[examples] add Slack idle-notification policy example

[NiveditJain]

Summary

• Adds slack-on-idle-notification policy to examples/policies-advanced/index.js
  demonstrating the Notification hook
• Posts a Block Kit Slack message on idle notifications with Claude's message, project path,
  and session ID
• Uses SLACK_WEBHOOK_URL env var; silently no-ops if unset
• Updates docs/custom-hooks.md to document notification_type and note Notification
  hooks must always return allow()

Test plan

• Verify syntax in examples/policies-advanced/index.js is valid
• Set SLACK_WEBHOOK_URL, install example, trigger idle notification, confirm Block
  Kit message appears in Slack
• Unset SLACK_WEBHOOK_URL and confirm policy skips silently

🤖 Generated with Claude Code

Summary by CodeRabbit

• Documentation

  • Updated Notification event payload documentation with new notification_type field and clarified behavior for custom hooks.

• Examples

  • Added example policy demonstrating integration for forwarding idle notifications to Slack.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Free

Run ID: a395a1f9-31a3-4ce3-a155-5966bcadfffb

📥 Commits

Reviewing files that changed from the base of the PR and between 365f60e and 72aa0f2.

📒 Files selected for processing (2)

• docs/custom-hooks.md
• examples/policies-advanced/index.js

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📝 Walkthrough

Walkthrough

Documentation for the Notification event payload was updated to include a notification_type field with values such as "idle" and "permission_prompt", noting that custom hooks must always return allow() and cannot block notifications. An example custom policy was added that forwards idle notifications to a Slack webhook.

Changes

Cohort / File(s)	Summary
Documentation docs/custom-hooks.md	Updated Notification event payload documentation to include notification_type field; clarified that custom hooks must always return allow() for notifications and cannot block them.
Slack Integration Example examples/policies-advanced/index.js	Added slack-on-idle-notification custom policy that listens for Notification events, filters for notification_type === "idle", constructs a Slack Block Kit payload with session metadata, and sends it to a webhook URL via non-blocking fetch with error suppression.

Sequence Diagram

sequenceDiagram
    participant System as Notification System
    participant Policy as Custom Policy<br/>(slack-on-idle-notification)
    participant Slack as Slack Webhook API
    participant Env as Environment<br/>Variables

    System->>Policy: Trigger Notification event<br/>(notification_type: "idle")
    Policy->>Env: Read SLACK_WEBHOOK_URL
    alt Webhook URL exists and type is idle
        Policy->>Policy: Construct Block Kit payload<br/>with message & session metadata
        Policy->>Slack: fetch(webhook_url, payload)
        Slack-->>Policy: Response (may fail)
        Policy->>Policy: Suppress errors via .catch()
    end
    Policy->>System: return allow()

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 A notification arrives, the idle time ticks on,
Custom hooks catch the whisper, send word to Slack—no frown,
Payloads dance through the ether, webhooks gleam bright,
Always returning allow(), never blocking the light!
Documentation clarified, the path now shines clear. ✨

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Note

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