fix: add missing header when CHANGELOG_PENDING.md pre-exists but is empty

The repo already had an empty CHANGELOG_PENDING.md from 2026-03-30, so the
FileNotFoundError branch that adds the header/marker never fired -- the
first automated entry landed with no header, just leading blank lines.
Treat an existing-but-blank file the same as a missing one. Also fixes up
the header on the entry already drafted by the previous run. [skip ci]

.github/scripts/changelog-draft.py

@@ -83,6 +83,8 @@ def main():
     try:
         with open("CHANGELOG_PENDING.md", "r") as f:
             existing = f.read()
+        if not existing.strip():
+            existing = PENDING_HEADER  # pre-existing but empty placeholder file
     except FileNotFoundError:
         existing = PENDING_HEADER
 

CHANGELOG_PENDING.md

@@ -1,5 +1,8 @@
+# Pending Changelog Entries
 
+Drafted automatically from commit messages since the last processed push. Review, edit as needed, and fold into CHANGELOG.md -- then clear this file.
 
+<!-- PENDING_ENTRIES -->
 ## Pending -- 2026-07-18
 
 ### Fixed