Export to Markdown or text, and import text as nodes (stage 9c)

:export md writes the document as Markdown headings in the clipboard's
format (the user's pick): # for the root and each loose node, ## for
their children, down to ######, the tags between --- lines, then the
body. :export txt writes an indented outline, tags after each title and
the body under it after "| " (the user's pick), from the new
storage::plain_text. The file goes next to the document, named after it,
or where it's told; as vim's :w to another file does, an existing file
needs :export! (the user's pick). Typed in visual mode, :export writes
just the selection, named after its first branch (the user's pick).

:import file reads Markdown headings, a list or indented lines with the
clipboard's reader, now also taking #tags at the end of a line and "| "
body lines, so a text export reads back whole. The nodes go under the
cursor's node, laid out as a mind map, as one undo step (the user's
pick).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/command/parse.rs

@@ -109,7 +109,10 @@ pub enum Call {
     Export {
         format: ExportFormat,
         path: Option<String>,
+        /// `:export!`: write over a file that's there.
+        force: bool,
     },
+    Import(String),
 }
 
 /// What the command line can name, from the app: names are checked against
@@ -265,7 +268,10 @@ fn build(spec: &Spec, bang: bool, args: &[Option<&str>], sources: &Sources) -> R
         Id::Help => Call::Help(first.map(str::to_string)),
         Id::Version => Call::Version,
         Id::Theme => Call::Theme(exactly("theme", text, &sources.themes)?.to_string()),
-        Id::Export => Call::Export { format: export_format(text)?, path: second.map(str::to_string) },
+        Id::Export => {
+            Call::Export { format: export_format(text)?, path: second.map(str::to_string), force: bang }
+        }
+        Id::Import => Call::Import(text.to_string()),
     })
 }
 
@@ -471,7 +477,7 @@ mod tests {
         assert_eq!(call("color none"), Ok(Call::Color(None)));
         assert_eq!(
             call("export md out.md"),
-            Ok(Call::Export { format: ExportFormat::Markdown, path: Some("out.md".into()) })
+            Ok(Call::Export { format: ExportFormat::Markdown, path: Some("out.md".into()), force: false })
         );
     }
 
@@ -543,6 +549,7 @@ mod tests {
             ("set", "mouse"),
             ("theme", "light"),
             ("export", "md"),
+            ("import", "plants.md"),
         ];
         for spec in registry::SPECS {
             let argument =