Document how to pass CLI options to OpenCode agent

The OpenCode sandbox page was missing the "Pass options at runtime"
section that other agent pages include, showing how to forward CLI
options using the `--` separator.

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

Author: dvdksn

content/manuals/ai/sandboxes/agents/opencode.md

@@ -64,6 +64,20 @@ OpenCode uses a TUI interface and doesn't require extensive configuration
 files. The agent prompts you to select a provider when it starts, and you can
 switch providers during a session.
 
+### Pass options at runtime
+
+Pass OpenCode CLI options after `--`:
+
+```console
+$ sbx run opencode --name <sandbox-name> -- <opencode-options>
+```
+
+For example, to resume an existing session in a named sandbox:
+
+```console
+$ sbx run <sandbox-name> -- -s <session-id>
+```
+
 ### TUI mode
 
 OpenCode launches in TUI mode by default. The interface shows: