Previously, typing a /command that isn't a built-in, plugin, or skill
would silently fall through to the LLM as plain text. The model often
interprets it as a loose instruction and invents unrelated tool calls —
e.g. a stray /claude_code slipped through and the model fabricated a
delegate_task invocation that got stuck in an OAuth loop.
Now we check GATEWAY_KNOWN_COMMANDS after the skill / plugin /
unavailable-skill lookups and return an actionable message pointing the
user at /commands. The user gets feedback, and the agent doesn't waste
a round-trip guessing what /foo-bar was supposed to mean.
