Improve type safety and fallback logic in isDutyLeaveConstraintError

[Copilot]

Addresses review feedback on duty-leave constraint error detection: parameter type collapsed to any, and nested details check prevented message fallback.

Type Safety

• Parameter changed from DatabaseError | any | null | undefined to unknown
• Added runtime type narrowing with typeof checks and explicit casting

Nested Error Detection

• details property now validated as object before accessing nested fields
• Removed early return to allow message fallback when details is non-object (e.g., string)

Before:

if (error.details) {
  return (
    error.details.code === "P0001" &&
    error.details.hint === "..."
  );
}
// Message fallback unreachable if details is truthy

After:

if (errorObj.details && typeof errorObj.details === "object") {
  const details = errorObj.details as Record<string, unknown>;
  const isNestedMatch = details.code === "P0001" && details.hint === "...";
  if (isNestedMatch) {
    return true;
  }
}
// Message fallback can now execute

Test Coverage

• Added test for details as non-object value to prevent regression

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[Copilot]

Pull request overview

This PR refines isDutyLeaveConstraintError to be safer under strict TypeScript settings while improving its fallback behavior when details exists but isn’t a nested object.

Changes:

• Changed the function parameter type to unknown and added runtime narrowing before property access.
• Updated nested details handling to only inspect details.code/details.hint when details is an object, avoiding blocking message-based fallback.
• Added a regression test covering details as a non-object value.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/lib/error-handling.ts	Tightens input typing to unknown, adds runtime guards, and fixes fallback flow when details is truthy but not an object.
src/lib/tests/duty-leave-error-handling.test.ts	Adds test coverage for details being a non-object while still allowing message fallback detection.

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