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.

tests/hermes_cli/test_destructive_slash_confirm_gate.py

@@ -0,0 +1,86 @@
+"""Tests for the approvals.destructive_slash_confirm config gate.
+
+Destructive session slash commands (/clear, /new, /reset, /undo) discard
+conversation state.  This config key (default True) gates a three-option
+confirmation prompt — "Always Approve" flips the key to False so future
+destructive commands run silently.
+
+See gateway/run.py::_maybe_confirm_destructive_slash and
+cli.py::_confirm_destructive_slash for the runtime gate.
+"""
+
+from __future__ import annotations
+
+from hermes_cli.config import DEFAULT_CONFIG
+
+
+class TestDestructiveSlashConfirmDefault:
+    def test_default_config_has_the_key(self):
+        approvals = DEFAULT_CONFIG.get("approvals")
+        assert isinstance(approvals, dict)
+        assert "destructive_slash_confirm" in approvals
+
+    def test_default_is_true(self):
+        # New installs confirm by default — destructive commands must not
+        # silently wipe history without an explicit user "yes".
+        assert DEFAULT_CONFIG["approvals"]["destructive_slash_confirm"] is True
+
+    def test_shape_matches_other_approval_keys(self):
+        approvals = DEFAULT_CONFIG["approvals"]
+        assert isinstance(approvals.get("destructive_slash_confirm"), bool)
+        # Sibling key shape sanity — same flat dict level as mcp_reload_confirm.
+        assert isinstance(approvals.get("mcp_reload_confirm"), bool)
+
+
+class TestUserConfigMerge:
+    """If a user has a pre-existing config without this key, load_config
+    should fill it in from DEFAULT_CONFIG (deep merge preserves keys the
+    user didn't override)."""
+
+    def test_existing_user_config_without_key_gets_default(self, tmp_path, monkeypatch):
+        import yaml
+
+        home = tmp_path / ".hermes"
+        home.mkdir()
+        cfg_path = home / "config.yaml"
+        legacy = {
+            "approvals": {"mode": "manual", "timeout": 60, "cron_mode": "deny"},
+        }
+        cfg_path.write_text(yaml.safe_dump(legacy))
+
+        monkeypatch.setenv("HERMES_HOME", str(home))
+        import importlib
+        import hermes_cli.config as cfg_mod
+        importlib.reload(cfg_mod)
+
+        cfg = cfg_mod.load_config()
+        assert cfg["approvals"]["destructive_slash_confirm"] is True
+
+    def test_existing_user_config_with_false_key_survives_merge(
+        self, tmp_path, monkeypatch,
+    ):
+        """A user who clicked "Always Approve" (key=false) must keep that
+        setting — the default-true value must not win on later loads.
+        """
+        import yaml
+
+        home = tmp_path / ".hermes"
+        home.mkdir()
+        cfg_path = home / "config.yaml"
+        user_cfg = {
+            "approvals": {
+                "mode": "manual",
+                "timeout": 60,
+                "cron_mode": "deny",
+                "destructive_slash_confirm": False,
+            },
+        }
+        cfg_path.write_text(yaml.safe_dump(user_cfg))
+
+        monkeypatch.setenv("HERMES_HOME", str(home))
+        import importlib
+        import hermes_cli.config as cfg_mod
+        importlib.reload(cfg_mod)
+
+        cfg = cfg_mod.load_config()
+        assert cfg["approvals"]["destructive_slash_confirm"] is False