fix(history): resolve review advisories from #1477 and #1480

[Alan-TheGentleman]

Problem

Native review left five non-blocking advisories on #1477 and #1480:

1. drainGlobal ignores history-global.jsonl.carry-*.jsonl siblings written when a sweep carry append fails.
2. The session-derived delete path's hide-failure notice needed verification.
3. A partially written carry append can leave a torn fragment that corrupts the next line.
4. The live overlayOptions margin and visibility functions were not covered by tests.
5. The full scope radio fit check was off by one column at the exact boundary width.

Expected

Real defects fixed with regression tests; non-defects proven by tests.

Follow-up to #818.