The delete action looked up the target with startswith() to capture
full_id, but then re-applied startswith() to filter the list — so a
short or ambiguous memory_id silently deleted every memory whose id
shared the prefix, while the success message reported only the first
match. The edit action used the first match and stopped, so the two
actions disagreed on multi-match behaviour. Use full_id for both.
Caught by #1303.
