docs: move cross-context faq to troubleshooting

docs/help/troubleshooting.md

@@ -61,6 +61,33 @@ Disable Advanced Security or add `docs.clawd.bot` to the allowlist, then retry.
 - [Models](/cli/models)
 - [OAuth / auth concepts](/concepts/oauth)
 
+### “Cross-context messaging denied” (Telegram → Discord, etc.)
+
+Clawdbot blocks **cross‑provider** sends by default. If a tool call is bound to
+Telegram, it won’t send to Discord unless you explicitly allow it.
+
+Enable cross‑provider messaging for the agent:
+
+```json5
+{
+  agents: {
+    defaults: {
+      tools: {
+        message: {
+          crossContext: {
+            allowAcrossProviders: true,
+            marker: { enabled: true, prefix: "[from {channel}] " }
+          }
+        }
+      }
+    }
+  }
+}
+```
+
+Restart the gateway after editing config. If you only want this for a single
+agent, set it under `agents.list[].tools.message` instead.
+
 ### `/model` says `model not allowed`
 
 This usually means `agents.defaults.models` is configured as an allowlist. When it’s non-empty,