fix(tui): refuse empty truncation on prompt.submit to prevent silent session wipe (#70516)

[webtecnica]

Problem

Stale truncate_before_user_ordinal=0 from a desynced frontend causes replace_messages() to DELETE all session messages silently (observed: 308 messages lost). No log, no confirmation.

Fix

• Empty-truncation guard: refuse truncation when truncated==[] unless confirm_empty_truncate=true is passed (error 4025)
• Logging: every truncation logged at WARNING (session id, history N→M, ordinal)
• Covers the exact wipe reported: ordinal=0 on an ordinary submit from stale frontend

Fixes #70516

[alt-glitch]

This was generated by AI during triage.

Duplicate of #70570. It covers the same empty prompt.submit truncation guard, uses strict confirmation parsing, and updates intentional Desktop first-turn flows.

[kshitijk4poor]

Closing as the fix has been merged to main in commit 819e01c by @HexLab98 (#70570), which implements the same guard using is_truthy_value() with desktop frontend coverage. The error code collision (4025) you would have hit was also fixed in 6de7c0f (changed to 4028). Thank you for the contribution — your PR correctly identified the root cause and the guard pattern.