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/run.py

@@ -892,6 +892,14 @@ class GatewayRunner:
         # Key: session_key, Value: True when a prompt is waiting for user input.
         self._update_prompt_pending: Dict[str, bool] = {}
 
+        # Slash-confirm state lives in tools.slash_confirm (module-level),
+        # so platform adapters can resolve callbacks without a backref to
+        # this runner.  Keep a local counter for confirm_id generation so
+        # IDs stay compact (button callback_data has a 64-byte cap on
+        # some platforms).
+        import itertools as _itertools
+        self._slash_confirm_counter = _itertools.count(1)
+
         # Persistent Honcho managers keyed by gateway session key.
         # This preserves write_frequency="session" semantics across short-lived
         # per-message AIAgent instances.
@@ -3805,6 +3813,50 @@ class GatewayRunner:
                     )
                 _update_prompts.pop(_quick_key, None)
 
+        # Intercept messages that are responses to a pending /reload-mcp
+        # (or future) slash-confirm prompt.  Recognized confirm replies are
+        # /approve, /always, /cancel (plus short aliases).  Anything else
+        # falls through to normal dispatch — a stale pending confirm does
+        # NOT block other commands.
+        #
+        # Important: if a dangerous-command approval is ALSO pending (agent
+        # blocked inside tools/approval.py), the tool approval takes
+        # precedence — /approve there unblocks the waiting tool thread.
+        # Slash-confirm only catches /approve when no tool approval is live.
+        from tools import slash_confirm as _slash_confirm_mod
+        _pending_confirm = _slash_confirm_mod.get_pending(_quick_key)
+        _tool_approval_live = False
+        try:
+            from tools.approval import has_blocking_approval
+            _tool_approval_live = has_blocking_approval(_quick_key)
+        except Exception:
+            _tool_approval_live = False
+        if _pending_confirm and not _tool_approval_live:
+            _raw_reply = (event.text or "").strip()
+            _cmd_reply = event.get_command()
+            _confirm_choice = None
+            if _cmd_reply in ("approve", "yes", "ok", "confirm"):
+                _confirm_choice = "once"
+            elif _cmd_reply in ("always", "remember"):
+                _confirm_choice = "always"
+            elif _cmd_reply in ("cancel", "no", "deny", "nevermind"):
+                _confirm_choice = "cancel"
+            elif _raw_reply.lower() in ("approve", "approve once", "once"):
+                _confirm_choice = "once"
+            elif _raw_reply.lower() in ("always", "always approve"):
+                _confirm_choice = "always"
+            elif _raw_reply.lower() in ("cancel", "nevermind", "no"):
+                _confirm_choice = "cancel"
+            if _confirm_choice is not None:
+                _resolved = await _slash_confirm_mod.resolve(
+                    _quick_key, _pending_confirm.get("confirm_id"), _confirm_choice,
+                )
+                return _resolved or ""
+            # Stale pending + unrelated command: drop the pending state so
+            # the confirm doesn't block normal usage indefinitely.  The user
+            # clearly moved on.
+            _slash_confirm_mod.clear_if_stale(_quick_key)
+
         # PRIORITY handling when an agent is already running for this session.
         # Default behavior is to interrupt immediately so user text/stop messages
         # are handled with minimal latency.
@@ -8200,8 +8252,91 @@ class GatewayRunner:
             logger.error("Insights command error: %s", e, exc_info=True)
             return f"Error generating insights: {e}"
 
-    async def _handle_reload_mcp_command(self, event: MessageEvent) -> str:
-        """Handle /reload-mcp command -- disconnect and reconnect all MCP servers."""
+    async def _handle_reload_mcp_command(self, event: MessageEvent) -> Optional[str]:
+        """Handle /reload-mcp — reconnect MCP servers and rebuild the cached agent.
+
+        Reloading MCP tools invalidates the provider prompt cache for the
+        active session (tool schemas are baked into the system prompt).  The
+        next message re-sends full input tokens, which is expensive on
+        long-context or high-reasoning models.
+
+        To surface that cost, the command routes through the slash-confirm
+        primitive: users get an Approve Once / Always Approve / Cancel
+        prompt before the reload actually runs.  "Always Approve" persists
+        ``approvals.mcp_reload_confirm: false`` so the prompt is silenced
+        for subsequent reloads in any session.
+
+        Users can also skip the confirm by flipping the config key directly.
+        """
+        source = event.source
+        session_key = self._session_key_for_source(source)
+
+        # Read the gate fresh from disk so a prior "always" click takes
+        # effect on the next invocation without restarting the gateway.
+        user_config = self._read_user_config()
+        approvals = user_config.get("approvals") if isinstance(user_config, dict) else None
+        confirm_required = True
+        if isinstance(approvals, dict):
+            confirm_required = bool(approvals.get("mcp_reload_confirm", True))
+
+        if not confirm_required:
+            return await self._execute_mcp_reload(event)
+
+        # Route through slash-confirm.  The primitive sends the prompt and
+        # stores the resume handler; the button/text response triggers
+        # ``_resolve_slash_confirm`` which invokes the handler with the
+        # chosen outcome.
+        async def _on_confirm(choice: str) -> Optional[str]:
+            if choice == "cancel":
+                return "🟡 /reload-mcp cancelled. MCP tools unchanged."
+            if choice == "always":
+                # Persist the opt-out and run the reload.
+                try:
+                    from cli import save_config_value
+                    save_config_value("approvals.mcp_reload_confirm", False)
+                    logger.info(
+                        "User opted out of /reload-mcp confirmation (session=%s)",
+                        session_key,
+                    )
+                except Exception as exc:
+                    logger.warning("Failed to persist mcp_reload_confirm=false: %s", exc)
+            # once / always → run the reload
+            result = await self._execute_mcp_reload(event)
+            if choice == "always":
+                return (
+                    f"{result}\n\n"
+                    "ℹ️ Future `/reload-mcp` calls will run without confirmation. "
+                    "Re-enable via `approvals.mcp_reload_confirm: true` in config.yaml."
+                )
+            return result
+
+        prompt_message = (
+            "⚠️ **Confirm /reload-mcp**\n\n"
+            "Reloading MCP servers rebuilds the tool set for this session "
+            "and **invalidates the provider prompt cache** — the next "
+            "message will re-send full input tokens.  On long-context or "
+            "high-reasoning models this can be expensive.\n\n"
+            "Choose:\n"
+            "• **Approve Once** — reload now\n"
+            "• **Always Approve** — reload now and silence this prompt permanently\n"
+            "• **Cancel** — leave MCP tools unchanged\n\n"
+            "_Text fallback: reply `/approve`, `/always`, or `/cancel`._"
+        )
+        return await self._request_slash_confirm(
+            event=event,
+            command="reload-mcp",
+            title="/reload-mcp",
+            message=prompt_message,
+            handler=_on_confirm,
+        )
+
+    async def _execute_mcp_reload(self, event: MessageEvent) -> str:
+        """Actually disconnect, reconnect, and notify MCP tool changes.
+
+        Split out from ``_handle_reload_mcp_command`` so the confirmation
+        wrapper can invoke the same path whether the user confirmed via
+        button, text reply, or has the confirm gate disabled.
+        """
         loop = asyncio.get_running_loop()
         try:
             from tools.mcp_tool import shutdown_mcp_servers, discover_mcp_tools, _servers, _lock
@@ -8343,6 +8478,102 @@ class GatewayRunner:
             logger.warning("Skills reload failed: %s", e)
             return f"❌ Skills reload failed: {e}"
 
+    # ------------------------------------------------------------------
+    # Slash-command confirmation primitive (generic)
+    # ------------------------------------------------------------------
+    # Used by slash commands that have a non-destructive but expensive
+    # side effect worth an explicit user confirmation (currently only
+    # /reload-mcp, which invalidates the prompt cache).  Two delivery
+    # paths:
+    #   1. Button UI — adapters that override ``send_slash_confirm``
+    #      (Telegram, Discord, Slack, Matrix, Feishu) render three
+    #      inline buttons.  The adapter routes the button click back via
+    #      ``tools.slash_confirm.resolve(session_key, confirm_id, choice)``.
+    #   2. Text fallback — adapters that don't override the hook get a
+    #      plain text prompt.  Users reply with /approve, /always, or
+    #      /cancel; the early intercept in ``_handle_message`` matches
+    #      those replies against ``tools.slash_confirm.get_pending()``.
+
+    async def _request_slash_confirm(
+        self,
+        *,
+        event: MessageEvent,
+        command: str,
+        title: str,
+        message: str,
+        handler,
+    ) -> Optional[str]:
+        """Ask the user to confirm an expensive slash command.
+
+        ``handler`` is an async callable ``handler(choice: str) -> str``
+        where ``choice`` is ``"once"``, ``"always"``, or ``"cancel"``.
+        The handler runs on the event loop when the user responds; its
+        return value is sent back as a gateway message.
+
+        Returns a short acknowledgment string to send immediately (before
+        the user's response).  If buttons rendered successfully the ack
+        is ``None`` (buttons are self-explanatory); if we fell back to
+        text the message itself IS the ack.
+        """
+        from tools import slash_confirm as _slash_confirm_mod
+
+        source = event.source
+        session_key = self._session_key_for_source(source)
+        confirm_id = f"{next(self._slash_confirm_counter)}"
+
+        # Register the pending confirm FIRST so a super-fast button click
+        # cannot race the send_slash_confirm return.
+        _slash_confirm_mod.register(session_key, confirm_id, command, handler)
+
+        adapter = self.adapters.get(source.platform)
+        metadata = self._thread_metadata_for_source(source)
+
+        used_buttons = False
+        if adapter is not None:
+            try:
+                button_result = await adapter.send_slash_confirm(
+                    chat_id=source.chat_id,
+                    title=title,
+                    message=message,
+                    session_key=session_key,
+                    confirm_id=confirm_id,
+                    metadata=metadata,
+                )
+                if button_result and getattr(button_result, "success", False):
+                    used_buttons = True
+            except Exception as exc:
+                logger.debug(
+                    "send_slash_confirm failed for %s on %s: %s",
+                    command, source.platform, exc,
+                )
+
+        if used_buttons:
+            # Buttons rendered — no redundant text ack.
+            return None
+        # Text fallback — return the prompt message as the direct reply.
+        return message
+
+    def _read_user_config(self) -> Dict[str, Any]:
+        """Read the user's raw config.yaml (cached) for gate lookups.
+
+        Used by slash-confirm gates that must reflect on-disk state changes
+        (e.g. a prior "Always Approve" click) without a gateway restart.
+        """
+        try:
+            from hermes_cli.config import load_config
+            cfg = load_config()
+            return cfg if isinstance(cfg, dict) else {}
+        except Exception:
+            return {}
+
+    def _thread_metadata_for_source(self, source) -> Optional[Dict[str, Any]]:
+        """Build the metadata dict platforms need for thread-aware replies."""
+        thread_id = getattr(source, "thread_id", None)
+        if thread_id is None:
+            return None
+        return {"thread_id": thread_id}
+
+
     # ------------------------------------------------------------------
     # /approve & /deny — explicit dangerous-command approval
     # ------------------------------------------------------------------