feat(gateway,cli): confirm /reload-mcp to warn about prompt cache invalidation

Reloading MCP servers rebuilds the tool set for the active session, which
invalidates the provider prompt cache (tool schemas are baked into the
system prompt). The next message re-sends full input tokens — can be
expensive on long-context or high-reasoning models.

To surface that cost, /reload-mcp now routes through a new slash-confirm
primitive with three options: Approve Once / Always Approve / Cancel.
'Always Approve' persists approvals.mcp_reload_confirm: false so future
reloads run silently.

Coverage:

* Classic CLI (cli.py) — interactive numbered prompt.
* TUI (tui_gateway + Ink ops.ts) — text warning on first call; `now` /
  `always` args skip the gate; `always` also persists the opt-out.
* Messenger gateway — button UI on Telegram (inline keyboard), Discord
  (discord.ui.View), Slack (Block Kit actions); text fallback on every
  other platform via /approve /always /cancel replies intercepted in
  gateway/run.py _handle_message.
* Config key: approvals.mcp_reload_confirm (default true).
* Auto-reload paths (CLI file watcher, TUI config-sync mtime poll) pass
  confirm=true so they do NOT prompt.

Implementation:

* tools/slash_confirm.py — module-level pending-state store used by all
  adapters and by the CLI prompt. Thread-safe register/resolve/clear.
* gateway/platforms/base.py — send_slash_confirm hook (default 'Not
  supported' → text fallback).
* gateway/run.py — _request_slash_confirm helper + text intercept in
  _handle_message (yields to in-progress tool-exec approvals so
  dangerous-command /approve still unblocks the tool thread first).

Tests:

* tests/tools/test_slash_confirm.py — primitive lifecycle + async
  resolution + double-click atomicity (16 tests).
* tests/hermes_cli/test_mcp_reload_confirm_gate.py — default-config
  shape + deep-merge preserves user opt-out (5 tests).

Targeted runs (hermetic): 89 passed (slash-confirm, config gate,
existing agent cache, existing telegram approval buttons).

gateway/platforms/discord.py

@@ -2910,6 +2910,43 @@ class DiscordAdapter(BasePlatformAdapter):
         except Exception as e:
             return SendResult(success=False, error=str(e))
 
+    async def send_slash_confirm(
+        self, chat_id: str, title: str, message: str, session_key: str,
+        confirm_id: str, metadata: Optional[dict] = None,
+    ) -> SendResult:
+        """Send a three-button slash-command confirmation prompt."""
+        if not self._client or not DISCORD_AVAILABLE:
+            return SendResult(success=False, error="Not connected")
+
+        try:
+            target_id = chat_id
+            if metadata and metadata.get("thread_id"):
+                target_id = metadata["thread_id"]
+
+            channel = self._client.get_channel(int(target_id))
+            if not channel:
+                channel = await self._client.fetch_channel(int(target_id))
+
+            # Embed description limit is 4096; message usually fits easily.
+            max_desc = 4088
+            body = message if len(message) <= max_desc else message[: max_desc - 3] + "..."
+            embed = discord.Embed(
+                title=title or "Confirm",
+                description=body,
+                color=discord.Color.orange(),
+            )
+
+            view = SlashConfirmView(
+                session_key=session_key,
+                confirm_id=confirm_id,
+                allowed_user_ids=self._allowed_user_ids,
+            )
+
+            msg = await channel.send(embed=embed, view=view)
+            return SendResult(success=True, message_id=str(msg.id))
+        except Exception as e:
+            return SendResult(success=False, error=str(e))
+
     async def send_update_prompt(
         self, chat_id: str, prompt: str, default: str = "",
         session_key: str = "",
@@ -3643,6 +3680,103 @@ if DISCORD_AVAILABLE:
             for child in self.children:
                 child.disabled = True
 
+    class SlashConfirmView(discord.ui.View):
+        """Three-button view for generic slash-command confirmations.
+
+        Used by ``/reload-mcp`` and any future slash command routed through
+        ``GatewayRunner._request_slash_confirm``.  Buttons map to the
+        gateway's three choices:
+
+          * "Approve Once"   → ``choice="once"``
+          * "Always Approve" → ``choice="always"``
+          * "Cancel"         → ``choice="cancel"``
+
+        Clicking calls the module-level
+        ``tools.slash_confirm.resolve(session_key, confirm_id, choice)``
+        which runs the handler the runner stored for this ``session_key``.
+        Only users in the adapter's allowlist can click.  Times out after
+        5 minutes (matches the gateway primitive's timeout).
+        """
+
+        def __init__(self, session_key: str, confirm_id: str, allowed_user_ids: set):
+            super().__init__(timeout=300)
+            self.session_key = session_key
+            self.confirm_id = confirm_id
+            self.allowed_user_ids = allowed_user_ids
+            self.resolved = False
+
+        def _check_auth(self, interaction: discord.Interaction) -> bool:
+            if not self.allowed_user_ids:
+                return True
+            return str(interaction.user.id) in self.allowed_user_ids
+
+        async def _resolve(
+            self, interaction: discord.Interaction, choice: str,
+            color: discord.Color, label: str,
+        ):
+            if self.resolved:
+                await interaction.response.send_message(
+                    "This prompt has already been resolved~", ephemeral=True,
+                )
+                return
+            if not self._check_auth(interaction):
+                await interaction.response.send_message(
+                    "You're not authorized to answer this prompt~", ephemeral=True,
+                )
+                return
+
+            self.resolved = True
+
+            embed = interaction.message.embeds[0] if interaction.message.embeds else None
+            if embed:
+                embed.color = color
+                embed.set_footer(text=f"{label} by {interaction.user.display_name}")
+
+            for child in self.children:
+                child.disabled = True
+
+            await interaction.response.edit_message(embed=embed, view=self)
+
+            # Resolve via the module-level primitive.  If the handler
+            # returns a follow-up message, post it in the same channel.
+            try:
+                from tools import slash_confirm as _slash_confirm_mod
+                result_text = await _slash_confirm_mod.resolve(
+                    self.session_key, self.confirm_id, choice,
+                )
+                if result_text:
+                    await interaction.followup.send(result_text)
+                logger.info(
+                    "Discord button resolved slash-confirm for session %s "
+                    "(choice=%s, user=%s)",
+                    self.session_key, choice, interaction.user.display_name,
+                )
+            except Exception as exc:
+                logger.error("Discord slash-confirm resolve failed: %s", exc, exc_info=True)
+
+        @discord.ui.button(label="Approve Once", style=discord.ButtonStyle.green)
+        async def approve_once(
+            self, interaction: discord.Interaction, button: discord.ui.Button,
+        ):
+            await self._resolve(interaction, "once", discord.Color.green(), "Approved once")
+
+        @discord.ui.button(label="Always Approve", style=discord.ButtonStyle.blurple)
+        async def approve_always(
+            self, interaction: discord.Interaction, button: discord.ui.Button,
+        ):
+            await self._resolve(interaction, "always", discord.Color.purple(), "Always approved")
+
+        @discord.ui.button(label="Cancel", style=discord.ButtonStyle.red)
+        async def cancel(
+            self, interaction: discord.Interaction, button: discord.ui.Button,
+        ):
+            await self._resolve(interaction, "cancel", discord.Color.greyple(), "Cancelled")
+
+        async def on_timeout(self):
+            self.resolved = True
+            for child in self.children:
+                child.disabled = True
+
     class UpdatePromptView(discord.ui.View):
         """Interactive Yes/No buttons for ``hermes update`` prompts.