[vistart]

Description

This PR aligns python-activerecord-testsuite with the new semantic error taxonomy and execute-phase contract:

• Adds feature/backend/errors/test_error_taxonomy.py: hierarchy, retry hints, diagnostics, and bulk dual-inheritance checks.
• Runs without a database, so every backend can execute it as an installed contract.

Adds # (no issue)

Type of change

• feat: A new feature
• test: Adding missing tests or correcting existing tests (for the new feature)
• docs: Documentation only changes (if related to the new feature)
• perf: A code change that improves performance (if part of the feature)
• chore: Changes to the build process or auxiliary tools and libraries suchs as documentation generation (if related to the new feature)
• ci: Changes to our CI configuration files and scripts (if related to the new feature)
• build: Changes that affect the build system or external dependencies (if related to the new feature)
• revert: Reverts a previous commit

Breaking Change

• Yes, for end-users (backward-incompatible API changes)
• Yes, for backend developers (internal architectural changes that may affect custom implementations)
• No breaking changes

Impact on End-Users:
No backward-incompatible changes: concrete error classes keep their names, and every error remains a DatabaseError. Behavioural change: auto-commit failures now raise TransactionError instead of being logged and ignored, and transient connection retries now actually run.

Impact on Backend Developers (Custom Implementations):
No signature changes. Custom _handle_error implementations should raise taxonomy errors; the core pipeline adds a defensive fallback when a handler returns.

Related Repositories/Packages

• python-activerecord PR #139 (feature/error-taxonomy).
• Nine backend PRs pin this branch until the release merge.
• CI pins in this repository currently point at feature/error-taxonomy for both core and testsuite, and will be restored to release branches after the merge.

Testing

• I have added new tests to cover my changes.
• I have updated existing tests to reflect my changes.
• All existing tests pass.
• This change has been tested against the backend matrix via CI.

Test Plan:

Local: 11 passed. No CI pipeline exists for this repository.

Reproduction:

PYTHONPATH=src:tests pytest tests -k 'test_execute_error_contract or test_driver_error_mapping or test_error_taxonomy_contract'

Checklist

• My code follows the project's code style guidelines.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation (Docstrings, README.md, etc.).
• My changes generate no new warnings.
• I have added a Changelog fragment (changelog.d/<issue_number>.<type>.md).
• I have verified that my changes do not introduce SQL injection vulnerabilities.
• I have checked for potential performance regressions.

Additional Notes

• The changelog fragment is added as changelog.d/<PR>.added.md once the PR number exists, because the checker requires the fragment number to equal the PR number.
• CI intentionally installs core and testsuite from feature/error-taxonomy; restore release pins after this PR and the core PR merge.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud