fix: a site preview writes its own config

generate_site --docs-dir sent the pages elsewhere but always rewrote the tracked mkdocs.yml, outside the lock taken on that folder, with the navigation of the work in progress. Two previews into two folders both wrote it. Another folder now gets <name>.mkdocs.yml beside it, docs_dir set and its paths rebased, which mkdocs builds with -f.

scripts/generate_site.py

@@ -4116,6 +4116,22 @@ def _build_emulator_file_index(profiles: dict) -> dict[str, dict]:
     }
 
 
+def _mkdocs_config(docs: Path, text: str) -> tuple[Path, str]:
+    """Where the site's config goes, and its text for that place.
+
+    The tracked mkdocs.yml belongs to docs/. A preview into another folder
+    rewrote it anyway, with the navigation of work in progress, and mkdocs
+    kept reading docs/. Another folder gets its own config beside it, its
+    paths taken from there.
+    """
+    if os.path.normpath(str(docs)) == DOCS_DIR:
+        return Path("mkdocs.yml"), text
+    where = docs.parent
+    for relative in ("scripts/mkdocs_hooks.py", "docs_assets/overrides"):
+        text = text.replace(relative, os.path.relpath(relative, where).replace(os.sep, "/"))
+    return where / f"{docs.name}.mkdocs.yml", f"docs_dir: {docs.name}\n" + text
+
+
 # mkdocs.yml nav generator
 
 
@@ -4752,7 +4768,8 @@ validation:
   unrecognized_links: warn
   anchors: warn
 """
-    write_if_changed("mkdocs.yml", mkdocs_static + nav_yaml)
+    config_path, config_text = _mkdocs_config(Path(docs), mkdocs_static + nav_yaml)
+    write_if_changed(str(config_path), config_text)
 
     total_pages = (
         1  # home