feat: confirm prompt for destructive slash commands (#4069) (#22687)

/clear, /new, /reset, and /undo now ask the user to confirm before
discarding conversation state — three-option prompt routed through the
existing tools.slash_confirm primitive.

Native yes/no buttons render on Telegram, Discord, and Slack (their
adapters already implement send_slash_confirm); other platforms get a
text-fallback prompt and reply with /approve, /always, or /cancel.

The classic prompt_toolkit CLI uses the same three-option flow via the
established _prompt_text_input pattern (see _confirm_and_reload_mcp).
TUI keeps its existing modal overlay (#12312).

Gated by new config key approvals.destructive_slash_confirm (default
true). Picking 'Always Approve' flips the gate to false so subsequent
destructive commands run silently — matches the established
mcp_reload_confirm UX.

Out of scope: /cron remove (separate domain — scheduled jobs, not
session history). Existing TUI overlay env-var (HERMES_TUI_NO_CONFIRM)
left unchanged; cosmetic unification can come later.

Closes #4069.

hermes_cli/config.py

@@ -1204,6 +1204,15 @@ DEFAULT_CONFIG = {
         # "Always Approve" to silence the prompt permanently; that flips
         # this key to false.
         "mcp_reload_confirm": True,
+        # When true, destructive session slash commands (/clear, /new, /reset,
+        # /undo) ask the user to confirm before discarding conversation state.
+        # Three-option prompt (Approve Once / Always Approve / Cancel) routed
+        # through tools.slash_confirm — native yes/no buttons on Telegram,
+        # Discord, and Slack; text fallback elsewhere.  Users click "Always
+        # Approve" to silence the prompt permanently; that flips this key to
+        # false.  TUI has its own modal overlay (HERMES_TUI_NO_CONFIRM=1 to
+        # opt out there).
+        "destructive_slash_confirm": True,
     },
 
     # Permanently allowed dangerous command patterns (added via "always" approval)