hermes - 💡(How to fix) Fix [Feature]: Mattermost: Add interactive button-based approval for dangerous commands

Problem or Use Case

The Mattermost gateway adapter is effectively unusable for any user interaction that requires slash commands — most critically, the /approve and /deny flow for dangerous command approval.

Root cause: Mattermost intercepts all messages starting with / Both the Mattermost server and client intercept any message beginning with / and try to execute it as a native slash command.

The message never reaches the Hermes bot.

Proposed Solution

Current state

1. No interactive buttons — Unlike Discord (which has send_exec_approval() with ExecApprovalView — 4 clickable buttons), the Mattermost adapter has no button-based approval mechanism.
2. Fallback is broken — When send_exec_approval() is absent from the adapter, gateway/run.py falls back to a plain text message instructing the user to reply with /approve once etc. Since / is intercepted, this instructs the user to do something that's impossible.
3. All slash commands are broken — /yolo, /retry, /help, /model, /skills — none work from any Mattermost client.

Existing Platform Parity

Proposed Solution

1. Interactive approval buttons

Mattermost supports interactive message buttons via post attachments with actions[].integration. The approach mirrors Discord's:

Send approval message:

async def send_exec_approval(self, chat_id, command, session_key, description, metadata):
    payload = {
        "channel_id": chat_id,
        "message": "⚠️ Command Approval Required",
        "attachments": [{
            "title": description,
            "text": f"```\n{command}\n```",
            "actions": [
                {
                    "name": "Allow Once",
                    "integration": {
                        "url": f"{self._gateway_callback_url}/approval",
                        "context": {"session_key": session_key, "action": "once"}
                    }
                },
                {
                    "name": "Allow Session",
                    "integration": {
                        "url": f"{self._gateway_callback_url}/approval",
                        "context": {"session_key": session_key, "action": "session"}
                    }
                },
                {
                    "name": "Always Allow",
                    "integration": {
                        "url": f"{self._gateway_callback_url}/approval",
                        "context": {"session_key": session_key, "action": "always"}
                    }
                },
                {
                    "name": "Deny",
                    "integration": {
                        "url": f"{self._gateway_callback_url}/approval",
                        "context": {"session_key": session_key, "action": "deny"}
                    }
                }
            ]
        }]
    }

Handle the callback: The gateway already has an HTTP server infrastructure. Register a route that receives Mattermost interactive message callbacks, calls resolve_gateway_approval(session_key, choice) (same function Discord uses), and returns the updated message with disabled buttons to confirm the action.

Authorization: Verify that the clicking user is the same user who initiated the command (or is in MATTERMOST_ALLOWED_USERS), matching Discord's _check_caller_authorized() behavior.

2. Register slash commands via Mattermost REST API

Following the existing Discord/Discord pattern, register all COMMAND_REGISTRY gateway commands as Mattermost custom slash commands on adapter startup via POST /api/v4/commands:

• trigger: command name (approve, deny, help, yolo, retry, etc.)
• url: gateway HTTP endpoint to receive the command
• method: P (POST)
• auto_complete: true
• display_name: Hermes: /{name}

This matches the approach already proposed in #6296 and gives Mattermost feature parity with Telegram, Slack, and Discord.

Benefits

• Dangerous command approval works — the most critical UX flow, fully interactive with buttons
• All slash commands work — /approve, /deny, /yolo, /help, /retry etc. from every Mattermost client
• Autocomplete — users see all Hermes commands when typing / in Mattermost
• Feature parity — Mattermost gets the same first-class experience as Discord/Telegram/Slack
• Reuses existing infrastructure — resolve_gateway_approval(), COMMAND_REGISTRY, and the gateway HTTP server are already there

Scope

• send_exec_approval() implementation: ~50 lines in gateway/platforms/mattermost.py
• interactive callback handler: ~40 lines in gateway/platforms/mattermost.py
• slash command registration: ~30 lines in the connect() method
• gateway HTTP route registration: ~10 lines in gateway/run.py

Impact

Unblocks Hermes usage on Mattermost for all users. Without this, no one can approve dangerous commands or use any slash command from Mattermost — the platform is effectively crippled for Hermes interaction.

Alternatives Considered

No response

Feature Type

Gateway / messaging improvement

Scope

Medium (few files, < 300 lines)

Contribution

• I'd like to implement this myself and submit a PR

Debug Report (optional)