feat: map user-facing file extensions to pandoc format names in export URIs

Users hitting /api/v1/export/threads/{id}.md got 'Unsupported format: md'
because pandoc's internal name is 'markdown'. Add EXTENSION_ALIASES +
resolve_format() so common extensions map to the right pandoc format:
  .md    -> markdown
  .html  -> html5
  .tex   -> latex
  .txt   -> plain
  .epub  -> epub3
  .wiki  -> mediawiki
  .adoc  -> asciidoc
  ...
Pandoc's own format names pass through unchanged (commonmark_x, docbook5,
fb2, etc.) via fallback.

remarkbox/api/export.py

@@ -24,6 +24,7 @@ from remarkbox.lib.pandoc import (
     node_tree_to_markdown,
     namespace_to_markdown,
     get_available_output_formats,
+    resolve_format,
     CONTENT_TYPES,
     FILE_EXTENSIONS,
     BINARY_FORMATS,
@@ -35,10 +36,14 @@ log = logging.getLogger(__name__)
 
 
 def _parse_format_from_subpath(subpath):
-    """Extract format from the subpath (e.g. 'abc-123.epub' -> ('abc-123', 'epub'))."""
+    """Extract format from the subpath (e.g. 'abc-123.md' -> ('abc-123', 'markdown')).
+
+    Extensions are resolved through EXTENSION_ALIASES so users can hit common
+    file extensions (.md, .html, .tex) instead of pandoc's internal names.
+    """
     if "." in subpath:
-        parts = subpath.rsplit(".", 1)
-        return parts[0], parts[1]
+        stem, ext = subpath.rsplit(".", 1)
+        return stem, resolve_format(ext)
     return subpath, "markdown"
 
 

remarkbox/lib/pandoc.py

@@ -111,6 +111,50 @@ FILE_EXTENSIONS = {
 }
 
 
+# URL extension → pandoc format name. Lets users hit intuitive extensions
+# (`thread.md`, `thread.html`, `thread.tex`) instead of pandoc's internal
+# names (`markdown`, `html5`, `latex`).
+EXTENSION_ALIASES = {
+    "md": "markdown",
+    "markdown": "markdown",
+    "htm": "html5",
+    "html": "html5",
+    "tex": "latex",
+    "txt": "plain",
+    "1": "man",
+    "wiki": "mediawiki",
+    "adoc": "asciidoc",
+    "asciidoc": "asciidoc",
+    "rst": "rst",
+    "org": "org",
+    "rtf": "rtf",
+    "docx": "docx",
+    "odt": "odt",
+    "epub": "epub3",
+    "pdf": "pdf",
+    "pptx": "pptx",
+    "fb2": "fb2",
+    "jira": "jira",
+    "typ": "typst",
+    "texi": "texinfo",
+    "opml": "opml",
+    "icml": "icml",
+    "json": "json",
+    "xml": "docbook5",
+    "ipynb": "ipynb",
+}
+
+
+def resolve_format(ext):
+    """Map a URL extension (lowercase) to its pandoc format name.
+
+    Falls back to the raw extension so pandoc's own format names
+    (`commonmark_x`, `docbook5`, etc.) pass through unchanged.
+    """
+    ext = ext.lower()
+    return EXTENSION_ALIASES.get(ext, ext)
+
+
 def get_available_output_formats():
     """Return the set of output formats pandoc supports on this system."""
     try: