Give the leaf block an arg slot, and drop the branch the leaf collapse orphaned

corpus/round-trip/block-nodes/task-list.json

@@ -75,6 +75,12 @@
                 }
               ],
               "type": "taskItem"
+            },
+            {
+              "attrs": {
+                "state": "TODO"
+              },
+              "type": "taskItem"
             }
           ],
           "type": "taskList"

corpus/round-trip/block-nodes/task-list.md

@@ -14,5 +14,6 @@ Then sign off.
 :::taskItem TODO {localId=01a033bd-a22d-7fb5-be9d-89d1aa261112}
 Nested step
 :::
+::taskItem TODO
 ::::
 :::::

spec/flavour.md

@@ -86,7 +86,8 @@ fence or opaque carry is content. Canonical form uses minimal lengths.
 Directive fence lines follow code-fence indentation (up to three spaces relative to their
 container); trailing whitespace on a fence line is tolerated in input, never emitted.
 
-**Leaf block**: `::name {attrs}` — a block-position node with no body.
+**Leaf block**: `::name arg {attrs}` — a block-position node with no body, `arg` reading as
+above.
 
 **Claiming at block level**, symmetric with inline: a line whose leading run of two or more
 colons is followed immediately by a name character is claimed and must parse fully as a container

src/adf-to-markdown.ts

@@ -132,7 +132,6 @@ function emitDirectiveBlock(node: AdfNode, directive: BlockDirective, path: Conv
 }
 
 function emitInlineBody(content: readonly AdfNode[], path: ConvertErrorPath): Result<EmittedBody> {
-  if (content.length === 0) return success({ fenceColons: 0, text: '' })
   const line = emitInlineLine(content, 'paragraph', path)
   if (!line.ok) return line
   return success({ fenceColons: 0, text: line.value })