Document message tool and add integration test

[Copilot]

The message tool implementation was complete but undocumented. Users had no configuration examples, and there was no test demonstrating tool usage within the agent loop.

Changes

Documentation (docs/example-daemon.yaml)

• Added channels section with configuration examples for Discord webhooks, Matrix rooms, and generic webhooks
• Included body template syntax and custom header examples

Integration test (test/agent.test.ts)

• Added test demonstrating message tool execution within the agent ReAct loop
• Verifies tool call flow: LLM requests tool → tool executes → LLM processes result

Example Configuration

channels:
  discord-general:
    type: "discord-webhook"
    url: "https://discord.com/api/webhooks/123/token"
  
  matrix-ops:
    type: "matrix"
    homeserver: "https://matrix.org"
    room_id: "!room:matrix.org"
    access_token: "${MATRIX_TOKEN}"
  
  alerts:
    type: "webhook"
    url: "https://example.com/webhook"
    headers:
      "X-Custom-Header": "value"
    body_template: '{"text": "{{content}}"}'

The tool itself (src/tools/message.ts, src/config.ts, test/message.test.ts) was already implemented with proper validation, error handling, and 15 unit tests.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Implement message tool for channel communication</issue_title>
<issue_description>## Problem
Rook cannot communicate via Discord/Matrix channels autonomously. External webhook triggers work, but no outbound messaging.

Requirement

Implement message tool:

• Parameters: {channel, content, target?}
• Abstract channel via config (daemon.yaml)
• Start with Discord webhook (simplest path)
• Future: Matrix, other protocols

Acceptance Criteria

• Tool registered in registry
• Channel config in daemon.yaml (webhook URLs)
• Discord webhook implementation
• Message content validation (length limits, formatting)
• Error handling for network failures, invalid channels
• Unit tests (mocked webhook)
• Integration test with agent loop

References

• Gap Analysis P1-4
• Discord webhook API: simple POST with JSON body

Priority

P1 - Required for full Rook autonomy</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Implement message tool for channel communication #133

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