Type of Change

Please check all that apply:

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🔒 Contract enforcement (adding/updating @icontract decorators)
• 🧪 Test enhancement (scenario tests, property-based tests)
• 🔧 Refactoring (code improvement without functionality change)

Contract-First Testing Evidence

Required for all changes affecting CLI commands or public APIs:

Contract Validation

• Runtime contracts added/updated (@icontract decorators on public APIs)
• Type checking enforced (@beartype decorators applied)
• CrossHair exploration completed: hatch run contract-test-exploration
• Contract violations reviewed and addressed

Test Execution

• Contract validation: hatch run contract-test-contracts ✅
• Contract exploration: hatch run contract-test-exploration ✅
• Scenario tests: hatch run contract-test-scenarios ✅
• Full test suite: hatch run smart-test / hatch test --cover -v ✅

Test Quality

• CLI commands tested with typer test client
• Edge cases covered (namespace validation, collision, serialization)
• Error handling tested with invalid inputs
• Rich console output verified manually or with snapshots

How Has This Been Tested?

Contract-First Approach: New unit tests in tests/unit/models/test_schema_extensions.py, tests/unit/models/test_module_package_metadata.py, tests/unit/specfact_cli/registry/test_extension_registry.py; TDD evidence in openspec/changes/arch-07-schema-extension-system/TDD_EVIDENCE.md.

Manual Testing

• Tested CLI commands manually
• Verified rich console output
• Tested with different input scenarios
• Checked error messages for clarity

Automated Testing

• Contract validation passes
• Scenario tests cover extension field and registry behavior
• All existing tests still pass (merge with dev verified)

Test Environment

• Python version: 3.11
• OS: Linux

Checklist

• My code follows the style guidelines (PEP 8, ruff format, isort)
• I have performed a self-review of my code
• I have added/updated contracts (@icontract, @beartype)
• I have added/updated docstrings (Google style)
• I have made corresponding changes to documentation
• My changes generate no new errors (basedpyright 0 errors; existing warnings unchanged)
• All tests pass locally
• I have added tests that prove my fix/feature works
• Any dependent changes have been merged (merged origin/dev)

Quality Gates Status

• Type checking ✅ (hatch run type-check)
• Linting ✅ (hatch run lint)
• Contract validation ✅ (hatch run contract-test-contracts)
• Contract exploration ✅ (hatch run contract-test-exploration)
• Scenario tests ✅ (hatch run contract-test-scenarios)

Screenshots/Recordings (if applicable)

N/A — model and registry changes; no CLI UI change.

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OpenSpec Change: arch-07-schema-extension-system