chore: import upstream snapshot with attribution

scripts/_lib.py

@@ -0,0 +1,59 @@
+"""Shared helpers for scripts/ tools.
+
+Currently provides:
+- parse_frontmatter: minimal YAML-subset parser for `--- ... ---` blocks in markdown.
+
+No external dependencies. Python 3.10+ (PEP 604 unions in type hints).
+"""
+
+from __future__ import annotations
+
+
+def parse_frontmatter(text: str) -> dict[str, object] | None:
+    """Parse a YAML-subset frontmatter block at the top of a markdown string.
+
+    Returns the parsed key/value mapping, or None when no frontmatter is present
+    or the closing `---` is missing.
+
+    Supports:
+    - bare strings: `key: value`
+    - single-quoted: `key: 'value'`
+    - double-quoted: `key: "value"`
+    - lists: `key: [a, b, "c"]`
+    - inline comment lines beginning with `#`
+    """
+    if not text.startswith("---\n"):
+        return None
+    # Closing delimiter: "\n---\n" inside the file, or "\n---" at EOF.
+    end = text.find("\n---\n", 4)
+    if end == -1 and text.endswith("\n---"):
+        end = len(text) - 4
+    if end == -1:
+        return None
+    block = text[4:end].strip("\n")
+    result: dict[str, object] = {}
+    for raw in block.splitlines():
+        # Anchor at column 0: skip comments + indented lines.
+        if not raw or raw.startswith("#") or raw[0] in (" ", "\t"):
+            continue
+        if ":" not in raw:
+            continue
+        key, _, value = raw.partition(":")
+        key = key.strip()
+        if not key:
+            continue
+        value = value.strip()
+        if value.startswith("[") and value.endswith("]"):
+            inner = value[1:-1].strip()
+            result[key] = (
+                [item.strip().strip("'\"") for item in inner.split(",") if item.strip()]
+                if inner
+                else []
+            )
+        elif (value.startswith('"') and value.endswith('"')) or (
+            value.startswith("'") and value.endswith("'")
+        ):
+            result[key] = value[1:-1]
+        else:
+            result[key] = value
+    return result