docs: document tool output truncation settings

packages/web/src/content/docs/config.mdx

@@ -353,6 +353,27 @@ You can manage the tools an LLM can use through the `tools` option.
 
 ---
 
+### Tool output
+
+You can control when tool output is truncated using the `tool_output` option. When output exceeds either threshold, OpenCode saves the complete output to disk and returns a truncated preview with the saved file path.
+
+```json title="opencode.json"
+{
+  "$schema": "https://opencode.ai/config.json",
+  "tool_output": {
+    "max_lines": 2000,
+    "max_bytes": 51200
+  }
+}
+```
+
+- `max_lines` - Maximum number of lines before output is truncated (default: `2000`).
+- `max_bytes` - Maximum size in bytes before output is truncated (default: `51200`).
+
+These thresholds apply to output handled by OpenCode's shared truncation layer, including MCP and plugin tool output. Individual tools that page or cap their own results can have separate limits.
+
+---
+
 ### Models
 
 You can configure the providers and models you want to use in your OpenCode config through the `provider`, `model` and `small_model` options.