# System & Safety Nodes

> Applies to: ChengOS v0.2.0+ ｜ Last verified: 2026-09-25 ｜ Source: `crates/cheng-nodes/src/nodes/builtin/utils`

Three nodes that guard the edges of an execution. `utils/credential` injects a stored secret by
reference — it is the reason no workflow needs an API key typed into a plain field. `utils/approver`
stops the run and waits for a human decision, which is how an otherwise autonomous graph gets a
checkpoint before something irreversible. `utils/preview` renders intermediate content so you can see
what a step actually produced while you are still building the graph.

## Credential Injection — `utils/credential`

Load saved credentials and expose them as env vars for downstream nodes. Supports provider auto-match, provider/name selection, and legacy UUID refs.

### Inputs

| Field | Type | Required | Default | Description |
|---|---|:-:|---|---|
| `bindings` | object | ✅ | — | Map each env var name to a credential ref. Ref supports `provider` (auto-select), `provider/name` (pick one), or UUID (legacy). Example: {"OPENAI_API_KEY":"openai", "GITHUB_TOKEN":"github/work"} |
| `context_name` | string | — | `null` | Context label shown in log and error messages. |
| `strict` | boolean | — | `true` | When enabled, any missing credential stops the node. When disabled, returns resolved env vars and lists failed keys in `missing_bindings`. |
| `user_id` | string | — | `null` | Optional user UUID override. Leave empty to use the current workflow caller. |

### Outputs

| Field | Type | Description |
|---|---|---|
| `env_vars` | object | Resolved env var values for downstream nodes (sensitive). |
| `missing_bindings` | array<string> | Env var keys that could not be resolved (only populated when Strict Mode is off). |
| `resolved_count` | integer | How many bindings were resolved successfully. |

## Approval Gate — `utils/approver`

Pause execution and request user authorization before performing a high-risk action. Supports one-time, session-level, and skip decisions.

### Inputs

| Field | Type | Required | Default | Description |
|---|---|:-:|---|---|
| `action_name` | string | ✅ | — | Name of the action requiring authorization |
| `risk_level` | enum | — | `medium` | Assessed risk of the action (low / medium / high / critical). Control: `select`. Options: `low`, `medium`, `high`, `critical` |
| `description` | string | — | `null` | Human-readable explanation of what the action will do |
| `param_summary` | string | — | `null` | JSON summary of action parameters shown in the approval card |
| `extra_whitelist` | string | — | `null` | Extra comma-separated action names to auto-approve in addition to session whitelist |
| `timeout_secs` | integer | — | `300` | Seconds to wait before auto-rejecting if no response (default 300) |

### Outputs

| Field | Type | Description |
|---|---|---|
| `approved` | boolean | True when the action is allowed to proceed |
| `approved_out` | boolean | Runtime-conditional boolean emitted only when approval is granted. |
| `outcome` | enum | Detailed approval outcome. Options: `approved` (User approved the action (or a whitelist rule matched).), `rejected` (User rejected the action.), `skipped` (User asked to skip this action and return feedback.), `timed_out` (No response was received within the timeout window.) |
| `whitelist_hit` | boolean | True if action was auto-approved via whitelist |
| `scope` | string | Scope granted by the user |
| `reason` | string | User-provided reason or feedback |
| `request_id` | string | UUID identifying this approval request |

## Content Preview — `utils/preview`

Display output results in preview window, supports multiple formats and statistics

### Inputs

| Field | Type | Required | Default | Description |
|---|---|:-:|---|---|
| `data` | any | — | — | Data to preview |
| `context` | any | — | — | Context from Chat node |
| `artifact` | object (port) | — | — | Artifact to preview (metadata only). Connection port, not a form field. |
| `artifacts` | object (port) | — | `[]` | Artifact list to preview (metadata only). Connection port, not a form field. |
| `artifactUri` | string | — | — | artifact:// URI to preview |
| `currentPage` | integer | — | `1` | Current page number. Control: `number` |
| `displayFormat` | enum | — | `raw` | Select preview display format. Control: `select`. Options: `raw` (原始格式), `json` (JSON 格式化), `table` (表格视图), `codeblock` (代码块格式), `assistantmessage` (提取助手消息) |
| `pageLength` | integer | — | `1000` | Characters per page; shorter content displays directly, longer content is paginated. Control: `number` |
| `showStats` | boolean | — | `true` | Whether to show character count, line count and other statistics. Control: `switch` |

### Outputs

| Field | Type | Description |
|---|---|---|
| `original_data` | any | Original input data |
| `preview_content` | string | Formatted preview content |
| `statistics` | string | Data statistics |
| `pagination` | string | Pagination info (provided when content needs pagination) |

## Next steps

- [Flow Control Nodes](/docs/nodes-utils-flow)
- [Approvals & Human Review](/docs/exec-approvals-reviews)
- [Authentication](/docs/api-authentication)