Extract generate::safe_overwrite helper to eliminate DRY violation

The "safe overwrite" pattern (diff -q tmp dest, then rm or mv) was
duplicated in template, gemfeed (2x), and notes modules. Extracted
into a shared helper with unit tests covering all three cases (no
dest, identical dest, differing dest).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 1 insertions, 7 deletions

diff --git a/lib/template.source.sh b/lib/template.source.sh
index 9488ea8..5d9f4dd 100644
--- a/lib/template.source.sh
+++ b/lib/template.source.sh
@@ -71,13 +71,7 @@ template::_generate_file () {
     template::_generate < "$tpl" > "$dest.tmp"
 
     # Only overwrite if content actually changed, preserving mtime for caches
-    if [[ -f "$dest" ]] && diff -q "$dest.tmp" "$dest" >/dev/null 2>&1; then
-        rm "$dest.tmp"
-        log VERBOSE "Template output unchanged for $dest"
-    else
-        mv "$dest.tmp" "$dest"
-        log INFO "Done generating $dest"
-    fi
+    generate::safe_overwrite "$dest.tmp" "$dest"
     cd - >/dev/null
 }