test(signal): cover inbound prompt body contract

docs/concepts/messages.md

@@ -93,8 +93,11 @@ OpenClaw keeps that boundary explicit:
 
 OpenClaw separates the **prompt body** from the **command body**:
 
-- `Body`: prompt text sent to the agent. This may include channel envelopes and
-  optional history wrappers.
+- `BodyForAgent`: primary model-facing text for the current message. Channel
+  plugins should keep this focused on the sender's current prompt-bearing text.
+- `Body`: legacy prompt fallback. This may include channel envelopes and
+  optional history wrappers, but current channels should not rely on it as the
+  primary model input when `BodyForAgent` is available.
 - `CommandBody`: raw user text for directive/command parsing.
 - `RawBody`: legacy alias for `CommandBody` (kept for compatibility).
 
@@ -114,6 +117,8 @@ already in the session transcript.
 Directive stripping only applies to the **current message** section so history
 remains intact. Channels that wrap history should set `CommandBody` (or
 `RawBody`) to the original message text and keep `Body` as the combined prompt.
+Structured history, reply, forwarded, and channel metadata are rendered as
+user-role untrusted context blocks during prompt assembly.
 History buffers are configurable via `messages.groupChat.historyLimit` (global
 default) and per-channel overrides like `channels.slack.historyLimit` or
 `channels.telegram.accounts.<id>.historyLimit` (set `0` to disable).