docs: add known issue — slash session hijacks plugin commands

Document OpenClaw gateway bug (#26895, #54485) where telegram:slash
sessions interfere with registerCommand plugin routing. Include
workaround script and warning not to add ocp to agent skills lists.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -317,6 +317,31 @@ openclaw gateway restart
 - Session management with `--resume`
 - Full tool access, system prompt, MCP config support
 
+## Known Issues
+
+### `/ocp` command intermittently returns "Unknown skill: ocp"
+
+This is a known OpenClaw gateway bug ([#26895](https://github.com/openclaw/openclaw/issues/26895), [#54485](https://github.com/openclaw/openclaw/issues/54485)). The gateway creates a `telegram:slash` session on the first `/ocp` invocation, and subsequent calls get routed to this session (sent to the agent) instead of the plugin command handler.
+
+**Workaround:** Delete the slash session entries and restart the gateway:
+
+```bash
+# Remove slash sessions for all agents
+python3 -c "
+import json, glob
+for f in glob.glob('~/.openclaw/agents/*/sessions/sessions.json'):
+    d = json.load(open(f))
+    keys = [k for k in d if 'slash' in k]
+    for k in keys: del d[k]
+    if keys: json.dump(d, open(f, 'w'), indent=2); print(f'Cleaned {len(keys)} slash sessions from {f}')
+"
+
+# Restart gateway
+openclaw gateway restart
+```
+
+**Important:** Do not add `ocp` to agent `skills` lists in `openclaw.json` — this creates a routing conflict with the plugin and makes the problem worse. OCP should only be registered as a plugin, never as a skill.
+
 ## License
 
 MIT