feat(isc): fix comment parsing, description multiline value, empty fields

- Main loop: scan # comments without consuming newline (was eating 2 lines)
- Codemod: handle 'description:' with multi-line quoted value on next line
- Tests converter: preserve # comments verbatim
- Empty fields (just identifier) accepted via lookahead

Verification: 177/289 maps equivalent (61%).

Author: ronaldtse

exe/codemod-imp-to-isc

@@ -102,7 +102,8 @@ module Interscript
         until @scanner.eos?
           if @scanner.scan(/\s+/m)
             @out << @scanner.matched
-          elsif @scanner.scan(/#\s.*?$/)
+          elsif @scanner.scan(/#[^\n]*/)
+            # Line comment (without consuming newline)
             @out << @scanner.matched
           elsif @scanner.scan(/metadata\b/)
             @out << "metadata"
@@ -204,12 +205,32 @@ module Interscript
           elsif @scanner.scan(/\}/)
             depth -= 1
             @out << "}"
-          elsif @scanner.scan(/(?:\A|\n)([ \t]+)description[ \t]*:[ \t]*\|/)
+          elsif @scanner.scan(/(?:\A|\n)([ \t]+)description[ \t]*:[ \t]*\|[ \t]*\n/)
             # Heredoc form: `description: |` followed by indented body.
             indent = @scanner[1]
             @out << "\n#{indent}description {"
             convert_indented_block_until_dedent(indent)
             @out << "\n#{indent}}"
+          elsif @scanner.scan(/(?:\A|\n)([ \t]+)description[ \t]*:[ \t]*\n[ \t]+/)
+            # `description:` with value on subsequent indented line(s).
+            # Capture as brace block with raw text.
+            indent = @scanner[1]
+            @out << "\n#{indent}description { "
+            # Read until dedent or close brace
+            until @scanner.eos?
+              if @scanner.check(/\n[ \t]{0,#{indent.length}}\S/) || @scanner.check(/\n[ \t]{0,#{indent.length}}\}/)
+                @out << " }"
+                break
+              elsif @scanner.scan(/[^\n]+/)
+                @out << @scanner.matched
+              elsif @scanner.scan(/\n[ \t]+/)
+                @out << " "
+              elsif @scanner.scan(/\n/)
+                @out << " "
+              else
+                break
+              end
+            end
           elsif @scanner.scan(/(?:\A|\n)([ \t]+)notes[ \t]*:[ \t]*\|[ \t]*\n/)
             # Heredoc-form notes: `notes: |` followed by indented body that's
             # one big multi-line note.