feat(render): list_ignore_newline / text_ignore_newline = false → <br>

Implements the deferred half of these options: a soft line break inside a
paragraph / list item can render as <br /> instead of a space.

- Parser: soft breaks now emit a dedicated InlineNode::SoftBreak node
  (parse_inline_seq K::Newline + the list-continuation synthetic join) instead
  of collapsing to Text(" "). Added SoftBreakNode + the variant.
- All inline consumers treat SoftBreak as whitespace: AST visitor (no-op),
  text extraction (index.rs + lib.rs → space), nav/semantic_tokens span_of_inline,
  semantic emit (skip like Text), parser span_of_inline.
- Renderer: render_inlines_break renders top-level SoftBreaks as the
  context-specific string; render_paragraph uses text_ignore_newline,
  render_list_item uses list_ignore_newline; default render_inline → space.
  with_newline_handling builder; export.rs wires both from HtmlConfig.

Default (true/true = upstream default) behaviour is unchanged (space). Updated
3 core tests + 1 parser test that asserted the old Text(" ") shape to treat
SoftBreak as whitespace. New test render_page_html_ignore_newline_controls_soft_breaks.

Gap doc: P3 Config item closed — only the deferred markdown cluster remains.
Full rust suite + clippy clean; Neovim 307, Vim 301/18/21.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/nuwiki-core/src/render/html.rs

@@ -61,6 +61,12 @@ pub struct HtmlRenderer {
     /// vimwiki `emoji_enable` (default `false` in the renderer; set from
     /// config): substitute `:alias:` shortcodes with their emoji glyph.
     emoji_enable: bool,
+    /// vimwiki `text_ignore_newline` (default `true`): a soft break in a
+    /// paragraph renders as a space; `false` → `<br />`.
+    text_ignore_newline: bool,
+    /// vimwiki `list_ignore_newline` (default `true`): a soft break in a list
+    /// item renders as a space; `false` → `<br />`.
+    list_ignore_newline: bool,
 }
 
 impl Default for HtmlRenderer {
@@ -80,9 +86,20 @@ impl HtmlRenderer {
             header_numbering_sym: String::new(),
             valid_html_tags: Vec::new(),
             emoji_enable: false,
+            text_ignore_newline: true,
+            list_ignore_newline: true,
         }
     }
 
+    /// Set vimwiki `text_ignore_newline` / `list_ignore_newline`. When `false`,
+    /// a soft line break in a paragraph / list item renders as `<br />`
+    /// instead of a space.
+    pub fn with_newline_handling(mut self, text_ignore: bool, list_ignore: bool) -> Self {
+        self.text_ignore_newline = text_ignore;
+        self.list_ignore_newline = list_ignore;
+        self
+    }
+
     /// Set the inline HTML tags allowed through export unescaped (vimwiki
     /// `valid_html_tags`). `span` is always added so colour spans render.
     pub fn with_valid_html_tags(mut self, mut tags: Vec<String>) -> Self {
@@ -294,7 +311,8 @@ impl HtmlRenderer {
 
     fn render_paragraph(&self, n: &ParagraphNode, w: &mut dyn Write) -> io::Result<()> {
         w.write_all(b"<p>")?;
-        self.render_inlines(&n.children, w)?;
+        let sb = if self.text_ignore_newline { " " } else { "<br />" };
+        self.render_inlines_break(&n.children, sb, w)?;
         w.write_all(b"</p>\n")
     }
 
@@ -371,7 +389,8 @@ impl HtmlRenderer {
             }
             None => w.write_all(b"<li>")?,
         }
-        self.render_inlines(&n.children, w)?;
+        let sb = if self.list_ignore_newline { " " } else { "<br />" };
+        self.render_inlines_break(&n.children, sb, w)?;
         if let Some(sublist) = &n.sublist {
             w.write_all(b"\n")?;
             self.render_list(sublist, w)?;
@@ -526,6 +545,24 @@ impl HtmlRenderer {
         Ok(())
     }
 
+    /// Like [`render_inlines`] but renders top-level soft breaks as `soft_break`
+    /// (a space or `<br />`). Used by paragraphs / list items, which are the
+    /// only blocks that contain `SoftBreak` nodes.
+    fn render_inlines_break(
+        &self,
+        nodes: &[InlineNode],
+        soft_break: &str,
+        w: &mut dyn Write,
+    ) -> io::Result<()> {
+        for n in nodes {
+            match n {
+                InlineNode::SoftBreak(_) => w.write_all(soft_break.as_bytes())?,
+                _ => self.render_inline(n, w)?,
+            }
+        }
+        Ok(())
+    }
+
     fn render_inline(&self, n: &InlineNode, w: &mut dyn Write) -> io::Result<()> {
         match n {
             InlineNode::Text(t) => self.render_text(t, w),
@@ -543,6 +580,9 @@ impl HtmlRenderer {
             InlineNode::ExternalLink(t) => self.render_external_link(t, w),
             InlineNode::Transclusion(t) => self.render_transclusion(t, w),
             InlineNode::RawUrl(t) => self.render_raw_url(t, w),
+            // Default rendering (e.g. inside a heading): a space. Paragraphs
+            // and list items use render_inlines_break for `<br />` support.
+            InlineNode::SoftBreak(_) => w.write_all(b" "),
         }
     }