fix(history): reliability follow-ups and query-aware Home/End

[Alan-TheGentleman]

Problem

Non-blocking native-review advisories on the merged prompt-history slices (#1391, #1393, #1394, #1475) and one selector UX bug remained open:

• GC could lose lines appended to a claimed file after it was read (carry-over ran after unlink).
• GC rewrote the compact file on every shutdown when it could not reduce the file count.
• A failed carry append during a delete sweep could drop concurrently appended lines.
• The partial-delete notice claimed the prompt was hidden before the tombstone write ran.
• A malformed Customize capture preference produced a generic "off" message.
• A session-writer test read the real home directory.
• In the selector, Home/End always jumped the list (and End loaded every record) even while editing a search query.

Expected

Each defect fixed with regression tests; Home/End move the search caret when the query is non-empty and keep the documented list jumps when it is empty.

Follow-up to #818.