What does this PR do?

Add Discord Message Component v1 support to the send_message tool, enabling agents to send messages with clickable buttons and string-select menus. Component interactions route back to the agent as MessageEvent instances.

Two send paths are supported:

• WebSocket — discord.py attaches a discord.ui.View to channel.send(), interactions handled automatically via AgentComponentView
• REST — _build_discord_components() builds raw JSON payloads; an on_interaction handler acknowledges and routes orphaned interactions via ComponentStore

Related Issue

None — feature addition.

Type of Change

• ✨ New feature (non-breaking change that adds functionality)
• ✅ Tests (adding or improving test coverage)

Changes Made

• gateway/platforms/discord_components.py (NEW) — ComponentStore, AgentComponentView, build_view_from_spec(), helpers (_truncate_custom_id, _format_interaction_text)
• gateway/platforms/discord.py — _normalize_component_spec() format adapter, on_interaction REST handler, View attachment in send()
• tools/send_message_tool.py — components JSON schema, _build_discord_components() REST builder, _prefix_custom_id(), ComponentStore registration after REST send
• tests/gateway/test_discord_components.py (NEW) — 62 tests across 10 classes covering all public functions and edge cases

How to Test

1. Run the test suite: pytest tests/gateway/test_discord_components.py -v (62 tests)
2. Start the gateway and use send_message with components parameter to send button/select messages to a Discord channel
3. Click buttons and select menu options — verify interactions route back to the agent as MessageEvent instances
4. Test edge cases: disabled buttons, link buttons (no custom_id), >5 row truncation, label/custom_id length clamping, empty component specs

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (feat(discord):, style(discord):)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (62 tests across 10 classes)
• I've tested on my platform: Ubuntu 24.04 (Linux)

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — N/A (no user-facing docs changes needed; tool schema is self-documenting)
• I've updated cli-config.yaml.example if I added/changed config keys — N/A (no new config keys)
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — N/A (additive change, no architecture changes)
• I've considered cross-platform impact (Windows, macOS) — N/A (Discord API is platform-agnostic)
• I've updated tool descriptions/schemas if I changed tool behavior (components schema added to send_message)

{
  "components": [
    {
      "components": [
        { "type": "button", "style": "primary", "label": "Approve", "custom_id": "approve" },
        { "type": "button", "style": "link", "label": "Docs", "url": "https://..." }
      ]
    },
    {
      "components": [
        {
          "type": "string_select",
          "custom_id": "priority",
          "label": "Priority",
          "placeholder": "Choose...",
          "options": [
            { "label": "High", "value": "high" },
            { "label": "Low", "value": "low" }
          ]
        }
      ]
    }
  ]
}