[Repo Assist] fix: handle EmbedParagraphs in Markdown.ToMd serialiser (#1145)

* fix: handle EmbedParagraphs in Markdown.ToMd serialiser

Previously EmbedParagraphs fell through to the catch-all '| _' branch in
MarkdownUtils.formatParagraph, emitting a debug printfn to stdout and
yielding an empty string.  All other formatters (HTML, LaTeX) delegate
to cmd.Render() and recurse; this commit brings the Markdown-to-Markdown
back-end into line with them.

The now-dead catch-all branch is removed so the exhaustiveness checker
will catch any new MarkdownParagraph cases that are added without a
corresponding formatParagraph clause.

Fixes: the debug 'can't yet format' output that appeared on stdout
whenever a document containing EmbedParagraphs was serialised via
Markdown.ToMd.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* ci: trigger checks

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Don Syme <dsyme@users.noreply.github.com>

Author: 3 people

RELEASE_NOTES.md

@@ -3,6 +3,7 @@
 ## [Unreleased]
 
 ### Fixed
+* Fix `Markdown.ToMd` silently dropping `EmbedParagraphs` nodes: the serialiser now delegates to the node's `Render()` method and formats the resulting paragraphs, consistent with the HTML and LaTeX back-ends.
 * Fix `Markdown.ToMd` dropping link titles in `DirectLink` and `DirectImage` spans. Links with a title attribute (e.g. `[text](url "title")`) now round-trip correctly; without this fix the title was silently discarded on serialisation.
 * Fix `Markdown.ToMd` serialising inline code spans that contain backtick characters. Previously, `InlineCode` was always wrapped in single backticks, producing syntactically incorrect Markdown when the code body contained backticks. Now the serialiser selects the shortest backtick fence that does not collide with the body content (e.g. a double-backtick fence for bodies containing single backticks, triple for double, etc.), matching the CommonMark spec.
 

src/FSharp.Formatting.Markdown/MarkdownUtils.fs

@@ -280,9 +280,7 @@ module internal MarkdownUtils =
                       yield "> " + line
 
                   yield ""
-          | _ ->
-              printfn "// can't yet format %0A to markdown" paragraph
-              yield "" ]
+          | EmbedParagraphs(cmd, _) -> yield! cmd.Render() |> Seq.collect (formatParagraph ctx) ]
 
     /// Strips <c>#if SYMBOL</c> / <c>#endif // SYMBOL</c> conditional compilation lines from an .fsx code block
     /// so that format-specific sections are removed from non-target output formats.

tests/FSharp.Markdown.Tests/Markdown.fs

@@ -1417,3 +1417,17 @@ let ``ToMd round-trip: indirect image with unresolved reference`` () =
     let result = Markdown.ToMd(doc)
     // When key is not resolved, should preserve the indirect form
     result |> should contain "![alt text][unknown-ref]"
+
+[<Test>]
+let ``ToMd serialises EmbedParagraphs by delegating to Render()`` () =
+    // EmbedParagraphs was previously falling through to the catch-all '| _' branch,
+    // emitting a debug printfn and yielding an empty string.  It should instead
+    // delegate to the Render() method and format the resulting paragraphs.
+    let inner =
+        { new MarkdownEmbedParagraphs with
+            member _.Render() =
+                [ Paragraph([ Literal("embedded text", MarkdownRange.zero) ], MarkdownRange.zero) ] }
+
+    let doc = MarkdownDocument([ EmbedParagraphs(inner, MarkdownRange.zero) ], dict [])
+    let result = Markdown.ToMd(doc)
+    result |> should contain "embedded text"