fix(wiki): unwrap fenced diagram placeholders

Author: PorunC

backend/app/services/wiki/sources/rendering.py

@@ -6,6 +6,11 @@
 from backend.app.services.wiki.sources.urls import _source_file_href, _source_ref_href
 
 DIAGRAM_SLOT_RE = re.compile(r"^\s*\[\[DIAGRAM:(?P<slot>[a-zA-Z0-9_-]+)\]\]\s*$", re.MULTILINE)
+FENCED_DIAGRAM_SLOT_RE = re.compile(
+    r"(?m)^[ \t]*`{3,}[ \t]*\n"
+    r"[ \t]*\[\[DIAGRAM:(?P<slot>[a-zA-Z0-9_-]+)\]\][ \t]*\n"
+    r"[ \t]*`{3,}[ \t]*$"
+)
 DIAGRAM_HEADING_CANDIDATES = {
     "component": ("## System Context", "## Architecture", "## Core Components", "## Overview"),
     "data_flow": ("## Control Flow", "## Core Workflows", "## System Context"),
@@ -143,7 +148,8 @@ def replace_slot(match: re.Match[str]) -> str:
         used_slots.add(slot)
         return _diagram_markdown(diagram, source_refs)
 
-    placed = DIAGRAM_SLOT_RE.sub(replace_slot, markdown)
+    placed = FENCED_DIAGRAM_SLOT_RE.sub(replace_slot, markdown)
+    placed = DIAGRAM_SLOT_RE.sub(replace_slot, placed)
     unused_diagrams = [diagram for diagram in diagrams if diagram.slot not in used_slots]
     placed = _insert_unused_diagrams(placed, unused_diagrams, source_refs)
     return _strip_unknown_diagram_slots(placed)

tests/backend/test_wiki_generator.py

@@ -1099,6 +1099,33 @@ def test_page_markdown_repairs_conjoined_mermaid_fence_headings() -> None:
     assert "```\n### Training a Skill interaction sequence" in rendered
 
 
+def test_diagram_placeholders_inside_plain_fences_do_not_wrap_mermaid() -> None:
+    diagram = MermaidDiagram(
+        slot="component-relationships",
+        kind="component",
+        title="User Guide component relationships",
+        heading_hint="System Context",
+        reason="test diagram",
+        lines=["graph TD", "  A --> B"],
+    )
+    markdown = (
+        "# User Guide\n\n"
+        "## Purpose and Scope\n\n"
+        "The page explains user workflows.\n\n"
+        "## System Context\n\n"
+        "```\n"
+        "[[DIAGRAM:component-relationships]]\n"
+        "```\n\n"
+        "## Configuration\n\n"
+        "Configuration follows."
+    )
+
+    rendered = _compose_page_markdown(markdown, [diagram], [])
+
+    assert "```\n### User Guide component relationships" not in rendered
+    assert "### User Guide component relationships\n\n```mermaid\ngraph TD\n  A --> B\n```" in rendered
+
+
 def test_unknown_diagram_placeholders_are_validation_errors() -> None:
     errors = _validate_diagram_placeholders(
         "# Page\n\n## Purpose and Scope\n\n[[DIAGRAM:invented]]",