fix: Model.from_storage should handle missing optional fields

[nycomp]

Summary

Fixes #418 - The Model.from_storage() method was raising KeyError when loading storage records that were missing optional fields (fields with default values).

Problem

When campus OAuth tokens (which don't have refresh_token) were stored in MongoDB and then retrieved, the OAuthToken.from_storage() method would raise KeyError: 'refresh_token' because:

1. MongoDB stores sparse documents (missing keys for null/undefined values)
2. Model.from_storage() used direct dictionary access record[field.name]
3. Even though refresh_token: str | None = None has a default, the code didn't use it

Solution

Modified Model.from_storage() to handle missing fields gracefully:

• Returns value from record if key exists
• Falls back to field.default for fields with default values
• Falls back to field.default_factory() for fields with factory defaults
• Raises helpful KeyError only for truly required fields (no defaults)

Tests

Added tests/unit/model/test_base.py with comprehensive coverage:

• from_storage with all fields present
• from_storage with missing optional field (uses None)
• from_storage with missing default field (uses default value)
• from_storage with missing default_factory field (calls factory)
• from_storage with missing required field (raises KeyError with helpful message)
• Roundtrip serialization tests
• Sparse record handling (simulates MongoDB documents)

Test Results

All tests pass:

• sanity checks: PASS
• type checks: PASS
• unit tests: PASS (141 tests)
• integration tests: PASS (30 tests)

🤖 Generated with Claude Code