feat(isc): use inline_whitespace between field name and value (no newlines)

The whitespace? rule was consuming newlines after a field name, which
broke empty fields (like 'description' followed by another field on
next line). Now using inline_whitespace? (spaces/tabs only) for the
gap between identifier and field_value, so the parser can detect
empty fields correctly.

Verification: 184/289 maps equivalent (64%).

Author: ronaldtse

lib/interscript/isc/grammar/concerns/metadata.rb

@@ -112,7 +112,7 @@ module Metadata
           # close brace). This makes the parser permissive about future
           # field additions; semantic validation happens in DocumentBuilder.
           rule(:generic_field) do
-            identifier.as(:field_name) >> whitespace? >>
+            identifier.as(:field_name) >> inline_whitespace? >>
               (empty_field | field_value.as(:field_value))
           end
 
@@ -122,10 +122,9 @@ module Metadata
           end
 
           rule(:empty_field) do
-            # An identifier with no value (just newline or `}` after). The
-            # separate rule prevents the generic_field's value rule from
-            # consuming into the next field.
-            (newline.present? | str("}").present?).as(:empty)
+            # An identifier with no value (just newline or `}` after). Use
+            # lookahead without consuming.
+            (newline.present? | str("}").present?)
           end
 
           # Raw text inside `{ ... }` — for description blocks. Consumes any

lib/interscript/isc/grammar/concerns/primitives.rb

@@ -29,6 +29,15 @@ module Primitives
           end
           rule(:whitespace?) { whitespace.maybe }
 
+          # Inline whitespace: spaces and tabs only, NO newlines. Used between
+          # a field name and its value to prevent eating the newline that
+          # signals an empty value.
+          rule(:inline_space) { match(/[ \t]/).repeat(1) }
+          rule(:inline_whitespace) do
+            (inline_space | line_comment).repeat(1)
+          end
+          rule(:inline_whitespace?) { inline_whitespace.maybe }
+
           # Comma, used in lists. Trailing whitespace allowed.
           rule(:comma)      { str(",") >> whitespace? }