Error handling added to MVP according to error_handling.md guideline

tests/test_errors.py

@@ -0,0 +1,43 @@
+"""Tests for shared error taxonomy and helpers."""
+
+import pytest
+
+from transcription.errors import AppError, ErrorCategory, classify_unexpected_error, new_error_id
+
+
+@pytest.mark.unit
+class TestErrorCategoryContract:
+    """Verify stable category identifiers."""
+
+    def test_category_values_match_policy_contract(self):
+        """Error category values match docs/error_handling.md identifiers."""
+        assert ErrorCategory.VALIDATION.value == "validation_error"
+        assert ErrorCategory.USER_INPUT.value == "user_input_error"
+        assert ErrorCategory.NOT_FOUND.value == "not_found_error"
+        assert ErrorCategory.CONFLICT.value == "conflict_error"
+        assert ErrorCategory.EXTERNAL_PROVIDER.value == "external_provider_error"
+        assert ErrorCategory.INFRA_TRANSIENT.value == "infrastructure_transient_error"
+        assert ErrorCategory.INFRA_PERSISTENT.value == "infrastructure_persistent_error"
+        assert ErrorCategory.INTERNAL_UNEXPECTED.value == "internal_unexpected_error"
+
+
+@pytest.mark.unit
+class TestAppErrorHelpers:
+    """Verify helper behavior for IDs and normalization."""
+
+    def test_new_error_id_returns_short_identifier(self):
+        """new_error_id returns a short non-empty identifier."""
+        value = new_error_id()
+        assert isinstance(value, str)
+        assert len(value) == 8
+
+    def test_classify_unexpected_error_returns_internal_unexpected(self):
+        """Unexpected exceptions are normalized to internal_unexpected_error."""
+        err = classify_unexpected_error(RuntimeError("boom"), operation="unit.test")
+
+        assert isinstance(err, AppError)
+        assert err.category == ErrorCategory.INTERNAL_UNEXPECTED
+        assert "unit.test" in err.message
+        assert "boom" in err.message
+        assert err.suggestion
+        assert err.error_id