Add text features: trusted triggers, context cache, response policy, MCP config tools

docs/core-bridge.md

@@ -59,6 +59,7 @@ Event line:
 | `state.get` | none | The current user, the guilds, and the channels. Cache-only. |
 | `message.send` | `channelId`, `content` | `{ channelId, sent: true }` |
 | `message.read` | `channelId`, `limit` | `{ cached, messages }`. Cache-only. |
+| `message.fetch` | `channelId`, `limit`, optional `before` or `after` | `{ fetched, messages }`. Fetches from Discord. |
 | `dm.send` | `userId`, `content` | `{ userId, channelId, sent: true }` |
 
 ## Validation rules
@@ -73,6 +74,8 @@ The core validates all input. The daemon cannot bypass these rules.
   `GUILD_TEXT`, `DM`, `GROUP_DM`, `GUILD_ANNOUNCEMENT`, `ANNOUNCEMENT_THREAD`, `PUBLIC_THREAD`,
   and `PRIVATE_THREAD`.
 - `limit` must be an integer from 1 to 100.
+- `before` and `after` must be snowflakes. They are mutually exclusive. `message.fetch` uses them
+  to walk history.
 - A request line must not be larger than 64 KiB.
 
 ## Core rate limit
@@ -100,6 +103,7 @@ The core rate limit is a safety net. It does not replace the daemon pacing.
 | `NOT_SENDABLE` | The channel type cannot receive messages. |
 | `SEND_FAILED` | Discord rejected the message. |
 | `DM_UNAVAILABLE` | The client cannot create a DM channel. |
+| `NOT_SUPPORTED` | The client does not offer the internal action. |
 | `RATE_LIMITED` | The core rate limit rejected the action. |
 | `INTERNAL` | An unexpected error occurred. The details go to the local log only. |