handle-errors

Create one errors.New value per rejection reason in the domain document, named Err{what was rejected}, in an errors.go file in the aggregate package. Write the message in Japanese without periods, and add a trailing comment citing the document's wording.

Use fmt.Errorf with a single %w verb once per package boundary, in the form "<operation> <business ID>: %w". Never use %v, err.Error(), or errors.New(err.Error()), since those sever the chain and prevent errors.Is from reaching the sentinel.

Keep a single codeTable in handler/error_table.go that maps sentinels to codes via errors.Is, applied by the outermost Logging interceptor. Handler bodies return errors as-is and never call connect.NewError; unmapped errors become Internal with a fixed message.

In the repository layer, use errors.AsType[*pgconn.PgError] and match on named constraints, mapping exclusion violations to domain sentinels and unique violations to ErrConflict. Map pgx.ErrNoRows to ErrNotFound only for the aggregate's current row, not dependent rows.

Return (T, bool) when the document states the operation has no rejection reason and simply changes nothing, such as expiring a hold whose deadline has not arrived. Reserve (T, error) for operations that can actually be rejected or fail.

Sentinels carry only the rejection identity, not values like a suspension end time. When a caller needs such values, create one operation-specific typed error whose Is method answers the sentinel, and never build generic Reason/Kind error types.